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Medullary thyroid cancer

Medullary thyroid carcinoma (MTC) is a subtype of thyroid cancer which accounts for 5-10% of all thyroid malignancies 1. It occurs both sporadically (80%) and as a familial form 4.

It is characterised by consistent production of a hormonal marker, calcitonin, calcification of both primary and metastatic sites, and association with other endocrine neoplasms. Metastatic involvement may be seen in up to 50% at the time of presentation 4.

Epidemiology

In nonfamilial cases it typically peaks in the 3rd to 4th decades.

Pathology

Thought to arise from parafollicular C cells of the thyroid 4. Amyloid components may be seen on histology.

Associations

When familial, it is seen as a component of multiple endocrine neoplasia type II (MEN-II) syndromes (both MEN IIa and MEN IIb). Other associations include:

Radiographic features

Ultrasound

Punctate high echogenic foci resembling calcification may be seen both within the primary thyroid lesion as well as metastatic regional lymph nodes 3 and distant metastatic sites. Involved lymph nodes typically calcify.

CT

Both primary and metastatic lesions usually have irregular dense calcific foci within 1.

In the chest, bullae formation and pulmonary fibrosis might happen as a result of a desmoplastic reaction.

Nuclear imaging
  • radioactive iodine: lesions do not concentrate radioactive iodine since the tumour does not arise from thyroid follicular cells
  • FDG-PET: avid uptake
  • Tl-201: It has been shown to concentrate Thallium-201 5
  • I-123 MIBG: 30% of MTCs show uptake if the thyroid is blocked with Lugol solution prior to the scan

Treatment and prognosis

Total thyroidectomy and neck dissection is a consideration. Prognosis in general tends to be worse than papillary and follicular thyroid cancer subtypes 1.  


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