Cerebellopontine angle syndrome

David Goldemund M.D.
Updated on 11/06/2024, published on 22/01/2024

the cerebellopontine angle (CPA) is the space between the cerebellum and the pons, filled with cerebrospinal fluid (CSF)
the main structures located in the CPA are:
- vestibulocochlear nerve (CN VIII)
- facial nerve (CN VII)
pathological processes in this area (most commonly vestibular schwannoma), therefore, lead to damage to these nerves
the initial clinical manifestations depend on the nature and location of the pathological process

most commonly schwannoma (neuroma) ~ 80-90% of cases
meningioma (often involving the apex → Gradenigo syndrome)
- more homogeneous, though cysts can also be present
- attached to the dura
- no internal acoustic meatus enlargement
- calcifications are more commonly present
arachnoiditis (e.g., from otogenic infection)
ependymoma
- younger patients
- absence of internal acoustic meatus enlargement
epidermoid
- no contrast enhancement
- high signal on DWI
- absence of internal acoustic meatus enlargement
metastasis
- relatively rare
cholesteatoma
glomus jugulare

vestibular schwannoma (also called acoustic neuroma) accounts for ~ 7.5% of all intracranial tumors and about 80-90% of all CPA tumors
benign encapsulated tumor of Schwann cells (WHO grade 1); schwannoma is composed of spindle cells and arises eccentrically from the parent nerve, with the nerve fibers splayed along their surface
most lesions are sporadic and unilateral (90%)
bilateral schwannomas are found in:
- neurofibromatosis type 2 (NF2)
- familial forms without other manifestations of NF2
schwannomatosis presents with multiple schwannomas without the concomitant involvement of CN VIII
peak presentation between the 4^th and 6^th decades; earlier manifestation is typical for NF2 (~ by the 3^rd decade)

presentation depends on the location of the tumor, and symptoms are due to local mass effect or dysfunction of the nerve they arise from
the first symptoms usually arise from the cochlear branch lesion:
- irritation of the nerve causes tinnitus
- later, a loss of hearing on the affected side develops
vestibular disturbances (in the form of peripheral vestibular syndrome) are usually more troublesome:
- initially, the lesion may cause tonic deviations towards the healthy side and nystagmus towards the affected side (potentially leading to misidentification of the side of the vestibular disorder)
- soon, tonic deviation towards the side of the disorder and nystagmus beating in the opposite direction occur
less commonly, the CPA syndrome begins with paresis of the facial nerve
- paresis may sometimes be preceded by irritation of the nerve, causing intermittent hemispasm

CPA tumors cause additional symptoms due to their growth and compression of nearby structures
upward and medial propagation compresses the cerebellum, particularly the cerebellar hemisphere, leading to ipsilateral neocerebellar symptoms
medial or downward propagation leads to compression of the brainstem:
- contralateral pyramidal symptoms + ipsilateral lesion of CN VI and further progression may affect CN IX, X, and even CN XI

enlargement of the internal acoustic meatus (schwannoma)
signs of adjacent bone remodeling
variable density on non-contrast scans with possible cystic component
contrast enhancement (homogenous in small tumors, heterogeneous in the larger ones) – schwannoma, meningioma, metastasis

method of choice – optimally visualized on post-contrast T1-weighted images (T1C+)
the most common schwannoma has a typical radiological appearance
- nodular lesion with an intracanalicular component, leading to enlargement of the internal acoustic meatus
- T1 – hypo- to isointense
- T2 – hyperintense
- T1C+ – intense contrast-enhancement
- larger tumors may show cystic changes or hemorrhage (detectable on GRE/SWI), calcifications are uncommon in schwannomas
- → Koos grading scale here

enhancing mass	T1 hyperintense mass	CSF density
vestibular schwannoma: most common by far (~80%) meningioma: second mostcommon (~10%) trigeminal schwannoma facial nerve schwannoma ependymoma metastasis (e.g., breast, lung, melanoma)	hemorrhagic vestibular schwannoma neurenteric cyst thrombosed berry aneurysm cerebellopontine angle lipoma ruptured intracranial dermoid cyst	epidermoid cyst: third most common (~5%) arachnoid cyst

neurosurgical procedure is the treatment of choice (various surgical approaches are used)
- schwannomas do not infiltrate the nerve and thus can usually be separated from it
stereotactic radiosurgery
- extensive tumor, high-risk patient
conservative approach – observation of benign lesions, such as schwannoma or meningioma
- in older patients and smaller tumors where slow growth can be expected