Cerebellopontine Angle Mass

Question 1

The combination of __ and __ is suggestive of a cerebellopontine mass

Answer 1

The combination of hearing loss and facial paralysis is suggestive of a cerebellopontine mass

Question 2

Acoustic neuroma / Vestibulocochlear schwannoma

Answer 2

• Benign tumor derived from Schwann cells arising from the vestibular portion of the acoustic nerve
• Most common tumor found in the CPA (accounting for 80% of cases)
• Age of onset: ~30-60 years if idiopathic, 18-24 years if NF2-associated
• Presentation: Unilateral sensorineural hearing loss. Sometimes vertigo, headaches, facial nerve palsy.
• Most cases are idiopathic, some are associated with NF2
• Treatment: Stereotactic radiotherapy available for tumors up to 3 cm in size. If larger, conventional neurosurgery.

Question 3

Cerebellopontine angle

Answer 3

The angle between the cerebellum pons, and temporal lobe

This space contains cranial nerves V through XI

Question 4

Two most common cerebellopontine angle masses

Answer 4

1. Acoustic neuroma / Vestibulocochlear schwannoma
2. Vascular malformation

Question 5

Meningiomas of the CPA

Answer 5

• Symptoms really depend upon location, but in the CPA usually involve the vestibulocochlear or facial nerves
• Will have a dural tail on imaging
• These tumors are overwhelmingly benign and surgical therapy is curative

Question 6

Epidermoid tumor of the CPA

Answer 6

Benign tumor composed of squamous epithelial elements.

Thought to arise from congenital nests.

Question 7

Glomus tumor of the CPA

Answer 7

• Aka, a paraganglioma
• Highly vascular tumors that arise from neuroepithelial cells
• Named for the tissue/structure they arise from
• Pheochromocytoma/paraganglioma rule of 10’s:
  
  • 10% of these tumors produce catecholamines, 20^ are bilatreal, 10% are familial, 10% are malignant

Question 8

Three options for dealing with a posterior fossa tumor

Answer 8

• Observation and serial imaging
• Stereotactic radiosurgery
• Conventional neurosurgery

Question 9

Outcomes in gamma knife therapy for CPA tumors

Answer 9

• Tumor control rates are very high for benign disease (>90%)
• Trigeminal and facial nerve preservation rates are >90%
• However, preservation of unilateral hearing is ~50%
• If tumor cannot be controlled by stereotactic radiotherapy, this unfortunately makes subsequent conventional neurosurgery in the area more difficult

Question 10

For which types of tumor is stereotactic radiotherapy not an option?

Answer 10

Meningioma

Epidermoid tumor

Question 11

Drawbacks of stereotactic radiotherapy

Answer 11

• No tissue specimen to confirm the diagnosis
• Only ~50% preservation rate of hearing
• If unsuccessful, outcomes are worse than primary neurosurgery alone
• Cannot be used for meingioma or epidermoid tumor

Question 12

Stereotactic radiotherapy should never be used for a CPA tumor when . . .

Answer 12

. . . the pathologic diagnosis is in doubt

Question 13

What is the single best test to elucidate the etiology of a unilatreal sensorineural hearing loss?

Answer 13

MRI of the internal auditory canal with gadolinium contrast

Unfortunately, it is not entirely specific, but it can shed light on the nature of the pathology.

Question 14

Evidence suggests that Bell’s palsy is probably due to ___

Answer 14

Evidence suggests that Bell’s palsy is probably due to recrudescence of HSV within the facial nerve

Question 15

By definition, Bell’s palsy is. . .

Answer 15

. . . a diagnosis of exclusion