Diagnostic role of target lesion on diffusion-weighted imaging: a case of cerebral aspergillosis and review of the literature.

BACKGROUND/
PURPOSE: Target lesions on diffusion-weighted imaging are uncommon and their significance not well appreciated. To assess the diagnostic value of this neuroimaging finding, a case of cerebral aspergillosis is presented and the literature reviewed.
METHODS: The diffusion-weighted magnetic resonance imaging features of target lesions in a case of cerebral aspergillosis with neuropathologic correlate is presented and 8 other cases manifesting this neuroimaging finding are reviewed for etiology, patient immune status, lesion number, enhancement, and location.
RESULTS: The etiologies included cerebral aspergillosis, Balo concentric sclerosis, and acute necrotizing encephalopathy. The cerebral aspergillosis cases were immunocompromised with multiple lesions in 4 of 5 patients. The acute necrotizing encephalopathy and Balo concentric sclerosis patients were immunocompetent with bilateral thalamic lesions in the former and multiple random or solitary lesions in the later. Enhancement was seen in 5 patients.
CONCLUSION: Target lesions on diffusion-weighted imaging are compelling for a diagnosis of cerebral aspergillosis in immunocompromised patients and for acute necrotizing encephalopathy in immunocompetent patients when lesions are bilateral thalamic and Balo concentric sclerosis when white matter is involved.