Tumor thrombus in the great veins from papillary carcinoma of the thyroid: 131I scan findings.

Tumor invasion of great veins and forming thrombus is a rare complication in papillary carcinoma of thyroid. Contrast computed tomography, ultrasound, and positron emission tomography scan can demonstrate the thrombus but will not help to diagnose the nature of the thrombus. Demonstration of the cause of the thrombus by (131)I scan is possible because tumor tissue in the vein will be iodine avid, but simple thrombus will not.