Differential Diagnoses Of Ring Enhancing Lesions

When a patient undergoes a magnetic resonance imaging (MRI) or computerized tomographic scan (CT scan), the doctor or radiologist expects to see a couple of signs which could suggest specific lesions in the body. One of the signs which may be seen is a ring-enhancing lesion.

In this article:
A. What is a ring enhancing lesions
B. What causes a ring enhancing lesion?
C. Mnemonic for causes of ring enhancing lesions
D. Radiographic features

What is a ring enhancing lesions

A ring-enhancing lesion is an abnormal radiologic sign on magnetic resonance imaging (MRI) or computerized tomographic scan (CT scan) characterized by a central area of reduced density (i.e. hypodense area) surrounded by a bright rim. The bright rim is due to concentration of an enhancing radiocontrast dye injected by the radiologist while performing the scan.

What causes a ring enhancing lesion?

Ring enhancing lesions can be a feature of many disease states.

In the brain, it can occur with an early brain abscess as well as in Nocardia infections associated with lung cavitary lesions. In patients with HIV the major differential is between CNS lymphoma and CNS Toxoplasmosis.

Below is an MRI image of Glioblastoma multiforme (GBM) exhibiting a "ring" or "ring-like" zone of contrast enhancement around a dark (hypodense) central area of necrosis.

MRI showing a ring-enhancing lesion in the brain of a patient with glioblastoma multiforme (credit)

Mnemonic for causes ring enhancing lesions

The mnemonic, MAGIC DR, can be used as a easy recall prompt for the etiologies of ring enhancing lesions:

• Metastases;
• Abscess, including pyogenic abscess and abscess caused by atypical organisms, such as bacterial pathogens (Mycobacteria, Nocardia, Actinomyces, Rhodococcus, and Listeria); fungal pathogens (zygomycosis, Histoplasma, Coccidioides, Aspergillus, and Cryptococcus); and parasitic pathogens (neurocystircercosis, Echinococcus, and Entamoeba);
• Glioma and other primary CNS neoplasms (eg, lymphoma);
• Infarction;
• Contusion;
• Demyelination (multiple sclerosis, acute disseminated encephalomyelitis); and
• Resolving hematoma/radionecrosis.

The medical conditions listed above are differentials for peripheral or ring enhancing cerebral lesions.

Radiographic features

No single feature is pathognomonic. 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
  • low T2 signal 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
• 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 (<1-2cm) lesions with thin walls especially if other calcific foci are present suggest neurocysticercosis.

Do you know of any other helpful mnemonic for differentials of a ring-enhancing lesion? Please share with us below!

Reference
1). Fauci A: Harrison's Principles of Internal Medicine, New York, McGraw Hill Medical, 2008
2). Radiopaedia: Cerebral ring enhancing lesions. Accessed 11.06.2012. Available here: https://radiopaedia.org/articles/cerebral-ring-enhancing-lesions