Answer: Encephalocele

Histology: The specimen consists of middle ear mucosa with slightly increased stromal cellularity that is entirely compatible with non-specific fibrosis. In this case, however, the clinical and radiographic suspicion for an encephalocele was very high. A GFAP immunostain confirmed that the stroma was, in fact, glial tissue.

Discussion: It is rare to see glial tissue outside of the cranial cavity. In the head and neck, this scenario is most common in the nose, but can also occur in the ear. When isolated neuroglial tissue (i.e., not as a component of a teratoma) is encountered, the two main diagnostic considerations are glial heterotopia and an encephalocele. The distinction is not trivial, as an ecephalocele, by definition, means that there is a patent connection with the cranial cavity which puts the patient at risk for meningitis. Conversely, heterotopic glial tissue has been congenitally separated from the cranial cavity. The presence of dura/leptomeninges or well-organized glial tissue with neurons favors an encephalocele, but these features are often lost in longstanding lesions (indeed, in this case the patient had a history of a violent ear injury approximately 50 years ago). Ultimately, the distinction requires clinical and radiographic input, but most experts believe that the vast majority (if not all) of cases of middle ear glial tissue represent acquired encephaloceles.

GFAP

Reference(s):
– Heffner DK. Brain in the middle ear or nasal cavity: heterotopia or encephalocele? Ann Diagn Pathol. 2004;8 (4):252-7.
– Gyure KA, et al. Clinicopathological study of 15 patients with neuroglial heterotopias and encephaloceles of the middle ear and mastoid region. Laryngoscope. 2000. 110:1731–1735.