123I-metaiodobenzylguanidine (MIBG) Scintigraphy for the Detection of Adrenal and Extra-adrenal Phaeochromocytomas: CT and MRI Correlation

Context: Evidence regarding the accuracy of [(123)I] 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 [(123)I]MIBG has been evaluated and correlated with cross-sectional imaging.

Design: We identified 76 patients with both preoperative [(123)I]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): [(123)I]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 [(123)I]MIBG result.

Results: The overall sensitivity of [(123)I]MIBG was 75%. Tumour detection was lower for extra-adrenal (58%) vs. adrenal (85%) phaeochromocytomas (P = 0.005). For extra-adrenal tumours, [(123)I]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 [(123)I]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 [(123)I]MIBG negativity, although two large [(123)I]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 [(123)I]MIBG. Tumoural necrosis or haemorrhage do not consistently relate to [(123)I]MIBG uptake, although adrenal phaeochromocytomas containing minimal solid tissue due to extensive necrosis may predict a negative [(123)I]MIBG result.