Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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November 9, 2023
Cerebral Nocardiosis
Background:
- Nocardia is an acid-fast as well as Gram-positive aerobic filamentous bacteria found in soil and water.
- Most patients are immunocompromised hosts, distinctly cell-mediated immunodeficient, such as those on long-term steroids and chemotherapy, as well as those who are HIV-positive.
- Infection is acquired through inhalation or direct inoculation leading to primary pulmonary or cutaneous disease, and most of the time pulmonary or cutaneous manifestations are subclinical. Due to special tropism to CNS, the brain is one of the common sites in disseminated nocardiosis. CNS involvement commonly has features such as meningo-encephalitis and brain abscesses; rarely diffuse cerebral or spinal cord infections.
Clinical Presentation:
- Though most patients are immunocompromised, various clinical presentations have been described. Patients present with gradual onset without significant signs of septicemia with seizures, focal neurologic deficits, or nonfocal findings. Subclinical or self-resolving pulmonary symptoms are seen prior to CNS symptoms.
Key Diagnostic Features:
- Multiple abscesses with satellite small abscess with T2 hypo- and hyperintense wall
- Dual rim sign on SWI and diffusion-restricting contents
- Peripheral rim of contrast enhancement and lipid lactate peak on MR spectroscopy
Differential Diagnoses:
- Bacterial abscess: Overlapping imaging features; usually presents with high-grade fever with local paranasal sinus or ear infection; predilection for basifrontal and temporal lobe location; MRS may show amino acid peak.
- Fungal abscess: Presence of irregular enhancing projections into the abscess cavity may be seen.
- CNS tuberculosis: Most abscesses are associated with meningoencephaltis with basal exudates and hydrocephalus.
- Glioblastoma multiforme: The peripheral enhancing rim in GBM is peripheral to the T2-hypointense rim and it is thick, irregular, incomplete, and discontinuous. High perfusion map in the periphery with diffuse infiltrate into adjacent brain parenchyma are hallmarks of GBM.
Treatment:
- Most patients undergo burr-hole techniques to drain the abscesses. If not, craniectomy is an option to drain.
- Aggressive intravenous antibiotics and long-duration (6-12 months) oral antibiotics are a must for nocardiosis. Conventionally, cotrimoxazole is the antibiotic of choice though pus culture–sensitive antibiotics should be.