Renal nutcracker syndrome (ORPHA:71273)
A rare, syndromic renal disease characterized by the entrapment of left renal vein (LRV) between the superior mesenteric artery (SMA) and the abdominal aorta, resulting in increased luminal pressure, renal hilar varices, hematuria and, at the microscopic level, rupture of thin-walled veins into the collecting system in renal fornices.
Epidemiology
The exact prevalence is not known. Most cases have been reported from the Far-East. Women are more commonly affected than men.
Clinical description
Patients with renal nutcracker syndrome (NCS) are usually asthenic, tall and thin. Many patients remain asymptomatic and are incidentally discovered during radiological imaging for other causes. Symptomatic cases present mostly in second/third decade of life with urological or gynecological symptoms. Urological manifestations include left loibdominal pain, left-sided macroscopic or microscopic hematuria (on endoscopy, varicocele, or lower limb varices. Gynecological symptoms resemble pelvic congestion syndrome and include symptoms of dysmenorrhea, dyspareunia, post-coital ache, lower abdominal pain, dysuria, pelvic/vulvar/gluteal/gonadal or thigh varices, and emotional disturbances. Three types of renal nutcracker syndrome have been defined, according to the site of LRV compression: anterior nutcracker syndrome, posterior nutcracker syndrome and combined nutcracker syndrome.
Etiology
Normally SMA separates from the abdominal aorta (AA) at a 90-degree angle. The LRV lies anterior to the aorta in the fork between the SMA and AA. In anterior NCS, the SMA arises from the aorta at an acute angle, compressing the LRV causing left renal venous hypertension. In posterior NCS, the LRV courses posterior to the AA and is compressed between the aorta and the vertebral column. In combined NCS, the anterior branch of the duplicated LRV is compressed between the aorta and the SMA, while the posterior is sandwiched between the aorta and the vertebral column.
Diagnostic methods
Diagnosis should be suspected upon presentation with left-sided loin pain and hematuria. Diagnostic tests include urine analysis, ultrasound scan, color Doppler scan, CT or MR angiography, and left renal vein phlebography and manometry. Doppler sonography is usually the first imaging tool, which can detect collateral veins around LRV, whose presence sustains venous hypertension and are a radiological criterion for NCS. The ''gold standard'' for diagnosis remain phlebography, intravascular pressure measurement and intravascular ultrasound through which the venous pressure gradient between LRV and inferior vena cava and the renal vein diameter can be measured. Patients usually show an LRV/inferior vena cava pressure gradient >1 mmHg. Computed tomography venography and magnetic resonance venography are noninvasive evaluation tools which provide good definition of LRV compression and grade of involvement of other organs.
Differential diagnosis
Compression of LRV leading to loin pain and hematuria can be seen in pancreatic neoplasms, paraortic lymphoadenopathy, retroperitoneal masses, overarching testicular artery, lordosis, reduced retroperitoneal and mesenteric fat or too much fibrolymphatic tissue between SMA and AA.
Management and treatment
Surveillance is appropriate in pubertal patients, who may undergo spontaneous remission with physical development and weight gain, and in patients with insignificant symptoms and microscopic hematuria, or intermittent painless gross hematuria with a normal hemogram. Open surgery procedures with good outcomes include vascular transpositions and renal auto transplantation. Extra-vascular stenting can be performed through open or laparoscopic surgery. Intravascular stenting is a treatment option in which a self-expanding metallic stent is deployed in the stenotic region of the LRV.
Prognosis
As this is a benign condition, overall prognosis is excellent. In highly symptomatic patients, with severe pain, frank/recurrent hematuria requiring blood transfusion, active intervention needs to be considered. Prognosis following intervention is excellent.

                            Last update: 
                            March 2019


                            - Expert reviewer(s): 
                            Dr Max Christoph LIEBAU | ERKNet*


                                * European Reference Network