Metastatic Medullary Thyroid Carcinoma Presenting As an Incidental Posterior Mediastinal Mass

Medullary thyroid carcinoma (MTC) is an uncommon neuroendocrine tumour that is usually asymptomatic at its onset and therefore may not present clinically until the patient has developed advanced or metastatic disease. Common metastatic sites include cervical lymph nodes, liver, bone and lung. This is the case of a patient who presented with an incidental posterior mediastinal mass. Because the posterior mediastinum is an unusual location for MTC, MTC was not a consideration and preliminary histopathological testing did not include calcitonin, which would have been diagnostic. This case highlights the importance of testing for calcitonin more regularly when encountering a mass of unknown origin with neuroendocrine morphology, which may lead to earlier detection of MTC and thus improved prognosis.