Intraventricular masses (an approach)

The ventricular system of the brain plays host to a variety of unique tumours, as well as tumours more frequently seen elsewhere (e.g. meningiomas). In addition some intra-axial (parenchymal) masses can be mostly exophytic and thus appearing mostly intraventricular. A systematic approach taking into account location, patient demographic and imaging appearances can often substantially narrow the differential, and in most cases suggest one diagnosis as by far the most likely. This is especially important if the mass is benign and can be safely ignored / observed. 

Intraventricular masses

The main lesions to be considered are:

• tumours
  • ependymoma
  • central neurocytoma
  • subependymoma
  • subependymal giant cell astrocytoma / subependymal hamartomas of tuberous sclerosis
  • intraventricular meningioma
  • choroid plexus papilloma / choroid plexus carcinoma
  • choroid plexus metastases
  • craniopharyngioma
• cysts
  • colloid cyst
  • intraventricular simple cysts (including arachnoid cysts, ependymal cysts and large choroid plexus cysts)
  • choroid plexus xanthogranuloma
  • cavum septum pellucidum
  • cavum vergae
  • cavum velum interpositum
• infection
  • neurocysticercosis
  • tuberculoma
• intraventricular haemorrhage

In addition parenchymal lesions which can be periventricular should also be considered, such as: 

• glioblastoma
• primary CNS lymphoma
• cerebral metastases
• medulloblastoma / sPNET
• haemangioblastoma
• pilocytic astrocytoma
• atypical teratoid / rhabdoid tumour 
• pineal region masses

Imaging

As is the case with most intracranial pathology, MRI is the modality of choice for assessment of intraventricular masses, although CT and DSA both have roles to play. Transcranial ultrasound is particularly useful in infants. 

A typical MRI protocol would include three plane imaging (essential if the relationship of the mass to the ventricle is to be confidently determined) and post contrast studies (the pattern of enhancement is particularly useful in distinguishing a number of the aforementioned lesions). 

Approach

Aunt Minnie lesions

Perhaps more so than in most other regions of the brain, there are a number of intraventricular masses which have very characteristic appearances, and offer little in the way of a realistic differential diagnosis (or at most between two lesions which are difficult to distinguish on imaging). These can be considered Aunt Minnies and the only way to approach them is to be familiar with their appearance. Example of such lesions include:

• colloid cyst
• intraventricular simple cysts
• choroid plexus xanthogranuloma
• cavum septum pellucidum
• cavum vergae
• cavum velum interpositum
• subependymal giant cell astrocytoma / subependymal hamartomas of tuberous sclerosis
• central neurocytoma

Intraventricular vividly enhancing mass

Finding a vividly enhancing mass in the ventricular system has a limited differential, including:

• choroid plexus papilloma
  • peak incidence: young children
  • location: typically in the trigone of children and fourth ventricle of adults
  • associated with hydrocephalus
  • highly lobulated
  • extremely vividly enhancing
  • choroid plexus carcinoma can appear identical although usually there is evidence of heterogeneity (necrosis / haemorrhage) and brain invasion
• intraventricular meningioma
  • peak incidence: middle age to older adults
  • location: 85% in trigone of lateral ventricle
  • solid and well circumscribed and rounded / spherical or with a few large lobulations
  • homogeneous signal intensity
  • moderate restricted diffusion
  • heavy calcification is characteristic
• ependymoma
  • peak incidence: children and young adults
  • location: typically floor of 4th ventricle in children
  • enhancement heterogeneous
  • haemorrhage common
• metastasis
  • peak incidence: usually older patients
  • location: choroid plexus or anywhere with the ventricles
  • heterogeneous
  • often multiple lesions
• haemangioblastoma (not intraventricular, but can mimic an intraventricular mass)
  • peak incidence: young adults
  • location: posterior fossa
  • cystic component
  • large flow voids