Malignant transformation of an intraaxial-supratentorial neurenteric cyst - case report and review of the literature.

Neurenteric cysts are "rare benign mass forming developmental abnormalities" that usually affect young adults. Neurenteric cysts are thought to be derived from primitive endoderm, and form as a result of faulty endodermal-notochordal separation at 3 weeks of embryogenesis. Neurenteric cysts are lined by simple-to-pseudostratified respiratory/gastrointestinal-like epithelium; as such, these lesions closely resemble colloid and Rathke's cleft cysts. Anatomically, neurenteric cysts most frequently arise in an intradural-extraaxial location anterior to the cervical-thoracic spinal cord. Intracranial neurenteric cysts are uncommon but have a tendency to reside in the infratentorial compartment. Malignant transformation of the epithelial component of neurenteric cysts is decidedly rare. Of the 3 reported cases of neurenteric cysts with malignant transformation, all were intracranial (2 infratentorial and 1 supratentorial) and extraaxial. We describe a 58-year-old female with a supratentorial-intraaxial lesion that is consistent with a neurenteric cyst exhibiting malignant transformation into an invasive mucinous papillary cystadenocarcinoma. Areas of direct transition between typical benign neurenteric cyst epithelia and malignant epithelia (i.e., carcinoma in situ), highlighted by an abrupt change in the Ki-67 proliferative index, were identified, and supported the primary nature of this brain neoplasm. Metastatic workup at the time of presentation was unremarkable, and immediately up until being lost to follow-up 38 months after gross total resection, routine follow-up MR imaging had not detected a recurrence. To our knowledge, this would be the first reported case of malignant transformation within a supratentorial-intraaxial neurenteric cyst.