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Skull Base Flashcards

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1
Q

What are paragangliomas?

A

Neoplasm that originated from chromaffin cells

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2
Q

Where do jugular foramen schwannomas arise from?

A

CN9 and 10 > 11 or sympathetic chain

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3
Q

What are the boundaries of the jugular foramen?

A

Junction between the petrous temporal and occipital bones

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4
Q

What are the segments of the jugular foramen?

A 
Anterior = IPS
Middle = CN9, 10 & 11
Posterior = Sigmoid sinus and Jugular bulb with meningeal branches from the occipital and ascending pharyngeal arteries
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5
Q

What are the contents of the pars nervosa of the jugular foramen?

A

CN9, tympanic nerve (branch of CN9) and IPS

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6
Q

What are the contents of the pars venosa of the jugular foramen?

A

CN10, auricular branch of CN10, CN11, Jugular bulb and posterior meningeal branch of the ascending pharyngeal artery

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7
Q

What separates the pars venosa from the pars nervosa of the jugular foramen?

A

The jugular spine (fibrous septum in 80% and bony in 20%)

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8
Q

Which cranial nerve is completely separate from the others in the Jugular foramen?

A

CN9 lies within a connective tissue sheath

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9
Q

What is the grading system for Jugular foramen tumours?

A 
A = Intracranial
B = Intraosseous
C = Extracranial
D = Saddle shaped tumours spanning the above
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10
Q

What is the approach of choice for Jugular foramen tumours with large intradural components?

A

Retrosigmoid approach - but cannot access the Intraosseous or Extracranial components;
This can be extended via the transcondylar approach by removing the occipital condyle and jugular tubercle

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11
Q

What is the approach of choice for dumbbell tumours of the jugular foramen?

A

Presigmoid, transcondylar infra labyrinthine approach

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12
Q

What is the aim of surgery for glomus jugulare tumours?

A

Total surgical resection

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13
Q

Should the sigmoid sinus and jugular bulb be ligated if the veins are occluded?

A

No as they will recannalise once the tumour has been removed

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14
Q

How would you approach a jugular foramen tumour extending intracranially to the CP angle?

A

Retrosigmoid +/- transcondylar route

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15
Q

How would you approach an Extracranial jugular foramen tumour?

A

Cervical approach

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16
Q

How are dumbbell tumours of the jugular foramen approached?

A

Presigmoid, transcondylar, infralabyrinthine approach

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17
Q

What % of meningiomas are at the foramen magnum?

A

2%

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18
Q

Where do most foramen magnum tumours have their dural attachment?

A

Anterior-lateral in 75%

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19
Q

What are the approaches for anterior foramen magnum meningiomas?

A

Transoral, far lateral or the extreme / anterio-lateral approach

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20
Q

What is the main difference between the far lateral and the extreme lateral approaches?

A

The extreme lateral approach requires transposition of the vertebral artery to allow occipital condyle drilling

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21
Q

What are the factors that influence resection of foramen magnum meningiomas?

A

Anterior location, tumour size (larger tumours are easier due to bigger surgical corridor), invasion, extradural extension, vertebral artery encasement and arachnoid plane.

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22
Q

Which tumours can affect the optic nerves?

A 
Meningioma
Optic Gliomas
Pituitary adenoma
Craniopharyngioma
Chordoma
Fibrous dysplasia
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23
Q

What is the most common histology for an optic nerve sheath Glioma?

A

Pilocytic astrocytoma

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24
Q

Which patients are most likely to develop optic nerve sheath Gliomas?

A

NF 1

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25
Bilateral optic nerve sheath gliomas are pathognomonic for which condition?
NF1
26
How do optic nerve sheath Gliomas present?
Proptosis if unilateral or visual deterioration if bilateral
27
When is surgery undertaken for optic nerve sheath Glioma?
Once vision is lost and if the tumour is growing towards the chiasm
28
What is the rate of malignant transformation of fibrous dysplasia?
1%
29
What is fibrous dysplasia?
Where normal bone is replaced with fibrous connective tissue
30
When is surgery undertaken with fibrous dysplasia?
With visual deterioration, rapid growth or cosmesis. There is no preventative surgery for fibrous dysplasia!
31
Where do chordomas arise?
In the Clivus and sacrum
32
What do chordomas arise from?
Notochord remnants
33
What is the treatment of choice for chordomas?
Maximal resection and proton beam therapy
34
How do chordomas present?
Classically with headache and CN6 palsy. Visual deterioration if optic nerves are compressed.
35
How can hearing be improved in patients with an intact CN8?
Cochlear implant
36
How can hearing be improved in patients with a deficient CN8?
Brainstem auditory implant
37
How do brainstem auditory implants work?
Through direct stimulation of the cochlear nucleus in the brainstem
38
What are the outcomes of auditory brainstem implants?
50% have >50% average correct sentence recognition which improves to 70% with lip reading
39
Why were penetrating electrodes now used for auditory brainstem implants?
Different tone pitches are represented in different layers of the cochlear nucleus so penetrating electrodes allows access to these but overall does not improve hearing
40
How can hearing be improved in patients with damaged cochlear nuclei?
Inferior colliculus stimulation via auditory midbrain implants
41
When should a spontaneous CSF leak be suspected?
In cases of recurrent meningitis
42
What is a Hyrtl's fissure?
A pseudo typano-meningeal duct in which there is an intracranial-Extracranial CSF connection along the CN9 to the tympanic canal.
43
What proportion of pituitary tumours occur in children?
5% are
44
What genetic conditions are most likely to result in paediatric pituitary tumours?
MEN1, Carney complex and familial isolated pituitary adenoma (FIPA)
45
What is the most common paediatric pituitary region tumour?
Craniopharyngioma (90%)
46
What is the age specific incidence of craniopharyngioams?
Bimodal between 5-14 years and then >50 years
47
What is the treatment for Craniopharyngioma?
Surgical resection followed by radiotherapy
48
What is the incidence of craniosynostosis?
1:2500
49
What are the incidences of single suture synostosis?
Sagittal (Scaphocephaly) 50% Coronal (brachycephaly) 30% Metopic (Trigonocephaly) 10% Lamdoid (Posterior plagiocephaly) 1%
50
What environmental factors predispose to craniosynostosis?
Valproate use during pregnancy Uterine anomaly Multiple pregnancies
51
What is the inheritance pattern of most syndromic craniosynostosis?
Autosomal dominant (Except Carpenter's syndrome which is recessive)
52
Which gene mutations are most commonly involved with craniosynostosis?
FGFR3 , FGFR2, TWIST1 and EFNB1
53
Which patients with craniosynostosis should undergo genetic testing?
FGFR3, FGFR2 and TWIST1 should be tested in all patients with coronal and multi suture synostosis
54
What lesions occurs at the petrosphenoid junction?
Chondrosarcoma
55
What lesions can occur at the bony petrous apex?
Cholesterol granuloma, Trigeminal schwannomas and Epidermoid cyst
56
What is the differential diagnosis of a jugular foramen tumour?
``` Paraganglioma (glomus jugulare) (80%) Schwannoma (10%) Meningioma Epidermoid Clival chordoma ```
57
Where is the petrolingual ligament?
Underneath the Trigeminal ganglion overlying the petrous ICA
58
What is the differential diagnosis of a petrous apex lesion?
Within the bone - cholesterol granuloma Extradural - Trigeminal schwannoma, Chondrosarcoma, meningioma Intradural - (look it up)
59
Which syndrome is associated with endolymphatic sac tumorus?
VHL
60
Which nerve is found exiting the suboccipital triangle?
The greater occipital nerve
61
Where does the hypoglossal nerve lie during the far lateral approach?
Above the V3 segment of the vertebral artery
62
What is the differential diagnosis of a cystic pituitary region lesion?
``` Pituitary adenoma Craniopharyngioma Rathke's cleft cyst Epidermoid cyst Germinomas Arachnoid cyst ```
63
Options for management of a craniopharyngioma?
``` VP shunt Cyst aspiration +/- reservoir Cyst-ventricular shunt / Cyst fenestration marsupilisation Tumour debulking (Radiotherapy) ```
64
What are the surgical approaches used for craniopharyngioma?
Pterional Fronto-lateral Interhemispheric (transbasal / transglabella)
65
What is Sternberg's canal?
Look it up: | A widening between the sphenoid body and wing which results in a connection and is a cause of a spontaneous CSF leak.
66
What is a Hyrtl's fissure?
A congenital connection between the posterior fossa and the middle ear which usually closes by 24 weeks. Can be a congenital cause of a spontaneous CSF leak.
67
What is the most common skull base tumour?
Meningioma
68
What meningioma types are atypical (have brain invasion)?
Chordoid and clear cell
69
What meningioma types are anaplastic?
Papillary and rhabdoid
70
What mutation occurs in most meningiomas?
Loss 22q (reason why meningiomas are common in NF2!)
71
What protein is encoded by the NF2 gene?
Merlin
72
What are the biological therapies for meningiomas?
Vismodegib - inhibits SHH pathway
73
What proportion of chordomas metastasise?
40%
74
What cells are found in chordomas?
Physaliferous cells
75
What types of craniopharyngioma have a BRAF mutation?
Papillary (Adult) type
76
What is the lowest part of the anterior cranial fossa?
The olfactory fossa
77
Enlargement of the sella occurs with which pathology?
Meningioma (not adenoma)
78
Patient with a tuberculum meningioma and something in the nose. What is in the nose?
Either growth of the meningioma into the nose or a MUCOCELE
79
How do you manage an asymptomatic meningoma?
Monitor the lesion with serial scans to assess the natural history. Remove if growing / causing mass effect and conservative management if not.
80
What is OCT?
Optic coherence tomography
81
What approach for olfactory groove or planum meningioma can preserve smell?
Unilateral supra-orbital / pterional craniotomy approaching from the side where the smell is worse. Note: Endonasal approaches are transcribiform so loss of smell always occur.
82
What is the classification of vestibular schwannoma?
Koos classification from 1-4 based on size i.e. <10mm, 10-20mm, 20-30mm and >30mm
83
What is the classification for hearing?
Gardener-Robertson classification: | Serviceable hearing = <50Db / >50 discrimination rule (On PTA and speech discrimination)
84
What is the management algorithm for vestibular schwannoma?
<15mm - observe 15-25 mm - SRS (surgery if trigeminal dysfunction or disabling vertigo) >30 or cystic or mass effect - microsurgery
85
What is the hearing preservation following SRS/microsurgery for acoustic neuroma?
Good hearing preservation if the hearing is unaffected to begin with. If hearing is diminished to begin with, then will deteriorate with time. Overall about 50%
86
When is a middle fossa approach done for vestibular schwannoma?
Small intra-cannalicular approach for hearing preservation
87
How is facial nerve preserved during acoustic neuroma microsurgery
Subtotal resection of acoustic neuroma followed by SRS to remnant if >5 mm
88
What medical treatment is given for vestibular schwannoma in NF2?
Avastin (bevacizumab) if growth rate >4mm / year; VEGF inhibitor that has to be taken longterm.
89
How is hearing reconstructed following acoustic neuroma resection?
Auditory brainstem implant | Or cochlear nerve implant if cochlear nerve preserved
90
What happens to hearing in NF2 patients?
Eventually will loose hearing so hearing preservation is not possible so. Work on hearing reconstruction!
91
What are the causes of hydrocephalus in acoustic neuroma?
1) Mass effect causing obstructive hydrocephalus | 2) Proteinaceous fluid release resulting in communicating hydrocephalus

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