Arachnoid cysts of the internal auditory canal: An underappreciated entity?

To describe the histopathologic findings and clinical presentation of arachnoid cysts (ACs) within the human temporal bone.

Retrospective cohort analysis.

An analysis of all medical records of patients diagnosed with an AC was performed. Temporal bones underwent standard processing for histologic examination. The slides were examined by light microscopy. The histologic findings were compared to premortem clinical data.

Twenty-seven ACs were identified in 22 patients. Twenty ears (74%) had no identified risk factor for AC development. The median volume was 12.8 mm³ . The most prevalent location of the ACs was at the fundus (16 ACs) followed by the middle portion of the internal auditory canal (IAC) (six ACs). Nine ACs were asymptomatic. Among the 18 symptomatic ACs, the most common presentation was sensorineural hearing loss (SNHL) (94%), followed by tinnitus (22%). The most affected structure was the cochlear nerve (59%), followed by the vestibular nerve (41%). The average hearing threshold was of moderately severe SNHL and speech discrimination was in the range of 50% on monosyllabic word tests. The median time interval from initial presentation to death was 12 years. No correlation was found between duration of symptoms and AC volume.

AC of the IAC is not uncommon. Its presentation is variable, ranging from asymptomatic to SNHL, with poor speech discrimination, tinnitus, and vertigo. This diagnosis should be kept in the differential diagnosis of retrocochlear pathologies.

4 Laryngoscope, 129:1667-1674, 2019.