Arachnoid cyst: middle ear mass diagnosis to consider.

Matthew Clary, MD Thomas Jefferson Univ, Dept Oto-HNS 925 Chestnut St, 6th Fl Philadelphia, PA 19107 [email protected] Objective We introduce the inclusion of arachnoid cysts in the differential diagnosis of a middle ear mass, as well as discuss the presentation, radiologic findings, and management of arachnoid cysts of the fallopian canal. Methods We present a very rare but clinically important presentation of a fallopian canal arachnoid cyst that presented as a middle ear mass causing a conductive hearing loss. Results A 57 year old woman presenting with a conductive hearing loss, life-long chronic otitis media, and opacification of the middle ear and mastoid with minimal bony erosion. Surgical exploration revealed a mass based off of the tympanic segment of the fallopian canal filling the middle ear space. Post-operative MRI showed the mass to be an arachnoid cyst of the fallopian canal with enlargement of the tympanic segment of the canal through the geniculate ganglion. On vestibular testing, there was also a peripheral vestibulopathy on the side of the lesion. Conclusions To our knowledge, this is the first ever report of a fallopian canal arachnoid cyst presenting as a middle ear mass. Arachnoid cysts are benign collections of cerebrospinal fluid that are predominantly congenital although may be acquired. Cysts involving the fallopian canal are exceedingly rare, with only a few previously reported cases in the literature. They are typically clinically silent, but can manifest with compressive symptoms or with cerebrospinal fluid otorrhea. Management consists of observation, surgical decompression, or resection. Arachnoid cysts must be considered in the differential diagnosis of the middle ear mass. Arachnoid Cyst: Middle EarMass Diagnosis to Consider