Retrocochlear and the CANS Pathway Flashcards
What are retrocochlear disorders?
Disorders that affect the auditory nerve and its connections to the central auditory nervous system
What are neoplasms?
New growth
Abnormal growth of mass tissue
Disorder of the cell cycle
What is the growth of neoplasms like?
Uncoordinated and exceeds that of normal tissue
Grows in an excessive manner
Competes with normal cells/tissue for energy and nutrition
Grows at the host’s expense
Do neoplasms have purpose?
No
They are purposeless, prey on the host, and are almost autonomous
What are intracranial neoplasms?
Brain tumors
What are some types of intracranial neoplasms?
Benign and malignant tumors
Mass lesions (such as cysts) of the brain parenchyma (functional tissue of an organ)
Tumors in the meninges
Tumors from structures near the brain tissue (pituitary gland and pineal gland tumors) or other sites in the body that affect brain tissue and function
What is the incidence of intracranial neoplasms?
4 to 12 per 100,000
What cells do 45% of intracranial neoplasms arise from?
Neuroglial cells
What are neuroglial cells?
Non-excitable support cells of the CNS (not neurons which as excitable)
Smaller than neurons, lack axons, and do not synapse with other cells
Outnumber neurons
Make up 1/2 the volume of the CNS
What are the 4 main types of neuroglial cells?
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
What are astrocytes?
Star-shaped
Support nerve cells and function as electrical insulators
Provide a barrier at synapses
Play a role in the formation of the blood-brain barrier
What are oligodendrocytes?
Active in the formation of myelin sheaths for central nerve fibers
What are microglia?
Small glial cells
Activated in the presence of inflammation and degenerative processes with the CNS
Phagocytic function (ingest and remove neural residue)
What are ependymal cells?
Epithelial cells that line the CSF filled brain cavities and spinal cord
Some are ciliated and facilitate CSF circulation
Involved in the production of CSF
What are some characteristics of benign neoplasms?
Typically slow growing
Well-defined borders (surgery effective treatment)
Does not spread to other areas of the body
Generally not life-threatening
When will a benign neoplasm kill?
When it is locally destructive or it is located in areas of the brain that control vital functions
What are some characteristics of malignant neoplasms?
Cell structure significantly different than normal brain cells
Grow faster and cause invasion and destruction
Life-threatening
Can spread throughout the body
Even though malignant tumors can spread throughout the body, is it rare for a primary brain tumor to spread beyond the brain or spine?
Yes
Is the distinction between benign and malignant brain tumors always clear cut?
No
A large benign tumor may lead to serious medical problems and even death
A small malignant tumor may escape detection for a while if they are in an area where they can grow
What are intra-axial or intrinsic tumors?
Tumors originating within the brain tissue
What are some examples of intra-axial tumors?
Astrocytoma, glioblastoma, and cerebral metastases
What are extra-axial tumors or extrinsic tumors?
Originate from tissue that is neither neuronal or glial
What are some of the originating sites of extra-axial tumors?
All tissue that encase or support the brain substance, including the meninges
Pineal and pituitary glands
Cranial nerve sheaths
Cerebral metastases
What are the most common extra-axial tumors?
Meningiomas
What are cerebral metastases?
What is the temporal bone positioned between?
The middle and the posterior cranial fossa
What are the 4 segments of the temporal bone?
Petrous (hardest part and houses inner ear)
Squamous
Mastoid
Tympanic (poorly developed at birth and matures by 3 years, forms most of the EAC)
Are most vascular tumors of the temporal bone benign?
Yes
What are the 2 categories of vascular tumors?
Hemangiomas
Vascular malformations
What are hemangiomas?
Typically present during first month of life (resulting from malformation of angioblastic fetal tissue)
Initial rapid growth followed by a slow period of shrinkage
Should cavernous hemangiomas be classified as a vascular malformation?
Maybe
REVIEW
What are vascular malformations?
More common than hemangiomas, but still rare
Always present at birth (but may not be visible)
Grow in proportion with the body growth and do not regress
Can grow to a large size
Where do the majority of vascular malformations present?
In the IAC or geniculate ganglion of the VII N in the facial canal (extensive blood supply here)
They may arise in the ME cavity or EAC, but rarely
Is there a difference in cell structure between vascular malformations and hemangiomas?
Yes
But clinically, there is still confusion in their diagnosis
What are some signs and symptoms for both vascular malformations and hemangiomaa?
Present with symptoms around the 3rd decade of life
VIIth N dysfunction (when the geniculate ganglion is the site of origin)
Hemifacial spasm
Tinnitus
CHL (eroding into ME)
Progressive SNHL (common with IAC site)
Vertigo
How are vascular malformations and hemangiomas diagnosed?
Case Hx
CT scan
MRI with contrast (lesions appear hyper-intense on T2 (fluid bright) because vascular is fluid)
Geniculate lesions may be difficult to visualize with MRI (can be done with CT)
What is the differential diagnosis for vascular malformations and hemangiomas?
Other temporal bone tumors
Meningioma (irregular margins)
VIIth N schwannoma (less localized and causes facial nerve symptoms)
Cholesteatoma (vascular lesion in ME cavity and can invade other structures)
What is the treatment for vascular malformations and hemangiomas?
Surgical removal with low likelihood of recurrence
What is a schwannoma?
A benign tumor that comes from the schwann cells
Most common tumor of the temporal bone and CPA
What is the myelin sheath in the CNS formed by?
Oligodendrocytes
What is the myeline sheath formed by in the PNS?
Schwann cells
Specifically, what is the myeline sheath of the schwann cells referred to as?
Nurilemmal sheath of schwann
What are the thee typical sites for a schwannoma?
In the IAC from the CN VIII (most common)
In the jugular foramen for IX and X, superior to the jugular bulb (often mistaken as paraganglioma)
In the fallopian canal of CN VII
Do schwannomas that originate in the IAC originate equally from either the superior or inferior vestibular division of CN VIII?
Yes
Do schwannomas often originate from the cochlear division of the CN VIII?
No
What portion of the IAC do schwannomas arise in?
Medial
What are some other names for vestibular schwannomas?
Acoustic neuroma, acoustic neurofibroma, acoustic neurilemmomas, or just brain tumors
Are schwannomas extra-axial?
Yes
Not coming from primary brain tissue
Are schwannomas typically unilateral?
Yes
Except for NF2 and metastases
Are schwannomas slow growing?
Yes
They will only grow 0.1 to 0.2 mm per year
What is significant growth for a schwannoma?
At or greater than 2 mm
Indication for treatment
What is the incidence for vestibular schwannomas?
Rare before thirty-years of age
Generally, present between 40 and 60 years, with a diagnosis typically most common after the 6th decade
Slightly higher incidence in females
What is the typical growth pattern for vestibular schwannomas?
Most commonly, origination within the IAC
Grows into the CPA involving the VII and VIII cranial nerves
Once in the CPA, the tumor can grow to large proportions
At this stage, the tumor consists of a stalk within the internal auditory canal attached to a mass in the CPA
Further enlargement can lead to brainstem compression and CN V involvement
Large tumors can cause hydrocephalus and death
Are the signs and symptoms for vestibular schwannomas related to pressure and can be divided into two phases?
Yes
The otologic phase and the neurologic phase
What is the otologic phase of vestibular schwannomas?
The tumor compresses structures in the IAC
Symptoms, particularly hearing loss, occur either due to compression of the vascular supply of CN VIII or direct compression of CN VIII in the IAC
What is the neurologic phase of vestibular schwannomas?
The tumor compresses other intracranial structures
Are signs and symptoms almost always ipsilateral for vestibular schwannomas?
Yes
When do otologic signs and symptoms usually occur for vestibular schwannomas?
When it is about 1 to 4 cm in size
What are the initial symptoms of the otologic phase of vestibular schwannomas?
Hearing loss (53 to 97%)
Headache (0 to 20%)
Tinnitus (0 to 18%)
Unsteady gait (0 to 8%)
Imbalance/dizziness (4 to 7%) (but not true vertigo because central compensation occurs due to the slow growth rate of the tumor)
Facial paralysis (rare - 0 to 2%) (because CN VII appears resistant to pressure from these tumors)
Can there be some involvement of the facial nerve as the tumor grows?
Yes
Facial sensory disturbances and facial twitching
In the neurologic phase
Can nystagmus also be seen in the neurologic phase of a vestibular schwannoma?
Yes
What can happen if the tumor is very large?
Compresses the 4th ventricle
(Increased intracranial pressure, hydrocephalus, coma, and death)
What are the pure tone audiometry findings for vestibular schwannomas?
80 to 95% present with unilateral, high frequency SNHL
Typically, asymmetrical though asymmetry is not severe and is more pronounced at higher frequencies
Brain stem lesions may show a flat, unilateral SNHL
Tone decay can be positive (generally positive across more frequencies and tone decay will not diminish with increasing intensity)
What are the OAE results for vestibular schwannomas?
Probably normal if the hearing loss is not significant
Decreased contralateral suppression of OAEs
What are the WRS results for vestibular schwannomas?
WRS may be markedly worse than expected based on pure-tone thresholds; WRS worse in noise
Positive rollover ratio > 0.45 (> 0.25 for NU-6-word lists)
What are the tympanogram findings for vestibular schwannoma?
Generally normal
What are the ART findings for vestibular schwannoma?
Abnormal or absent
VIII N lesion: sound effect (abnormal when sound is in the affected ear)
Brainstem lesion: crossover pathways affected, ipsi normal
Are ARTs 100% sensitive to vestibular schwannomas?
No
It is possible to have normal ARTs with a CN VIII schwannoma
What will larger tumors result in?
Depending on the location and size, some or all of the reflexes will be absent
Due to the large number of nuclei in the pons, other neurological symptoms expected too
What are the acoustic reflex decay findings for vestibular schwannoma?
Contralateral decay generally positive at 500 and 1000 Hz (only done at those freq)
Ipsi is not as sensitive, so it’s not clinically relevant
Why don’t you do decay at 2000 and 4000?
Everyone decays too quickly, even those with normal hearing
What are the tone decay findings for vestibular schwannoma?
> 30 dB is positive for retrocochlear pathology
The more frequencies that show decay, the greater the probability of retro
Both ears tested
What are the ABR findings for vestibular schwannoma?
Abnormal in 95% of cases of CN VIII tumors greater than or equal to 1 cm
Increased absolute wave v latency (> 6 ms)
Increased I-V interwave latency (> 4 ms)
Absent/abnormal wave v on affected side
When comparing wave v latency between ears, what is a positive sign of vestibular schwannoma?
When the difference in latency between ears is greater than or equal to 0.3 or 0.4 ms
IT5
Is the ABR response directly related to the degree of SNHL?
No
Abnormal ABR is observed in patients with a VIII N tumor with little or no hearing loss
Tumor causes dys-synchronous nerve discharge because fewer nerve fibers may be left intact
How do you get definitive diagnosis of vestibular schwannoma?
MRI (T1, gold standard)
CT (not as sensitive for small tumors)
What is the treatment for vestibular schwannoma?
Observation (watch and wait, serial MRIs and audios performed)
Stereotactic radiosurgery (advanced form of radiation therapy, to reduce the size)
Surgery (lose hearing, preserve facial nerve function)
What is a meningioma?
One of the most common benign brain tumors of the CNS
Arise from the meninges and generally superficial
Almost always single
Circumscribed, lobulated, white-gray masses
What is the incidence of meningioma?
Appears middle to later decades in life
More common in females (2:1)
Associated with progesterone levels and breast cancer
What is the etiology of meningioma?
Uncertain
Association with NF2 (1/5 of adolescents with meningioma have NF2)
Radiation therapy to the head (4x higher incidence)
Genetics (cell changes on chromosomes 1, 7, 10, and 14, telomerase activation, DiGeorge syndrome)
What is DiGeorge syndrome?
It is an AD syndrome caused by deletion of parts of 22q
Associated with early tumor formation in some cases
Can be a genetic basis for meningiomas
How large are meningiomas?
Related to the location
Large tumors located in areas with more space to grow (may not produce symptoms until large)
May originate and grow in the CPA (subtle audiologic symptoms)
May originate in the IAC (mimic an acoustic neuroma both clinically and on imaging)
Are meningiomas aggressive and locally invasive?
Yes
Can make removal problematic
Can invade cranial nerve
Are meningiomas vascular?
Yes
Can show cystic changes or occasionally calcification
What are the audiometric symptoms of meningiomas?
Progressive unilateral SNHL hearing loss
Only ~60% of patients with meningioma involving the temporal bone present with a SNHL
Vertigo
Tinnitus (pulsatile tinnitus if tumor involves the jugular foramen)
Nausea/vomiting (because of irritation of the meninges)
VIII CN involvement (mimics a vestibular schwannoma)
Abnormal ARTs on affected side, if unilateral; tympanogram normal
Positive acoustic reflex decay
Positive roll-over and poorer scores on speech-in-noise tests
Involvement of auditory system almost always demonstrates abnormal ABR findings
Normal OAEs if hearing is relatively normal
What is the differential diagnosis for meningiomas?
Otitis media (if gains access to ME)
Glomus tumor
Facial nerve involvement
Vestibular schwannoma
What is the treatment for locally destructive meningiomas with the ability to invade cranial nerves?
Surgical excision (may be followed by radiation), complete resection, hearing preservation (more likely for CPA meningiomas than CN VIII if hearing sensitivity is normal)
High recurrence rate
Long term follow up
What is the treatment for small meningiomas?
Conservative
Symptomatic management
What are other benign tumors of the temporal bone?
Osteoma
Paraganglioma (glomus tumor)
NF2
Facial nerve schwannoma
Do cortical tumors that affect the auditory cortex show abnormal results for peripheral tests?
May not
Only WRS may be poorer and inconsistent with pure tone thresholds especially in noise
Will an ABR be normal if there are cortical tumors?
Yes, ABRs only go up to the brainstem
Higher responses may be abnormal
Are headaches and dizziness often reported with cortical tumors?
Yes
With cortical tumors, are the signs and symptoms on the opposite side of the lesion?
Yes
What are some examples of malignant tumors of the temporal bone?
Adenocarcinoma and osteosarcoma
When are malignant tumors of the temporal bone diagnosed?
Often in the late stages and present a dismal prognosis
What are the audiologic symptoms for malignant tumors of the temporal bone?
Similar to chronic suppurative otitis media
Aural discharge with or without blood
Otalgia
Hearing loss
Tinnitus
What the other symptoms of malignant tumors of the temporal bone?
Facial paralysis
Headache
Cochleovestibular deficits (SNHL and vestibular symptoms)
What are metastatic tumors of the temporal bone (from other sites)?
Breast cancer (most common)
Lung cancer
Renal carcinoma, GI, and liver adenocarcinoma
Lymphoma and leukemia
Thyroid cancer
Osteoblastoma (childhood cancer of the bone)
Melanoma (skin cancer)
Are metastatic tumors malignant?
Yes, it moves sites so its malignant
