Beyond Aqueductal Stenosis: A Case of an Atypical Teratoid/Rhabdoid Tumor Presenting With Neonatal Hydrocephalus.

An atypical teratoid/rhabdoid tumor (ATRT) is a rare and highly aggressive embryonal tumor in the central nervous system, with the highest incidence in infants. Neonatal cases frequently experience delayed diagnosis due to nonspecific symptoms, with imaging findings that may mimic more prevalent congenital anomalies such as aqueductal stenosis. We report a case of a full-term male neonate with prenatal findings of severe lateral and third ventriculomegaly, initially misdiagnosed to be due to an obstructive etiology due to hemorrhage in the fourth ventricle/aqueduct. Later, on a postnatal MRI, a non-enhancing hemorrhagic mass was suspected to be arising from the tectum, which on histopathology was confirmed to be an ATRT with loss of SMARCB1 (INI1) expression.