Medullary thyroid carcinoma with poor differentiation and atypical radiographic pattern of metastasis

A diagnosis of sporadic medullary thyroid carcinoma (MTC) is complicated. On first diagnosis it may present with distant metastasis. There has been inconsistency regarding metastatic MTC tissue expression of calcitonin, its tumor marker. Adding to the difficulty is the fact that the radiographic pattern of pulmonary metastasis from MTC may vary substantially among patients. Herein is reported the case of a 73-year-old man who presented with two ill-defined pulmonary opacities, clinically resembling primary lung carcinoma. MTC was diagnosed on histopathology of tissue obtained from a total thyroidectomy. The pulmonary biopsy specimens were confirmed to be MTC metastasis on positive immunohistochemical staining of chromogranin-A and synaptophysin, even though only a few cells were stained for calcitonin. To the authors' knowledge this is the first reported case of MTC presenting initially as complex pulmonary metastasis with weakened expression of calcitonin in the metastatic lesion.