A case of split notochord syndrome: an adult with a spinal endodermal cyst mimicking an intramedullary tumor

Intraspinal endodermal cysts are very rare congenital cysts, usually composed of a thin-walled cyst the lining of which mimics gastrointestinal or respiratory epithelium. Diagnosis is usually established during the first or second decade of life. These cysts are frequently associated with vertebral or spinal cord abnormalies and dual malformation with mediastinal or abdominal cysts. Collectively, they are called split notochord syndrome. The authors describe their experience in the treatment of a 57-year-old man having an endodermal cyst mimicking an intramedullary tumor at the level of Th1-2. He was admitted to our institution for evaluation of an intraspinal mass diagnosed by MRI at a local hospital after experiencing temporary numbness and weakness of the lower left extremity. T1-weighted sagittal MRI demonstrated the lesion with signal intensity iso- to slightly hypointense to the spinal cord without enhancement after administration of gadolinium. Although T2-weighted sagittal images demonstrated as hyperintense to the spinal cord, axial images revealed a passage between the mass and subarachnoid space. We could not completely rule out the presence of an intramedullary tumor and undertook a laminectomy with a posterior approach. Histopathological analysis revealed an endodermal cyst and the authors found syringomyelia, which was clearly separated from the cyst in the preoperative sagittal MRI and intraoperative ultrasonography study. To the best of our knowledge, this is the first report in the English literature of a thoracic endodermal cyst requiring differential diagnosis from a spinal cord tumor.