Miscellaneous Intracranial Metastases

KEY FACTS

TERMINOLOGY

• Brain metastases in locations other than skull/meninges or

parenchyma

IMAGING

• General features

○ > 95% of brain metastases parenchymal

○ Only 1-2% in ventricles, pituitary gland, etc.

○ Sites generally very vascular

○ Extraventricular metastases more diffuse, infiltrative

than parenchymal metastases (usually round)

• Location

○ Choroid plexus ± ventricular ependyma

○ Pituitary gland infundibulum

○ Eye (choroid)

○ Cranial nerves

○ Pineal gland

○ Preexisting neoplasm ("collision tumor")

• Best imaging tool: MR with T1WI C+ FS

○ Metastases almost always enhance

TOP DIFFERENTIAL DIAGNOSES

• Varies with location

• Choroid plexus, ventricle = meningioma

• Pituitary gland, infundibular stalk

○ Pituitary macroadenoma

○ Lymphocytic hypophysitis

○ Lymphoma

• Cranial nerves = neurofibromatosis type 2, lymphoma

• Eye (globe)

○ Ocular melanoma

○ Retinal or choroidal detachment

○ Choroidal hemangioma

DIAGNOSTIC CHECKLIST

• Look for "secret sites" outside parenchyma when imaging

brain for possible metastatic disease

(Left) Submentovertex graphic

shows the typical sites for

miscellaneous

nonparenchymal CNS

metastases. These include the

choroid plexus and ventricles

﬈, pituitary gland,

infundibular stalk ﬊, and eye

(choroid of the retina) st.

(Right) Coronal T1WI C+ MR in

an elderly woman with known

breast carcinoma shows a

thickened, enhancing

infundibular stalk ſt. This was

the only intracranial

metastasis identified in this

patient.

(Left) Axial T1 C+ FS in a

patient with diplopia and

known esophageal cancer

shows an enhancing nodule on

the left 3rd cranial nerve ſt,

as well as on the left optic

nerve/sheath ﬇. Cranial

nerve metastases from

extracranial tumors are less

common than from

hematopoietic neoplasms

(e.g., lymphoma). (Right) Axial

T1 C+ FS in a patient with

systemic B-cell lymphoma

shows multiple metastases to

the choroid plexus ſt. Subtle

ependymal metastases ﬇ are

present along with diffuse

dura-arachnoid thickening.

Cysts, and Disorders

Brain: Pathology-Based Diagnoses: Neoplasms,

151