Neoplasms Overview

(Left) Graphic depicts the

relative prevalence of brain

tumors in adults. Nearly 1/2

are metastases from systemic

cancers; the other 1/2 are

primary neoplasms. (Right)

Graphic depicts brain tumors

in children. Metastases,

anaplastic astrocytoma (AA),

and glioblastoma (GBM) are

rare. Pilocytic astrocytoma

and primitive

neuroectodermal tumors

(PNETs) in children are more

common than in adults.

(Left) Graphic depicts adult

astrocytomas. Low-grade

astrocytoma ﬉ (WHO II)

often becomes anaplastic ﬈.

GBM ﬊ is the most common

(shown here in the corpus

callosum). Pleomorphic

xanthoastrocytoma is a cystic

tumor with nodule abutting/

thickening the meninges ﬈.

(Right) Graphic shows

childhood astrocytomas.

Brainstem "gliomas" ﬈,

pilocytic astrocytoma (PA) ﬉

are common. Except for PAs

around the optic

nerves/chiasm ﬇,

supratentorial astrocytomas

﬊ are less frequent.

(Left) Axial T2WI in a 58-yearold man with 2 seizures

demonstrates a

heterogeneously hyperintense

mass ﬈ infiltrating the right

basal ganglia, frontal lobe,

external capsule, and posterior

limb of the internal capsule.

(Right) T1WI C+ MR in the

same patient shows a few

enhancing foci ﬈ in the

center of the mass. Its location

(frontal lobe) and large

nonenhancing areas suggest

this tumor is likely a secondary

GBM. Biopsy disclosed

IDH1(+), EGFR(-), MGMT(+),

p53 70% (+), PTEN 25% (+),

and MIB1 90%.

Brain: Pathology-Based Diagnoses: Neoplasms,

Cysts, and Disorders

128

Low-Grade Diffuse Astrocytoma

KEY FACTS

TERMINOLOGY

• Well-differentiated but infiltrating neoplasm, slow growth

pattern

• Primary brain tumor of astrocytic origin with intrinsic

tendency for malignant progression, degeneration into

anaplastic astrocytoma (AA)

IMAGING

• Focal or diffuse nonenhancing white matter mass

• T2 homogeneously hyperintense mass

• May expand adjacent cortex

• Usually no enhancement

○ Enhancement suggests progression to higher grade

• MRS: High choline, low NAA typical but not specific

• Perfusion: Relatively lower rCBV compared with AA

• Cerebral hemispheres most common location

○ Supratentorial 2/3: Frontal and temporal lobes

• Infratentorial 1/3: Brainstem (50% of brainstem "gliomas"

are low-grade astrocytoma)

• Low-grade astrocytoma may be indistinguishable from

other tumors

• May appear circumscribed on imaging, but tumor cells are

often found beyond imaged signal abnormality

TOP DIFFERENTIAL DIAGNOSES

• Other neoplasms: AA, oligodendroglioma

• Nonneoplastic mimics: Ischemia, cerebritis

PATHOLOGY

• WHO grade II

• If IDH-1(-) (nonmutated), will behave clinically like AA,

glioblastoma

CLINICAL ISSUES

• Seizure is most common presenting feature

• Majority occur between ages of 20-45 years, mean: 34 years

• Median survival: 6-10 years

• Increased survival: Young age, gross total resection

• More favorable prognosis: IDH1(+), ATRX(+), MGMT(+)

(Left) Coronal graphic shows

an infiltrative mass centered

in the white matter expanding

the left temporal lobe. Axial

insert shows mild mass effect

upon the midbrain. Low-grade

astrocytomas typically affect

young adults. (Right) Axial T2

MR in a 34-year-old man with

seizures shows a hyperintense

infiltrative mass ﬈ centered

in the right temporal lobe

white matter with extension

to the overlying cortex. No

enhancement was present on

contrast-enhanced images.

WHO grade II astrocytoma

was diagnosed at resection.

(Left) Axial FLAIR MR shows a

relatively homogeneous

hyperintense mass with mild

local mass effect, typical of a

WHO grade II diffuse

astrocytoma. These infiltrative

tumors may be focal or

diffuse. Fibrillary astrocytoma

is the most frequent histologic

variant. (Right) Axial MR

perfusion in the same patient

shows a low relative cerebral

blood volume ﬇ in the

frontotemporal mass,

suggesting a low-grade tumor.

Perfusion MR has been shown

to be helpful in preoperative

tumor grading, predicting

survival, and guiding biopsy.

Cysts, and Disorders

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129