BMJ Case Reports 2013; doi:10.1136/bcr-2013-009141

Ring lesions in the brain: a harmless commensal?

  1. Robin Howard2
  1. 1Department of Respiratory Medicine, Watford General Hospital, Watford, UK
  2. 2Department of Neurology, St Thomas’ Hospital, London, UK
  1. Correspondence to Dr Justin Garner, justin.garner{at}, justingrnr{at}


A 72-year-old gentleman, type 2 diabetic, was admitted in the hospital with a head injury which was a result of a fall. Several weeks before, he had been investigated and treated for a community-acquired pneumonia, left pleural effusion and confusion. CT brain showed right frontal encephalomalacia.

On re-examination, drowsiness, extensor plantar responses and signs of a left pleural effusion were recorded. He was afebrile.

His white cell count was 12.3 (4.0–11.0×109), neutrophils 10.8 (1.5–7.0×109), C reactive protein 5 (0–4) mg/l, urea 5.0 (1.7–8.3) mmol/l and glucose 6.8 (4.0–7.0) mmol/l. Repeat CT and MRI scans of the brain revealed ‘new multiple bi-hemispheric ring-enhancing lesions’, thought to represent abscesses (figure 1).1 Blood cultures were sterile. Transthoracic echocardiogram was normal. A persisting pleural effusion was noted: aspirate of pus revealed Gram-positive cocci identified as Streptococcus milleri on PCR.

Figure 1

(A) Gadolinium-enhanced T1-weighted axial MRI showing multiple small ring-enhancing lesions within both cerebral hemispheres including the left basal ganglia and thalami. (B) On T2-weighted axial MRI, these lesions have high T2 signal centrally with a rim of low T2 signal and surrounding oedema. (C) The lesions have high central signal on diffusion-weighted MRI with corresponding restriction on the apparent diffusion coefficient map (D), in keeping with cerebral abscesses.

He was prescribed a 6-week course of intravenous ceftriaxone, oral metronidazole and a short course of dexamethasone. Continuing clinical and radiological improvement has been documented up to 12 weeks.

The causes of ring-enhancing lesions include infection (eg, pyogenic, tuberculosis, toxoplasmosis and neurocisticercosis), inflammation (eg, sarcoidosis) and malignancy (eg, lymphoma).1 MRI is the non-invasive modality of choice to characterise cerebral lesions. Restricted diffusion (of water molecules) in an abscess is a feature aiding differentiation from centrally necrotic tumours; however, it is not pathognomonic. Microbiological diagnosis is crucial, and is dependent on adequate sampling, including for anaerobes, of bronchial secretions, blood and pus, before antimicrobial therapy.2 ,3 A biopsy of a brain lesion may be necessary. Unrecognised brain abscess is fatal.

Learning points

  • MRI is the non-invasive modality of choice to characterise cerebral lesions.

  • However, distinguishing brain abscesses and multiple metastases is challenging: a biopsy of a brain lesion may be necessary.

  • The Streptococcus milleri group of commensals, inhabiting the oropharynx, gut and vagina, is increasingly recognised as an important cause of brain abscess and empyema in compromised individuals, for example, diabetics, alcohol-dependents, etc.


  • Contributors JG contributed to the concept and drafting the article and RH performed the critical revision.

  • Competing interests None.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.


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