TUMOUR SIZE: THE ONLY PREDICTIVE FACTOR FOR 131I MIBG UPTAKE IN PHAEOCHROMOCYTOMA AND PARAGANGLIOMA

Background: 131I Meta-iodobenzylguanidine (131I MIBG) scintigraphy can detect chromaffin tumours with a high specificity but its sensitivity remains limited. In this study, the influence of clinical features and tumour pathology on the results of 131I MIBG of patients with phaeochromocytomas and paragangliomas was examined. Methods: The records of 104 patients operated on for chromaffin tumours who had pre-operative 131I MIBG were reviewed. Demographic data, clinical features, biochemical results and pathology of tumours were analysed. The size of the tumour was assessed by the three measured diameters of the specimen and its calculated volume. Univariate relationship between tumours’ characteristics and the results of 131I MIBG were examined. Results: Out of 119 tumours, 104 (87%) were detected by 131I MIBG. Mean ± SD largest diameter and volume of the tumours were 6.0 ± 2.4 cm (range 0.8–11.5 cm) and 68 ± 74 cm3 (range 0.2–421 cm3). Results of 131I MIBG were significantly correlated with both the largest diameter of the tumour (P < 0.01) and by its volume (P < 0.001). 131I MIBG was negative in 35.5% of tumours < 20 cm3 and in 2.6% of those < 20 cm3. No other criteria were correlated with positive 131I MIBG, including aetiology, pathology or catecholamine secretion pattern. Conclusions: The result of 131I MIBG scanning in patients with chromaffin tumours is significantly correlated with the size of the tumour.