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MR of Toxoplasma Encephalitis: Signal Characteristics on T2-Weighted Images and Pathologic Correlation

Brightbill, T. C.; Post, M. Judith Donovan; Hensley, George T.; Ruiz, Armando

Journal of Computer Assisted Tomography: May-June 1996 - Volume 20 - Issue 3 - p 417-422

Purpose Our goal was to determine if there are any T2-weighted MR signal characteristics of Toxoplasma encephalitis that might be useful in diagnosis and/or in gauging the effectiveness of medical therapy.

Method We retrospectively analyzed the MR, CT, thallium-201 SPECT brain scans, and medical records of 27 patients with medically proven (26) and biopsy prover (1) Toxoplasma encephalitis, supplemented by autopsy findings in 4 additional patients, 2 of whom had postmortem MR correlation. The neuropathologic literature was also reviewed.

Results Among the 27 patients, we discovered three distinct imaging patterns. Ten (37%) patients had predominantly T2-weighted hyperintense lesions and had been on medical therapy an average of 3 days (excluding one outlier). Ten (37%) patients had T2-weighted isointense lesions and had received medical therapy an average of 61 days. Seven (26%) patients had lesions with mixed signal on T2-weighted images and had been on treatment an average of 6 days. Analysis of autopsy material from the four additional patients revealed the presence of organizing abscesses in three and necrotizing encephalitis in one, while the patient who had a brain biopsy demonstrated both types of pathologic lesions. In both cases having postmortem MRI, organizing abscesses appeared isointense to hypointense on T2-weighted images.

Conclusion There is a definite variation in the appearance of lesions of Toxoplasma encephalitis on T2-weighted images that precludes a definitive diagnosis based on signal characteristics alone. Pathologically, our data suggest that T2-weighted hyperintensity correlates with necrotizing encephalitis and T2-weighted isointensity with organizing abscesses. Furthermore, in patients on medical therapy the T2-weighted MR appearance may be a transition from hyperintensity to isointensity as a function of a positive response to antibiotic treatment, indicating that the signal change might be used to gauge the effectiveness of medical therapy.

From the Departments of Radiology, Neuroradiology Section (T. C. Brightbill, M. J. D. Post, and A. Ruiz), and Pathology (G. T. Hensley), University of Miami School of Medicine/Jackson Memorial Medical Center, Miami, FL, U.S.A.

Address correspondence and reprint requests to Dr. M. J. D. Post at MRI Center (R-308), University of Miami School of Medicine, 1115 NW 14 St., Miami, FL 33136, U.S.A. This work was presented at the Annual Meeting of the Southeastern Neuroradiological Society, October 1994, Orlando, FL, U.S.A.

© Lippincott-Raven Publishers