Octreotide Case 7 Answers

1) Is there any evidence of metastatic disease?

There are raised areas of uptake in the right neck, mediastinum and in both hila. There is faint uptake seen overlying the right cerebellar hemisphere on the posterior image, consistent the cerebellar mass seen on CT. Subsequent chest radiographs and chest CT demonstrated a miliary pattern of lung metastases, not seen on this study.

2) Explain the rationale behind the choice of radiopharmaceutical

Medullary thyroid carcinoma (MTC) is a tumour of its C cells. These are neuroendocrine or APUD type cells in which somatostatin plays an important role in its secretory activity. In common with such neuroendocrine tumours, they have upregulated somatostatin receptors that are amenable to imaging with radiolabelled octreotide in around 65-80% of cases.

Its strengths are in detecting metastatic disease, particularly in lymph nodes and bone as these can be commonly overlooked on CT. High uptake in symptomatic metastatic MTC may herald a good response to long-acting somatostatin receptor blockers.

The drawbacks of octreotide imaging in MTC are insensitivity for intrathyroid tumour and liver metastases (due to high normal uptake); Insensitivity for minimal bulk recurrent disease; Some tumours do not take up the tracer; These tumours lack somatostatin receptors and there is some evidence that these tumours are less differentiated

It is at least as sensitive a method of indium labelled anti-CEA antibody fragment imaging. Some tumours demonstrate uptake on MIBG scintigraphy.

3) Explain why serum calcitonin levels may be high

C cells of the thyroid secrete calcitonin and tumours usually secrete high levels of the protein. As a result, calcitonin may be used as a marker of disease activity. Carcinoembryonic antigen (CEA) serum levels are also commonly elevated.

4) If the patient was less than 20, what underlying syndrome should you consider and why is this important?

Patients who present with MTC at a young age are much more likely to have multiple endocrine neoplasia type 2 (MEN2 - Sipple's syndrome). This is associated with multiple bilateral MTC necessitating total thyroidectomy (often performed prophylactically at an early age) but unsuspected phaeochromocytoma can be fatal if not detected pre-operatively.

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The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.