Q&A: Ring Enhancing Brain Lesions in Immunocompetent Individuals

The differentials 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, thrombosed aneurysm, and necrotising leukoencephalopathy after methotrexate.

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This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find the Brain and Nerve articles more useful, or one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.

In this article:
MCQ: clinical scenario
MCQ: answer
MCQ: explanation

MCQ: clinical scenario

A 35-year-old woman is referred to a tertiary hospital for a brain biopsy. The patient initially presented to a local community hospital following 5 days of blurred vision associated with headache and 2 days of left face, arm, and leg numbness. These symptoms had come on gradually, were becoming progressively worse, and were accompanied with generalized fatigue and anxiety. She also complained of a dry cough and dyspnea on exertion. She denied any fever, chills, night sweats, or weight loss. She reported no contacts with other sick individuals and no recent travel outside her hometown. She did not own any pets.

The patient underwent head computed tomography (CT) and magnetic resonance imaging (MRI) of the brain. These showed multiple, bilateral lesions with surrounding edema on fluid-attenuated inversion recovery (FLAIR) images, which appeared ring-enhancing on postgadolinium images.

Which of the following would be the least likely cause of ring-enhancing brain lesions in an immunocompetent patient?

a). Metastases
b). Pyogenic abscess
c). Toxoplasmosis
d). Multiple sclerosis
e). Primary brain tumours

MCQ: answer

The correct answer is C.
Toxoplasmosis is the least cause in immunocompetent individuals.

MCQ: explanation

A ring-enhancing lesion is an abnormal radiologic sign on MRI or CT scans obtained using radiocontrast. On the image, there is an area of decreased density surrounded by a bright rim from concentration of the enhancing contrast dye. This enhancement may represent breakdown of the blood-brain barrier and the development of an inflammatory capsule. This can be a finding in numerous 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, with CT imaging being the appropriate next step to differentiate between the two conditions.

The differential diagnosis of ring-enhancing lesions largely depends on the immune status of the patient. In the immunocompetent host, tumors – both primary and metastatic – and pyogenic abscesses remain the most likely diagnoses; abscesses caused by atypical organisms and demyelinating disease must also be considered. In the immunocompromised host, the leading diagnoses are toxoplasmosis and primary CNS lymphoma. Furthermore, these patients are at risk for abscesses, from both pyogenic and atypical organisms, and tumors. Tuberculous brain abscess should be considered in endemic regions in both immunocompetent and immunocompromised hosts.

A helpful mnemonic is MAGIC DR. See the separate article, Differential Diagnoses Of Ring Enhancing Lesions.

Magnetic resonance imaging (MRI) is the imaging study of choice in brain abscess as it is more sensitive than the computed tomography (CT) scan. Diffusion-weighted magnetic resonance imaging (DWI) is, in addition, more capable of differentiating ring-enhancing lesions due to brain abscess from neoplastic lesions. Abscesses are usually hyperintense on DWI (indicating restricted diffusion, characteristic of viscous materials, such as pus), while neoplastic lesions are hypointense or show variable hyperintensity that is lower than the intensity seen with an abscess.

Reference(s)
1). Irene Cortese, MD, Fellow and Avindra Nath, MD, Professor: Case 11: A Young Woman With Ring-Enhancing Brain Lesions. MedGenMed. 2006; 8(1): 3. Published online 2006 Jan 5. PMCID: PMC1681925 PMID: 16915133
2). UpToDate: Pathogenesis, clinical manifestations, and diagnosis of brain abscess. Available online: https://www.uptodate.com/contents/pathogenesis-clinical-manifestations-and-diagnosis-of-brain-abscess
3). Radiopaedia: Cerebral ring enhancing lesions. Available online: https://radiopaedia.org/articles/cerebral-ring-enhancing-lesions
4). Fauci A. Harrison's Principles of Internal Medicine, New York, McGraw Hill Medical, 2008