Secondary lymphoma involving metastatic follicular thyroid carcinoma to the skull: a unique example of tumor-to-tumor metastasis.

Tumor-to-tumor metastases to the skull, presenting as a scalp mass, and thyroid follicular carcinoma presenting in that location are extremely rare. We present the case of a patient with recently diagnosed retroperitoneal diffuse large B-cell lymphoma and an 8-year history of a non-tender large scalp-based mass. The scalp mass was an osteolytic enhancing lesion on imaging studies and diagnosed as metastatic thyroid carcinoma to the skull. The patient had no pre-existing history of thyroid cancer. This metastatic carcinoma was also secondarily involved with diffuse large B-cell lymphoma. This case illustrates a unique and previously unreported example of tumor-to-tumor metastasis in which both malignancies represent metastatic tumors to the skull with soft tissue extension presenting as a large scalp mass.