Classic Case

Rosette-forming glioneuronal tumors (RGNTs) are rare, sporadic, WHO grade 1 tumors typically diagnosed in young adult patients. These tumors are relatively well circumscribed on MRI and are often located in the midline, involving the fourth ventricle and/or cerebral aqueduct. They exhibit variable solid-cystic components and heterogeneous contrast enhancement, and they can be entirely cystic in nearly 25% of cases. In this case, imaging studies revealed an expansile lesion occupying the aqueduct of Sylvius and the upper portion of the fourth ventricle (A, red arrows), with signal intensity slightly higher than CSF on T1WI and a small central CSF-filled cavity (A, yellow arrow) communicating with the ventricular system. There was no abnormal enhancement on postgadolinium T1-weighted images (B, arrow), nor signs of hemorrhage, calcification, or associated vasogenic edema. This mass caused superior deviation of the quadrigeminal plate, deformation of the anterior and superior portions of the cerebellar vermis, and obstructive hydrocephalus (A), which explained the patient's clinical symptoms. Furthermore, the lesion exhibited neither diffusion restriction on DWI nor relative cerebral blood volume (rCBV) elevation on DSC perfusion mapping (C, arrow), supporting the hypothesis of a nonmalignant tumor. The diagnosis of RGNT was confirmed by pathology.