Intra-axial masses that restrict

• Lymphoma - homogenous restriction

• GBM - heterogenous restriction

• Medulloblastoma

• Pilocytic astrocytom

• Ganglioglioma

Cortically Based Tumors

• DNET

• Oligodendroglioma

• Ganglioglioma

Classic Pearls

Enhancement

• Things that enhance

  • Extra-axial masses (meningioma for example)

  • Aggressive processes that invade and disrupt the BBB (infection, masses etc.)

    • This is why low grade masses do not enhance and high grade tumors do enhance

  • Exceptions

    • Pilocytic astrocytoma - enhances and low grade

    • Ganglioglioma - enhances and low grade

Brain Masses

• Intra-Axial

  • Glial (astrocytomas, oligodendrogliomas, ependymomas,

    • Astrocytomas

      • Pilocytic Astrocytoma

      • Pilomyxoid Astrocytoma

      • Sub-ependymal Giant cell Astrocytoma

      • Pleomorphic Xanthoastrocytoma & Anaplasic Xanthoastrocytoma

      • Diffuse Astrocytoma

      • Anaplastic astrocytoma

      • Glioblastoma

    • Oligodendrogliomas

    • Ependymomas

Posterior Fossa

• Adult

  • Mets (lung and breast most commonly)

  • Hemangioblastoma (most commonly primary)

  • Sub-ependymoma

  • Choroid plexus papilloma

  • Schwannoma

Astrocytomas

• Two major groups

  • Circumscribed

    • Looks more like an actual mass with borders - hence they’re names circumscribed

    • Pilocytic astrocytomas

      • Juvenile pilocytic astrocytoma (JPA)

        • Cerebellar cyst with adjacent mural nodule

        • Enhances even though low grade (WHO 1) - exception to the rule

        • Optic nerve gliomas - basically same cell grade as JPA - seen inf NF-1

    • Pilomyxoid astrocytomas

    • Subependymal giant cell astrocytoma (SEGA)

      • Arise from the wall of the lateral ventricle

        • Will enhance because technically extra-axial

      • Assoicated with TS

    • Pleomorphic xanthoastrocyoma & Anaplastic xanthoastrocyoma

    • Well circumscribed enhancing mass with an internal or adjacent non-enhancing cyst

      • In cerebellum and a kid? —> think pilocytic astrocytoma

      • In supra-sellar region? —> think pilomyxoid astrocytoma

      • At foramen of Monro? —> think supendymal giant cell astrocytoma

      • Peripherally located and invasive? —> think Pleomorphic xanthoastrocyoma & Anaplastic xanthoastrocyoma

  • Diffuse/Infiltrative

    • Tend to blend into the brain and just looks like the normal anatomy is being expanded

    • Diffuse Astrocytoma

    • Anaplastic astrocytoma

    • Expansile parenchymal lesions, hypoattenuating on CT, hyperintense on T2, poor to no enhancement

      • Very similar to oligodendroglioma, may not be able to differentiate on imaging alone

  • Glioblastoma

    • Given its own section due to its prevalence, imaging findings, and poor prognosis

• Hemangioblastoma presents the same as pilocytic astrocytoma however PA will be in a child and hemangioblastoma will be in an adult

Brainstem Glioma

• A mass encasing the basilar artery is nearly pathognomonic for a brainstem glioma

• Enhancement at presentation = worse prognosis

Glioblastoma

• WHO grade 4 astrocytoma

• Methylation of MGMT (O6-methylguanine DNA methyltransferase) which is a repair protein

• 90% = IDH wildtype aka primary GBM, 10% IDH mutatnt aka secondary GBM

• Imaging characteristics

  • Heterogenous enhancement with edema and necrosis

  • Ring enhancement is classic finding

  • Calcification and hemorrhage may be seen

• Butterfly glioma

  • basically a GBM that crosses the corpus callosum to involve both hemispheres

  • Note two major masses that do this are GBM and primary CNS lymphoma BUT lymphoma will be homogenously enhancing (not heterogenous as is seen in GBM) and CNS lymphoma typically does not bleed (GBM does bleed)

Gliomatosis Cerebri

• Low grade glioma with diffuse infiltration

  • Low grade hence does not enhance

• Must involve 3+ lobes

• Extensive T2/FLAIR hyperintensity

Lymphoma

• Homogenous enhancement

• Crosses midline

• Restricts diffusion

• Thallium positive

• Intravascular/Angiocentric Lymphoma

  • Presents clinically like a stroke with multifocal areas of microhemorrhage and infarcts

Oligodendroglioma

• Most commonly seen in frontal lobes

• Classically cortically based and expands the cortex

• Imaging findings are essentially the same as diffuse astrocytomas

  • Although more likely to have calcifications

• 1p19q mutation

  • Most important prognostic factor

Posterior Fossa (Adults)

• Mets (lung and breast most commonly)

• Hemangioblastoma (most commonly primary)

• Sub-ependymoma

• Choroid plexus papilloma

• Schwannoma

Esthesioneuroblastoma (Olfactory neuroblastoma)

• originate from CN1 or something

Ependymoma

• Arise from ependymal cells which line the ventricles and central canal of spinal cord

• Pathology: perivascular pseudo-rosettes

• Imaging findings:

  • Heterogenous, enhancing mass with internal clacifications

  • Hemosiderin cap sign —> peripheral hemorrhage which looks like surrounding dark outlining circle

  • Kids - classically in 4th ventricle

    • Differentiate from choroid plexus tumors which prefer the lateral ventricles

  • Can invade brain parenchyma

• Subependymoma

  • Mass arising from small layer of glial cells deep to the ependymal lining

  • WHO 1

  • Adults

  • Can result in obstructive hydrocephalus

  • EMA negative

    • key differentiation from ependymomas

  • Imaging findings

    • 4th ventricle > lateral ventricles > other locations

    • T1 hypointense, T2 hyperintense, non-enhancing

    • Heterogenous appearance

    • Hypovascular (less enhancement on post-con)

      • key differentiation from ependymomas

Ependymoma

• Bimodal - 1-5 yo & >30 yo

• Classically from floor of 4th ventricle and through lushka & magendie

• Does not restrict

• Drop mets present

• Toothpaste sign

• More likely to have hemorrhage and calcs

Meningioma

• Does not invade IAC

• Enhances homogenously

• Can calcify

Choroid Plexus

Choroid Plexus Xanthogranuloma

• Benign mass of choroid plexus

• Restrict on diffusion but not malignant

DNET

• Cortically based “bubbly” lesions

• Typically in temporal lobe

• T2 bright

Cerebellar-Pontine Angle

Pineal Region

• If looking at a child brain, there should be almost no calcification in pineal region in kid younger than 12, if calcification is present look for a mass!

• Pineocytoma, Pinealblastoma, Pineal cyst, Germinoma, Quadrigeminal Retinoblastoma

• Caution for Parinaud syndrome

Pineaocytoma

• Age 20+ years old

• WHO grade 1

• Well circumscribed, slow growing

• Peripheral calcificiations

• T1 - hypo

• T2 - solid part iso, cystic part = cystic

• Strong enhancement

Meningioma

• Extra-axial tumor or meninges

• Isointense to gray matter on T1 & T2

• Vivid enhancement on MR & CT

Colloid Cyst

• Benign cyst located at foramen of monro almost 100% of the time

• Can cause obstructive hydrocephalus, otherwise asymptomatic

• Contain mucin (looks like mucus on gross pathology)

• CT

  • Hyperdense, cystic appearance

  MR

Cholesterol Granuloma

• Petrous temporal bone/petrous apex

• Young adults & children

• Expansile lesion with osseous erosions

• T1 & T2 central hyperintense, peripheral hypointense

• Not FLAIR hyperintense

• No enhancement

• No restricted diffusion

Chloroma (Myeloid sarcoma)

• Basically AML but in mass form

  • So look for history of AML

• Extramedullary (at least originally)

  • The images I have seen look like its intramedullary though

• Can occur anywhere in body, included here because one place commonly seen is the skull

Pituitary Region

Other Masses

Non-masses that will have pituitary stalk involvement

• Langerhans cell histiocytosis

• Neurosarcoidosis

Ectopic Neurohypophysis

• Basically posterior pituitary that did not fully descend to normal location

• Infundibulum is typically hypoplastic

• T1 bright lesion

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