51-year-old male with no significant past medical history presented with 3+ months H/O intermittent dizziness, intermittent headaches, difficulty going down stairs and 3+ days H/O tingling and numbness on the right side of face, right hand and foot. MRI revealed increased T2 signal and swelling of the entire pons including the middle cerebellar peduncles with effacement/obliteration of the prepontine and CP angle cisterns. Center of the lesion was heterogeneously T2 hypointense and showed heterogeneous contrast enhancement, small focus of diffusion restriction, focal area of increased CBV and high choline to creatine ratio (2.18) & a tall lactate peak on MR spectroscopy. Differential diagnoses at this point included metastasis, high-grade glioma, lymphoma and sarcoid.
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These were our differential diagnoses. Do you want to add any other differential diagnosis?
CT scan of chest, abdomen and pelvis were done in search of primary tumor. On CT chest, there were bilateral asymmetric hilar adenopathy and lower lobe predominant nodular densities. The overall chest findings were not typical for sarcidosis. Bronchoscopy-guided biopsy of the hilar nodes revealed non-caseating granulomas. CT of the abdomen and pelvis were unremarkable.
A diagnosis of sarcoidosis was presumed and the patient was put on steroids. Patient got better clinically and an MRI after 5 days revealed significant improvement of the T2 signal abnormality and mass effect. There was no appreciable change in the size of the enhancing lesion. Patient was discharged home with the diagnosis of sarcoidosis and was advised to continue steroids.
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2 weeks later the patient came back with new onset diplopia as a result of left 6th nerve palsy. MRI at this point showed interval enlargement of the mass, FLAIR abnormality and enhancement. Central T2 hypointense area was more heterogeneous. At this point of time, atypical infection was on the top of our differential diagnoses.
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Due to relatively rapid progression of clinical symptoms, the lesion was biopsied. It was fungal abscess due to blastomycosis!!
Blastomyces dernatitidis is the causative agent for blastomycosis. Blastomycosis is an uncommon, but potentially serious fungal infection, endemic in Mississippi and Ohio River basins and in the regions of Great Lakes and the St Lawrence River. Occasionally. it can be found in non-endemic areas as well. There is no predilection for any age, sex, race or occupation but it occurs more frequently in the immunocompromised hosts, particularly in AIDS patients. It primarily affects the lungs. CNS dissemination accounts for 5-10% of extrapulmonary blastomycosis and is usually manifested as intracranial mass lesion, abscess of the spinal cord or epidural abscess and meningitis in rare cases. Cerebellum is most commonly involved, but it can involve any area of brain. Multiple lesions throughout the brain mimicking multiple cerebral metastases has also been described in literature. CSF analysis is not very sensitive for the diagnosis as is the CSF culture. CNS blastomycosis is usually treated with Amphotericine B in combination with oral azoles.
References:
1. Bariola JR, Perry P, Pappas PG, et al. Blastomycosis of the central nervous system: a multicenter review of diagnosis and treatment in the modern era. Clin Infect Dis 2010;50:797-804.
2. Borgia SM, Fuller JD, Sarabia A, El-Helou P. Cerebral blastomycosis: a case series incorporating voriconazole in the treatment regimen. Med Mycol 2006;44:659-64.
