Thallium-201 SPECT of orbital tumors

Thallium-201 ((201)Tl) SPECT is utilized as a diagnostic imaging tool for a variety of tumors, such as lung cancer, brain tumors, etc., but there is hardly any literature on this type of imaging in orbital lesions. We examined 22 patients with orbital lesions and unilateral exophthalmos to evaluate the usefulness of (201)Tl-SPECT in the diagnosis of orbital tumors. All 22 cases had a confirmed histopathological diagnosis. The patients underwent (201)Tl-SPECT imaging before therapy. Early images were obtained 15 minutes after the intravenous administration of 74 MBq (201)Tl-chloride, and delayed images were taken 3 hours later. The intensities of (201)Tl accumulation in the early and delayed images were measured. Three out of four patients with cavernous hemangiomas, one of two with neurinomas, all three with pleomorphic adenomas, one with lipoma, and one with dermoid cyst had negative scans, but the other 13 patients all displayed ( 201)Tl accumulation in the area of the tumor. Four malignant lymphomas, two reactive lymphoid hyperplasias, one meningioma, one neurinoma, one adenoid cystic carcinoma and one plasmacytoma showed increased uptake, especially in the early phase. The most intense uptake was seen in the metastic renal cell carcinoma, in both early and delayed phases. We conclude that (201)Tl-SPECT can be useful in predicting the histopathological diagnosis of orbital tumors, especially by comparing the accumulation rate in the early and delayed phases.