Clinical significance of 99mTc-N-pyridoxyl-5-methyltryptophan (99mTc-PMT) in the diagnosis of intrahepatic masses

Hepatobiliary scintigraphy with 99mTc-N-pyridoxyl-5-methyltryptophan (99mTc-PMT) was carried out on 48 patients with intrahepatic masses, 44 with hepatocellular carcinoma and one each of hepatocellular adenoma, focal nodular hyperplasia, cholangiocellular carcinoma, and adenoid cystic carcinoma. Scans were performed twice, early scan (30 min post i.v.) and delayed scan (2.5 h post i.v.), and the delayed scan was used for assessing the accumulation of 99mTc-PMT in the intrahepatic masses. In the hepatocellular carcinoma group, based on individual patients, 17 out of 44 (38.6%) showed accumulation of 99mTc-PMT in various degrees; and based on individual masses, accumulation was noted in 21 out of 55 masses (38.2%). However, only the cases which had not received transarterial infusion of anti-cancer drugs (TAI) and/or blocking agents (TAE) were taken into consideration, 9 out of 18 patients (50%) and 12 out of 25 masses (48.0%) were found capable of picking up 99mTc-PMT. A case of hepatocellular adenoma showed a strong accumulation of 99mTc-PMT in the mass which was depicted as a defect on the 99mTc-colloid scan and did not show a significant accumulation of 67Ga. In a case of focal nodular hyperplasia, there were two space-occupying lesions (SOLs), one of which showed a clear-cut defect on the 99mTc-colloid scan and the other which showed only a distorted uptake pattern. However, both masses were strongly positive with 99mTc-PMT. 99mTc-PMT scintigraphy is useful in connection with 99mTc-colloid scan and sometimes with 67Ga-citrate in the diagnosis of intrahepatic masses originating from hepatocytes.