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Parenchymal Metastases

KEY FACTS

TERMINOLOGY

• Secondary brain tumors (metastases) arise from

○ Tumors outside CNS spreading to CNS (usually via

hematogenous dissemination)

○ Primary CNS neoplasms spreading from 1 site to another

(usually geographic extension, e.g., along WM tracts)

IMAGING

• General features

○ Round enhancing lesion(s) at gray-white interface

(arterial border zones)

○ Most metastases are circumscribed/discrete > >

infiltrating, spherical > > linear

○ 50% are solitary; 20% have 2 metastases

○ 30% of patients have 3 or more

• MR signal intensity varies with

○ Cellularity, nuclear:cytoplasmic ratio

○ Presence/absence of hemorrhage

• Usually no restriction on DWI

○ Exception: Densely cellular metastases may restrict

TOP DIFFERENTIAL DIAGNOSES

• Abscess (solitary or multiple)

• Glioblastoma multiforme

• Cerebral infarction (multiple embolic)

• Demyelinating disease (e.g., tumefactive MS)

PATHOLOGY

• Metastases represent at least 50% of all brain tumors

• In 10% of cases, brain is only site

CLINICAL ISSUES

• Progressive increase in size and numbers is typical

• Median survival with whole-brain XRT = 3-6 months

• Stereotactic radiosurgery alone > whole-brain XRT

• Survival advantage, if 1-4 metastases, avoids deleterious

effects of whole-brain XRT on quality of life, cognition

• Resection of solitary metastasis may improve survival

(Left) Axial graphic shows

parenchymal metastases ﬈

with surrounding edema ﬊.

The gray-white matter

junction is the most common

location. Most metastases are

round, not diffusely

infiltrating. (Right) Close-up

view of an axial section

through an autopsied brain

shows a classic metastasis ﬈

in the classic location, the

gray-white matter junction.

Note the round shape, central

necrosis, and relative lack of

edema. Diffuse

leptomeningeal metastatic

spread ﬇ is also present.

(Left) Axial T2WI MR in a 52-

year-old man with a seizure,

history of melanoma, shows

multiple lesions ſt at the

gray-white matter interfaces.

Moderate edema surrounds

the lesions. One of the lesions

has a hypointense nodule ﬇,

suggesting that at least 1 is a

hemorrhagic metastasis.

(Right) T1 C+ FS MR (same

case) shows that the lesions

enhance ſt. Note small

metastasis st in the right

ventricle choroid plexus that

was not appreciated on T2WI.

The extensive occipital edema

is also from a metastasis (not

seen on this image).

Brain: Pathology-Based Diagnoses: Neoplasms,

Cysts, and Disorders

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