Beyond the fourth ventricle - Epidermoid cyst of the conus medullaris on the floor of a ventriculus terminalis (fifth ventricle).

Background: Intracranial epidermoid cysts, although rare, are well-documented in the literature. However, spinal epidermoid cysts are even rarer. A comprehensive understanding of these lesions is critical for accurate diagnosis, surgical planning, and management In this study, we present a clinically rare case of an epidermoid cyst in the conus medullaris, discuss the findings against the background of the limited number of cases published to date, and thus provide an initial review of the current literature. Case presentation: A 56-year-old male patient presented to our clinic with a history of progressive claudication symptoms. Neurological examination revealed no motor or sensory deficits. Contrast-enhanced lumbosacral magnetic resonance imaging (MRI) demonstrated a well-circumscribed, intramedullary lesion within the conus medullaris at the level of Th12-L1. CT imaging further confirmed the presence of a hyperdense lesion, with internal calcifications. Results: Following diagnostic confirmation, the patient underwent a posterior midline approach with hemilaminectomy at the L1-L2 level to expose the conus medullaris. Intraoperatively, a well-defined cystic lesion was identified. Microsurgical techniques were employed to carefully open the spinal cord and achieve complete resection of the cyst. Histological examination of the lesion confirmed the diagnosis of an epidermoid cyst. The patient's postoperative course was initially uneventful, with complete regression of pain. However, two weeks later, he developed a severe headache and noticed swelling at the surgical site. MRI revealed a cerebrospinal fluid (CSF) leak. The patient was successfully treated with inpatient admission and placement of a lumbar drainage system. One week later, he was discharged without complications and had fully recovered. Apart from our case, a thorough literature review identified only two other reported cases of intramedullary epidermoid cysts (and another intradural extramedullary epidermoid cyst). Conclusion: Intramedullary epidermoid cysts in the conus medullaris are exceedingly rare, with only a few cases documented to date. Our case adds to the limited body of literature and emphasizes the significance of a correct diagnosis and management of such rare spinal lesions.