Nocardial Brain Abscesses Mimicking Metastatic Lung Cancer

November 1, 2008

A 55-year-old man with no past medical problems presented with headache, difficulty in walking, and loss of balance of 3 days' duration. Physical examination findings and laboratory test results were unremarkable except for lethargy, slurred speech, positive Romberg sign, hyponatremia, and leukocytosis with left shift.

A 55-year-old man with no past medical problems presented with headache, difficulty in walking, and loss of balance of 3 days' duration. Physical examination findings and laboratory test results were unremarkable except for lethargy, slurred speech, positive Romberg sign, hyponatremia, and leukocytosis with left shift.

A noncontrasted CT scan of the head showed large areas of cerebellar vasogenic edema with pressure on the fourth ventricle and aqueduct, causing mild hydrocephalus. An MRI scan of the head revealed ring-enhancing lesions with surrounding edema without midline shift (Figure 1). A contrast-enhanced CT scan of the chest showed soft tissue thickening along the bronchoalveolar margin of the superior segment of the right lower lobe. Lung cancer with metastases to the brain was suspected, but after lack of enhancement was seen on positron emission tomography, the diagnosis fell into doubt.

Figure 1 -

ThisnoncontrastT1-weighted MRIsequence, takenat presentation,shows peripherallyenhancing necroticmasses in theright cerebellummeasuring 18 mm(blue arrow) and leftoccipital lobesupratentoriallymeasuring 11 mm(white arrow)

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Suboccipital craniotomy for resection of the cerebellar lesions was performed. The lesions were found to be capsular, with purulence noted on incision. Hematoxylin and eosin, Gomori methenamine-silver, and acid-fast bacilli stains of brain tissue revealed Nocardia farcina (Figure 2). A 6-week treatment regimen with intravenous ceftriaxone and oral trimethoprim/sulfamethoxazole (TMP/ SMX) was started. Two weeks after treatment was started, an MRI scan showed enlargement of existing lesions and development of new lesions (Figure 3). The intravenous antibiotic was switched to imipenem/cilastatin, and the treatment was continued for 6 weeks. Serial MRI scans of the head demonstrated shrinkage of the lesions, and clinical improvement occurred.

Figure 2 -

With high-powermagnification, a mixedinflammatory infiltrate canbe seen in brain tissue stainedwith hematoxylin and eosinstain (A). A Gomorimethenamine-silver stain(B) and an acid-fast bacillistain (C) reveal aggregatesof a filamentous organismand confirm the diagnosis ofnocardial brain abscess(arrows)

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Figure 3 -

A T1-weighted MRIsequence withgadoliniumperformed 20 daysafter presentationshows an enlargedright cerebellar lesionmeasuring 30 mm(blue arrow) anda left occipital lesionmeasuring 20 mm(thick white arrow)and also the appearanceof a new 10-mmright occipital lesion(thin white arrow)

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Discussion
In the case described here, multiple brain abscesses in an immunocompetent patient were misdiagnosed as metastatic lung cancer. After initial treatment with intravenous ceftriaxone and oral TMP/SMX failed, a correct diagnosis of N farcina infection was made. Treatment with a combination of imipenem/cilastatin and TMP/SMX led to complete clinical and radiological improvement.