THALLIUM CHLORIDE TL-201 COMBINED WITH SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY (SPECT) IN THE EVALUATION OF VESTIBULAR SCHWANNOMA GROWTH

Thallium chloride Tl-201 combined with SPECT was performed in a series of 29 patients with neuroradiological evidence of vestibular schwanno ma (VS). The relative tumor uptake (U) and relative tumor concentratio n (C) of the radiotracer Tl-201 was determined, and the cerebellum ser ved as a reference. The relative tracer concentration and uptake were correlated to tumor volume determined by gadolinium DTPA enhanced MR, to prediagnostic duration of symptoms, to tumor vascularity expressed by the average number of intratumoral vessels using the endothelial ma rker CD31, and to the proliferative activity in the tumors expressed b y positive staining with the monoclonal antibody MIB-1 for Ki-67. A po sitive Tl-201 enhancement was detected in 17 tumors (n = 17). Tumors U and C were statistically unrelated to tumor volume (p = 0.236 and p = 0.439). SPECT demonstrated all tumors >0.8 cm(3), but it had its limi tation as a diagnostic modality of small intracanalicular tumors, when compared with gadolinium DTPA enhanced MR. Relating U and C in all tu mors (n = 29) and the prospectively registered data on the prediagnost ic duration of symptoms, a statistical significance was found (p = 0.0 12 and p = 0.015). No statistically significant correlation was observ ed between U and C and the proliferative activity of the tumors expres sed by positive staining with the monoclonal antibody MIB-1 for Ki-67 (p = 0.063 and p = 0.086). A statistically significant correlation was noted between C and U in the operated group (n = 12) and tumor vascul arity expressed by the average number of the intratumoral vessels (p = 0.003 and p = 0.014). SPECT was found to be superior to MR in determi ning VS growth potentials as it expresses tumor vascularity, which is essential for tumor growth. It seems that we now have an in vivo funct ional radiological modality capable of providing data on VS vascularit y and determination of growth potential in the individual tumor. A hig h radioactive tracer uptake in the tumor corresponded to high tumor va scularity, indicating a high growth rate and vice versa.