Discussion
NCS is an uncommon condition that presents in varied ways. However, this review demonstrates that commonalities exist among NCS patients, which should raise suspicion among clinicians. The majority of patients were young, female, and present with left flank pain and/or hematuria, which is likely due to the rupture of thin-walled varices formed from renal hypertension into the collection system. [3] Features of pelvic congestion, such as dyspareunia, dysmenorrhea, scrotal or testicular pain, or urinary issues, might also evince NCS. Even refractory headaches can be related to LRV compression. Any of these symptoms in this patient population should raise suspicion of NCS in the absence of a more obvious diagnosis. Additionally, a normal to low BMI also appears to be associated with NCS. Not enough reports in this review included BMI information for us to include this data, but anecdotally, most reports of NCS occur in normal or underweight patients. A decreased aortomesenteric angle–or the angle between the SMA and aorta, risks compression of the LRV as it does to the duodenum in SMAS. [19, 45] This is more likely to be found in underweight patients, who have decreased retroperitoneal and mesenteric fat.
There are multiple imaging modalities that can be used to diagnose NCS. While the gold standard is retrograde venography, this invasive procedure is not always necessary. It is established that a pressure gradient between the LRV and inferior vena cava less than 1 mm Hg is normal, whereas greater than 3 mm Hg evinces nutcracker phenomenon and NCS with symptoms. [19, 46]. It has been suggested that this pressure gradient can be estimated fairly accurately from Doppler ultrasound, by measuring differences in flow velocities. [46] Additionally, the size of the LRV can similarly be measured with Doppler ultrasound, to demonstrate a stenosis. [15, 39, 46]. CT imaging can also show a decreased aortomesenteric angle, which when less than 38 to 45 degrees is considered abnormal. [45, 46] CT imaging can also show LRV compression. CT venography is preferable but not necessary in many of the studies we reviewed, which used CT of the abdomen pelvis or CT angiography to arrive at an NCS diagnosis. Overall, when NCS is suspected, invasive procedures are not necessary to arrive at a diagnosis. Relatively low risk procedures such as Doppler ultrasound and CT are available and should be used.
Regarding treatment, endovascular stenting was predominant. Some therapies aim at alleviating specific symptoms without disturbing the renal vein, such as gonadal vein transposition for pelvic congestion syndrome or lumbar vein embolization for headaches. Unfortunately, there was also not enough information in the reports regarding post-treatment course to determine if any of the treatment modalities are effective in the long term, and which would be preferable. More research is needed to determine the best methods of treatment. Future studies might directly compare the long-term effectiveness of conservative modalities, such as nutritional support, with endovascular or surgical options. There is still significant variation in treatment modalities. It may be that these should be adjusted to individual cases.
Our study was deficient in several ways. As stated, we did not include statistics on BMI. We also were unable to include information on outcomes of therapy, as most records did not state this. This study is retrospective in nature. Overall this was a small study population. It also included numerous institutions in different countries, which likely have different standards of practice. We did not include pediatric patients in this review.