Subependymomas

• Small well-demarcated intraventricular mass (typically <2 cm) most commonly in the fourth ventricle with T2 hyperintensity and minimal or no enhancement
• T2/FLAIR bright signal with iso-to-hypointense T1 appearance and absence of surrounding brain edema or significant mass effect
• Calcifications present in up to 50% of cases visible on CT as hyperdensities and on MRI as susceptibility-related signal dropout on T2

• CT demonstrates isodense to hypodense intraventricular mass typically without enhancement; calcifications are present in up to 50% of cases.
• MRI T1 signal is iso-to-hypointense to white matter, usually homogeneous but may show heterogeneity in larger lesions with generally well-defined, round to oval lobulated contours.
• MRI T2 signal is hyperintense to adjacent white and gray matter with potential intratumoural cysts; heterogeneity may be seen in larger lesions with susceptibility-related signal dropout from calcifications.
• FLAIR imaging shows very bright signal intensity, making this an excellent sequence for lesion conspicuity.
• T1 post-gadolinium contrast shows usually no enhancement, although mild enhancement may occasionally be present, distinguishing it from highly enhancing tumors like choroid plexus papillomas.
• DWI/ADC demonstrates facilitated diffusion with high ADC values reflecting the low-cellularity nature of the tumor.
• No adjacent parenchymal vasogenic edema or mass effect is typical because subependymomas do not invade adjacent brain tissue.
• Digital subtraction angiography shows no or minimal vascularity, consistent with the hypovascular histology.

• Ependymomas:
• More commonly seen in children and younger adults, with generally more rapid lesional growth tendencies
• Often demonstrates extraventricular involvement with parenchymal invasion
• Cystic and calcified components also commonly seen
• Heterogenous enhancement pattern, although this is not always reliable [4, 5]
• Choroid plexus papilloma:
• Also more commonly seen in children and younger adults
• Frond-like morphology particularly with contrast-enhanced images
• Vivid, homogenous enhancement with gadolinium as opposed to minimal to nonenhancement in subependymomas [4, 5]
• Central neurocytoma:
• Tendency for continued growth and rapid progression of symptoms
• Often demonstrate punctate calcific components, as well as cystic regions (particularly in larger tumors)
• Hyperattenuating on CT scans
• Tumor blush can be seen on angiography, as well as moderate enhancement on T1 post-contrast images
• Very rarely present in the 4th ventricle, and most commonly affect the lateral ventricles, often with some involvement/attachment to the septum pellucidum [
• Subependymal giant cell astrocytoma:
• Pathognomonic of and often associated with tuberous sclerosis
• Classically arise from the lateral ventricles or foramen of Monro
• Multiloculated in appearance often containing cysts and calcifications
• Often show marked enhancement on postcontrast images.
• Subependymal nodules:
• seen almost exclusively in tuberous sclerosis and distinguished by the clinical context of known TSC.
• Ring-shaped lateral ventricular nodules: small lesions <10 mm in diameter that may mimic subependymomas but are typically smaller and often have different imaging characteristics.

Describe subependymomas as "a small, well-demarcated intraventricular mass with T2/FLAIR hyperintensity, iso-to-hypointense T1 signal, minimal or absent post-contrast enhancement, and no surrounding edema or significant mass effect," specifying the location (e.g., fourth ventricle, frontal horn) and whether calcifications or obstructive hydrocephalus are present.

• Mistaking a subependymoma for an ependymoma by overlooking the age of presentation (subependymomas in middle-aged/older patients) and the degree of enhancement (subependymomas typically do not enhance).
• Overestimating the significance of heterogeneous signal in larger subependymomas and missing the characteristic low cellularity and benign nature; size alone should not trigger unnecessary intervention in asymptomatic patients.
• Confusing subependymomas with choroid plexus papillomas based on location within the ventricle; remember that papillomas show vivid enhancement and are usually in younger patients.
• Failing to recognize that absence of surrounding edema and lack of mass effect are key features that support a benign diagnosis and argue against higher-grade intraventricular neoplasms.