Unusual cause of hearing loss and tinnitus

A 51-year-old female presented with painful pressure on both ears and tinnitus as well as episodes of nausea and vomiting. The audiological examination demonstrated progressive sensorineural hearing loss. An MRI examination was requested to exclude retrocochlear pathology.

The performed MRI shows a space-occupying lesion in both cerebellopontine angles (CPA), with left predominance, causing compression on the surrounding structures, specifically: left cerebellar hemisphere, left middle cerebellar peduncle and left surface of the brainstem. There is also a displacement of cranial nerves VII and VIII. In addition, these nerves are not visible in the internal auditory canal (IAC) on the left side, probably due to extension of the lesion in the IAC with compression of the nerves as a result.

The lesions show a subtle T2 hypointense wall and follow the signal intensity of cerebrospinal fluid (CSF) on all sequences: fluid attenuation on FLAIR and lack of diffusion restriction and enhancement.

In conclusion, cystic lesions are present in both CPA cisterns, with left predominance and possible extension into the left internal auditory canal, causing mass-effect on cranial nerves and the brain.

Arachnoid cysts account for 1% of all intracranial masses [1-6] and only 10% of them are located in the posterior fossa. [1-4,6] They are congenital and thought to occur due to duplication of the arachnoid membrane creating a CSF sac. [1,3,6]

In most cases, an arachnoid cyst is an incidental finding. [1,2,4,6] When these lesions are symptomatic it’s usually due to direct compression on cerebral structures and/or due to increased intracranial pressure. [1,4] In the CPA this may cause a variety of symptoms. Nonspecific symptoms include headache, nausea, vomiting and vertigo, but patients may also present with cranial nerve palsies, sensorineural hearing loss being the most frequent complaint. [1,4]
An arachnoid cyst, as shown in this case, is a sharply demarcated extra-axial cystic mass which may show a subtle dark wall on high-resolution T2 imaging. The lesion is isointense to CSF on all sequences. [1,3,6] It shows complete fluid attenuation on FLAIR and lack of diffusion restriction, both differentiating it from an epidermoid cyst. Furthermore, there is no enhancement, discriminating it from other CPA masses such as (cystic) vestibular schwannomas and (cystic) meningiomas. [1,6] When symptomatic they are usually large.[1,4]
Treatment of an arachnoid cyst is reserved for those cases where there is a clear relation between symptoms and the location of the arachnoid cyst.[1] When treated a decompression via fenestration is favoured since this is the least invasive approach.[1,4,5] Because of that a fenestration of the left arachnoid cyst was performed in this case.

In summary, arachnoid cysts may cause symptoms when large due to direct compression on brain parenchyma and/or cranial nerves. In the CPA differentiation with an epidermoid cyst, (cystic) vestibular schwannomas and (cystic) meningiomas is possible using FLAIR, DWI and post gadolinium T1 sequences. In symptomatic cases, fenestration is a therapeutic option.