The differential diagnosis of middle ear masses includes a wide array of typically benign diseases, with cholesteatoma as the leading entity. Other lesions frequently considered include glomus tumors, schwannomas, choristomas, and other vascular variants. Arachnoid cysts, despite being present in 4% of the population, are seldom considered.1
Arachnoid cysts are cerebrospinal fluid (CSF) filled spaces that usually form within the arachnoid membrane covering the brain and spinal cord. Most commonly, arachnoid cysts present in the middle cranial fossa.1 Their presentation in the middle ear space has been described as typically due to erosion through the tegmen tympani. We present the case of a patient with a middle ear mass that ultimately was found to be an arachnoid cyst isolated to the tympanic segment of the fallopian canal. We use this previously undescribed (to our knowledge) presentation to discuss the clinical and radiologic characteristics of this entity, as well as its treatment. Institutional review board approval was not required for this report.
Clary MS, Walker R, Nicholas BD, Goodman JF, Kori G, Artz GJ. Arachnoid CystMiddle Ear Mass Diagnosis to Consider. Arch Otolaryngol Head Neck Surg. 2011;137(4):398-400. doi:10.1001/archoto.2011.31