Prone scintimammography in patients with non-palpable breast lesions

Non-palpable breast lesions are a clinical problem due to the low specificity of mammography and the resulting difficulty in choosing the type and extent of surgery. Twenty-four patients with non-palpable mammographic lesions underwent prone scintimammography after the i.v. injection of 740 MBq of 99m Tc-SestaMIBI (MIBI). For this purpose, we designed a special bed which allows the widest exposure of the breast to the detector and better visualisation of deep mammary tissue without interference from intra-thoracic activity. The day after the scintigraphy, all patients underwent quadrantectomy or a more limited excision. The specimens were X-rayed to check the presence of mammographic microcalcifications or opacities. All surgical specimens were histologically evaluated. The mammographic and scintigraphic findings were compared with the histological ones. Under these conditions, we observed that the MIBI scan has a good specificity (90%) but low sensitivity (50%) for this selected population. When the MIBI scan was positive, the probability of breast cancer was very high (positive predictive value of the test = 88%) as a consequence, a wider excision would be the most accurate surgical choice. On the other hand, if the MIBI scan is normal, the high number of false negative results does not allow any final diagnosis (negative predictive value of the test = 56%). The preliminary results of this work suggest that radionuclide imaging can help the surgeon in surgical planning.