Intravascular small cell neuroendocrine tumor in the neck.

A 40-year-old man presented with a painless enlarging right neck mass over several weeks without a history of trauma or infection. Ultrasound, contrast-enhanced CT, and MRI showed a mass in an expanded vein extending into the parotid gland. Blood-stained fine-needle aspiration biopsy demonstrated atypical lymphoid cells, but there was insufficient material for a diagnosis. The mass was intensely avid on 18F-FDG PET/CT and was suggestive of a neoplasm. Excision confirmed a mass within the external jugular vein with areas of invasion through the vessel wall. A diagnosis of small cell neuroendocrine carcinoma was made on histology.