Neurotology

Question 1

List the differential diagnosis of a soft tissue mass overlying the promontory 7

Answer 1

1. Glomus tympanicum
2. High riding jugular bulb (defined if superior limit above the floor of the IAC, or EAC floor clinically)
3. Congenital cholesteatoma
4. Schwannoma
5. Adenoma
6. Persistent stapedial artery
7. Aberrant carotid artery

Encephalocele

Question 2

What are the differences between vagal schwannoma and carotid body tumor on angiography? 3

Answer 2

• Schwannoma will push vessels anterior and lateral (vagal most common in jugular foramen)
• Carotid body tumor will splay ECA and ICA apart (Lyre sign)
• Filling defect from vessel ingrowth is also seen in carotid body tumors

Question 3

Discuss the anatomic relationships of the skull base.

WHat are the pathways for tumor spread at the skull base?

Answer 3

1. Sphenoid Bone:
   - Think of like a bow tie
   - Contains foramen spinosum & ovale
2. Occipital Bone:
   - Contains foramen magnum and hypoglossal foramen

Between the two bones (sphenoid and occipital), the petrous apex is wedged there - contains the carotid canal and jugular bulb, and the apex of the petrous apex is the foramen lacerum

Pathways for tumor spread:
- Space between the sphenoid bone and the petrous is the PETROSPHENOIDAL FISSURE
- Space between petrous and occipital bone is the PETROCLIVAL FISSURE

Medial anterior surface of the petrous apex:
- Foramen for GSPN (towards lacerum)
- LSPN from tympanic plexus –> foramen ovale to otic ganglion

Sphenoid: https://prod-images-static.radiopaedia.org/images/19310196/a144a8b64ac4ac96353ef804fd81b2_gallery.jpeg

Occipital Bone: https://anatomy.net/uploads/382f049c-e6bb-464e-a939-2e4da6313fea.png?width=1024

Petrous Apex:
https://lmhofmeyr.co.za/wp-content/uploads/2017/03/Screen-Shot-2017-03-08-at-10.04.49-PM-e1492372073249.png

Question 4

What are the boundaires of the petrous apex?
What separates it into anterior and posterior compartments?

Answer 4

Anterior: Greater wing of the sphenoid
Posterior: Occipital bone
Medial: Foramen lacerum
Lateral: Squamous portion of the temporal bone

Separated into anterior and posterior by the IAC (internal auditory canal)

Question 5

What is the anastomotic vein of Labbe?

Answer 5

• Drains the temporal lobe - 66% present in the right, 77% on the left
• Anastomotic vein that communicates the superficial middle cerebral vein (ie. sylvain fissure vein) with the transverse/sigmoid sinus (medial to superior petrosal sinus)
• Occlusion (eg. Sigmoid sinus thrombosis) will cause temporal lobe edema or infarction, resulting in speech and language deficits, possibly followed by coma and death

https://ars.els-cdn.com/content/image/3-s2.0-B978032365377000012X-f12-02-9780323653770.jpg

Vancouver 308

Question 6

Describe the staging for tumors of the lateral temporal bone

Answer 6

MODIFIED PITTSBURG SYSTEM

T-Staging:
1. T1: Limited to the EAC without bony erosion or soft-tissue extension
2. T2: Limited to the EAC with bone erosion (not full-thickness) or limited soft-tissue involvement (< 0.5cm)
3. T3: Erosion through the osseous EAC (full thickness) with limited soft tissue involvement (< 0.5cm), or tumor involvement in the middle ear and/or mastoid
4. T4: Erosion of the cochlea, petrous apex, medial wall of the middle ear, carotid canal, jugular foramen, or dura; Extensive soft tissue involvement (>0.5cm, such as involvement of the TMJ or styloid process), or evidence of facial paresis

Regional LN metastases are rare (10-15%), as are distant metastases, but both have a poor prognosis

Question 7

Describe the surgical approaches to the lateral temporal bone

Answer 7

1. Sleeve resection (Pittsburgh T1)
   - Removes cartilaginous EAC & some or all of the bony canal wall skin circumferentially WITHOUT bone removal
   - For malignancies localized to the cartilaginous EAC
2. Lateral Temporal Bone resection (Pittsburgh T2, some T3)
   - Removes en bloc the entire osseous and cartilaginous EAC with the TM, malleus, incus, and parotidectomy for access to anterior EAC
   - For malignancies localized to the osseous EAC without encroachment on medial mesotympanum + extended facial recess approach
3. Subtotal Temporal Bone resection (Pittsburgh T3)
   - En Bloc resection of the medial surfaces of the mesotympanum + portions of bony labyrinth, without air cells of petrous apex
   - For tumors involving the middle ear
4. Total Temporal Bone resection
   - En Bloc resection of the temporal bone, including petrous apex and sigmoid sinus, IAC, IX, X, and XI

Vancouver 309

Question 8

Describe the access provided by the Fisch A-C approaches

Answer 8

FISCH A:
- Disseciton entails radical mastoidectomy, anterior transposition of the facial nerve, exploration of the posterior infratemporal fossa, and cervical dissection
- Access to jugular bulb, vertical petrous carotid, posterior infratemporal fossa

FISCH B:
- Access to petrous apex, clivus, superior infratemporal fossa
- Transposition of FN not needed

FISCH C:
- Access to nasopharynx, peritubal space, rostral (superior) clivus, parasellar area, pterygopalatine fossa, anterosuperior infratemporal fossa

Question 9

What is the primary indication for a Fisch A approach?

Answer 9

Main indication is for paragangliomas of the temporal bone or petrous apex

Question 10

What are 11 steps in order of procedure for a Fisch A approach?

Answer 10

1. Postauricular incision with neck extension
2. Neck dissection - exposure CNIX-XII, ICA, IJV
3. Superficial parotidectomy with identification of CNVII
4. Wide field mastoidectomy - removal of mastoid tip, entire EAC, middle ear contents
5. Identification of CNVII in middle ear, removal from canal and anterior translocation
6. Anterior mobilization of mandible
7. Taking sigmoid and exposure of posterior and middle cranial fossa aura for intracranial extension
8. Ensure to ligate inferior petrosal sinus prior to sigmoid
9. Removal of disease
10. Obliteration of cavity with abdominal fat, rotated temporalis muscle, or tensor fascia lata
11. Layered closure and compression dressing application

https://www.youtube.com/watch?v=ciT0CtFbAPQ

Question 11

What is the Jugular Foramen formed by? What are the contents of the Jugular Foramen?

Answer 11

JUGULAR FORAMEN: Formed by the occipital and temporal bones

Two classification systems for contents

A. ANATOMICAL
1. Anterior Compartment
- Inferior petrosal sinus
2. Middle Compartment
- Glossopharyngeal nerve (IX)
- Vagus nerve (X)
- Spinal accessory nerve (XI)
- Meningeal branch of ascending pharyngeal artery (MBA) - posterior branch
3. Posterior Compartment
- Jugular vein
- Occipital artery
- Emissary veins

B. RADIOLOGICAL (based on Jugular spine)
1. Pars Nervosa (anterior to jugular spine)
- Inferior petrosal sinus
- Glossopharyngeal & Jacobsen’s nerve (IX)
2. Pars Vascularis
- Vagus and Arnold’s nerve (X)
- Spinal accessory nerve (XI)
- Meningeal branch of ascending pharyngeal artery - posterior branch
- Jugular bulb
- Nodes of Krause - lymph nodes whose engorgement can lead to jugular foramen syndromes

Note: Tympanic Canaliculus between ICA and Jugular foramen is where Jacobsen’s nerve runs to the tympanic plexus

Jugular Spine: https://prod-images-static.radiopaedia.org/images/618/81027e2e7d2c8be8f711f39b1c236e_gallery.jpeg

Tympanic Canaliculis: https://web.donga.ac.kr/ksyoo/department/education/grossanatomy/doc/image/temporal-inf.jpg

https://www.youtube.com/watch?v=9qVz5426r8A

“JOE studied classes from 9-11 and did his MBA and then became an IPS officer (Indian Police officer)” (from posterior to anterior)

Vancouver Pg 309/310

Question 12

Describe the 7 major types of Jugular Foramen Syndromes

Answer 12

1. Vernet Syndrome: CN IX, X, XI palsies
   - Due to jugular foramen neoplasm, most commonly lymphadenopathy of Krause’s nodes
2. Collet-Sicard Syndrome: CN IX, X, XI, XII palsies
   - Most commonly due to extradural tumor of posterior fossa or retroparotid space
3. Villaret syndrome: CN IX, X, XI, XII palsies, sympathetic chain involvement leads to Horner’s
   - Suggests lesion distal to jugular foramen, usually retrosyloid area
4. Hughlings-Jackson syndrome: CN X, XI, XII palsies
   - Similar to Collet-Sicard but does not include glossopharyngeal (extradural tumor of posterior fossa or retroparotid space)
5. Tapia Syndrome: CN X + XII
   - Lesions below level of inferior ganglion of CNX (vocal palsy seen, palate in tact)
   - Usually due to lesion in neck (usually traumatic)
6. Schmidt Syndrome (Vagal-Accessory): CNX + XI
   - Paralysis of soft palate, pharynx, and larynx
   - Flaccid weakness and atrophy of SCM & Trapezius
   - Due to lesion of NUcleus Ambiguous and Bulbar spinal nuclei of the accessory
7. Avellis Syndrome: CNX
   - Alternating palsy of vocal folds, soft palate, and contralateral pain and temperature sensation loss
   - Nucleus ambiguous/pyramidal tract injury

Mind trick (doesn’t work for Avellis except for 10)
9 = Ends in “et” (Vernet, Collet, Villaret)
10 = All syndromes have 10 (applies to Avellis)
11 = Syndromes DON’T contain “p”
12 = Syndromes contain “a”
Villaret also has sympathetic chain

Vernet - 9, 10, 11
Collet-Sicard - 9, 10, 11, 12
Villaret - 9, 10, 11, 12 + sympathetic chain
Hughlings-Jackson - 10, 11, 12
Tapia - 10, 12
Schmidt - 10, 11
Avellis - 10

Question 13

Discuss air embolism during surgery:
1. How does it occur in Otology?
2. How much air will lead to symptoms?
3. What are the symptoms of air embolism?

Answer 13

CAUSE:
- Usually through diploic veins in skull into jugular system and sigmoid sinus
- 30cc of air will cause signs & symptoms

S/S:
- Hypotension
- Cardiovascular collapse
- Churning precordial sounds

Question 14

What are the measures that should be taken in the management of air embolism during surgery?

Answer 14

1. Initially place your finger on the bleeding vessel while you ask for supplies
2. Pack surgical wound with wet sponges
3. Trendelenburg prevents further leaks (head up)
4. Left lateral decubitus position traps air in right heart and prevents lung embolism
5. Oxygenate with 100% O2 until patient stabilizes (air absorbed) or aspirate air via venous catheter
6. Fix source of air leak
7. Definitive treatment: therapeutic recompression and hyperbaric oxygen therapy

Question 15

What are glomus tumors? How are they categorized?

Answer 15

GLOMUS TUMOR = Paraganglioma of the temporal bone
- Most frequently encountered temporal bone neoplasm after vestibular schwannoma

Paraganglioms = derived from neural crest elements; associated with the jugular bulb adventitia, and Jacobson’s and Arnold’s nerves

Glomus Tympanicum (Tympanic PGL):
- Arises from neuroendocrine cells around middle ear (associated with jacobsen’s nerve), contain baroreceptors and have arterioles feeding into them (and venules leaving)
- Aka. Tumors of glomus bodies
- More common than glomus jugulare

Glomus Jugulare (Jugular PGL):
- Arises from neuroendocrine cells around jugular bulb

Question 16

What are the main cells types of normal paraganglia?

Answer 16

TYPE 1: Chief cells/granular cells
- Dense granules (norepi/dopamine) filled with catecholamnines
- Arranged in “Zell-ballen” pattern
- Polygonal with abundant eosinophilic cytoplasm

TYPE 2: Supporting/Sustenacular cells
- Elongated cells that closely resemble Schwann cells
- Peripherally surround Type 1 cells

Question 17

Describe the histologic findings and immunohistochemistry stains of paragangliomas

Answer 17

HISTOLOGY:
- Zellballen pattern: Chief cell clusters enclosed in fibrous septa and supporting cells surrounding them in a vascular network
- Malignant PGLs cannot be identified on pathology, only on clinical behaviour
- Neuroendocrine origin, non-chromaffin (no staining from chromium containing stains) - pheochromocytomas contain chromaffin cells, unlike PGLs, and the stain can be used to differentiate

IMMUNOHISTOCHEMISTRY STAINS:
1. Chromogranin
2. Synaptophysin
3. Neuron specific enolase (NSE) - chief cells
4. CD56

S-100 (Sustenacular cells) - but not common for other neuroendocrin origin

Question 18

What are tumors that share the same staining characteristics as paragangliomas?

Answer 18

Any tumor of neuroendocrine origin, including: “MMSP”
1. Merkel cell carcinoma
2. Medullary thyroid carcinoma
3. Small cell lung carcinoma
4. Pheochromocytoma

Will stain positive for:
1. Synaptophysin
2. Chromogranin A
3. CD56
4. Neuron specific enolase (NSE)

Question 19

Describe the common locations for paraganglioma tumors

What % are found in the head and neck? Among the head and neck, what are the top 3 most common?

Answer 19

• 90% adrenal gland (pheochromocytoma)
• 10% Extra-adrenal (rule of 10s)

Among the Extra-adrenal sites:
- 85% in abdomen
- 12% in thorax
- 3% in head/neck

Within head/neck, most common:
1. Carotid body tumor
2. Jugulotympanic
3. Vagal

Question 20

Describe the epidemiology of paraganglioma presentation.

Which side do they predominate?
What is the preference for sex, age, laterality, secretory function and malignancy?

Answer 20

RULE OF 10s:
- 10% familial, with multiple lesions in 26%
- 10% extra-adrenal
- 10% bilateral
- 10% multiple lesions
- 10% malignant (5-10%) - Clinical signs of invasion of surrounding structures and lymph node metastasis
- 10% arise in childhood
- 10% secretory (in truth < 5%) - Clinical symptoms = flushing, diarrhea, palpitations, headache, hypertension, perspiration, orthostasis; treated with alpha and beta blockade

OTHER:
- Left sided predominant
- 5th decade common
- F:M 6:1

Pretty much any question with paraganglioma what “%”, likely safe to say “10%”

Question 21

What are the associated syndromes of paragangliomas? 6

Answer 21

1. MEN 2A/2B
2. Von-Hippel-Lindau (reintal angiomas, cerebellar hemangioblastomas, endolymphatic sac tumors)
3. NF1
4. Carney Triad
5. PGL-PCC Syndrome (Hereditary PGL-pheochromocytoma syndrome)
6. SDH deficiency

MVP NCS

Question 22

What is found in the Carney triad?

Answer 22

(PGL, pulmonary chondroma, gastric leiomyosarcoma)

Question 23

What is the genetics and inheritance of Hereditary PGL syndrome?

Answer 23

Autosomal dominant
SDH (Succinate dehydrogenase genetic mutation) - encodes for SDH subunits D, B, and C

Higher frequency of bilateral/multiple tumors, earlier onset of tumors

Question 24

What is the common blood supply that feeds temporal bone paragangliomas?

Answer 24

1. Ascending pharyngeal artery (most common)
2. Post auricular
3. Occipital
4. Internal maxillary
5. Ipsilateral or contralateral internal carotid artery branches (caroticotympanic)

AAO-MI

Question 25

Discuss the clinical presentation of temporal bone paragangliomas/glomus tumors? 7 What are 3 objective signs that can be seen? Describe them

Answer 25

1. Pulsatile tinnitus 2. Conductive hearing loss 3. Cranial nerve deficits 4. Horner's syndrome 5. Jugular foramen syndromes (Vernet, Collet-Sicard, Villaret) 6. Bruit on auscultation 7. Endocrine symptoms (flushing, sweating, palpitations, hypertension) SIGNS: 1. Brown's sign: Red mass behind the tympanic membrane that blanches on pneumatoscopy when the pneumatic pressure exceeds the systolic BP 2. Rising sun sign: Reddish mass arising up from hypotympanum (looks like a 'rising sun') 3. Aquino sign: Cessation of pulsatile tinnitus or pulsation of the mass with compression of the ipsilateral carotid. Can also be defined as blanching of mass with compression of ipsilateral carotid.

Question 26

What are the two staging systems for glomus tumors?

Answer 26

1. Fisch classification - includes both glomus tympanicum and glomus jugulare 2. Glasscock-Jackson has a separate classification for glomus tympanicum and glomus jugulare

Question 27

Describe the Fisch Classification for Jugulotympanic paragangliomas (ie. glomus tumors)

Answer 27

- A: Limited to the middle ear (ie. Glomus tympanicum only) - B: Limited to tympano-mastoid area with or without erosion of jugular bulb - C: Involvement and/or destruction of infralabyrinthine and apical compartments 1. C1. Carotid canal involvement 2. C2. Vertical carotid involvement 3. C3. Horizontal carotid involvement 4. C4. Foramen lacerum involvement - D: Intracranial extension 1. D1. Intracranial extension < 2 cm in greatest diameter 2. D2. Intracranial extension >2cm in greatest diameter 3. D3. Inoperable intracranial invasion

Question 28

Discuss the Glasscock-Jackson classification of Glomus Tympanicum (Tympanic PGL)

Answer 28

I. Promontory only II. Filling middle ear III. Filling middle ear and mastoid IV. Extension through EAC or anteriorly to carotid artery

Question 29

Discuss the Glasscock-Jackson classification of Glomus Jugulare (Jugular PGL)

Answer 29

I. Small tumor involving the jugular bulb, middle ear, and mastoid II. Tumor extending under the IAC; there may be intracranial extension III. Tumor extending into the petrous apex; there may be intracranial extension IV. Tumor extending beyond the petrous apex into the clivus and infratemporal fossa; there may be intracranial extension

Question 30

What is the classification of carotid paragangliomas?

Answer 30

Shamblin Classification: 1. Type 1: Minimally attached to carotid vessels 2. Type 2: Partially surrounds carotid vessels 3. Type 3: Completely encases carotids ## Footnote Kevan Otology Page 104

Question 31

What are the classic imaging findings of a paraganglioma?

Answer 31

1. Salt and pepper appearance on MRI (Due to vascularity and flow voids) 2. May have bony erosion of jugular foramen, temporal bone

Question 32

What investigations should be performed for patients with suspected paragangliomas?

Answer 32

1. Serum catecholamines and metanephrines 2. 24 hour Urine VMA (vanillylmandelic acid) and metanephrines and 5-HIAA (hydroxyindoleacetic acid) 3. Pre-operative angiography ± selective embolization (should be considered with any large tumor)

Question 33

What is the general management for patients with paragangliomas of the temporal bone?

Answer 33

1. Pre-operative optimization: alpha blockade, followed by beta blockade, if secretory 2. Pre-operative embolization (reduces risk of severe bleeding) 3. Surgical resection: Fisch approaches 4. XRT if unfit for surgery, inoperative, recurrent, residual, or metastatic 5. Observation if small, stable, asymptomatic, or if contraindications for intervention

Question 34

What are the general surgical approaches for glomus jugulare and tympanicum?

Answer 34

Tympanicum: - Type I: Endaural resection - Type II-IV: Extended facial recess approach Jugulare: - Fisch Type A infratemporal fossa approach *Note: efficacy of pre-operative embolization is disputed*

Question 35

Discuss the use of radiotherapy in the management of paragangliomas. What is the MOA

Answer 35

Indications: - High risk surgical patients - Incompletely excised or recurrent lesions - Bilateral lesions - Metastatic lesions MOA: - Chief cells are unaffected - Causes obliterative endarteritis of tumor vessels, and controls rate of tumor growth in 90% Overall, not the management of choice, can reduce tumor mass, useful for management of recurrences or unresectable lesions

Question 36

A patient with a six month history of right pulsatile tinnitus and progressive hearing loss. He has no past history of ear problems and denies trauma to his head or ears. He recently developed some difficulty swallowing. Examination reveals a large red mass behind an intact tympanic membrane. His audiogram shows mostly conductive hearing loss. What is the most likely diagnosis? Excluding the possibility of associated tumors, what other manifestations do you expect to see on H&N examination? What is the best investigation to establish a diagnosis?

Answer 36

Diagnosis: Glomus Jugulare Tumor Findings: 1. Paralysis of the soft palate on the right side (X) 2. Right vocal fold paralysis (X) 3. Right SCM/trapezius paralysis (XI) Test: Carotid angiography

Question 37

Discuss the anatomy of the internal acoustic canal

Answer 37

Anterior-Superior: Facial nerve + Nervus intermedius Anterior-inferior: Cochlear nerve Posterior-Superior: Superior vestibular nerve Posterior-inferior: Inferior vestibular nerve Bill's bar (Crista Verticalis): Separates Anterior and Posterior on the Superior side only Falciform crest (Crista Falciformis/Transverse crest): Separates Superior and inferior

Question 38

Discuss the borders of the cerebellar pontine angle (CPA) 6

Answer 38

- Anterior: Petrous bone, lateral clivus - Posterior: Cerebellar Peduncle/Cerebellum/flocculus - Medial: Brainstem (middle cerebellar peduncle, pons, ventral cerebellum; prepontine cistern with basilar artery and origin of abducens nerve) - Lateral: Posterior and medial surface of the petrous bone - Superior: Middle cerebellar peduncle, cisterna ambiens with trochlear nerve and superior cerebellar artery - Inferior: Arachnoid over lower cranial nerves/cerebellar tonsil, cerebellomedullary cisterna with CN9-12, vertebral artery and PICA, inferior petrosal vein ## Footnote https://skullbasesurgeryatlas.stanford.edu/wp-content/uploads/2020/07/1.2_figure_2-scaled.jpg Kevan Otology Page 96

Question 39

What are the contents of the CPA? 6

Answer 39

CONTENTS: 1. CSF cisterna 2. CN 3, 6, 7, 8, 9, 10, 11, 12 3. AICA - anterior inferior cerebellar artery 4. Vertebral artery 5. PICA - posterior inferior cerebellar artery 5. Superior petrosal vein, inferior petrosal vein

Question 40

Looking at the CPA, starting superiorly, what nerves do you see and which are the most superficial?

Answer 40

1. Facial nerve and nervus intermedius 2. Vestibular nerve (separated by a blood vessel from the cochlear nerve) 3. Cochlear nerve

Question 41

List the differential for common CPA tumors 8

Answer 41

1. Vestibular schwannoma (80% - most common adult lesion) 2. Meningioma (5-10% - 2nd most common adult lesion) 3. Epidermoid cyst (3-5% - 3rd most common adult lesion) 4. Arachnoid cyst (1%) 5. Facial schwannoma (1%) 6. Lipoma 7. Paraganglioma 8. Hemangioma

Question 42

List a differential for uncommon CPA lesions 8

Answer 42

1. Metastatic malignant tumor 2. Lipoma 3. Dermoid 4. Teratoma 5. Chordoma 6. Chondrosarcoma 7. Giant cell tumor 8. Hemangiopericytoma

Question 43

What is the Obersteiner-Redlich Zone?

Answer 43

The transition zone where the lining of the vestibulocochlear nerve changes from oligodendrocytes (CNS) to Schwann cells (PNS) Historically, it was thought that the transition zone was the most common site of a vestibular schwannoma. Now, it is felt that the most common location is Scarpa's ganglion (vestibular nerve ganglion, located within the internal auditory meatus)

Question 44

Regarding vestibular schwannoma, discuss: 1. What are they? 2. What is the etiology? List 3 possibilities 3. What are the symptoms? Name 5 symptoms and 2 signs

Answer 44

VESTIBULAR SCHWANNOMA: - Most common CPA lesion (80%) - Benign nerve sheath tumor involving either the superior or inferior vestibular nerve (inferior more common) - Historically thought to involve the Obersteiner-Redlich Zone (junction between oligodendrocytes of the CNS and Schwann cells of the PNS) - Now thought to most commonly arise from Scarpa's ganglion ETIOLOGY: 1. 95% Sporadic 2. NF2 (22q2 deletion; affects the merlin protein) - early/bilateral vestibular schwannoma 3. NF1 (chromosome 17 defect) - 5% vestibular schwannomas SYMPTOMS: 1. Tinnitus 2. Hearing loss (including SSNHL in 20% of patients) 3. Facial hypesthesia (diminshed ability to perceive simple sensation) 4. Dysequilibrium (acute vertigo is uncommon due to progressive vestibular loss, unless there is acute bleeding into the tumor) 5. Nystagmus (Brun's nystagmus if large) 6. Hitselberger's sign (decreased sensation in the area of the conchal bowl due to compression of the CNVII sensory roots - posterior auricular nerve) 7. Other cranial neuropathies if large

Question 45

Describe the audiometric findings and ABR abnormalities for patients with vestibular schwannoma. 5 Audiometric findings 9 ABR findings What is the rate of false normal ABRs?

Answer 45

1. PTA: Asymmetric SNHL - 20dB in 1 frequency OR 15dB in 2 frequencies OR 10dB in 3 frequencies - OR Saliba's rule 3000: 15dB discrepancy at 3000Hz - 65% have high frequency SNHL, 10% present with SSNHL (but only 5% of SSNHL is VS); 5% normal hearing 2. SDS: Out of proportion to PTA (worse than expected) - Presence of rollover as well 3. Stapedial reflex: Decay - More than 50% drop over 5 seconds (measured by change in compliance of TM) - 88% will have absent reflex or positive decay 4. Rollover: Discrimination actually gets worse as you increase the volume of the stimulus beyond pure tone threshold 5. Auditory fatigue: Change of auditory threshold with continuous acoustic stimulus (threshold worsens over time) ABR FINDINGS/ABNORMALITIES: 1. Interaural wave V delay > 0.2ms (40-60%) 2. Wave I-III latency (most sensitive for retrocochlear) - > 2msec 3. Wave I-V latency (sensitive for retrocochlear, more affected by cochlear impairment) - >4msec 4. #2 and 3 are most specific; can also get Wave III-V latency 5. Absent Wave V (Absent wave V in presence of replicated wave I or III is a definite diagnostic indicator of a retrocochlear lesion) 6. Absolute wave V latency > 5.7msec 7. Wave I only wave present (10-20%) 8. Absent waveforms overall (20-30%) 9. Abnormal morphology NORMAL ABR 10-15% - 18-30% False negative rate for small intracanalicular tumors

Question 46

What is the sensitivity of ABR for retrocochlear tumors < 1cm? What technique can improve this?

Answer 46

- Since the advent of Gadolinium-enhanced MRI, ABR false-negative rate (missing tumor diagnosis) has been 18-30% for intracanalicular tumors - STACKED ABR TESTING can improve sensitivity for detecting intracanalicular vestibular schwannomas Stacked ABR testing: - Tests hearing spectrum in a frequency specific fashion, followed by temporal alignment of the results (e.g. aligning the wave V peaks) - Results in a more sensitive identification of changes in amplitude - Remains a research tool currently ABR still useful in patients where imaging is impractical or unfeasible or if the concern is to rule out a large tumor only

Question 47

Describe the imaging features of a vestibular schwannoma based on: 1. Location 2. Bone changes 3. Shape 4. CT density 5. CT enhancement 6. T1-weighted MRI 7. Gadolinium enhancement 8. T2-weighted MRI

Answer 47

1. Location - centered on the internal auditory canal (porous acousticus) 2. Bone changes - Enlarge the IAC/porus acousticus 3. Shape - Spherical or ovoid, with an acute bone-tumor angle 4. CT density - Mostly isodense to brain, rare calcifications and central necrosis, possibly cystic if large 5. CT enhancement - Moderate to marked, often inhomogeneous and variable 6. T1-weighted MRI - Isointense to brain (so slightly brighter than CSF) or hypointense 7. Gadolinium enhancement - MARKED 8. T2-weighted MRI - Hyperintense to brain Overall features: - Centered on porous acousticus - Acute angles to temporal bone - Homogeneous enhancement with rare calcifications - No dural tail - May have intracanalicular component, causing enlarged IAC (>2mm compared to contralateral side) - Rare extension anteriorly and superiorly - Almost never dumbbel into MCF - Intralabyrinthine - cochlea/vestibule enhance on T1+gad (Meniere's-like symptoms)

Question 48

Describe the results of vestibular testing in Vestibular Schwannoma. What would the expected VNG findings be? 2

Answer 48

1. ENG abnormal in 80%, usually unilateral weakness on affected side 2. Tumors arising from Inferior vestibular nerve will be missed on calorics (calorics only test Lateral SCC - Superior vestibular nerve)

Question 49

Discuss the histopathology of vestibular schwannoma

Answer 49

- Alternating regions of compact spindle cells (Antoni A) and loose hypocellular areas (Antoni B) - Nuclei are spindled and PALISADE, forming "Verocay bodies" - Whorled or palisading appearance of Antoni A cells Stains: 1. S100 positive 2. NSE positive 3. Vimentin positive Differential: 1. Carcinoma 2. Neuroendocrine tumor 3. Medullary thyroid cancer 4. Middle ear adenoma ## Footnote Vancouver Page 316

Question 50

What is the Koos classification of Vestibular Schwannoma?

Answer 50

1. GRADE I: Tumors are completely confined to the IAC 2. GRADE II: Tumors have both intra- and extra-meatal components, extending into the cerebellopontine angle (CPA) but do not contact the brainstem 3. GRADE III: Tumors contact the brainstem but do not compress it 4. GRADE IV: Tumors cause brainstem compression and/or displacement of adjacent cranial nerves Most common staging used

Question 51

What is the Jackler staging for intracanalicular vestibular schwannoma?

Answer 51

- Small: < 1cm - Medium: 1-2.5cm - Large: 2.5-4cm - Giant: >4cm

Question 52

What are the phases of Vestibular Schwannoma growth? 4

Answer 52

1. INTRACANALICULAR: Hearing loss, vertigo 2. CISTERNAL: Worsening HL, dysequilibrium (vertigo diminishes) 3. COMPRESSIVE: Occipital headache, CN V2 paresthesias (brainstem compression, cornea hypoesthesia, ataxia) 4. HYDROCEPHALIC: 4th ventricle compressed; worsening of trigeminal symptoms, gait deteriorates, visual loss with increased ICP, lower CN dysfunctions, death due to tonsillar herniation

Question 53

Discuss the management options of vestibular schwannoma

Answer 53

A. OBSERVATION - Average growth rate of 0.2cm/year - 90% will grow eventually B. STEREOTACTIC RADIATION - Cyberknife (frameless, LINAC based) - Gamma knife (head frame, cobalt beam) C. SURGERY - Middle cranial fossa - Retrosigmoid - Translabyrinthine

Question 54

Regarding the use of Observation for management of Vestibular Schwannoma, discuss: 1. What are the growth categories? 2. What are the indications for observation? 3. What is the follow-up regimen for observational management? 4. What are the disadvantages of observation over surgery?

Answer 54

GROWTH CATEGORIES: (Establish growth rate by 2 MRIs separated by 6 months) 1. Slow/non (40%) - < 0.2cm per year 2. Limited - 0.2-1cm per year 3. More Rapid - approximately 1cm per year Average growth ~2mm per year - 30% will grow in 1-3 years - 50% will grow after 5 years (50% don't grow) Intervention: Generally require ~6mm growth to require intervention (30-50% of patients) If no or minimal growth, continue observation: 1. MRI q6mos for 1 year, then 2. MRI q1year for 2 years, then 3. MRI q2 years indefinitely DISADVANTAGES OF OBSERVATION OVER SURGERY: 1. Advancing patient age (once ready for surgery, they may be older) 2. Larger tumor to treat over time 3. Lose opportunity for XRT (< 3cm) 4. Lose opportunity for hearing preservation 5. Anxiety regarding "untreated" tumor 6. Time and expense for ongoing radiology scans

Question 55

What are the indications for radiotherapy for vestibular schwannoma? What is a relative contraindications? 1

Answer 55

1. Older patients with growing small to medium size tumors (ie. < 3cm) 2. Relatively contraindicated in NF2 due to risk of malignant transformation

Question 56

Regarding radiation treatment for the management of Vestibular Schwannomas, discuss: 1. What are the different radiation options? 2. What are the side effects/risks? 3. What are the disadvantages of stereotactic radiosurgery for vestibular schwannoma? (11)

Answer 56

OPTIONS: 1. Stereotactic Radiosurgery - Multiple convergent beams in a single dose of radiation - Can be delivered via Gamma knife or a Linear accelerator (LINAC) 2. Fractionated Stereotactic Radiotherapy - Fractionated radiation, given 1.8-2Gy per fraction; or hypofractionated 3. Proton beam therapy (least studied) - may be the modality with the least surrounding damage SIDE EFFECTS/RISKS: 1. 40% Hearing loss 2. 20% delayed facial weakness DISADVANTAGES: 1. Only small tumors can be radiated (< 3cm) 2. Tumor is not excised; just stops the tumor growth 3. Delayed facial weakness can occur 4. Not hearing preserving (delayed hearing loss same as the rate of HL in surgery) 5. Trigeminal Neuralgia (20%) 6. Imbalance (30%) 7. Post-radiation scarring makes salvage surgery more difficult 8. Radiation-induced malignancy of concern in younger patients 9. Risk of Osteoradionecrosis 10. Cystic tumors = less radiosensitive 11. Indefinite monitoring required

Question 57

What are the four main goals of surgery in the CPA angle?

Answer 57

1. Avoid complications/death 2. Preserve facial nerve 3. Preserve hearing (balance generally destroyed by mass) 4. Complete disease removal

Question 58

What are the indications for surgery for vestibular schwannoma?

Answer 58

1. Younger patients with growing tumors 2. Large tumors (>2.5cm) 3. Compressive symptoms

Question 59

What are the criteria to allow for hearing preservation in Vestibular schwannoma surgery? (3)

Answer 59

1. Less than 30dB PTA and >70% SDS (or 50/50) 2. Less than 2cm extension into CPA 3. Fundus (most lateral end) of IAC is free of disease

Question 60

What are the surgical approaches for vestibular schwannoma? What are the advantages and disadvantages of each? Name 2-3 for each

Answer 60

A. TRANSLABYRINTHINE APPROACH 1. Advantages: - Excellent visualization of the CPA and direct approach to IAC - No need for cerebellar retraction - Safest for facial nerve preservation - Wide exposure not limited by tumor size 2. Disadvantages: - NOT a hearing preservation approach (total hearing eradication) - Higher risk of CSF leak (but less than Retrosig) B. RETROSIGMOID / SUBOCCIPITAL 1. Advantages: - Excellent Hearing preservation approach (approach CPA from posterior to the sigmoid sinus at the level of the occiput) - Useful for larger tumors with limited lateral IAC involvement - Less risk to Facial nerve compared to MCF 2. Disadvantages: - Requires cerebellar retraction for visualization (increased risk of post-operative headaches) - Contraindicated if tumor extends to fundus (most lateral part) of IAC - Increased risk to CNVII compared to translabyrinthine - 10% postoperative headaches (persistent) - Highest rate of air embolism and CSF leak C. MIDDLE CRANIAL FOSSA (supraauricular lateral craniotomy) 1. Advantages: - Hearing preservation approach - Useful in small lateral IAC tumors with the need for hearing preservation - Lowest risk of CSF leak 2. Disadvantages: - Requires temporal lobe retraction (post-op headaches, seizures) - Facial nerve overlies tumor in this view - higher risk - Challenging visualization and technically difficult - Contraindicated if >1cm of extension into CPA (limited in the medial direction by temporal lobe retraction) - Contraindicated in older patients (>60yr) due to higher risk of bleeding and stroke ## Footnote Vancouver 317

Question 61

How does age affect the surgical approach used?

Answer 61

Older population: - Retrosigmoid favourable - cerebral/cerebellar atrophy improves access and reduces the need for cerebellar retraction - MCF less favourable - dura more adherent, leads to more dura tears and increased CSF leak likely

Question 62

What are the 3 methods to identifying the IAC in a middle cranial fossa approach?

Answer 62

1. House method: Follow the GSPN back to geniculate and then follow the labyrinthine branch back to the IAC 2. Fisch Method: 45 degrees from the arcuate eminance (rounded bony prominence in the middle fossa that is associated with the superior semicircular canal below) 3. Jackler method: Between arcuate eminence and GSPN ## Footnote Vancouver 317

Question 63

What is the etiology of persistent headaches following retrosigmoid approach?5

Answer 63

Many people suffer from it, no one knows why it happens Theories/mechanisms: 1. Occipital nerve injury 2. Dura adhesions 3. Scalp adhesions 4. Neck muscle spasms 5. CSF leak related DONCS

Question 64

When do you consider a hearing preservation approach for vestibular schwannoma surgery?

Answer 64

If serviceable hearing, preference is to proceed with a hearing preservation approach

Question 65

What are the possible surgical complications of vestibular schwannoma excision? Besides GA, bleeding, infection, scar. 9

Answer 65

1. SNHL (~40% chance of significant hearing loss) 2. Facial nerve palsy 3. Hemorrhage 4. Meningitis 5. Air embolism 6. CSF leak 7. Cerebellar Ataxia 8. Headache 9. Recurrence

Question 66

What are 7 other approaches used for skull base lesions that require drainage or sectioning?

Answer 66

1. RETROLABYRINTHINE - Main indication is Vestibular nerve section - Also for resection of selected arachnoid cysts, meningiomas, metastatic CPA lesions - Minimal cerebellar retraction, hearing preservation 2. INFRALABYRINTHINE - After mastoidectomy, sigmoid sinus is decompressed and air cell tracts followed into petrous apex - May be impossible with a high jugular bulb 3. TRANSCOCHLEAR - Extension of translabyrinthine approach, removal of cochlea and displacement of facial nerve for access to petrous tip and clivus 4. TRANSOTIC - Similar to transcochlear, but facial nerve is skeletonized and left in the fallopian canal 5. TRANSCANAL INFRACOCHLEAR - Air cell tract between the IJV and ICA is followed into the apex - Permits dependent drainage, but requires EAC transection which heals over prolonged period, also requires exposure of petrous carotid artery 6. EXTENDED MIDDLE FOSSA - Extended by removal of petrous ridge and posterior aspects of temporal bone up to labyrinth 7. ENDOSCOPIC TRANS-SPHENOIDAL

Question 67

Regarding meningiomas of the CPA, discuss: 1. What are they? 2. Describe their pathology 3. What is their classification according to WHO?

Answer 67

MENINGIOMA: - Second most common CPA tumor (10%) - Benign unencapsulated tumor arising from arachnoid villi cells (around the tips), and "cap cells" PATHOLOGY: - Microscopic psammoma bodies (corresponds to calcifications seen on imaging) CLASSIFICATION (WHO): 15 variants, 9 are Grade I, 3 Grade II, 3 Grade III WHO Grade I (Benign, 90%): 1. Meningothelial 2. Fibrous 3. Transitional 4. Psammomatous 5. Angiomatous 6. Microcystic 7. Secretory 8. Lymphoplasmacyte-rich 9. Metaplastic My Friendly Tumor Parks Around My Skull Lying Meekly WHO Grade II (Atypical, 7%) 1. Atypical 2. Chordoid 3. Clear cell ACC WHO Grade III (Anaplastic/Malignant, 2%) 1. Rhabdoid 2. Anaplastic 3. Papillary RAP

Question 68

What are the classic features of CPA meningioma, with respect to: 1. Location 2. Bone changes 3. Shape 4. CT density 5. CT enhancement 6. T1-weighted MRI 7. Gadolinium enhancement 8. T2-weighted MRI

Answer 68

1. Location - Eccentric (slightly off) to the internal auditory canal 2. Bone changes - Occasional hyperostosis, unlikely to enlarge the porus acousticus 3. Shape - Hemispherical, rarely plaque-like; may herniate through tentorium, OBTUSE bone-tumor angle and DURAL TAIL (mushroom-cap appearance) 4. CT density - Slightly hypodense, some calcifications (from psammoma bodies) 5. CT enhancement - Marked and homogeneous 6. T1-weighted MRI - Isointense or hypointense; surface flow voids on MRI (correspond to marginal pial blood vessels) 7. Gadolinium enhancement - moderate 8. T2-weighted MRI - variable Overall features: - Obtuse angles to temporal bone - Dural tail present (50-75%) - May herniate into MCF/dumbbell (50%) - May show calcifications (25%) - Pial blood vessels with flow voids - No widening of porous acousticus - No intracanalicular component

Question 69

Describe the histopathology of meningiomas

Answer 69

- Lobulated groups of cells reminiscent of normal arachnoid granulations - Psammoma bodies often present (concentric lamellated calcified structures) - Hyperostosis of surrounding bone in 25% Immunohistochemistry: 1. Epithelial membrane antigen 2. Cytokeratin 3. S100

Question 70

What are the treatment options for CPA meningioma?

Answer 70

1. Surgery preferred 2. XRT if residual disease

Question 71

What are the main radiographic differences between Meningioma and Vestibular Schwannomas? (8)

Answer 71

1. M are more dense and homogeneous 2. M cause more hyperostosis of surrounding bone 3. M are sessile, broad base, obtuse angles to petrous bone 4. M eccentric over IAC where VS directly overlying or into 5. M uncommonly involve IAC, whereas VS have intracanalicular component 6. M frequently have a dural tail 7. M frequently have calcifications 8. VS exhibit greater, more homogeneous GAD enhancement

Question 72

What 10 sites do meningiomas commonly occur?

Answer 72

Order of most to least frequent: 1. Parasagittal 2. Convexity 3. Falx 4. Olfactory groove 5. Tuberculum sellae 6. Sphenoid ridge 7. CPA (petrous face) 8. Tentorium 9. Lateral ventricle 10. Clivus

Question 73

What immunohistochemistry can be performed for CPA chordomas and Chondrosarcomas? 3

Answer 73

CHORDOMAS: 1. S100 2. Cytokeratin 3. Vimentin CHONDROSARCOMA: 1. S100 2. Vimentin 3. NEGATIVE for cytokeratin

Question 74

Discuss CPA Epidermoids with respond to: 1. What is the epidemiology? 2. What are they? What are they formed by? 3. What are the four anatomic groups on where they can be found? 4. What are the Symptoms?

Answer 74

EPIDERMOIDS (CPA): - Aka primary cholesteatomas of the CPA - 1% of all intracranial tumors, 3% of all CPA lesions Entity: - Consists of stratified squamous epithelium that surrounds desquamated keratin - Originates from epithelial rests within the temporal bone or CPA that are entrapped - Slow growing lesion, infiltrative and expanding with local inflammatory reaction - Symptoms often not apparent until 2nd to 4th decades of life ANATOMIC GROUPS: 1. Petrous apex (most common) 2. CPA 3. Perigeniculate 4. Middle ear SYMPTOMS: 1. Facial twitching and weakness 2. Progressive facial paralysis more common than with schwannomas 3. Imbalance and hearing loss 4. Trigeminal numbness and pain

Question 75

Discuss the radiographic findings of CPA epidermoid with respect to: 1. Location 2. Bone changes 3. Shape 4. CT density 5. CT enhancement 6. T1-weighted MRI 7. Gadolinium enhancement 8. T2-weighted MRI 9. FLAIR and DWI

Answer 75

1. Location - Anterolateral or posterolateral to brainstem 2. Bone changes - Occasional erosion 3. Shape - Variable, irregular margins, eccentric to porus, tends to DUMBBELL into middle fossa or contralateral CPA cistern;; Cauliflower surface appearance 4. CT density - mostly hypodense, occasional peripheral calcium 5. CT enhancement - Does NOT enhance 6. T1-weighted MRI - Hypointense 7. Gadolinium enhancement - Does NOT enhance; however DOES enhance on DWI 8. T2-weighted MRI - Hyperintense 9. FLAIR intermediate, with hyperintense FOCI 10. DWI - bright (fluid restriction) - Similar to arachnoid cyst - therefore FLAIR and DWI more useful - Differentiates from cholesterol granuloma as it is hypointense on T1 but CG is hyperintense on T1

Question 76

What is the management of CPA epidermoids?

Answer 76

1. Surgical excision - complete excision near impossible, 30% recurrence 2. Should be differentiated from a cholesterol or arachnoid cyst, as drainage of these is often sufficient

Question 77

Why is complete resection of a temporal bone epidermoid so difficult? 2 reasons

Answer 77

- Lining creates an inflammatory reaction which becomes tightly adherent to the brainstem or cerebellum - Local neurovascular structures become enveloped instead of displaced or compressed - Complete removal is only possible in 50% and many have post-op cranial nerve deficits - Recurrence expected in 30% with subtotal resection

Question 78

Compare and contrast the imaging findings of Vestibular schwannoma, meningioma, and CPA epidermoid, with respect to: 1. Location 2. Bone changes 3. Shape 4. CT density 5. CT enhancement 6. T1-weighted MRI 7. Gadolinium enhancement 8. T2-weighted MRI

Answer 78

Vestibular schwannoma: 1. Location - centered on the internal auditory canal 2. Bone changes - Enlarge the IAC/porus acousticus 3. Shape - Spherical or ovoid, with an ACUTE bone-tumor angle 4. CT density - Mostly isodense 5. CT enhancement - Moderate to marked, often inhomogeneous and variable 6. T1-weighted MRI - Isointense or hypointense 7. Gadolinium enhancement - MARKED 8. T2-weighted MRI - Isointense or hypointense Meningioma: 1. Location - Eccentric (slightly off) to the internal auditory canal 2. Bone changes - Occasional hyperostosis, unlikely to enlarge the porus acousticus 3. Shape - Hemispherical, rarely plaque-like; may herniate through tentorium, OBTUSE bone-tumor angle and DURAL TAIL (mushroom-cap appearance) 4. CT density - Slightly hypodense, some calcifications (from psammoma bodies) 5. CT enhancement - Marked and homogeneous 6. T1-weighted MRI - Isointense or hypointense; surface flow voids on MRI (correspond to marginal pial blood vessels) 7. Gadolinium enhancement - moderate 8. T2-weighted MRI - variable Epidermoid: 1. Location - Anterolateral or posterolateral to brainstem 2. Bone changes - Occasional erosion 3. Shape - Variable, irregular margins, eccentric to porus, tends to DUMBBELL into middle fossa or contralateral CPA 4. CT density - mostly hypodense, occasional peripheral calcium 5. CT enhancement - Does NOT enhance 6. T1-weighted MRI - Hypointense 7. Gadolinium enhancement - Does NOT enhance; however DOES enhance on DWI 8. T2-weighted MRI - Hyperintense

Question 79

Describe the general radiographic features of arachnoid cyst on CT and MRI

Answer 79

General features: - Smooth surface CT: - Isodense to CSF MRI: 1. T1 - Isointense 2. T2 - Hyperintense to CSF 3. DWI - Suppressed

Question 80

What is the petrous apex? What are its borders?

Answer 80

Pyramid-shaped anteromedial part of the petrous portion of the temporal bone. Articulates with the posterior aspect of the greater wing of the sphenoid and occipital bones Lateral: inner ear Medial: petrooccipital fissure Anterior: petrosphenoidal fissure and petrous part of the ICA in the carotid canal Posterior: posterior cranial fossa Superior: Middle cranial fossa, meckel's cave, and petrous ICA Inferior: Jugular bulb, inferior petrosal sinus Division between anterior and posterior petrous apex - Internal Auditory Canal (IAC) ## Footnote https://d45jl3w9libvn.cloudfront.net/jaypee/static/books/9789351524632/Chapters/images/149-1.jpg

Question 81

What clinical features are expected from a petrous apex lesion?

Answer 81

1. Meckel's cave involvement --> trigeminal irritation --> retroorbital pain, numbness 2. Dorello's canal involvement --> VI palsy 3. Labyrinth involvement --> Hearing loss, tinnitus, vertigo

Question 82

What is Meckel's cave? What are its boundaries?

Answer 82

Aperture in medial portion of middle cranial fossa that is a conduit for trigeminal nerve Boundaries: Anterior - Foramen ovale/ rotundum Posterior - Petrooccipital fissure Superior - Sphenoid bone (greater wing) and arachnoid mater Inferior - Foramen ovale Medial - Dorsum sellae Lateral - Petrous portion of temporal bone

Question 83

What is the name of the canal that the abducen's nerve passes through? What else runs in this canal? Where does this canal end up? What are the boundaries of Dorello's canal?

Answer 83

Dorello's canal Contains the inferior petrosal sinus and abducens nerve (CNVI) Both structures then merge into the cavernous sinus Boundaries: Anterior / Medial = Clivus (sphenoid) Posterior / Lateral = Petrous part of temporal bone Superior = Sphenoid Inferior = basilar part of occipital bone

Question 84

What is the differential diagnosis for petrous apex lesions? Name 10

Answer 84

C's mnemonic: 1. Cholesterol granuloma (by far most common 20x more than #2 below) 2. Cholesteatoma (ie. Epidermoid cyst) 3. Chordoma 4. Chondrosarcoma 5. Cephalocele 6. Cyst (mucocele/retained mucous) 7. Carotid aneurysm (ICA aneurysm) Benign tumors: 1. Schwannoma 2. Lipoma 3. Paraganglioma (glomus tumors - tympanicum, jugulare) 4. Meningioma Malignant tumors: 1. Chordoma 2. Chondrosarcoma 3. Plasmacytoma 4. Lymphoma 5. Metastasis Other: 1. Petrous apicitis ± osteomyelitis 2. Langerhans cell histiocytosis

Question 85

Regarding Cholesterol Granulomas, discuss: 1. What is it? 2. What is the pathophysiology theories?

Answer 85

CHOLESTEROL GRANULOMA: - Most common lesion of the petrous apex - Thought to arise from local inflammatory granulomatous response to blood products, specifically cholesterol crystals PATHOPHYSIOLOGY (2 Theories): 1. OBSTRUCTION-VACUUM THEORY - Air cells in the petrous apex are obstructed, resulting in negative pressure - Negative pressure causes an effusion, inflammation, and hemorrhage - Local inflammatory response leads to formation of cholesterol crystals 2. EXPOSED MARROW THEORY - Progression of normal air cell pneumatization in the petrous apex exposes bone marrow, which hemorrhages - Local hemorrhage inflammatory response leads to formation of cholesterol crystals ## Footnote Pathology - looks like cholesterol crystals (path book Page 15)

Question 86

What is the pathology of a cholesterol granuloma?

Answer 86

"Empty" spaces contained cholesterol crystals prior to tissue processing

Question 87

Regarding cholesterol granulomas: 3. How is it typically diagnosed? 4. What may mimic cholesterol granuloma? How do you differentiate? 5. What is the treatment? How is this different from other petrous apex lesions? 6. What are the different surgical approaches and which ones are preferred?

Answer 87

DIAGNOSIS: 1. Often found incidentally 2. Larger masses may affect CNV (Meckel's cave), CNVI (Dorello's canal), CN VII/VIII 3. MRI: Hyperintense on BOTH T1 and T2 weighted images (Pathognomonic), NON-enhancing with gad NOTE: Asymmetric pneumatization of the petrous apex may mimic this - Can often be confused with true neoplasms - The fat content of bone marrow in a non-pneumatized petrous apex can produce a hyperintense appearance on T1 Non-contrast MRI How to differentiate from true neoplasm? - Cholesterol granuloma will also show hyperintensity on T2 (asymmetric pneumatization will be hypointense on T2) - No bone destruction or expansion on CT - No enhancement with gadolinium TREATMENT: - Total excision of cholesterol granulomas usually is unnecessary (unlike other petrous apex mass lesions) - Treatment for cholesterol granuloma is focussed around drainage and ventilation of the granuloma - Transmastoid or transcanal infralabyrinthine drainage approach preserves cranial nerve function - Transcanal infracochlear hypotympanotomy approach is preferred because it affords dependent drainage and the possibility of revision, if necessary, through a myringotomy. - Other approaches for unfavourable anatomy: infracochlear or infralabyrinthine drainage, middle fossa drainage

Question 88

Outline the imaging features for the following petrous apex lesions: 1. Cholesterol granuloma 2. Epidermoid cyst (cholesteatoma) 3. Mucocele 4. Marrow (asymmetric pneumatization) 5. Lipoma 6. Trapped fluid 7. Chondrosarcoma Based on the following imaging features: 1. CT intensity 2. T1 weighted 3. T1 + Gad contrast 4. T2 5. Borders of lesion 6. Diffusion weighted 7. Other

Answer 88

Note: Gadolinium highlights blood vessels (hence "contrast") CHOLESTEROL GRANULOMA 1. CT intensity: Isodense soft tissue mass 2. T1 weighted: Hyperintense (possibly central hypointensity) 3. T1 + Gad contrast: Non-enhancing 4. T2 weighted: Hyperintense (possibly central hypointensity) 5. Borders of lesion: Smooth 6. Diffusion weighted: No restricted diffusion (hypointense) 7. Other: Expansile mass EPIDERMOID CYST (CHOLESTEATOMA) 1. CT intensity: Hypodense 2. T1 weighted: Hypointense 3. T1 + Gad contrast: Nonenhancing, but if there is granulation tissue may have rim enhancement 4. T2 weighted: Hyperintense 5. Borders of lesion: Scalloped 6. Diffusion weighted: Restricted diffusion (hyperintense) 7. Other: Expansile mass MUCOCELE 1. CT intensity: Hypodense 2. T1 weighted: Hypointense 3. T1 + Gad contrast: Mass does not enhance, but rim enhances 4. T2 weighted: Hyperintense 5. Borders of lesion: Smooth 6. Diffusion weighted: No restricted diffusion (hypointense) 7. Other: Expansile mass MARROW (ASYMMETRIC PNEUMATIZATION) 1. T1 weighted: Hyperintense 2. T1 + Gad contrast: No enhancement 3. T2 weighted: Isointense 4. Other: T1 intensity disappears with fat suppression (because it's just like fat) LIPOMA 1. T1 weighted: Hyperintense 2. T1 + Gad contrast: No enhancement 3. T2 weighted: Hypointense TRAPPED FLUID 1. T1 weighted: Hypointense 2. T1 + Gad contrast: No enhancement 3. T2 weighted: Hyperintense CHONDROSARCOMA 1. T1 weighted: Hypointense 2. T1 + Gad contrast: YES enhancement 3. T2 weighted: Hyperintense 4. Other: Rare, but most common malignant primary of petrous apex ## Footnote Kevan Otology Page 41

Question 89

Regarding the common drainage approaches to the petrous apex, discuss: 1. What are the 5 main approaches? 2. What are the structures at risk of each approach? 3. Advantages of each 4. Disadvantages of each

Answer 89

INFRALABYRINTHINE 1. Structures at risk: - Jugular bulb - Bony labyrinth - Facial nerve 2. Advantages: - Direct approach, most familiar to most ENT 3. Disadvantages: - Difficult with high jugular bulb - Drainage into mastoid cavity far from eustachian tube TRANSCANAL INFRACOCHLEAR 1. Structures at risk: - Jugular bulb - Carotid artery - Cochlea 2. Advantages: - Direct drainage near the opening of the eustachian tube - Recurrence can be treated through myringotomy 3. Disadvantages: - Anatomy may be challenging to surgeons not familiar with hypotympanum and major vessels of temporal bone TRANSPHENOIDAL 1. Structures at risk: - Carotid artery - Optic nerve - Cavernous sinus - Maxillary nerve - Pituitary gland 2. Advantages: - Direct approach to large cysts that are in contact with posterior wall of sphenoid sinus - Opening into cyst may be directly observed in clinic with endoscope 3. Disadvantages: - Can be used only to "giant" cysts in contact with the sphenoid sinus TRANSLABYRINTHINE OR SUBTOTAL PETROSECTOMY 1. Structures at risk: - Labyrinth - Jugular bulb - IAC 2. Advantages: - Cyst and wall can be removed if desired 3. Disadvantages: - Profound hearing loss SNHL post-op MIDDLE CRANIAL FOSSA 1. Structures at risk: - Temporal lobe - Cochlea - Labyrinth - IAC - Greater superficial petrosal nerve 2. Advantages: - Drains out directly into bony eustachian tube 3. Disadvantages: - Middle fossa craniotomy poorly tolerated in elderly - Drainage is not dependent - Temporal lobe may obstruct drainage path

Question 90

What is the differential diagnosis of intra-axial tumors (within the brain parenchyma)? (4)

Answer 90

1. Hemangioblastoma 2. Medulloblastoma 3. Brainstem Glioma (most common pediatric CPA lesion) 4. Malignant Choroids plexus papilloma and ependymomas HMM Baby

Question 91

What is the FIESTA-C/CISS MRI sequences?

Answer 91

Summary - fluid and fat are bright, other structures not. Good for seeing neuro structures without contrast such as nerves Manufacturer sequences: - GA (FIESTA - Fast imaging employing steady-state acquision) - Siemens (CISS - constructive interference in steady state) Goals: - Employs a balanced steady state gradient echo sequence, a function of T1/2 - T1 remains constant so imaging is predominantly T2 weighted - Fluid and fat are bright in contrast to other structures (gray) - Low motion sensitivity: Good for seeing neuro structures without contrast (e.g. cranial nerves); fast imaging time and for people who cannot hold still/hold breath for long; also useful for brain imaging

Question 92

What is a FLAIR MRI sequences?

Answer 92

FLAIR = Fluid attenuated inversion recovery - Removed CSF signal (appears dark) and brain is otherwise in T2 - Helps to differentiate arachnoid cyst and epidermoid cyst (because arachnoid cyst contains CSF therefore will appear dark) Think of it as the fat suppression version for fluid

Question 93

What does Diffusion Weighted MRI mean?

Answer 93

MRI that demonstrates diffusion restriction. - Anything that has restricted fluid will light up (e.g. Cholesteatoma)

Question 94

If there is labyrinthine enhancement on an MRI before and after contrast on T1 sequence, what is this suggestive of?

Answer 94

BEFORE: - Blood (ie. trauma) AFTER: - Inflammation (ie. Labyrinthitis)

Question 95

What are the MRI characteristics (all possible, including T1, T2, Gad, FLAIR, DWI, Other) for the following CPA and Petrous Apex tumors: 1. Vestibular Schwannoma 2. Meningioma 3. Epidermoid Cyst (Cholesteatoma) 4. Arachnoid cyst 5. Paraganglioma 6. Cholesterol granuloma 7. Dermoid 8. Lipoma 9. Chordoma and Chondrosarcoma 10. Petrous Apicitis 11. Endolymphatic Sac tumor

Answer 95

VESTIBULAR SCHWANNOMA: 1. T1 - Iso/hypointense 2. T2 - Iso/Hyperintense 3. Gad - Very strong enhancement MENINGIOMA: 1. T1 - Iso/hypointense 2. T2 - Variable 3. Gad - Strong enhancement EPIDERMOID CYST: 1. T1 - Iso/hypointense 2. T2 - Hyperintense 3. Gad - NON-enhancing 4. DWI - Hyperintense 5. FLAIR - Isointense (note: FLAIR or DWI required to differentiate from arachnoid cyst - FLAIR will suppress CSF in the arachnoid cyst signal, but not in Epidermoid; DWI is restricted in Epidermoid therefore bright, but not arachnoid cyst) ARACHNOID CYST (Very well defined and round): 1. T1 - Hypointense 2. T2 - Hyperintense (like CSF) 3. Gad - Non-enhancing 4. DWI - Hypointense (no restriction) 5. FLAIR - Hypointense (CSF suppressed) PARAGANGLIOMA (Main features is salt and pepper on T1+T2, representing combination of punctate regions of hemorrhage or slow flow (salt), and flow voids (pepper)) 1. T1 - Iso/hypointense 2. T2 - Hyperintense 3. Gad - Strong enhancement CHOLESTEROL GRANULOMA (key feature is its bright on T1 and T2, no Gad; similar to Endolymphatic sac tumor) 1. T1 - Hyperintense 2. T2 - Iso/Hyperintense 3. Gad - Non-enhancing DERMOID 1. T1 - Hyperintense 2. T2 - Hypointense 3. Gad - Non-enhancing, but still hyperintense because of hyperintensity from T1 fat LIPOMA (same as dermoid; differentiate by using a fat-suppression sequence) 1. T1 - Hyperintense 2. T2 - Hypointense 3. Gad - Non-enhancing CHORDOMA & CHONDROSARCOMA 1. T1 - Iso/hypointense 2. T2 - Hyperintense 3. Gad - Strong enhancement PETROUS APICITIS 1. T1 - Hypointense 2. T2 - Hyperintense 3. Gad - Rim enhancement (infection) ENDOLYMPHATIC SAC TUMOR (Both T1 and T2 hyperintense) 1. T1 - Hyperintense 2. T2 - Hyperintense - Test TSH - cystic lesion that looks like thyroid metastasis - With VHL - 11% lifetime risk of developing, increases to 60% if HL is present

Question 96

What are the T1 Hyperintense CPA lesions?

Answer 96

1. Dermoid cyst (has fat in it) 2. Lipoma 3. Endolymphatic sac tumor 4. Cholesterol Granuloma

Question 97

What are the T2 Hyperintense CPA lesions? 9

Answer 97

1. Vestibular schannoma 2. Meningioma 3. Epidermoid cyst 4. Arachnoid cyst 5. Paraganglioma 6. Cholesterol granuloma 7. Endolymphatic sac tumor 8. Chondroma/Chondrosarcoma 9. Petrous apicitis

Question 98

What are the lesions that light up in the IAC with Gadolinium? 9

Answer 98

1. Any Schwannomas (VS, Facial) 2. Meningiomas 3. Inflammatory nerve lesions 4. AVMs 5. Vascular loops 6. Petrous bone metastasis 7. Paraganglioma 8. Chondroma/Chondrosarcoma 9. Petrous apicitis (rim enhancement)

Question 99

What are the two CPA lesions that are differentiated using DWI/FLAIR enhancement?

Answer 99

1. Epidermoid cyst (hyperintense on DWI; isointense on FLAIR) 2. Arachnoid cyst (hypointense on DWI; Hypointense on FLAIR)

Question 100

Regarding Endolymphatic Sac Tumors, discuss: 1. What are they? 2. Where are they most commonly located? 3. What syndromes are commonly associated? 4. What are the histopathologic findings? 5. What are the MRI features?

Answer 100

ENDOLYMPHATIC SAC TUMORS - Rare aggressive papillary tumors Most common location: Proximal sac SYNDROMES: 1. 50% associated with Von Hippel Lindau syndrome (11% with VHL have ELS tumors) HISTOPATHOLOGY: - Proteinaceous material similar to thyroglobulin, but do not stain positive for Tg MRI: (Similar to Cholesterol granuloma) 1. T1 hyperintense 2. T2 hyperintense 3. Ocacsionally a rim of intensity without contrast

Question 101

Regarding Trigeminal Schwannoma, discuss: 1. Where is this commonly located? 2. What are the typical symptoms? 3. What are the four types? | .

Answer 101

LOCATION: - Gasserian ganglion (semilunar ganglion) SYMPTOMS: 1. Facial neuralgia 2. Paresthesias 3. Retroorbital pain TYPES: Type A: Tumors of the middle cranial fossa in the interdural space (Meckel's cave) Type B: Tumors of the posterior fossa in the subdural space Type C: Dumbbell-shaped tumors (afflicting both middle and posterior fossa) Type D: May arise from any extracranial division of the trigeminal nerve ## Footnote Vancouver 320 Gasserian Ganglion aka. Semilunar Ganglion: https://upload.wikimedia.org/wikipedia/commons/8/83/Gray778.png

Question 102

What are two surgical approaches to the anterior cranial fossa?

Answer 102

1. ANTERIOR CRANIOFACIAL RESECTION - Bifrontal craniotomy combined with a transfacial exposure of nasal cavity, ethmoid, maxillary, and orbital areas 2. BASAL SUBFRONTAL - Similar to craniofacial resection approach but less extensive transfacial exposure, and target area is the sphenoid and clivus

Question 103

What are the surgical approaches to the central compartment of the middle cranial fossa?

Answer 103

1. Transseptal sphenoid 2. Transethmoidal sphenoid 3. Lateral rhinotomy 4. Transantral/Lefort I osteotomy 5. Midfacial degloving 6. Transpalatal 7. Transoral 8. Mandibulotomy 9. Extended Maxillotomy 10. Infratemporal fossa (Fisch B) - located by a line through medial pterygoid plate and occipital condyle on both sides

Question 104

What are the surgical approaches to the lateral compartment of the middle cranial fossa?

Answer 104

1. Intracranial - Temporal craniotomy 2. Transtemporal - Lateral, mainly extradural, anterior limit is intrapetrous ICA, adjuncts used in combination with other MCF approaches 3. Infratemporal 4. Transfacial - Facial translocation

Question 105

What are the methods of monitoring the cochlear nerve during IAC surgery?

Answer 105

1. ABR - Loss of waves I, II, III - Prolonged I-V latency - If pre-op SRT > 50, then accuracy here is poor 2. ECoG - Decreased amplitude of Action potential - Challenging to place, overall less sensitive 3. Brain stem auditory evoked potentials 4. Compound nerve action potentials

Question 106

Regarding a Chordoma of the Temporal Bone, discuss: 1. What is it? 2. What is the histopathology? Immunohistochemistry? 3. What are the major sites? 4. What are the pathological types? (3) 5. What are the symptoms? 6. What is the treatment? 7. What is the prognosis?

Answer 106

CHORDOMA: - Rare, slow growing skull base malignancy - Derived from NOTOCHORD REMNANT (embryologic derivative) HISTOPATHOLOGY: 1. Physaliferous cells (soap bubble appearance) in the myxoid stroma 2. Immunohistochemistry positive: - S100 - Vimentin - Cytokeratin MAJOR SITES: 1. Sacrococccygeal (2/3) 2. Sphenooccipital (1/3) 3. Vertebral rare PATHOLOGICAL TYPES: 1. Classic 2. Chondroid 3. Atypical SYMPTOMS: - Diplopia and Headache most common - Abducens palsy most common deficit TREATMENT: - Surgery - Radiotherapy for incomplete excision PROGNOSIS: - Poor 15-50% disease free progression in 10 years despite treatment ## Footnote Vancouver 320

Question 107

What are the most common sources of temporal bone metastases? 7

Answer 107

- Prostate - Thyroid - Breast - Lung - Larynx - Kidney - GI tract

Question 108

What are 3 ENT disorders associated with vascular loops?

Answer 108

1. Trigeminal neuralgia 2. Hemifacial spasm (Brissard phenomenon - Facial spasms from a lesions or CPA vessel loop) 3. Vestibular Paroxysma - Loops in the CPA or IAC have been proposed to be a cause for: SNHL, tinnitus, vertigo, and Meniere's (Controversial)

Question 109

Regarding vascular loops, discuss: 1. What are they? 2. What is the most common vessel? 3. What is the clinical presentation? 4. What is the recommended imaging of choice? 5. What is the proposed treatments?

Answer 109

VASCULAR LOOPS: - Aberrant artery in the IAC compressing CN VII/VIII Most common vessel: Anterior inferior cerebellar artery (AICA) Clinical presentation: - Can be asymptomatic (often found incidentally) - Pulsatile tinnitus - SNHL (from compression) - Brief episodic vertigo - Hemifacial spasm IMAGING: 1. MRI of IAC TREATMENT: 1. Vascular decompression for trigeminal neuralgia and hemifacial spasm is well accepted, but decompression for auditory/vestibular dysfunction has no good evidence (largely anecdotal) 2. Vessel loops often seen during CPA surgery in patients with no symptoms from this.

Question 110

What skull base lesions are associated with facial twitching/tics? 4

Answer 110

1. Epidermoid cyst 2. Facial nerve schwannomas 3. Facial nerve hemangioma 4. Vascular loop (AICA most common) FFEV