A 46-year-old African-American male presented to the hospital with a four-month history of progressive headache, left-sided weakness, and double vision. His past medical history was otherwise unremarkable, and he denied any recent history of fever, chills, respiratory symptoms, or systemic illness. He reported a history of intravenous drug use and having snorted cocaine within the past 12 months. On examination he had dysarthric speech, a partial right cranial nerve III palsy, and mild left hemiparesis (arm and leg). The remainder of his neurological examination was unremarkable. MRI of the head revealed a 2-cm ring-enhancing mass in the right pons (Figure 1). The mass had very low signal on T2-weighted images, and there was no evidence of reduced diffusion on diffusion-weighted imaging (DWI) (1.5 Tesla clinical scanner, single-shot echo-planar, diffusion gradient 0 and 1000 s/mm, acquired in three orthogonal directions). The apparent diffusion coefficient (ADC) of the mass ranged from 1.2 10 mm/s to 1.7 10 mm/s. Moderate T2 prolongation was noted in the pons, extending into the bilateral cerebellar hemispheres and superiorly into the right midbrain. The mass was presumed to be neoplastic based on the imaging findings, and workup for a systemic primary neoplasm was initiated. An open biopsy of the pontine mass was obtained through a right frontotemporal craniotomy with zygomatic osteotomy with image guidance. The lesion was extremely firm, and specimens sent for KOH preparation and frozen section demonstrated yeast. Additional specimens were sent for permanent section and culture. Having obtained a diagnosis, the wound was closed, and the patient was returned to the intensive care unit in stable condition. Amphotericin B therapy was initiated. Results of HIV testing, completed in the postoperative period, were positive, and his CD4 count was 10/ll. Permanent section pathology showed chronic inflammation with associated necrosis and fungal organisms (Figure 2). Biopsy culture grew Histoplasma capsulatum and was confirmed using a DNA probe. He was treated with a two-week course of amphotericin B, followed by a 10week course of IV itraconazole. He was then started on lifetime maintenance oral itraconazole. Highly active antiretroviral therapy (HAART) was initiated after four weeks of itraconazole therapy. DWI is an MRI-based technique that measures the random translational mobility of water molecules, also known as Brownian motion. The more the movement of water is restricted in a tissue, the higher the DWI signal intensity and the lower the ADC. DWI has been applied to multiple disease processes, including ring-enhancing intraparenchymal brain masses. Two of the main differential considerations in the setting of a ring-enhancing intraparenchymal brain lesion are abscess and necrotic tumor. Distinguishing these two lesions on conventional imaging is often
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Open Access
Jan 1, 2012
Mehtap Erdem + 5
