Middle Cranial Fossa Dehiscence as an Incidental Finding on CT

Abstract

Objectives:

Determine the prevalence of middle cranial fossa (MCF) dehiscence on computed tomography (CT) scans and establish its increase with age.

Methods:

All high-resolution temporal bone CT scans completed at a tertiary care center from 2011 to 2013, ordered by 1 otologist for any reason, were reviewed. Scans showing soft tissue, fluid, trauma, or previous operations were excluded. A total of 183 patients (296 ears) were reviewed blinded for age. The MCF floor was divided into 7 regions and systematically inspected. Ages of the patients were subsequently extracted from the medical record.

Results:

Logistic regression analysis confirmed increasing MCF dehiscence with age (P < .05, odds ratio [OR] 1.07, R = 0.584). Overall ages (1-88 years; average 38.5 years), 32% of MCF floors were dehiscent at any one site. For age 60 years and over, 55% were dehiscent. For 226 paired ears, if one ear was dehiscent, there was a 66% chance the other ear was dehiscent as well. Superior canal dehiscence (SCD) was seen in 7% of all patients, and only in combination with MCF dehiscence. SCD occurred in 16% of dehiscent ears. The most common sites were directly above the malleus head and above the additus ad antrum (36% and 28%, respectively).

Conclusions:

The incidence of MCF dehiscence increases with age. Over all ages, approximately 32% of ears show dehiscence. Over 60 years, approximately 55% show dehiscence. The increase of dehiscence with age is statistically significant. The most common sites along the MCF floor are in the epitympanum over the malleus head and additus ad antrum.