Sunday, July 18, 2010

MIBG vs. Octreotide in the Diagnosis of Neuroendocrine Tumors

MIBG and octreotide can both localize to neuroendocrine tumors (pheochromocytoma, paraganglioma, neuroblastoma, and carcinoid). In almost all cases, MIBG is the way to go. The exceptions are carcinoids and extraadrenal pheochromocytomas.

Neither seem to be that great for medullary thyroid cancer, but octreotide seems to offer better sensitivity for cervical and upper mediastinal lymph nodes in patients with occult disease.

Pheochromocytoma and Paragangliomas

MIBG is used to localize clinically suspected pheochromocytoma, to confirm that a mass is a pheochromocytoma, or to exclude metastatic disease. For adrenal pheochromocytomas, MIBG has close to 100% specificity but lower sensitivity (86%). Octreotide can also localize adrenal pheochromocytomas, but has a lower sensitivity than MIBG (20%-50%). It can be used in cases of negative MIBG scans.

In extraadrenal pheochromocytomas, on the other hand, MIBG has a lower sensitivity (72%) than octreotide (96%), especially those of the head and neck.


MIBG is the most effective indicator of neuroblastoma and is used in staging at presentation, restaging after treatment, searching for postsurgical residual tumor, monitoring the effect of treatment, and diagnosis of recurrence.

Octreotide has lower sensitivity (64%) compared to MIBG (94%) and does not have a well-defined indication in children with neuroblastoma. Since the presence of somatostatin receptors is associated longer survival, octreotide imaging may provide some prognostic information.


Octreotide has higher sensitivity (>80%) than MIBG in detecting primary and metastatic lesions. Octreotide also has higher sensitivity for localizing primary tumor and extra-hepatic involvement. MIBG and octreotide are of similar sensitivity and specificity in detecting liver metastases. In addition, some carcinoids not seen on octreotide imaging may have MIBG uptake.

Medullary Thyroid Carcinoma

Nuclear medicine plays a minor role in the preoperative evaluation of medullary thyroid carcinoma, but is an essential part in postoperative follow-up. Medullary thyroid carcinoma recurs in about 50% of patients and may present a diagnostic challenge, especially in the case of liver metastases which tend to be miliary.

MIBG provides high specificity but low (30%) sensitivity and is used primarily in locating adrenal medullary hyperplasia or pheochromocytoma in MEN syndromes. MIBG is also used to evaluated MIBG uptake in known lesions prior to 131I-MIBG therapy.

Octreotide seems to offer high sensitivity for cervical and upper mediastinal lymph nodes in patients with occult disease, but is less sensitive in patients with distant metastases and progressive disease.


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