[A case of posterior nutcracker syndrome occurring in pregnancy].

We have encountered a 23-year-old pregnant woman with macrohematuria, which occurred from the 8th or 9th week of gestation. Blood pressure and renal function were normal during the total course of pregnancy. Macrohematuria did not disappear after childbirth. Cystoscopy was conducted and the excretion of hematuria from the left ureter was confirmed. Therefore, a left renal venogram was performed although abdominal ultrasonography and CT scanning showed no abnormality. There were two branches of the left renal vein (LRV), such as the anterior and posterior branch. The pressure gradient was 4.4 cm H2O between the anterior branch of LRV and the inferior vena cava (i.v.c.). However, a significant pressure gradient (6.6 cm H2O) was demonstrated between the posterior branch of the LRV and IVC. From these findings we diagnosed this patient as venous hypertension in the posterior branch of the left renal vein (= posterior Nutcracker syndrome, PNS). Enlargement of the uterus in pregnancy might not be important in the occurrence of PNS because macrohematuria was observed from the 8th or 9th week of gestation. Functional hemodynamic change in pregnancy might cause a widening of the diameter or a shift of the aorta, that might result in compression of the posterior branch of the left renal vein. Persistence of macrohematuria after childbirth might have been due to irreversible hemodynamic alteration by the development of co-lateral circulation. To the best of our knowledge, this is the first case of PNS occurring in pregnancy.