TC-99M MIBI THORACIC SPECT FOR THE DETECTION OF INTRATHORACIC TUMOR MASSES

Thirty-one men (age range, 46-76 years; mean age, 64.8 years) with int rathoracic masses suggesting possible malignancy on the basis of chest radiography or CT underwent preoperative Tc-99m MIBI SPECT examinatio ns. Diagnosis was confirmed on pathologic examinations of samples obta ined either at thoracotomy, esophagectomy, or by biopsy. Twenty-five p atients had primary lung cancer, including squamous cell carcinoma, la rge cell carcinoma, adenocarcinoma, and small cell carcinoma. Two pati ents had lymphomas with spread to the mediastinum, and three patients had extrathoracic primary cancers (one squamous cell carcinoma of esop hagus, one squamous cell carcinoma originating from a head and neck tu mor, and one metastatic mediastinal leiomyosarcoma). One patient with a tuberculoma had negative results of the Tc-99m MIBI examination. Tc- 99m MIBI had a 86.7% sensitivity rate, a 0% false-positive rate, and a 100% positive predictive value to detect malignant intrathoracic mass es. There was a 13% false-negative rate, however, suggesting that MIBI -SPECT may underdiagnose malignant lesions. SPECT findings of these 31 patients can be classified as 1) mass with increased uptake, n = 23; 2) ring-like appearance of increased uptake, n = 3; 3) mass with absen t uptake, n = 4; and 4) photon-deficient mass, n = 1. Absent uptake in patients with mass lesions could be explained by necrosis of the lesi on (caseation necrosis or massive tumor necrosis with or without bleed ing). Most malignant intrathoracic masses are Tc-99m MIBI avid and may be detected with a high degree of sensitivity and with an excellent p ositive predictive value. A positive MIBI scan may help in the clinica l diagnosis of malignancy. The use of Tc-99m MIBI could serve not only as a tumor imaging agent, but also may be used to determine the exten t of spread and potentially the chemotherapeutic responsiveness of a t umor.