Introduction: Although rare, the malignant degeneration of epidermoid cysts is well documented. Its occurrence with leptomeningeal dissemination and malignant cells in CSF is scarce. To the best of our knowledge only four cases have been reported.
Case report: The authors report the case of malignant transformation of an epidermoid cyst with leptomeningeal carcinomatosis (which simulates aseptic meningitis) in a 54 year-old woman. Changes in CSF and radiological features are not correlated with the clinical course. Despite improvement of both the lesions on the scan images and the malignant cells in the CSF under chemotherapy the patient died.
Conclusion: The differential diagnosis of malignant degeneration of epidermoid cyst, and leptomeningeal carcinomatosis are discussed. The diagnosis of malignant transformation should be retained when MRI (or CT scan) shows contrast enhancement at the epidermoid site, and malignant cells are detected in CSF The prognosis is generally poor.