Nutcracker syndrome (NCS) is usually caused by a functional stenosis of the left renal vein (LRV) due to its compression between the superior mesenteric artery (SMA) and the aorta, which constitutes the anterior Nutcracker Syndrome.

Less frequently, the LRV is arranged in a retro aortic situation and is compressed between the aorta and the vertebral body, which constitutes the posterior Nutcracker syndrome.

It is more frequent in young patients, in the 3rd-4th decade of their lives, previously healthy, with a higher incidence in women. In rare cases, it occurs in adolescents.

A relationship has been seen with tall patients with an asthenic constitutional habit, low perirenal fat, renal ptosis, and accentuated lumbar lordosis.

Can also appear in pregnancy and get worse in the third trimester.

The etiology is unclear although it is believed to be due to an embryological abnormality in the separation between the aorta and SMA. Abnormal configuration of SMA origin or abnormal branching and abnormal course of the LRV behind the aorta or LRV bifurcation, are anatomical factors related to the NCS.

Extrinsic compression causes hypertension in the vein and hinders its drainage into the inferior vena cava.

Secondary, collateral circulation is generated and varicose veins are formed in the peripielico, pericalicial, and periureteral plexuses, in the gonadal vein, and in the ovarian veins.

Increased pressure in the urothelium can break the fornix and cause haematuria that is the most frequent symptom of the syndrome. Characteristically it is more intense with the orthostatic position, which increases the pressure, and with exercise. Orthostatic proteinuria and colic pain may also appear.

The NCS is, however, an infrequent cause of hematuria which makes it necessary to rule out, before considering it, all the usual etiologies.

Pelvic congestion syndrome is another frequent manifestation that occurs with dysmenorrhea, dyspareunia, post-coital ache, lower abdominal pain, dysuria, vulvar varicose veins, and varicocele. 

The demonstration, incidentally, of compression of the VRI in the absence of the mentioned clinic, represents an anatomical variant or Nutcracker Phenomenon. This finding is quite prevalent; however, the exact incidence of the NCS is not known.