What are the key imaging characteristics and clinical features of a subependymoma, and how can it be differentiated from similar intraventricular tumors?

Subependymoma is a WHO grade I tumor, typically asymptomatic and found incidentally. It appears as a well-circumscribed, lobulated intraventricular mass, often isodense to hypodense on CT, with frequent calcification (33%) and cystic degeneration (20%). On MRI, it shows low T1 and high T2 signal intensities, with hypointensity on T1-weighted images and hyperintensity on T2-weighted images. Enhancement is less diffuse compared to central neurocytoma. Key diagnostic features include its location near the fourth or lateral ventricles and its non-aggressive behavior. Clinical pearls include its benign nature and the importance of distinguishing it from more aggressive intraventricular tumors like ependymomas or central neurocytomas, which may show more diffuse enhancement.