Difference in mIBG uptake in foregut, midgut and hindgut carcinoid tumours

Carcinoid tumours are generally classified according to their origin as foregut, midgut or hindgut. 111In pentetreotide and 123I labelled mIBG are commonly used for diagnosis of these tumours. The aim of our study was to assess the difference in mIBG uptake in foregut, midgut and hindgut carcinoids. Fifty-two patients with carcinoid tumours (13 foregut, 30 midgut, 4 hindgut, and 5 unknown) underwent 123I labelled mIBG whole-body and liver SPECT imaging. The tumour uptakes were classified on visual analysis as grade 1 (tumour uptake less than liver), grade 2 (uptake equal to liver) and grade 3 (uptake greater than liver). Eighteen (34%) patients had grade 1 uptake (3 foregut, 14 mid and hindgut, 1 unknown), 18 (34%) had grade 2 uptake (7 foregut, 7 mid and hindgut, 4 unknown) and 16 (32%) had grade 3 uptake (3 foregut, 13 mid and hindgut). Grade 3 uptake was seen in more patients with mid and hindgut carcinoids (38%) than foregut (23%). 123I labelled mIBG demonstrated high uptake (grade 3) in mid and hindgut compared to foregut carcinoids and is more useful. The low to moderate uptake in foregut carcinoids could be due to the known cytochemical differences in these tumours.