A Case of Ecchordosis Physaliphora in the Prepontine Cistern: A Rare Entity in the Differential Diagnosis of an Epidermoid Cyst

Background Ecchordosis physaliphora (EP) is a benign notochordal remnant that is usually asymptomatic. We report a case of a symptomatic large EP mimicking an epidermoid cyst. Case Description A 44-year-old woman presented with right facial dysesthesia. Brain magnetic resonance imaging showed a mass with a diameter of 3.2 cm that was hypointense on T1-weighted imaging, hyperintense on T2-weighted imaging, isointense to hyperintense on diffusion-weighted imaging, and hyperintense on apparent diffusion coefficient map (1.2–1.6 × 10 −3 mm 2 /second). There was no apparent contrast enhancement. Differential diagnoses included epidermoid cyst, dermoid cyst, EP, chordoma, chondrosarcoma, neurenteric cyst, and arachnoid cyst. Clinicopathologic examination revealed that the mass was an EP. Conclusions EP in the prepontine cistern should be considered in the differential diagnosis of epidermoid cyst.