Ependymomas (WHO grade 2) are common slow-growing tumor arising from the differentiated ependymal cells lining the ventricle and central canal. They constitute around 2%-9% of pediatric brain tumors and almost one-third of all brain tumors in children younger than 3 years. They are the third most common pediatric brain tumors, after astrocytoma and medulloblastoma. Fourth ventricle is the most common location. Posterior fossa ependymoma has been called the “toothpaste” or “plastic tumor” for its propensity to fill the fourth ventricle and squeeze through the foramina of Magendie or Lushka into the adjacent basal cisterns (In contrast, medulloblastoma, which can also fill the fourth ventricle, does not typically squeeze through the foramina) (Fig1). On imaging, ependymomas appear as enhancing mass with  heterogeneity related to cystic/necrotic change, calcification, or hemorrhage.  

• Moderate enhancement
• Absence of large flow voids
• “Plastic” tumor
• On T2* (e.g. SWI) - foci of blooming from haemorrhage or calcification
• T1 isointense to hypointense, T2 hyperintense to white matter

Choroid plexus papillomas (Who grade 1) most often (70%) occur in the fourth ventricle in adults and in the lateral ventricles, with a predilection for the trigone - in children.

The tumours are usually well-defined lobulated masses, either iso- or somewhat hyperdense compared to the adjacent brain. There is associated hydrocephalus. The characteristic appearance on MRI is a cauliflower-like, lobulated, vividly enhancing intraventricular mass (Fig2). Higher grade is associated with larger size and more extensive surrounding white matter edema.

• T1 -typically isointense compared to the adjacent brain
• T2 -iso to hyperintense
• “Light bulb” enhancement
• Associated with hydrocephalus due to overproduction of CSF
• Sometimes have associated cysts
• Can have some central flow voids

Subependymal giant cell astrocytoma (SEGA) is a benign (WHO grade 1) tumor that is associated with tuberous sclerosis complex. Other common intracranial findings in tuberous sclerosis include subependymal nodules (hamartomas) (Fig3), cortical/subcortical tubers, and white matter radial bands. On imaging, they classically appear as an intraventricular mass near the foramen of Monro,  larger than 1 cm, showing calcifications, heterogeneous MRI signal, and marked contrast enhancement. 

• Vivid enhancement, lobulated
• At the foramen of Monro in a patients with tuberous sclerosis (cortical/subcortical tubers)
• T1: heterogeneous and hypo- to isointense to grey matter 
• T2: heterogeneous and hyperintense to grey matter; calcified components can be hypointense
• calcification is common and haemorrhage is possible

Central neurocytomas are WHO grade 2 neuroepithelial intraventricular tumors with fairly characteristic imaging features, appearing as heterogeneous masses of variable size and enhancement within the lateral ventricle, typically attached to the septum pellucidum (Fig4). Central neurocytomas are usually hyperattenuating compared to white matter. Calcification is seen in over half of cases. Cystic regions are frequently present (bubbly or Swiss cheese appearing), especially in larger tumours. Contrast enhancement is usually mild to moderate. Accompanying ventricular dilatation is often present. Extraventricular neurocytomas are rare.

• Attached to septum pellucidum
• Calcifications
• Prominent flow voids may be seen
• T1 C+ - mild-moderate heterogeneous enhancement
• T1 isointense to grey matter, T2 iso to somewhat hyperintense
• DWI - diffusion restriction of the solid component

Subependymoma is an indolent (WHO grade 1) tumor  of middle-aged and older adults, often found incidentally. They are slow-growing and non-invasive. The most common locations are the walls of the fourth and lateral ventricles. The tumor grows exophytically into the ventricle and does not cause parenchymal edema. It usually does not enhance significantly, unlike ependymomas (Fig5).

• Older patients
• T1 iso-hypointense to white matter
• T2 hyperintense to adjacent white and grey matter
• No adjacent parenchymal oedema or mass effects
• FLAIR: very bright signal
• T1 C+ : usually no enhancement
• Do not grow, do not cause hydrocephalus

In adults, atrial intraventricular meningiomas are among the most common tumors seen in the lateral ventricle. Although rare, accounting for only 0.7% of all meningiomas, most cases occur in the left lateral ventricle of middle-aged or older women. The cells of origin are believed to be arachnoid cap cells confined to the choroid plexus. CT reveals a sharply demarcated lobular mass with periventricular edema. On MRI, the lesion can appear as iso- to hypointense compared with gray matter on T1-weighted images and iso- to hypointense on T2-weighted images, with intense enhancement of the mass (Fig6). The low signal intensity on T2-weighted images is one of the key features of meningioma, greatly aiding in the correct imaging assessment.

• In the trigone
• Homogeneously enhanced
• Hypercellular

Choroid plexus xanthogranuloma is the most common choroid plexus mass in adults. They  represent collections of cholesterol and lipid-laden histiocytes. On MRI, they are hyperintense on T2-weighted images, do not attenuate completely on FLAIR. A helpful feature is that they usually have a quite high signal on diffusion-weighted imaging (DWI). This high signal is seen as a result of both true restricted diffusion and T2 shine through (Fig7).

Choroid plexus metastasis are rare,  they are seen most commonly in adults, although have also been found in children with extracranial childhood tumours. The lesion may be hypo or isodense on non-enhanced CT and may demonstrate moderate or marked enhancement, more commonly homogeneous. With larger lesions, there may be peritumoural oedema or invasion into adjacent brain parenchyma (Fig8).

Colloid cysts are benign developmental lesions that are usually incidental findings and account for the most common mass of the foramina of Monro.  Typically seen as a well-defined, rounded, sharply demarcated lesion at the roof of the third ventricle, which range in size from a few millimeters to 3-4cm. The “machine oil-like” contents appear hyperattenuating on CT and low signal intensity on T2-weighted images (Fig9).

• Variety of signal on T1/T2
• Calcification is uncommon
• T1 C+ No central enhancement. Because of close relationship with choroid plexus, it can spread the choroid plexus around it, mimicking enhancement of its walls.

Intraventricular simple cysts are rare and usually asymptomatic. They have appearances similar to arachnoid cysts elsewhere and follow CSF on all modalities and sequences with a very thin or imperceptible wall. Do not demonstrate restricted diffusion (Fig10). They are most frequently encountered in the trigone of the lateral ventricles.