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Diffuse intense lung uptake of TI-201 chloride without abnormal Ga-67 citrate in a case of cytomegalovirus pneumonitis in a patient with AIDS is presented. An autopsy performed within 4 days of imaging revealed no pulmonary pathology other than diffuse cytomegalovirus infection with abundant histiocytes and inclusion bodies and pulmonary congestive heart failure. Among the various mechanisms of TI-201 accumulation, active transport through Na-K ATPase appears to be predominant in this case, as suggested by innumerable histiocytes. It is the authors' experience that positive TI-201 uptake without abnormal Ga-67 accumulation is highly specific for pulmonary Kaposi sarcoma. The presence of such discrepancy between TI-201 and Ga-67 uptake in AIDS patients decreases the specificity of a TI-201 positive/Ga-67 negative lesion for pulmonary Kaposi sarcoma, especially with the rising incidence of both cytomegalovirus and Kaposi sarcoma in AIDS patients.

Diffuse Tl-201 uptake in the lungs could be because of cardiac, neoplastic, inflammatory, or interstitial lung disease. Examples from the different categories, differential diagnosis, and different patterns are presented. The authors discuss the different mechanisms of increased Tl-201 uptake in the lungs which vary according to the underlying pathology.