Specific Imaging Findings

Subependymomas are well-defined round to oval masses usually not exceeding 2 cm in greatest diameter that occur around the foramen of Monro and in the fourth ventricle. These neoplasms are hypodense on CT, of low to mildly increased T1 signal, and hyperintense on T2-weighted sequences, with characteristically very bright signal on FLAIR images. They are generally homogenous with absent or minimal focal contrast enhancement, although lobulated contours and intratumoral cysts may be encountered. Heterogenous signal intensities and/or internal calcifications are not unusual and some tumors may sho3w moderate to prominent enhancement on MR imaging. Diffusion of water molecules is higher than in the brain parenchyma resulting in high signal on ADC maps. Perfusion studies show very low blood volume. Subependymomas may very rarely arise in an intra-axial location, and even in those cases the presence of surrounding edema is an exception. MR spectroscopy shows normal choline peak and depressed NAA. Rare cases of recurrent subependymoma may demonstrate increased choline to creatine (Cho/Cr) ratio on MRS.

Pertinent Clinical Information

Subependymomas are rare, slow-growing, low-grade gliomas, the majority of which are asymptomatic and found incidentally at postmortem examination. They are typically associated with the ventricular system and become apparent clinically only when symptoms of hydrocephalus or mass effect develop. Their clinical features may vary widely, most commonly presenting with headache and vomiting in older adult patients.