The differential for peripheral or ring enhancing cerebral lesions includes:
tumefactive demyelinating lesion (incomplete ring)
postoperative change
lymphoma - in an immunocompromised patient
leukemia 4
necrotizing leukoencephalopathy after methotrexate 4,5
A helpful mnemonic is MAGIC DR
Radiographic features
No single feature is pathognomonic, although a cystic lesion that markedly restricts centrally (the fluid component) on DWI should be considered an abscess until proven otherwise.
Many features of the lesion, as well as clinical presentation and patient demographics, need to be taken together to help narrow the differential. Helpful rules of thumb include:
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enhancing wall characteristics
thick and nodular favors neoplasm
thin and regular favors abscess
incomplete ring often opened toward the cortex favors demyelination
intermediate to low T2 signal capsule favors abscess
restricted diffusion of enhancing wall favors GBM or demyelination
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surrounding edema
extensive edema relative to lesion size favors abscess
increased perfusion favors neoplasm (metastases or primary cerebral malignancy)
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central fluid content
restricted diffusion favors abscess
an absence of diffusion restriction favor a tumor with a central necrotic component (classically metastases)
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number of lesions
similar sized rounded lesions at grey-white matter junction favors metastases or abscesses
irregular mass with adjacent secondary lesions embedded in the same region of 'edema' favors GBM
small (<1-2 cm) lesions with thin walls, especially if other calcific foci are present, suggest neurocysticercosis.
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