A new notable compression source of left renal vein entrapment: right renal artery.

PURPOSE: To estimate the incidences of left renal vein (LRV) entrapment by right renal artery (RRA), a phenomenon primarily reported as case reports. METHODS: The cross-sectional study consecutively screened renal vessel CT data of 38 (Renal) patients with nephropathy and 305 (Non-renal) patients with peripheral arterial diseases in a teaching hospital in northeast China between November 2018 and March 2023. The LRV compression by adjacent anatomical structures, including but not limited to RRA and multiple compression-related parameters, were investigated through multiplanar analysis of the CT data. RESULTS: The overall LRV entrapment rates by adjacent structures were 41.93% (12/31) and 24.00% (6/25), the rates of RRA-sourced LRV compression 22.58% (7/31) and 20.00% (5/25), and the rates of compression by superior mesenteric artery (SMA) 16.13% (5/31) and 4.00% (1/25) in the Renal and Non-renal groups, respectively, with no significance. The venous segments distal to the RRA-compressed site had a significantly larger transectional lumen area than those of the non-compressed veins in both groups (3.09 ± 1.29 vs. 1.82 ± 0.23, p < 0.001 and 4.30 ± 2.65 vs. 2.12 ± 0.55, p = 0.006; maximum-to-minimum area ratios in Renal and Non-renal groups, respectively). Nearly 80% of RRAs were found arising anteriorly rightwards instead of passing straight to the right. CONCLUSION: RRA-sourced LRV compression was not rare, and its incidence was higher than that of the compression by SMA in both patient cohorts. RRA could be a more common compression source than SMA concerning LRV entrapment. Further investigations involving different populations, including healthy individuals, are needed.

Vascular compression syndromes in the abdomen and pelvis: a concise pictorial review.

Vascular compression syndromes are a diverse group of pathologies that can manifest asymptomatically and incidentally in otherwise healthy individuals or symptomatically with a spectrum of presentations. Due to their relative rarity, these syndromes are often poorly understood and overlooked. Early identification of these syndromes can have a significant impact on subsequent clinical management. This pictorial review provides a concise summary of seven vascular compression syndromes within the abdomen and pelvis including median arcuate ligament (MAL) syndrome, superior mesenteric artery (SMA) syndrome, nutcracker syndrome (NCS), May-Thurner syndrome (MTS), ureteropelvic junction obstruction (UPJO), vascular compression of the ureter, and portal biliopathy. The demographics, pathophysiology, predisposing factors, and expected treatment for each compression syndrome are reviewed. Salient imaging features of each entity are illustrated through imaging examples using multiple modalities including ultrasound, fluoroscopy, CT, and MRI.

Robotic Renal Vein Bypass: A Novel Technique for Treating a Challenging Case of Nutcracker Syndrome.

This case report highlights the successful application of a robotic-assisted surgical approach in managing Nutcracker syndrome. The patient, a 36-year-old female presented with severe symptoms and underwent robotic left renal vein transposition after failing conservative management. The procedure was performed through a minimally invasive approach utilizing the Da Vinci robotic system™ which offers enhanced visualization and precision. However, challenges arose during the renal vein anastomosis due to tension and poor flow through the transposition, requiring two revisions with a bovine pericardial patch. Ultimately, an 8 mm ringed PTFE bypass was anastomosed from the distal left renal vein to the Inferior Vena Cava. Despite these challenges, the patient experienced a successful outcome with complete symptom resolution of this complicated pathology.

Hemodynamics in nutcracker syndrome: implications for diagnosis.

BACKGROUND: Nutcracker syndrome is a disease characterized by complex symptoms, making its diagnosis challenging and often delayed, often resulting in a painful experience for the patients. OBJECTIVE: This study aimed to investigate the pathogenesis of nutcracker syndrome through the perspective of hemodynamics by simulating blood flow with varying compression degrees of the left renal vein. METHODS: 3D patient-specific vascular models of the abdominal aorta, superior mesenteric artery and left renal vein were constructed based on CT images of patients suspected of having nutcracker syndrome. A hemodynamic simulation was then conducted using computational fluid dynamics to identify the correlation between alterations in hemodynamic parameters and varying degrees of compression. RESULTS: The study indicated the presence of an evident gradient in velocity distribution over the left renal vein with relatively high degrees of stenosis (α ≤ 50°), with maximum velocity in the central region of the stenosis. Additionally, when the compression degree of the left renal vein increases, the pressure distribution of the left renal vein presents an increasing number of gradient layers. Furthermore, the wall shear stress shows a correlation with the variation of blood flow velocity, i.e., the increase of wall shear stress correlates with the acceleration of the blood flow velocity. CONCLUSIONS: Using computational fluid dynamics as a non-invasive instrument to obtain the hemodynamic characteristics of nutcracker syndrome is feasible and could provide insights into the pathological mechanisms of the nutcracker syndrome supporting clinicians in diagnosis.

Outcomes of conservative management in patients with nutcracker syndrome.

OBJECTIVE: This study aims to evaluate outcomes in nutcracker syndrome patients with tolerable symptoms and treated conservatively without invasive interventions. METHODS: This prospective study included patients treated conservatively. Promoting weight gain, the endpoint of the study was spontaneous resolution of symptoms. RESULTS: Sixteen patients (75% female and mean age 24.4 ± 3.5 years) underwent conservative management. Over a mean follow-up of 27.3 months [13-42, interquartile range (IQR)], the diameter ratio (5.5 [5-6.5, IQR] vs 4.3 [4.1-6], p = NS), the peak velocity ratio (6 [5-7, IQR] vs 4.8 [4.8-5.8], p = NS), beak angle (27° [24-30, IQR] vs 29° [24-32]; p = NS), and aortomesenteric angle (26° [23-29, IQR] vs 28° [24-30]; p = NS) exhibited no statistically significant changes. Complete resolution and improvement of symptoms were 28.5% and 31.4%, respectively, while 68.5% remained unchanged. CONCLUSIONS: This study shows that a conservative approach contributes to the spontaneous improvement or complete resolution in young adult patients with mild symptoms.

Treatment of Nutcracker Syndrome with Left Renal Vein Transposition and Endovascular Stenting.

BACKGROUND: Nutcracker syndrome is a rare condition that occurs as a result of the entrapment of the left renal vein (LRV) between the aorta and the superior mesenteric artery. It is typically associated with symptoms such as left flank pain, hematuria, proteinuria, and pelvic congestion. The current treatment approach may be conservative in the presence of tolerable symptoms, and surgical or hybrid and stenting procedures in the order of priority in the presence of intolerable symptoms. The aim of this study is to review our experiences to evaluate the results of both methods in this series in which we have a greater tendency toward surgery instead of stenting. METHODS: The clinical data of consecutive patients with nutcracker syndrome who underwent LRV transposition and LRV stenting between July 2019 and October 2023 were retrospectively reviewed. The patients were divided into 2 groups based on the methods of treatment: surgical and stenting. For procedure selection, LRV transposition was primarily recommended, with stenting offered to those who declined. Primary end points were morbidity and mortality. Secondary end points included late complications, patency, freedom from reintervention, and resolution of symptoms. Standard basic statistics and survival analysis methods were employed. RESULTS: Nineteen patients with nutcracker syndrome (female: 100%) were treated with LRV stentings (n = 5) and LRV transposition (n = 14). The mean age was 24 (20-27, interquartile range [IQR]) years. The mean follow-up was 23 (9-32, IQR) months. There were no major complications and mortality after both procedures. The most frequent sign and symptom associated with LRV entrapment were left flank pain 100% (n = 19), proteinuria 88% (n = 15), and hematuria 47% (n = 9). The mean peak velocity ratio on Doppler ultrasound was 6.13 (6-6.44, IQR). Aortomesenteric angle, beak angle (beak sign), and mean diameter ratio on computed tomography were 26° (22.6-28.5, IQR), 25° (23.9-28, IQR), and 5.3 (5-6, IQR), respectively. Venous pressure measurements were only used to confirm the diagnosis in 5 patients in the stenting group. The measured renocaval gradient was 4 (3.9-4.4, IQR) mm Hg. After both procedures, the classical symptoms, including left flank pain, proteinuria, and hematuria, resolved in 89.5% (n = 17), 57.8% (n = 11), and 82.3% (n = 15) of the cases, respectively. A total of 4 patients required reintervention, 3 patients after LRV transposition (occlusion, n = 2; stenosis, n = 1), and 1 patient after stenting (occlusion, n = 1). The 1-year and 3-year primary patency for the 19 patients was 87% and 80%, respectively. Three-year primary-assisted patency was 100%. Similarly, the 1-year and 3-year freedom from reintervention rate was 83% and 72%, respectively. Additionally, the 1-year and 3-year primary patency for the surgical group was 91% and 81%, respectively, and the 1-year and 3-year primary patency for the stenting group was 75%. CONCLUSIONS: Nutcracker syndrome should be kept in mind in cases where flank pain and hematuria cannot be associated with kidney diseases. Radiographic evidence must be accompanied by serious symptoms to initiate the treatment of nutcracker syndrome with LRV transposition and endovascular stenting procedures. Both procedures, along with their respective advantages and disadvantages, can be preferred as primary treatments for nutcracker syndrome. Our study demonstrates that both procedures can be safely and effectively performed, yielding good outcomes.

Nutcracker syndrome in pediatrics: initial findings and long-term follow-up results.

BACKGROUND: Nutcracker syndrome (NCS) describes a set of symptoms and signs resulting from compression of the left renal vein (LRV). There is a lack of knowledge about its natural course, diagnosis, and management, especially in children. Herein, we present our single-center experience with a large number of patients who have long-term follow-up results. METHODS: All patients with NCS diagnosed between January 2011 and March 2021 were included and their data were obtained retrospectively. RESULTS: A total of 123 NCS patients (85 females) were included. The median age at the time of diagnosis was 12 (IQR 10-14) years, and BMI percentiles were below 5% in 38% of the cases. At the time of diagnosis, two-thirds of the patients were asymptomatic. The most common laboratory finding was nephritic proteinuria (98%), followed by microscopic hematuria (16%). Signs of LRV compression were significantly more evident in upright position Doppler ultrasonography (DUS) examination. All patients have been followed conservatively; hematuria and/or proteinuria resolved in 43 of the 108 patients (40%) within 35.8 ± 25.8 months of follow-up. Control DUS was performed in 52 patients after a mean period of 39.1 ± 21.3 months. The median peak velocity and diameter ratios of the LRV in the upright position were found to be decreased significantly when compared to the initial assessment (p < 0.05). Normal DUS findings were noted in 13 patients at the final evaluation. CONCLUSIONS: In unexplained proteinuria and/or hematuria, NCS should be considered, especially in asthenic adolescents. Our results support conservative management in children as the first-line treatment approach.

Coexistència de la malaltia de Wilkie i la síndrome del trencanous / Coexistencia de enfermedad de Wilkie y síndrome del cascanueces / Simultaneous occurrence of Wilkie and nutcracker syndromes

Introducció. La síndrome de l’artèria mesentèrica superior,o malaltia de Wilkie, i la síndrome de compressió de lavena renal esquerra, o síndrome del trencanous, són pocfreqüents. Normalment estan provocades per una compressió extrínseca del duodè o de la vena renal esquerra, respectivament, a causa d’una disminució de l’angle entrel’artèria mesentèrica superior i l’aorta.Cas clínic. Adolescent de 15 anys que va consultar a urgències per dolor abdominal de cinc mesos d’evolució localitzata l’epigastri, acompanyat de vòmits, proteïnúria i pèrdua depes. La pacient havia consultat prèviament en altres centresi s’havien descartat patologies urgents quirúrgiques. Es vacompletar l’estudi amb una tomografia computada abdominal amb diagnòstic de síndrome de l’artèria mesentèricasuperior i síndrome del trencanous. La pacient va ingressara la planta d’hospitalització i es va tractar de forma conservadora amb una dieta hipercalòrica; el trànsit intestinal i laproteïnúria van millorar, i va poder ser remesa a domicili icontrolada ambulatòriament de forma multidisciplinària.Comentari. Els problemes secundaris a la compressió aortomesentèrica poden donar quadres compatibles amb la síndrome de l’artèria mesentèrica superior i la síndrome deltrencanous. El diagnòstic d’aquests quadres pot resultarcomplex per la incidència baixa i per la simptomatologiainespecífica que els caracteritza. El tractament conservador representa la primera línia de tractament, però en alguns casos pot no ser suficient. Per tot això és necessarifer un maneig multidisciplinari d’aquests pacients. (AU)

Introducción. El síndrome de la arteria mesentérica superior o deWilkie y el síndrome del cascanueces son poco frecuentes. Normalmente están producidos por una compresión extrínseca delduodeno o de la vena renal izquierda, respectivamente, debido a una disminución del ángulo entre la arteria mesentérica superior yla aorta.Caso clínico. Adolescente de 15 años que consultó a urgencias pordolor abdominal de cinco meses de evolución localizado en epigastrio, acompañado de vómitos, proteinuria y pérdida de peso. Lapaciente había consultado previamente en otros centros descartando patologías urgentes quirúrgicas. Se completó el estudio conuna tomografía computarizada abdominal con diagnóstico de síndrome de la arteria mesentérica superior o de Wilkie y síndrome delcascanueces. La paciente ingresó en planta de hospitalización y setrató de forma conservadora con una dieta hipercalórica con mejoría del tránsito intestinal y de la proteinuria, y pudo ser remitida adomicilio y controlada ambulatoriamente de forma multidisciplinar.Comentario. Los problemas secundarios a la compresión aortomesentérica pueden dar cuadros compatibles con el síndrome de laarteria mesentérica superior o de Wilkie y el síndrome del cascanueces. El diagnóstico de estos cuadros puede resultar complejo por subaja incidencia y por la sintomatología inespecífica que los caracteriza. El tratamiento conservador representa la primera línea de tratamiento, pero en algunos casos puede no ser suficiente. Por estosmotivos es necesario un manejo multidisciplinar de estos pacientes. (AU)

Introduction. The superior mesenteric artery syndrome or Wilkiesyndrome and the nutcracker syndrome are rare. They are normallycaused by extrinsic compression of the duodenum or the left renalvein respectively, due to a narrowing of the angle between the superior mesenteric artery and the aorta.Case report. A 15-year-old girl presented to the emergency roomwith a five-month history of abdominal pain located in the epigastrium, accompanied by vomiting, proteinuria, and weight loss. Thepatient had previously consulted in other centers, and urgent surgical conditions were ruled out. The study was completed with anabdominal computed tomography scan, which led to the diagnosisof superior mesenteric artery or Wilkie syndrome, and nutcrackersyndrome. The patient was admitted to the hospital and treatedconservatively with a hypercaloric diet with improvement in intestinal transit and proteinuria. She was discharged to continue thefollow-up with a multidisciplinary team. Comment. Problems secondary to aortomesenteric compression cangive symptoms like superior mesenteric artery or Wilkie syndromeand nutcracker syndrome. The diagnosis of these conditions canbe complex due to their low incidence and the non-specific symptomatology that characterizes them. Conservative treatment represents the first line of treatment, but in some cases it may not beenough. For these reasons, multidisciplinary management of thesepatients is necessary. (AU)

Síndrome de cascanueces: una causa infrecuente de hematuria / Nutcracker Syndrome: a Rare Cause of Hematuria

La hematuria en pediatría responde habitualmente a etiologías benignas. Una causa poco frecuente es el síndrome de cascanueces, que se define como la compresión de la vena renal izquierda entre la aorta y la arteria mesentérica superior, que deriva en una presión elevada en la vena renal izquierda con el desarrollo de venas colaterales y dilataciones varicosas. La prevalencia de este síndrome se desconoce. Cuando es sintomático ocasiona hematuria, proteinuria y dolor pélvico crónico. En la pubertad, el crecimiento rápido y el desarrollo de los cuerpos vertebrales pueden producir un estrechamiento del ángulo entre la aorta y la arteria mesentérica superior. Se describe el caso de una adolescente con diagnóstico de carcinoma mucoepitelial metastásico óseo múltiple que presenta hematuria anemizante. Se arribó al diagnóstico de síndrome de cascanueces y se discutieron las opciones de tratamiento. Finalmente, con el uso de realce del calzado para corrección de la escoliosis, se atenuó significativamente la hematuria. (AU)

In pediatrics, hematuria usually responds to benign etiologies. A rare cause is nutcracker syndrome, defined as compression of the left renal vein between the aorta and the superior mesenteric artery, resulting in elevated pressure in the left renal vein with the development of collateral veins and varicose dilatation. The prevalence of this syndrome is unknown. When symptomatic, it causes hematuria, proteinuria, and chronic pelvic pain. At puberty, the rapid growth and development of the vertebral bodies can produce a narrowing of the angle between the aorta and the superior mesenteric artery.We describe the case of a teenage girl diagnosed with multiple metastatic mucoepithelial carcinoma of bone who presented anemia-producing hematuria. The diagnosis of nutcracker syndrome was arrived at with consideration of the therapeutic options. Finally, with shoe enhancement for scoliosis correction, hematuria was significantly lessened. (AU)

Nutcracker Syndrome: Challenges in Diagnosis and Surgical Treatment.

BACKGROUND: Nutcracker syndrome (NCS) is an uncommon syndrome that presents with signs and symptoms caused by compression of the left renal vein (LRV), whereas 'nutcracker phenomenon' is solely used to refer to the anatomical configuration without clinical symptoms. Treatment for NCS may include nonoperative management, open surgical intervention, and in some instances endovascular stenting. We present a single-center retrospective case series of patients who presented with NCS managed with open surgical interventions. METHODS: A single-center, retrospective review of patients managed from 2010-2021. We diagnosed NCS via a thorough clinical examination and additional cross-sectional imaging studies including magnetic resonance venography and/or computed tomography venography. For further confirmation of the diagnosis, duplex ultrasound was frequently combined with contrast venography. RESULTS: Thirty eight patients were included in our study from 2010-2021. Twenty one (55.3%) patients presented with symptoms including flank pain, abdominal pain, hematuria, and fatigue. The remaining 17 (44.7%) patients had nutcracker phenomenon. Within the group of patients diagnosed with NCS, 11 patients underwent LRV transposition. Symptoms related to NCS improved in 10 patients. Hematuria in 1 patient did not improve. CONCLUSIONS: Transposition of the LRV is an effective treatment for NCS. Nonoperative management is an option for those patients experiencing less severe or nonspecific clinical symptoms.

Novel Use of Time-Resolved Magnetic Resonance Angiography to Evaluate Retrograde Lumbar Vein Flow and Epidural Venous Plexus Enhancement in Chronic Headache Patients With and Without Nutcracker Physiology.

OBJECTIVE: Compression of the left renal vein by the superior mesenteric artery, known as nutcracker phenomenon (NCP), can cause retrograde flow and congestion in communicating venous systems. It has recently been speculated that NCP can result in retrograde flow and congestion of the lumbar veins and epidural venous plexus (EVP), thereby affecting the central nervous system. This study describes the novel use of time-resolved magnetic resonance angiography (trMRA) to evaluate for retrograde left second lumbar vein (L2LV) flow and early EVP enhancement in patients with chronic daily headache (CDH) with and without NCP. METHODS: A retrospective analysis was performed of 31 patients with CDH (27 females and 4 males; median age, 38 years [range, 18-63 years]) who underwent trMRA centered over the L2LV to evaluate the direction of blood flow and presence of early EVP enhancement from May 2020 to March 2022. Descriptive statistics were performed, and anatomic associations were analyzed in patients with and without retrograde L2LV flow and early EVP enhancement. The accuracy of magnetic resonance imaging findings in detecting these flow patterns was also assessed. RESULTS: Patients with NCP who demonstrated narrowing of the left renal vein, a positive beak sign ( P = 0.052), decreased aortomesenteric distance ( P = 0.038), and decreased SMA angle demonstrated increased rates of retrograde L2LV flow and early EVP enhancement. A positive beak sign was 83% specific, and an aortomesenteric distance of ≤6.5 mm was 61% sensitive and 83% specific for identifying retrograde L2LV flow with early regional EVP enhancement in patients with CDH. CONCLUSIONS: Retrograde L2LV flow with early EVP enhancement in CDH patients can be effectively evaluated using trMRA and was seen with greater propensity in those patients with NCP.

Laparoscopic placement of left renal vein extravascular stenting in treatment of nutcracker syndrome: Techniques and long-term outcomes.

OBJECTIVES: We aimed to assess the feasibility and efficacy of laparoscopic extravascular stent in treatment of nutcracker syndrome by transperitoneal or retroperitoneal approach. METHODS: Seventy-six patients with nutcracker syndrome were retrospectively enrolled from a tertiary referral center, and underwent transperitoneal (63 patients) or retroperitoneal (13 patients) laparoscopic extravascular stent from March 2011 to December 2020. Surgical parameters, complications, imaging and clinical outcomes were collected and analyzed. RESULTS: All procedures were successfully carried out without open conversion. The median operation time, estimated blood loss, and postoperative hospital day were 120 (interquartile range [IQR]: 90-144) min, 20 (IQR: 10-30) ml, and 7 (IQR: 6-9) days. At a median follow-up of 52 (range: 9-127) months, 60 (79%) patients had complete symptom resolution, 14 (18%) patients had significant symptom improvement, and 2 (3%) patients reported no symptom improvement. Ninety-four percent (50/53) of hematuria, 91% (30/33) of proteinuria, and 89% (25/28) of flank/abdominal pain resolved after extravascular LRV stenting. No significant differences were detected in surgery parameters and recovery rates of clinical symptoms between two approaches (each p > 0.05). However, patients with transperitoneal approach need longer to achieve complete recovery compared with retroperitoneal approach (8.7 vs. 1.5 months, p = 0.016). CONCLUSIONS: Laparoscopic extravascular stent performed either transperitoneally or retroperitoneally is a feasible and effective option in treatment of nutcracker syndrome. Retroperitoneal laparoscopic extravascular stent required shorter time to achieve complete recovery, which should be considered whenever possible in surgical decision-making.

Síndrome de cascanueces y agenesia renal derecha. Una rara asociación / Nutcracker Syndrome and Right Renal Agenesis. A Rare Association

Introducción: El síndrome de cascanueces se considera una anomalía infrecuente y poco pensada en la práctica médica; su incidencia no está bien establecida debido a su sintomatología variada. La agenesia renal unilateral se estima entre 1/2500 y 1/4000 nacidos vivos. Objetivos: Describir una paciente de 18 años con sospecha prenatal de agenesia renal derecha confirmada por imágenes después del nacimiento, que ingresó por proteinuria. Presentación del caso: Paciente de 18 años con agenesia renal derecha conocida, en la que un examen de orina detectó proteinuria desde los 13 años. En su estudio se clasificó como proteinuria ortostática y evolutivamente refirió dolor lumbar izquierdo ligero y transitorio. En el ultrasonido renal, realizado para valorar crecimiento del riñón único, se detectó dilatación de la vena renal izquierda. Se repitió el estudio ecográfico para precisar ángulo aorto-mesentérico y dilatación de vena renal izquierda, y se confirmó el síndrome de cascanueces. Conclusiones: La asociación entre agenesia renal derecha y síndrome de cascanueces, resulta extremadamente rara, y, cuando se presenta con proteinuria ortostática y dolor lumbar ocasional, debe seguirse en forma expectante, pero no se necesita tratamiento quirúrgico en la mayoría de los casos(AU)

Introduction: Nutcracker syndrome is considered an infrequent and poorly thought out anomaly in medical practice; its incidence is not well established due to its varied symptomatology. Unilateral renal agenesis is estimated to be between 1/2500 and 1/4000 live births. Objectives: To describe an 18-year-old female patient with suspected pre-natal imaging-confirmed right renal agenesis after birth, who was admitted due to proteinuria. Case presentation: An 18-year-old female patient with known right renal agenesis, in whom a urine test detected proteinuria from the age of 13. In the study it was classified as orthostatic proteinuria and evolutionarily she referred mild and transient left low back pain. Renal ultrasound, performed to assess single kidney growth, showed dilation of the left renal vein. The ultrasound study was repeated to specify aorto-mesenteric angle and left renal vein dilation, and nutcracker syndrome was confirmed. Conclusions: The association between right renal agenesis and nutcracker syndrome is extremely rare, and, when it presents with orthostatic proteinuria and occasional low back pain, it should be followed expectantly, but surgical treatment is not needed in most cases(AU)

A systematic review on nutcracker syndrome and proposed diagnostic algorithm.

OBJECTIVE: Nutcracker syndrome (NCS) is an increasingly recognized venous compressive disease. Although people with NCS can experience debilitating symptoms, making an accurate diagnosis can often be challenging owing to the broad spectrum of clinical presentations and radiologic findings. In the present systematic review, we assessed the most frequent clinical and radiologic criteria used in establishing a diagnosis of NCS and have proposed a comprehensive framework for clinical decision-making. METHODS: We performed a systematic review to identify all observational studies or case series conducted within the previous 10 years that had studied patients with a clinical and radiologic diagnosis of NCS. The extracted data included details related to the study design, participant demographics, presenting clinical features, and radiologic criteria. These details were compared between studies and synthesized to establish a comprehensive diagnostic framework that would be applicable to clinical practice. RESULTS: In the present review, we included 14 studies with a total of 384 patients with NCS. The most common clinical features of NCS were hematuria (69.5%), left flank or abdominal pain (48.4%), pelvic pain (23.1%), and varicocele (15.8%). Computed tomography and ultrasound were the most commonly used imaging modalities, with a threshold for left renal vein stenosis of >80% the most frequently used diagnostic parameter. Eight studies had used venography, with the renocaval pressure gradient the most commonly measured parameter. Two studies had reported using intravascular ultrasound. The findings from our review have shown that a thorough clinical workup of NCS should include critical evaluation of the presenting clinical features and exclusion of alternative diagnoses. All patients should undergo duplex ultrasound with or without the addition of computed tomography or magnetic resonance imaging. Any patient considered for therapeutic intervention should also undergo diagnostic venography with measurement of the renocaval pressure gradient and, if available, intravascular ultrasound with measurement of the left renal vein diameters. CONCLUSIONS: NCS is a challenging condition in terms of the diagnosis and management both. We have proposed a comprehensive diagnostic framework based on the currently available literature to aid in clinical decision-making.

Left renal vein entrapment in postural proteinuria: the diagnostic utility of the aortomesenteric angle.

Nutcracker syndrome related to the left kidney vein compression is a cause of orthostatic proteinuria during childhood. Some studies have shown that the ratios between maximum velocities and anterior-posterior diameters of hilar and aortomesenteric segments of the left kidney vein between upright and supine positions must be more than 4 in order to make a Nutcracker syndrome diagnosis. Our aim was to investigate whether the use of a decrease in aortomesenteric angle between upright and supine positions in the presence of isolated orthostatic proteinuria can be a criterion for the diagnosis of Nutcracker syndrome. Relevant patient information, which included demographic data, clinical examination findings, laboratory data, urinary system ultrasound, and kidney color flow Doppler ultrasound results, were prospectively collected. Thirty-nine pediatric patients with orthostatic proteinuria were included in the study. Left kidney vein compression findings were demonstrated in 31 patients. The ratio of maximum velocities of hilar and aortomesenteric segments of the left kidney vein between upright and supine positions was above 4 in only 7 of our patients. Ratio of aortomesenteric angle between upright and supine positions was significantly decreased for patients with left kidney vein compression findings.  Conclusion: The use of a decrease in the ratio of aortomesenteric angle between upright and supine positions in the presence of orthostatic proteinuria, instead of the ratios for maximum velocities and anterior-posterior diameters of hilar and aortomesenteric segments, can be more helpful for the diagnosis of Nutcracker syndrome in the differential diagnosis of orthostatic proteinuria. What is Known: • Proteinuria may be a sign of an impending kidney disease • Nutcracker syndrome is a cause of orthostatic proteinuria. What is New: • Ratio of aortomesenteric angle between upright and supine positions > 0.6 can be used for Nutcracker syndrome diagnosis.