White Epidermoid of the Prepontine–Premedullary Cistern Causing Brainstem Compression: Case Report and Review of Literature

Abstract White epidermoid cysts (WECs) are an uncommon radiologic variant of intracranial epidermoid cysts, accounting for approximately 1.5 to 8% of cases. Unlike classic epidermoids, which are typically T1 hypointense, T2 hyperintense, and diffusion restricting, WECs characteristically demonstrate T1 hyperintensity, variable or low T2 signal, and absence of diffusion restriction. These atypical imaging features frequently lead to diagnostic confusion with dermoid cysts, proteinaceous arachnoid cysts, or neurenteric cysts. WECs arising in the ventral posterior fossa, particularly the prepontine and premedullary cisterns, are exceedingly rare. A 27-year-old woman presented with a 2-year history of intermittent occipital headaches without focal neurological deficits. Magnetic resonance imaging revealed a T1-hyperintense, T2-hypointense, nonenhancing extra-axial lesion in the prepontine and premedullary cisterns, more prominent on the left, causing ventral brainstem compression. Notably, the lesion showed no diffusion restriction, supporting the diagnosis of a WEC. The patient underwent microsurgical excision via a left far-lateral approach. Operative findings, histopathological characteristics, and postoperative outcomes were analyzed and correlated with available literature. Intraoperatively, the lesion contained thick, pearly-white to brown viscous keratinous material. The capsule was densely adherent to the medulla and vertebral artery. Near-total excision was achieved using meticulous microdissection and copious irrigation to minimize the risk of chemical meningitis. Histopathology confirmed an epidermoid cyst lined by stratified squamous epithelium with laminated keratin and cholesterol clefts. Postoperative computed tomography demonstrated effective decompression of the brainstem. The postoperative course was uneventful, with complete resolution of headache and no new neurological deficits at 2-month follow-up. WECs represent a biochemical and radiological variant within the epidermoid spectrum rather than a distinct pathological entity. Early recognition of their T1-bright, non-diffusion-restricting magnetic resonance imaging signature is critical for accurate diagnosis and surgical planning. For ventral posterior fossa lesions, the far-lateral skull-base approach allows safe resection with excellent clinical outcomes.