Intracranial epidermoid cyst including elements of old hematoma.

A 70-year-old female presented with symptoms of right-sided trigeminal neuralgia. Computed tomography showed a high-density mass in the prepontine cistern without enhancement. Magnetic resonance (MR) imaging showed the mass as heterogeneous with variable but largely high-signal intensity on T1-weighted images and low-signal intensity on T2-weighted images. At surgery, the lesion was found to be an epidermoid cyst filled with old blood and lipid debris. The high-signal intensity on the T1-weighted images may reflect lipid or methemoglobin with the low intensity on T2-weighted images representing hemosiderin. Most intracranial epidermoid cysts appear as low-intensity lesions on T1-weighted images and high-signal intensity on T2-weighted images. Typical MR imaging findings are neither specific for nor constant with epidermoid cysts, requiring critical differential diagnosis.