123I‐metaiodobenzylguanidine (MIBG) scintigraphy for the detection of adrenal and extra‐adrenal phaeochromocytomas: CT and MRI correlation

Summary Context  Evidence regarding the accuracy of [123I] metaiodobenzylguanidine (MIBG) imaging for phaeochromocytoma localization is currently limited to small series. Objective  We present the largest series of primary phaeochromocytomas in which the performance of [123I]MIBG has been evaluated and correlated with cross-sectional imaging. Design  We identified 76 patients with both preoperative [123I]MIBG and cross-sectional imaging for confirmed primary phaeochromocytoma between 1995 and 2005 at our institution. This comprised 60 adrenal tumours in 55 patients and 33 extra-adrenal tumours in 23 patients (2 patients had both adrenal and extra-adrenal tumours). Phaeochromocytoma metastases were not evaluated. Main outcome measure(s)  [123I]MIBG studies were independently reviewed and correlated with CT and MRI examinations, as well as tumour functional status, to identify features that may predict a false negative [123I]MIBG result. Results  The overall sensitivity of [123I]MIBG was 75%. Tumour detection was lower for extra-adrenal (58%) vs. adrenal (85%) phaeochromocytomas (P = 0·005). For extra-adrenal tumours, [123I]MIBG demonstrated 8 of 14 carotid body, 2 of 2 intrathoracic, 8 of 14 retroperitoneal and 2 of 3 pelvic phaeochromocytomas. Overall, MRI and CT demonstrated 68 of 68 and 72 of 74 primary phaeochromocytomas, respectively. Tumour size correlated with [123I]MIBG uptake for adrenal (P = 0·009) but not extra-adrenal tumours. When tumours were adjusted for size, no other imaging feature or functional status correlated with [123I]MIBG negativity, although two large [123I]MIBG negative adrenal tumours contained large areas of necrosis or haemorrhage. Conclusions  Extra-adrenal and small adrenal phaeochromocytomas are more likely to result in false negatives on [123I]MIBG. Tumoural necrosis or haemorrhage do not consistently relate to [123I]MIBG uptake, although adrenal phaeochromocytomas containing minimal solid tissue due to extensive necrosis may predict a negative [123I]MIBG result.