Case of the Month
Case of the Month
Left sensorineural hearing loss and tinnitus in a 50 year old patient.
Diagnosis: Acoustic Neuroma
Left Image: Initial T1 weighted imaging demonstrates an intermediate signal mass lying within the left internal auditory meatus (IAM).
Centre Image: Axial T2 CISS images (High resolution T2 weighted imaging) of the cerebellopontine angle-internal auditory canal (CPA-IAC) cistern demonstrate the low signal mass as an easily recognisable filling defect in the high signal cerebrospinal fluid (CSF) of the CPA-IAC cistern.
Right Image: Axial T1 weighted contrast enhanced imaging demonstrates a focal enhancing mass of the CPA-IAC cistern.
Acoustic Neuroma (aka Vestibular schwannoma) is a benign tumour of the Schwann cells that wrap the vestibulocochlear nerve in the CP angle-internal auditory canal (CPA-IAC) cistern.
It is the most common CPA-IAC mass (85% of all lesions found there) and the second most common extraaxial neoplasm in adults.
Clinical presentation is typically adults with unilateral sensorineural hearing loss (SNHL). Rare in children unless neurofibromatosis type 2 (NF2). Peak age is 40-60 years. Other symptoms include tinnitus (small acoustic neuromas), as well as trigeminal and/or facial neuropathy (large acoustic neuromas).
Classic imaging appearances are of a 'filling defect' in the high signal cerebrospinal fluid CSF of the CPA-IAC cistern on high-resolution T2 MRI, and a focal enhancing mass of the CPA-IAC Cistern on T1 contrast enhanced MRI.
Other MRI findings: 15% may have intramural cysts, 0.5% have an associated arachnoid cyst and 0.5% have haemorrhagic foci (thus display high signal on T1 pre-contrast imaging).
CT scanning is less sensitive for detection of small lesions, but may show a well delineated enhancing mass of the CPA-IAC cistern, no calcification (cf. meningioma) and may flare the IAC when larger.
The differential diagnosis includes epidermoid cyst, arachnoid cyst, meningioma, facial nerve schwannoma, metastases and lymphoma.
Multiple schwannomas confirm the diagnosis of NF2.
Natural history: 75% of acoustic neuromas grow gradually, 10% can grow rapidly. 15% grow very slowly, and can be treated conservatively in older patients.
Treatment: Translabyrinthine resection if no hearing preservation possible. Middle cranial fossa approach for intracanalicular acoustic neuromas. Retrosigmoid approach when CPA component present.
- Non-contrast limited brain MRI with high resolution T2 MR imaging of the CPA-IAC can be used as a screening exam to exclude acoustic neuroma.
- Full brain MR with T1 contrast enhanced imaging of the CPA-IAC is gold standard.
- CT scanning is not the optimal modality for either screening or assessment.