Protein S deficiency: imaging findings.

Protein S deficiency is an autosomal-dominant inherited disorder of coagulation associated with spontaneous and recurrent venous thrombosis. Approximately 5% of patients with deep venous thrombosis of the lower extremities who are less than 45 years old have a deficiency of protein S. Patients frequently have spontaneous and recurrent deep venous thrombosis and pulmonary embolism during young adulthood. Thrombosis occurs less commonly in the splanchnic and cerebral veins. Arterial thrombosis is rare but is seen in the cerebral circulation. Radiologists should include protein S deficiency in the differential diagnosis of unexplained thrombosis in young patients. This pictorial essay illustrates the range of imaging findings encountered in patients with this disorder.