The differential for peripheral or ring enhancing cerebral lesions includes:

• cerebral abscess

• tuberculoma

• neurocysticercosis

• metastasis

• glioblastoma

• subacute infarct/haemorrhage/contusion

• demyelination (incomplete ring)

• tumefactive demyelinating lesion (incomplete ring)

• radiation necrosis

• postoperative change

• lymphoma - in an immunocompromised patient

• leukaemia ⁴

• thrombosed aneurysm ⁴

• necrotising leukoencephalopathy after methotrexate ^4,5

• Baló concentric sclerosis

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:

• enhancing wall characteristics

  • thick and nodular favours neoplasm

  • thin and regular favours abscess

  • incomplete ring often opened toward the cortex favours demyelination

  • intermediate to low T2 signal capsule favours abscess

  • restricted diffusion of enhancing wall favours GBM or demyelination

• surrounding oedema

  • extensive oedema relative to lesion size favours abscess

  • increased perfusion favours neoplasm (metastases or primary cerebral malignancy)

• central fluid content

  • restricted diffusion favours abscess

  • an absence of diffusion restriction favour a tumour with a central necrotic component (classically metastases)

• number of lesions

  • similar sized rounded lesions at grey-white matter junction favours metastases or abscesses

  • irregular mass with adjacent secondary lesions embedded in the same region of 'oedema' favours GBM

  • small (<1-2 cm) lesions with thin walls, especially if other calcific foci are present, suggest neurocysticercosis.

See also

• cerebral ring enhancing lesions (mnemonic)

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