Approximately eighty per cent of medullary carcinomas are sporadic and twenty per cent familial, the latter showing an autosomal dominant inheritance with strong penetrance. In sporadic cases, the clinical presentation is usually that of a solitary hard thyroid nodule that is ΓÇÿcoldΓÇÖ on scan. Involvement of cervical lymph nodes at presentation is observed in some fifty per cent of cases, when chest radiography may show additional involvement of the upper mediastinum.
Medullary carcinomas are tumours of the calcitonin-secreting parafollicular C-cells and occur in males almost as frequently as in females. They represent a different entity from tumours of follicular cell origin since the parent C-cells are derived from neural crest cells that colonise the ultimobranchial bodies which fuse in early embryonic life with the thyroid anlage (which is itself derived from endodermal tissue).
