Case of the Week

Background:

• Synovial and ganglion cysts may arise from the temporomandibular joint. Intracranial extension is rare, with few reported cases in the literature.^1,2 The 2 entities are clinically and radiographically indistinguishable, however, histopathologically distinct—synovial cysts are lined by cells of synovial origin, while ganglion cysts are lined by a degenerated fibrous joint capsule.³ A limitation of this case was that histopathologic confirmation was not obtained. The diagnosis was made based on characteristic imaging features, significant radiologic improvement observed on the first follow-up scan, and subsequent radiologic stability over a 2-year period. The patient reported significant symptomatic improvement by the time of the initial follow-up exam, with subsequent spontaneous resolution of symptoms.

Clinical Presentation:

• Symptoms are nonspecific and may include preauricular or TMJ pain. Sensorineural deficits secondary to mass effect on nearby cranial nerves including the facial nerve as well as the auriculotemporal branch of the mandibular nerve have been reported.^1,4 Seizures arising from mass effect on the temporal lobe have also been reported.²

Key Diagnostic Features:

• Cystic intracranial lesion demonstrating contiguity with the glenoid fossa of the temporomandibular joint
• May demonstrate rim enhancement without solid nodular enhancing components
• No diffusion restriction

Differential Diagnoses:

• Arachnoid cyst (should not communicate with the TMJ)
• Intracerebral abscess (should restrict diffusion or extend extracranially)
• Cystic neoplasm (should not communicate with the TMJ, and should be expected to increase in size)

Treatment:

• Surgical resection is curative. Watchful waiting may be considered, as in the case reported here where the patient’s symptoms resolved spontaneously without any specific intervention.