Arteriovenous malformation and thyroid metastasis from underlying renal cell carcinoma, an unusual presentation of malignancy: A case report.

Renal Clear Cell Carcinoma (RCC) comprises over 80% of renal malignancies in adults. Thyroid gland metastasis is rare in RCC. Few studies have described cases of RCC mistaken for benign arteriovenous malformation (AVM). To the best of our knowledge, an AVM arising from underlying RCC metastasis to the brain has not yet been reported. The current study presents a case of RCC metastasis to the thyroid gland, with an AVM identified to be a result of metastatic involvement in the brain. A 45-year-old African-American female presented with left-sided weakness, slurred speech, facial droop and seizure. The patient's medical history was notable for a diagnosis of RCC, 2010 American Joint Committee on Cancer Tumor-Node-Metastasis Stage 1B (T1B, N0, M0) grade III status post-right partial nephrectomy. Computed tomography (CT) imaging revealed a soft-tissue mass, suspected to be metastasis, in the left lobe of the thyroid, in addition to a 1.9 cm right intracranial mass in the parietal lobe. Positron emission tomography/computed tomography revealed a hypermetabolic area in the thyroid. Fine needle aspiration of the thyroid, and subsequent histopathological analysis, suggested a diagnosis of RCC metastasis. Subsequent immunohistochemical analysis of the thyroid tumor confirmed RCC metastasis. The patient also underwent a right partial craniotomy with resection of the intra-axial mass. Initial pathology was suggestive of an AVM. After several months, the patient was readmitted with headache, nausea and vomiting. Repeat imaging revealed recurrence of a 3.9 cm mass that was negative for AVM on biopsy; however, the immunostaining markers were positive for RCC. Recent literature suggests a link between AVMs and RCC as each exhibit highly vascular characteristics. RCC is a particularly vascular tumor that has been demonstrated to lead to the abnormal expression of various angiogenesis-promoting growth factors, including vascular endothelial growth factor. These angiogenic factors are vital to the pathophysiological pathway involved in the tumorigenesis and progression of RCC, and may explain the development of AVMs within these neoplasms, as demonstrated in the case presented in the current study.