The differential diagnosis for an intracranial mass is dependent on a number of different factors. One of the most important is location. If the mass is extra-axial - outside of the brain parenchyma- it most likely represents a Meningioma if it is dural based or Schwannoma if it is associated with a cranial nerve. If the mass is intra-axial - inside of the brain parenchyma- it could represent a primary tumor, metastatic disease or a tumor mimic.

Tumors historically have been classified based on histology and cell of origin. In 2007, there was a paradigm shift, such that genetic markers were applied to preexisting categories to aid in prognosis.

In 2016, CNS WHO classification system was released which incorporates molecular parameters for classification and prognosis.

The primary glial markers are listed in the adjacent table which highlights which profile portends a more favorable/less favorable outcome.

Location: Most supratentorial

Imaging Features:

• Variable enhancement pattern: thick rim, solid, patchy nodular; Heterogenous, can have cysts, necrosis, hemorrhage, calcium rare

• High cerebral blood volume on perfusion

• Hypercellular elements T2 hypointense, restrict diffusion

Location: Most supratentorial

Imaging Features:

• Variable enhancement pattern: thick rim, solid, patchy nodular; Heterogenous, can have cysts, necrosis, hemorrhage, calcium rare

• High cerebral blood volume on perfusion

• Hypercellular elements T2 hypointense, restrict diffusion

Location: Two thirds are supratentorial, most frontal/temporal

Imaging Features:

• Often indistinguishable from Grade 2 tumors.

• Ill-defined T2/FLAIR hyperintense expansile white matter lesion

• Grade 3, more heterogeneous, can enhance

• elevated relative CBV compared to grade 2 tumors

Location: Two thirds are supratentorial, most frontal/temporal

Imaging Features:

• Ill-defined T2/FLAIR hyperintense expansile white matter lesion

• Grade II, more homogeneous, unlikely to enhance

• relatively lower CBV compared to grade 2 tumors.

Location: Most often occurs in the posterior fossa, can occur in the optic chiasm/hypothalamus

Imaging Features:

• Cyst with an enhancing mural nodule

• Favorable prognosis

• No diffusion restriction

Location: 80% supratentorial, most frontal

Imaging Features:

• T2/FLAIR hyperintense expansile white matter lesion

• Heterogenous, can calcify, have cysts, and enhance (50%)

• Prominent enhancement, hemorrhage or necrosis? more likely to be anaplastic/high grade

CNS Lymphoma can be Primary or Secondary

Location: Periventricular

Imaging Features

• Smooth margins, enhancing

• Dark on T2, diffusion restricting related to high cellularity

Secondary CNS lymphoma exhibit similar imaging features as primary CNS lymphoma. The primary difference is that they have disease outside of the CNS.

Epidemiology: Occurs in 1st 2 decades

• 94% survival at 10 yrs;

• Most common pediatric CNS glial neoplasm

• Symptoms related to mass effect

Location: Cerebellum, ON, Hypothalamus

Imaging Features: “Cyst with enhancing mural nodule”

Grade: WHO grade 4 (4 subtypes)

Epidemiology: Most common posterior fossa mass in children

Location:

• Arise from the vermis and grow into the 4^th ventricle

• Can be hemispheric

Imaging Features:

• Enhancing tumors, dark on T2 and diffusion restricting arising from the roof of the 4th ventricle

• Image the spine, drop metastasis may be present.

Grade: WHO Grade 2

Epidemiology: bimodal age peaks

Pathology: Glial tumor derived from differentiated ependymal cells that line the ventricles and central canal

Location: Floor of the 4th ventricle

Imaging Features:

• Soft malleable appearance, solid, calcification is common (40-80%); Variable enhancement

• Subarachnoid spread less common than medulloblastoma- but when present likely reflects higher grade tumor

Pathology: Rare, benign tumors of vascular origin

Epidemiology: More common in adults, uncommon in children- but can be seen, association with VHL

Location: Occur more commonly in cerebellum

Imaging Features:

• Cyst with vascular mural nodule- look for adjacent vessels

• Hemorrhage may be present

Pathology: benign tumors of nerve origin

Location: Can occur anywhere along the dura

Imaging Features:

• Enhancing masses associated with the dura, may have dural tail

• Calcification is a common feature

Pathology: benign tumors of nerve origin

Location: Occur more commonly in the internal auditory canal

Imaging Features:

• Enhancing masses involving nerves, most often seen involving CN8