Encephaloceles of the Posterior Fossa: A Series of 10 Cases

Objectives: (1) Describe 10 cases of posterior fossa encephaloceles. (2) Compare spontaneous posterior fossa encephaloceles to the more common middle fossa encephaloceles. Methods: This is a retrospective review of patients with surgically-confirmed encephaloceles of the posterior fossa managed at a tertiary care center from 2006 to 2013. Clinical presentation, imaging, and operative findings were reviewed. Patient demographics were summarized with descriptive statistics. Results: Ten cases of surgically confirmed posterior fossa encephaloceles were identified. The median age of diagnosis was 45.5 years; 6 subjects were female, 4 were male. The median length of follow-up was 18 months, with 2 subjects lost to follow-up. Seven of 10 cases followed temporal bone surgery, craniotomy, or trauma. The remaining 3 out of 10 were spontaneous. Two of 3 subjects with spontaneous encephaloceles presented with pneumocephalus and 1 with cerebrospinal fluid otorrhea. Computed tomography scans in all cases showed bone loss and soft tissue protrusion from posterior fossa into the mastoid, with a radiologic differential of arachnoid granulation versus encephalocele. At surgical exploration, there was brain tissue protruding from a defect of the posterior fossa in all cases. One subject had a concomitant tegmen defect. Conclusions: Posterior fossa encephaloceles are much less common than middle fossa encephaloceles, only 23 have been reported to date. The difference is presumably due to intracranial pressure differences in the upright position. Given the location of these 3 spontaneous posterior fossa defects, as well as intraoperative findings of cerebral tissue within the mastoid, we suggest that these lesions are true encephaloceles and not just arachnoid granulations.