Primary inferior vena cava thrombosis: report of nine cases.

All cases of inferior vena cava obstruction diagnosed at the Mayo Clinic between 1950 and 1973 were reviewed. Diagnosis was confirmed by surgery, phlebography, or postmortem examinations in 64 cases; the cause in 55 cases is described. Carcinoma of the kidney was the most common cause (31% pf cases). In nine cases, extensive laboratory investigation failed to reveal the cause of the process. These cases were considered to be primary inferior vena cava thrombosis and are reviewed in detail.