CT scan typically shows nonspecific homogenously enhanced round or oval-shaped pleural nodules or masses in the left hemithorax, which are multiple in 75% of cases and solitary in 25%. Differential diagnosis includes pleural metastases of a solid tumor, lymphoma, invasive thymoma, asbestos-related pleural plaques, mesothelioma, and neurogenic tumors. Conventional MRI scanning does not narrow this differential diagnosis. Ferumoxide-enhanced MRI scanning may be helpful, but to our knowledge, only one case report using this radiologic technique has been published for thoracic splenosis. The current diagnostic noninvasive technique of choice is nuclear scintigraphy. Using the unique ability of the reticuloendothelial system to filter out platelets, damaged, or aged erythrocytes, and sulfur colloid particles, nuclear scintigraphy with 99mTc heat-damaged erythrocytes, 111In-labeled platelets, or 99mTc sulfur colloid can accurately detect any ectopic splenic tissue. Definite data on the performance in terms of sensitivity and specificity of nuclear scintigraphy in the detection of thoracic splenosis are not available because (to our knowledge) no studies have compared nuclear imaging findings with tissue diagnosis in large series. In the setting of abdominal splenosis and when compared directly with the sulfur colloid test, scintigraphy using 99mTc heat-damaged erythrocytes has a 32% greater diagnostic yield.