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

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Abstract
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.

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