Undifferentiated Pleomorphic Sarcoma Invading the Internal Jugular Vein.

A 60-year-old woman received carbon ion radiotherapy (C-ion RT) (70.4 Gy [relative biological effectiveness]/16 fr) for undifferentiated pleomorphic sarcoma (UPS) (T4bN0M0) in the left pterygopalatine fossa. After 26 months, left parotid resection and left neck dissection were performed for lymph node metastasis in the left parotid gland (no irradiation field). Pathological findings revealed a lymph node with UPS metastasis in the left parotid gland. However, no other metastases in the left cervical lymph node or vascular invasion were observed. Four months after surgery, magnetic resonance imaging revealed an invasion of the left internal jugular vein. Pathological examination of the vascular lesion was not possible because the patient did not consent to surgery. Undifferentiated pleomorphic sarcoma most commonly metastasizes to the lung, and there is currently no known report of vascular invasion. In this case, vascular invasion possibly developed due to changes in the perivascular tissues after the left neck dissection, which may have facilitated tumor invasion into the vascular wall. Based on the images and the clinical course, a rare condition for vascular invasion from UPS recurrence was considered.