Imaging of neuroendocrine tumours

Phaeochromocytoma and other neural crest tumours can successfully be detected with 123I or 131I-MIBG. The molecular structure of MIBG has some similarity to noradrenaline. The scintigraphic study is done at intervals of 24, 48, and occasionally 72 hours after intravenous injections of 370 MBq of 123I-MIBG or 37 MBq of 131I-MIBG. With a sensitivity of 92% and specificity of nearly 100% in neuroblastoma, MIBG scintigraphy is a useful technique for the detection, staging, and follow-up of this disease. Additionally, it serves as an indicator for potential therapy using 131I-MIBG.

Somatostatin is a polypeptide hormone with a short biological halflife. Receptors for this hormone are present on many cells of neuroendocrine origin. A long-acting analogue, octreotide, was synthesized for therapy. 111In-octreotide was developed for imaging, performed 24 and 48 hours after injection of 111 MBq. The potential clinical value of somatostatin receptor scintigraphy is in the detection of occult primary tumours, screening of metastases for staging, follow-up of therapy, and selection of patients who might benefit from palliative treatment with unlabelled octreotide.

The cumulative sensitivity of 111In-octreotide scintigraphy for the detection of endocrine pancreatic tumours is around 75%, and for carcinoid tumours, around 85%. These tumours are often small and not easily recognized on CT or MRI.

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