Malignant Transformation of a Filum Terminale Dermoid Tumor into Adenocarcinoma

Background Intraspinal dermoid tumors are usually rare benign growths that occur as a result of defects during neural tube formation. They make up less than 1% of tumors in the spine and are associated with spinal dysraphisms or sinus tracts. Although rare, malignant transformation into squamous cell carcinoma has been previously reported. Malignant transformation into adenocarcinoma, however, represents a novel phenotypic differentiation pattern that is hitherto undescribed. Case Description A 45-year-old woman presented with acute symptoms of cauda equina syndrome. Imaging of the spine revealed a large intradural sacral mass. The lesion was surgically resected with pathology revealing a dermoid tumor with malignant transformation into adenocarcinoma. Metastatic workup revealed no other suspicious lesions. The patient had an uneventful postoperative course, gradually regaining micturition control. Conclusions Dermoid tumors, also known as benign cystic teratoma or mature teratoma, are usually benign congenital tumors comprising epithelial cells that arise from displaced embryonic ectoderm and mesoderm during neural tube formation. Although extremely rare, malignant transformation into squamous cell carcinoma has been reported. This case represents the first report of an intraspinal dermoid tumor transforming into adenocarcinoma. A comprehensive histopathologic analysis is key to identifying the lesion and guiding postsurgical management.