Current trends in the diagnosis and management of renal nutcracker syndrome: a review

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.

The Da Vinci Single-Port (SP) Treatment of Nutcracker Syndrome: A Case Report of a Novel Approach

Nutcracker syndrome (NCS) is a rare disease affecting the left kidney. Surgical management is the only choice of treatment. Minimal invasive surgeries can be effective and may prevent complications of the major surgery. We present the case of a 33-year-old woman suffering from chronic left flank pain, diagnosed with NCS and treated with extravascular stents. Robotic-assisted extravascular stent insertion was performed using the Da Vinci single-port (SP) (Intuitive Surgical, Inc., Sunnyvale, USA) system. This approach offers the advantages of minimal invasiveness, precise stent placement, and reduced operative time. To our knowledge, this is the first case of using Da Vinci SP for this indication. Further studies are needed to evaluate the long-term outcomes and safety.

Effect of left renal vein compression stenosis on functional status of left kidney in patients with pelvic venous disorders

OBJECTIVE

We evaluated the effect of left renal vein (LRV) compression stenosis on the functional state of the left kidney in patients with pelvic venous disorders (PeVDs).

METHODS

We examined 162 female patients with PeVD and diagnosed LVR compression stenosis using duplex ultrasound (DUS) in 40. Patients with clinical manifestations of PeVD (n = 26) had symptoms and signs of pelvic venous congestion but without pain in the left flank of the abdomen, typical for nutcracker syndrome (NS). The remaining patients were asymptomatic (n = 14). The parameters measured with DUS included the angle of the superior mesenteric artery (SMA) with the aorta, the LRV diameter (Dhilum/Dstenosis) ratio, and LRV velocity (Vstenosis/Vhilum) ratio. All the patients underwent laboratory testing (complete blood count, urinalysis, and biochemical blood testing) and dynamic renal scintigraphy to assess the secretory and evacuation functions of the renal tubular system.

RESULTS

The laboratory tests revealed no abnormalities, including no hematuria or proteinuria, in either group. The Dhilum/Dstenosis and Vstenosis/Vhilum ratios varied from 2.8 to 5.2 and from 2.9 to 8.3, respectively, and did not differ between the symptomatic and asymptomatic patients. All 40 patients with LRV compression stenosis were diagnosed with left gonadal vein reflux with a mean duration of 4.7 ± 0.6 seconds and 2.2 ± 0.6 seconds in the symptomatic and asymptomatic patients, respectively (P = .005). Eight patients had signs of NS on DUS, including five in the symptomatic group (SMA angle, 34.8° ± 2.7°; Dhilum/Dstenosis ratio, 5.2 ± 0.2; and Vstenosis/Vhilum ratio, 5.7 ± 0.4) and three in the asymptomatic group (SMA angle, 35° ± 2.8°; Dhilum/Dstenosis ratio, 5; and Vstenosis/Vhilum ratio, 5 ± 0.5). The groups did not differ significantly in the DUS parameters. Scintigraphy did not reveal any cases of secretory or evacuation dysfunction of the left kidney, including in the patients with DUS signs of NS. The maximum uptake time, elimination half-life, and effective renal plasma flow were within the normal ranges.

CONCLUSIONS

LRV compression stenosis without hematuria has no significant effects on the functional state of the left kidney, irrespective of the disease severity. In patients with PeVDs, dynamic renal scintigraphy provides an objective assessment of left kidney function.

Surgical treatment of nutcracker syndrome results in improved pain and quality of life

BACKGROUND

Left renal vein (LRV) compression, or nutcracker phenomenon, describes the compression of the LRV, most commonly between the aorta and the superior mesenteric artery. The outflow obstruction that occurs from the compression causes venous hypertension leading to the development of pelvic collaterals, lumbar vein engorgement and gonadal vein reflux. The symptoms associated with LRV compression include abdominal pain, left flank pain, back pain, headache, pelvic pain/pressure, and hematuria. Symptomatic LRV compression can cause chronic pain and disability that impedes activities of daily living. Left renal auto transplantation (LR-AT) is one mode of treatment, leading to decreased pain with no significant vascular or urological complications. Herein we present a five patient case series with symptomatic LRV compression who underwent LR-AT with improved pain and quality of life after surgery.

METHODS

Five patients underwent LR-AT between June 2020-December 2020 to resolve their symptomatic LRV compression. These patients were given three validated surveys pre- and post- intervention, then again at their three month follow up visit to assess their pain and health-related quality of life.

RESULTS

The five patients were all female with the average age of 36.8 years old (36-41) and underwent LR-AT to treat their symptomatic LRV compression. The average Numeric Rating Scale (NRS) pain score pre intervention was 8.3 (range 6.7 to 10) which improved to pain rating 5.22 (range 2.7 to 6) post intervention, p-value = 0.013. The average pain NRS score at 3 month follow up was 3.86 (range 1.3-6), p-value = 0.006 when compared to pre-intervention pain scores. The average pain intensity pre intervention was 4.5 (4 to 5) and 2.7 (1 to 4.3) post intervention, p-value = 0.024. The average pain intensity score at 3 month follow up was 2.24 (range 1.3-3.3), p-value = 0.002 when compared to pre-intervention. The VascuQoL-6 survey score pre intervention averaged score of 9.6 (range 7-12) which improved to an average score of 20.6 (range 18-24), p-value = 0.001. The average VascuQoL score at 3 month follow up was 22.6 (range 22-24), p-value = < 0.001 when compared to pre intervention QoL scores all showing a statistically significant improvement of health-related quality of life.

CONCLUSION

The diagnosis of LRV compression can be challenging due to the non-descript symptoms and overall lack of awareness. Understanding venous tributary pathways and drainage can help clarify why patients present with unusual symptoms. Surgical treatment of LRV compression through LR-AT can improve patients' pain and improve vascular quality of life.

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 non-operative 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

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 (MRV) and/or computed tomography venography (CTV). 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 one patient did not improve.

CONCLUSION

Transposition of the LRV is an effective treatment for NCS. Non-operative management is an option for those patients experiencing less severe or nonspecific clinical symptoms.

Systematic review of endovascular versus laparoscopic extravascular stenting for treatment of nutcracker syndrome

OBJECTIVE

The aim of the present study was to assess the current strategies of endovascular and laparoscopic extravascular stenting for symptomatic compression of the left renal vein (LRV), most frequently between the aorta and superior mesenteric artery (nutcracker syndrome [NCS]).

METHODS

We performed a systematic review of all studies of endovascular and laparoscopic extravascular LRV stenting for NCS using the PubMed/MEDLINE, Scopus, Embase, Cochrane, Science Citation Index Expanded, Emerging Sources Citation Index, and Epistemonikos databases. Data were collected in accordance with the PRISMA (preferred reporting items for systematic reviews and meta-analysis) guidelines. The English, Spanish, and German language literature was searched from January 1, 1946 to February 9, 2022. The outcomes assessed included symptom resolution, hematuria resolution, and reintervention at follow-up.

RESULTS

The search yielded 3498 reports. After removing the duplicates and those without the full text available, 1724 studies were screened. Of these, 11 studies were included in the present review. Of the 11 studies, 7 were on endovascular stenting and 4 on laparoscopic extravascular stenting; all 11 studies were retrospective, single-center case series. Of the 233 patients, 170 (80 women) had undergone endovascular stenting and 63 (9 women) had undergone extravascular stenting. The follow-up period varied from 1 to 60 months after endovascular stenting and 3 to 55 months after extravascular stenting. The symptoms had resolved in 76% (range, 50%-100%) after endovascular stenting and 83% (range, 71%-100%) after extravascular stenting. Hematuria had resolved in 86% (range, 60%-100%) after endovascular stenting and 89% (range, 77%-100%) after extravascular stenting. Of 185 patients, 9 had required reintervention after endovascular stenting and none after extravascular stenting.

CONCLUSIONS

Endovascular and laparoscopic extravascular stenting are less invasive and, thus, more attractive treatment options that have been more recently developed for the management of NCS. The results from the present study have shown that symptom and hematuria resolution must be provided before they can be considered preferred management options for patients affected by NCS. Given the limited number of patients involved, no definitive conclusion could be drawn regarding the superiority of one technique compared with the other.

Twenty-year analysis of the rarely diagnosed nutcracker syndrome

Aim: Nutcracker syndrome is a very rare cause in patients presenting to the emergency department with abdominal pain. Early consideration in differential diagnosis will reduce the time spent for diagnosis and morbidity, as well as provide the correct treatment. We aimed to contribute to the literature by determining the clinical relations of these cases with laboratory, imaging and treatment data. Material and Method: Twenty-seven patients over the age of 16 who presented to the emergency department with abdominal pain between January 2000 and December 2020 were included in this study. The ages of the patients were between 16-39 and the mean was 25.19±7.00 years. Demographic characteristics, clinical findings, laboratory parameters, radiological evaluations, and treatment modalities of patients were evaluated retrospectively. Results: Abdominal pain and flank pain were the most common reasons for admission to the emergency department of 27 patients included in the study. In the anterior group, 17 (77%) patients had flank pain, 10 (45%) patients had dysmenorrhea, 11 (50%) hematuria, 10 (45%) proteinuria, and 9 (40%) patients hematuria and proteinuria. In the posterior group, there was no hematuria, proteinuria, anorexia, nausea and vomiting, and oral intolerance. In cases with anteior nutcracker syndrome, 12 (54%) doppler ultrasonography, 13 (59%) computed tomography, 5 (22%) magnetic resonance imaging were performed. Conservative treatment was applied to 11 (40%) patients in the anterior group and 3 (11%) patients in the posterior group. Endovascular surgery was performed on 5 (22%) female patients. Conclusion: Nutcracker syndrome should be investigated in adult patients who present to the emergency department with abdominal pain and whose diagnosis is unclear. Early diagnosis is critical in terms of treatment and morbidity.

Diagnostic Clues in Pediatric Nutcracker Syndrome: From Two Clinical Cases to Current Literature Analysis

Nutcracker syndrome (NCS) is a rare pediatric disease caused by left kidney vein compression. Besides the "Triade's symptoms", including hematuria, proteinuria, and flank pain, a wide spectrum of clinical manifestations has been reported. As the significant hemodynamic changes secondary to the dilatation of the left renal vein, serious consequences such as renal vein thrombosis and severe anemia might occur in these children. NCS diagnosis includes a variety of invasive and non-invasive imaging tools, but cutoff values need to be further validated. A conservative treatment represents the most common therapeutic approach for these patients, but operative options are available in selected cases. To complicate matters, a standard diagnostic and treatment algorithm is currently lacking and scientific pediatric evidence in this field is still poor and limited. In this perspective, early recognition of NCS is crucial but challenging for pediatricians. Therefore, a better knowledge of the disease is recommended. Starting from two different clinical presentations of NCS, we aimed to provide a comprehensive overview of the disease in children.

Origins of abnormal placentation: why maternal veins must not be forgotten

The importance of uterine microvascular adaptations during placentation in pregnancy has been well established for decades. Inadequate dilatation of spiral arteries is associated with gestational complications, such as preeclampsia and/or intrauterine growth restriction. More recently, it has become clear that trophoblast cells invade and adapt decidual veins and lymphatic vessels 1 month before spiral arteries become patent and before intervillous space perfusion starts. Normal intervillous space hemodynamics is characterized by high volume flow at low velocity and pressure in the interseptal compartments surrounding the chorionic villi, hereby facilitating efficient maternal-fetal exchange. In case of shallow decidual vein dilatation, intervillous arterial supply exceeds venous drainage. This will cause congestion in the interseptal compartments with subsequently reduced perfusion and increased pressure. An efficient mechanism to counteract venous congestion and safeguard the viability of the conceptus is by reducing arterial inflow via shallow dilatation of the spiral arteries. This review made the case for intervillous space congestion as an unexplored trigger for inadequate spiral artery dilatation during the placentation process, eventually leading to abnormal systemic circulatory dysfunctions. An abnormal maternal venous function can result from an abnormal maternal immune response to paternal antigens with an imbalanced release of vasoactive mediators or can exist before conception. To get the full picture of abnormal placentation, maternal veins must not be forgotten.

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.

Nutcracker Syndrome: A Cause of Hematuria and Low Back Pain in Young Patients

Nutcracker syndrome is a clinical condition in which there is compression of the left renal vein in its path between the abdominal aorta and the superior mesenteric artery. This phenomenon can cause abdominal or low back pain and hematuria. It is a rare clinical entity, although probably underdiagnosed. The diagnosis is essentially clinical and based on imaging, but necessarily a diagnosis of exclusion. We present the case of a 21-year-old boy who came to the Emergency Department with hematuria and low back pain. After exhaustive study and exclusion of other possible clinical entities, the diagnosis was confirmed to be nutcracker syndrome. Despite its usually benign expression, this entity should not be forgotten in the diagnostic process of cases of hematuria and low back pain, especially in young patients.

Bibliometric and visual analysis of research on nutcracker syndrome from 1974 to 2021: A systematic review

BACKGROUND

At present, researchers have obtained fruitful results in the study of nutcracker syndrome (NCS), but there is still a lack of systematic research on the overall status of this disease. This article aims to describe the past and current status of research into NCS, and predict future research trends and popular research topics.

METHODS

Using bibliometric and visualization methods, 552 articles related to NCS collected from the Scopus database from 1974 to 2021 were analyzed from multiple perspectives.

RESULTS

Overall, the amount of literature related to NCS is on the rise every year, and the number of citations is the turning point in 2006. The United States has the largest number of publications and has the most extensive cooperation with other countries. The main contents of the co-authored study focused on the symptoms, surgical procedures, and concomitant diseases of NCS. Keywords such as peak velocity, ultrasonography, orthostatic proteinuria, etc appeared earlier, whereas diagnosis, chronic pelvic pain, endovascular stents, etc appeared later.

CONCLUSIONS

The literature utilization rate of NCS is relatively insufficient. The pathogenesis and pathological mechanisms need to be further studied, and the diagnostic criteria and surgical methods will continue to be favored by clinicians.

Evaluation of renal vascular variations with computed tomography

Background

It is important to know the renal vascular variations before renal surgeries and invasive procedures. The aim of this study is to evaluate the prevalence and types of variation of renal arteries and veins.

Methods

The abdominal CT images of 460 patients, taken between 2019 and 2021, were retrospectively analyzed in axial and coronal planes. The presence and number of accessory renal arteries and early branching in the main renal artery were evaluated. Then, bilateral renal vein variations were investigated. Finally, the compression of the left renal vein by different anatomical structures was evaluated.

Results

Of the 450 patients included in the study, the mean age was 53 years. No variations were detected in 378 renal arteries on the right side (84%) and 392 renal arteries on the left side (87.1%). The most common variation in renal arteries was an accessory inferior hilar artery in 7.5% and 6% rates on the right and left, respectively. An accessory inferior renal polar artery was observed at an overall rate of 1.3%. An accessory superior renal hilar artery was found at 3.3% and 2% rates on the left and the right, respectively. An accessory superior renal polar artery was found at an overall rate of 3.5%. Multiple variations in the renal arteries were observed at a rate of 6.4%. Early branching was observed at a rate of 4.9% on the right and 2.2% on the left. The presence of two and three right renal veins was observed at rates of 13.1% and 0.6%, respectively. Retroaortic and circumaortic left renal veins were found at 3.5% and 4.4% rates, respectively. The compression on the anterior and posterior left renal veins was observed at 4.6% and 0.9% rates, respectively.

Conclusion

Considering that variations in renal arteries and veins are too many and of different types to underestimate, a CT examination for the renal vascular anatomy before and at the planning phase of renal surgery or interventional procedures will be of great benefit to avoid potential complications.

Robotic-assisted renal autotransplant as a novel treatment option for nutcracker syndrome

Nutcracker syndrome can present with various disabling symptoms. To our knowledge, there are no reports that describe a robotic-assisted approach in its management. We present a patient who underwent robotic-assisted nephrectomy after the failure of conservative management of nutcracker syndrome and a second patient who underwent robotic-assisted nephrectomy with autotransplant. Surgery and immediate post-op courses were uncomplicated. Robotic-assisted nephrectomy with or without autotransplant can be a feasible, minimally invasive option for select patients with nutcracker syndrome.

Nutcracker syndrome: diagnosis and therapy

Nutcracker syndrome (NCS) is an extrinsic compression of the left renal vein (LRV) by the superior mesenteric artery (SMA) anteriorly and aorta posteriorly resulting in renal vascular congestion manifesting as hematuria, proteinuria, orthostatic hypotension, pain, or even renal dysfunction. Long-standing venous compression can encourage collateral drainage pathways through gonadal and pelvic veins, which may explain reported symptom and syndrome overlap with pelvic congestion syndrome. Diagnosis can be challenging and variable, frequently involving a combination of ultrasound Doppler, cross-sectional, and invasive imaging. Often, intravascular pressure measurements are required to prove a renocaval pressure gradient to aid in a definitive diagnosis. Conservative management is appropriate, especially in children, who tend to outgrow the disorder. In the interim, medical management with angiotensin converting enzyme inhibitors (ACEIs) is a useful therapy to manage orthostatic hypotension in the pediatric population. In adults, invasive therapies are more frequently pursued. These are aimed at relieving the extrinsic compression on the LRV. The standard of care is renal vein transposition, with renal autotransplantation reserved for recalcitrant cases. Endovascular stenting is a less invasive option. Laparoscopic placement of an exovascular stent is a newer therapy intended to minimize trauma to the LRV. In this review, we will discuss the clinical manifestations, diagnostic criterion, imaging features, and conservative and surgical therapies for this condition.

Atypical Posterior Nutcracker Syndrome in a 17-Year-Old Male Without Hematuria

Retro-aortic left renal vein (RLRV) is an anatomical variation, where the left renal vein (LRV) courses posterior to the aorta and anterior to the vertebrae before it eventually drains into the inferior vena cava (IVC). RLRV is a rare finding, with a prevalence of around 1%-2%, and only a small minority of RLRVs cause symptoms. RLRV symptoms occur secondary to compression of the LRV between the abdominal aorta and vertebrae, otherwise known as posterior nutcracker syndrome (PNCS). The most common symptoms of PNCS are hematuria and flank pain. We present a 17-year-old male, who came in with recurring left flank pain without hematuria, initially thought to be renal colic secondary to nephrolithiasis. On further investigations, an aberrant posterior renal vein was seen on CT suggestive of PNCS. The patient was treated successfully with RLRV vascular stent placement by interventional radiology. This case report adds to the limited number of PNCS cases observed in children and to the even rarer cases of PNCS without hematuria. This case also acts as a reminder for pediatricians to keep a wide scope of differentials in patients presenting with flank pain and provides an outline of both diagnostic and treatment modalities available for these patients.

An Uncommon Variant of Nutcracker Syndrome Secondary to Left Renal Vein Compression Between the Right Renal Artery and The Proper Hepatic Artery

Nutcracker syndrome refers to the compression of the left renal vein between the abdominal aorta and the superior mesenteric artery. The subsequent venous congestion of the left kidney, when symptomatic, could be associated with left flank pain, hematuria, varicocele, dyspareunia, dysmenorrhea, and proteinuria. Here we describe a 42-year-old female patient with simultaneous Dunbar syndrome and a rare variant of nutcracker syndrome in which the left renal vein (LRV) compression is secondary to the unusual path of the vein between the right renal artery and the proper hepatic artery. For both the nutcracker syndrome and the Dunbar syndrome, open approach by median mini-laparotomic access for transposition of LRV, and resection of the diaphragmatic pillars and arcuate ligament was attempted. During the intervention, due to anatomical issues, the LRV transposition was converted to endovascular stenting of the LRV, moreover the implanted stent was transfixed with an external non-absorbable suture to avoid migration. At the 12 months follow-up the patient was asymptomatic, and the duplex scan confirmed the patency of the celiac trunk without re-stenosis and a correct position of the LRV stent with no proximal or distal migration.

The Renal Vasculature: What the Radiologist Needs to Know

The physiologic role of the kidneys is dependent on the normal structure and functioning of the renal vasculature. Knowledge and understanding of the embryologic basis of the renal vasculature are necessary for the radiologist. Common anatomic variants involving the renal artery (supernumerary arteries and prehilar branching) and renal vein (supernumerary veins, delayed venous confluence, retroaortic or circumaortic vein) may affect procedures like renal transplantation, percutaneous biopsy, and aortic aneurysm repair. Venous compression syndromes (anterior and posterior nutcracker syndrome) can be symptomatic and can be diagnosed with a combination of radiologic features. Renal artery stenosis is commonly atherosclerotic and is diagnosed with Doppler US, CT angiography, or MR angiography. Fibromuscular dysplasia, the second most common cause of renal artery narrowing, has a characteristic string-of-beads appearance resulting from multifocal stenoses and dilatations. Manifestations of renal vasculitis differ depending on whether the affected vessels are large, medium, or small. Renal vascular injury is graded according to the American Association for the Surgery of Trauma (AAST) renal injury scale, which defines vascular injury and active bleeding in renal injuries. Both renal arteries and veins are affected by primary neoplasms or secondarily by neoplasms from adjacent structures. Differentiation between bland thrombus and tumor thrombus and the extent of involvement dictate management in malignancies, especially renal cell carcinoma. Aneurysms, pseudoaneurysms, arteriovenous malformations, and arteriovenous fistulas can affect renal vessels and can be diagnosed with specific imaging features. The radiologist has a critical role in identification of specific imaging characteristics and establishing the diagnosis in the varied pathologic conditions affecting the renal vasculature, which is critical for directing management. Thus, the renal vasculature should be an integral part of radiologists' checklist. ^©RSNA, 2021.

Nutcracker syndrome: A rare cause of chronic pelvic pain and left back pain

The Nutcracker Syndrome is a rare and often unrecognized cause of chronic pelvic pain and left back pain. These symptoms are due to the left renal vein compression between the aorta and the superior mesenteric artery (anterior nutcracker) or between the aorta and the spine (posterior nutcracker). The variety of clinical manifestations make the diagnosis difficult and commonly delayed. Therefore, imaging plays a key role in correcting the diagnosis by confirming the left renal vein stenosis and ruling out any differential diagnosis. Treatment options are discussed by a multidisciplinary team involving urologists, nephrologists and vascular surgeons for each patient. We report the case of 2 patients presenting chronic pelvic and lower back pain in whom clinical investigation and CT imaging findings were consistent with a nutcracker syndrome.

[Nutcracker syndrome: a rare cause of abdominal pain in adults that shouldn't be ignored: a case report]

De nos jours, la connaissance des anomalies vasculaires est primordiale pour tous les spécialistes en pratique clinique et peut prévenir de graves complications suite à des interventions précoces. Le syndrome de Casse-Noisette ou Nutcraker syndrome résulte d´une compression de la veine rénale gauche (VRG), généralement dans la fourchette formée par l´aorte abdominale et l'artère mésentérique supérieure (AMS), conduisant à la sténose de la partie aorto-mésentérique de la veine rénale gauche et dilatation de sa partie distale. La symptomatologie reste dominée par des douleurs lombaires, abdominales, pelviennes et hématurie. Son diagnostic est basé essentiellement sur les moyens d´imagerie moderne (tomodensitométrie, échographie-Doppler, phlébographie) et son traitement est controversé. Nous rapportons le cas d´une femme âgée de 43 ans, admise dans le cadre d´un bilan radiologique devant des douleurs épigastriques avec pesanteur pelvienne suite à un syndrome de Casse-Noisette.

Splenic vein enlargement, a rare cause of nutcracker syndrome

Abnormal enlargement of the splenic vein is one of the etiologies of nutcracker syndrome that should be considered when examining the causes of this syndrome. Because knowing rare etiologies can help correct diagnose and reduce mortality.

Diagnostic accuracy of the jetting sign and a dilatation ratio of left renal vein in CT urography for detecting anterior nutcracker syndrome

AIM

To investigate the diagnostic value of computed tomography (CT) urography findings of anterior nutcracker syndrome (NCS).

MATERIALS AND METHODS

The study included patients with left renal vein (LRV) compression at the aortomesenteric portion at CT urography who underwent renal venography or cystoscopy. Patients with a renocaval pressure gradient of ≥3 mmHg on renal venography or bloody urine jetting from the left ureteral orifice on cystoscopy were defined as the NCS group; the remaining patients comprised the non-NCS group. CT findings were analysed using the jetting of contrast medium flow from the LRV to the inferior vena cava (jetting sign), aortomesenteric distance, presence of collateral veins, and a dilatation ratio of LRV diameter at the aortomesenteric portion (arterial phase/delayed phases). Clinical findings, including age, gender, and body-mass-index, were also analysed. CT features and clinical findings were compared between the NCS and non-NCS groups. Diagnostic performance of CT parameters was assessed using receiver operating characteristic curve analysis.

RESULTS

A total of 70 patients (21 men, mean age 44.4 ± 17.2 years) with NCS (n=13) and non-NCS (n=57) were included. Younger age (<40 years), presence of the jetting sign, and a lower dilatation ratio of LRV diameter between the arterial and delayed phases (<1.7) were found to be significant independent factors for predicting the NCS group (OR 24.5, 18.9, 19.4, respectively, p<0.05 for all). The combination of the presence of the jetting sign and a dilatation ratio of LRV diameter of <1.7 obtained the highest AUC of 0.88.

CONCLUSION

The jetting sign and the dilatation ratio of LRV diameter between the arterial and delayed phases can both be very useful in the diagnosis of anterior nutcracker syndrome during CT urography.

The Vici venous stent for treatment of renal vein entrapment

The nutcracker syndrome results from compression of the left renal vein between the superior mesenteric artery and the aorta. We present the first reported case of symptomatic left renal vein compression treated with balloon angioplasty and stenting with the Vici stent system.

From Nutcracker Phenomenon to Nutcracker Syndrome: A Pictorial Review

Left renal vein (LRV) entrapment, also known as nutcracker phenomenon if it is asymptomatic, is characterized by abnormality of outflow from the LRV into the inferior vena cava (IVC) due to extrinsic LRV compression, often accompanied by demonstrable lateral (hilar) dilatation and medial (mesoaortic) stenosis. Nutcracker syndrome, on the other hand, includes a well-defined set of symptoms, and the severity of these clinical manifestations is related to the severity of anatomic and hemodynamic findings. With the aim of providing practical guidance for nephrologists and radiologists, we performed a review of the literature through the PubMed database, and we commented on the definition, the main clinical features, and imaging pattern of this syndrome; we also researched the main therapeutic approaches validated in the literature. Finally, from the electronic database of our institute, we have selected some characteristic cases and we have commented on the imaging pattern of this disease.

Combined Nutcracker and Ehlers-Danlos Syndromes: A Case Report

Introduction

Nutcracker syndrome refers to the clinical manifestations of left renal vein compression between the superior mesenteric artery and the abdominal aorta, causing urinary changes and low back pain.

Report

A 44 year old woman presented with low back and pelvic pain. Following the diagnosis of nutcracker syndrome, she underwent endovascular treatment with renal vein stent placement; however, the patient continued to complain of pain. Further examinations revealed left renal vein compression by the portal vein. The patient underwent a second procedure; however, improvement was temporary and her pain returned. Further investigation revealed previously undetected nephroptosis and hyperelasticity. A diagnosis of Ehlers-Danlos syndrome made, possibly explaining the mobility of viscera and unusual compression of the left renal vein by the portal vein.

Conclusion

Ehlers-Danlos syndrome can cause nutcracker syndrome and may give rise to visceral pain of mixed origin.

Doppler US and CT Diagnosis of Nutcracker Syndrome

Nutcracker syndrome (NCS) is a syndrome caused by compression of the left renal vein (LRV), between the abdominal aorta and the superior mesenteric artery, resulting in hypertension of the LRV and hematuria. Doppler ultrasonography (US) has been commonly used for the diagnosis of NCS. However, several technical issues, such as Doppler angle and sample volume, need to be considered to obtain satisfactory results. In addition, morphologic changes of the LRV and a jetting phenomenon across the aortomesenteric portion of the LRV on contrast-enhanced computed tomography (CECT) are diagnostic clues of NCS. With proper Doppler US and CECT, NCS can be diagnosed noninvasively.

Refractory hypertension and pelvic pain associated with nutcracker phenomenon

We represent a 35-year-old woman, with refractory hypertension and pelvic pain, and with nutcracker phenomenon diagnosed using computed tomographic angiography. Although surgical treatment was not performed because of the patients' nonconsenting, any other cause for the hypertension was not found by extensive work-up, supports the notion that it was either secondary to nutcracker phenomenon or idiopathic.

Microsurgical gonadal-inferior epigastric vein anastomosis to treat the nutcracker phenomenon with left gonadal vein varices with reflux

OBJECTIVE

To evaluate the effectiveness and safety of microsurgical gonadal-inferior epigastric vein anastomosis for the treatment of the nutcracker phenomenon (NCP) associated with left gonadal vein varices with reflux.

METHODS

Thirty-five patients with NCP associated with left gonadal vein varices with reflux diagnosed in our hospital from June 2016 to June 2018 were included. All patients underwent a shunt operation consisting of microsurgical gonadal-inferior epigastric vein anastomosis, and the patients were followed up for 1 year.

RESULTS

All patients were successfully operated on, with an average operation time of 96.5 ± 12.3 min. After a 1-year follow-up, the symptom of gross hematuria disappeared in 3 patients (including 1 woman). For the other 32 patients, the sperm concentration (27.43 ± 8.68 × 10⁶/ml) and motility (33.06 ± 4.27%) postoperatively were significantly higher than that preoperatively (16.21 ± 6.43 × 10⁶/ml and 23.48 ± 4.43%, respectively) (P < 0.05); among these patients, 2 had natural pregnancies with their spouses. The peak velocity (PV) at the aortomesenteric portion of the left renal vein (LRV) and the PV ratio between the aortomesenteric and hilar portion of the LRV significantly decreased after surgery (117.9 ± 30.4 cm/s vs 76.6 ± 18.5 cm/s; 7.3 ± 0.7 vs 4.1 ± 0.4). Two patients had complications of mild hydroceles requiring no intervention, and no major complications were observed during and after surgery.

CONCLUSION

Our results suggest that the microsurgical gonadal-inferior epigastric vein anastomosis is both effective and safe to treat patients with gonadal varicose veins caused by the nutcracker phenomenon.

Left renal vein aneurysm in a young woman with renal nutcracker syndrome

A 17-year-old girl presented to our institution with abdominal and pelvic pain found to be due to extrinsic compression of the left renal vein, causing a saccular aneurysm and renal vein dilation with varices consistent with nutcracker syndrome. She was managed with an open aneurysm resection and transposition of the left renal vein.

A case report of a young girl with recurrent hematuria: a missed diagnosis - renal nutcracker syndrome

BACKGROUND

Nutcracker syndrome is an easily missed cause of hematuria in children. It is characterized by left renal vein entrapment between the abdominal aorta and the superior mesenteric artery causing renal venous hypertension. Intermittent hematuria and orthostatic proteinuria with or without abdominal or flank pain are the common clinical manifestations. Presence of variable non-specific symptoms and non-significant physical findings results in a delayed diagnosis.

CASE PRESENTATION

We present a ten -year -old girl with four episodes of painless gross hematuria and recurrent microscopic hematuria since the age of two years. Doppler ultrasound showed left renal vein compression while 3 D computerized tomography angiography confirmed the diagnosis of an anterior nutcracker. The patient was conservatively treated with nutritional support (pediasure complete formula and high calorie food), iron supplements and followed up, monitored for anemia, hypertension and renal insufficiency.

CONCLUSION

Nutcracker syndrome is a rare cause of recurrent gross hematuria in children. A high index of suspicion and proper imaging is needed to reach a proper diagnosis and avoid the psychological and financial stress on the family.

Renal autotransplantation results in pain resolution after left renal vein transposition

Left renal vein transposition is often the preferred treatment of nutcracker syndrome. However, pain returns in some patients despite surgery. One solution to this problem is renal autotransplantation. Here we report our initial results of renal autotransplantation in patients with persistent flank pain despite a previous left renal vein transposition. We used the University of Wisconsin loin pain hematuria syndrome test as a diagnostic maneuver to determine who may benefit from renal autotransplantation; this procedure subsequently resulted in complete pain resolution in all three patients. All patients underwent successful renal autotransplantation and remain pain free. These cases support the test as a diagnostic maneuver to determine which patients may benefit from renal autotransplantation.

A minimally invasive alternative for the treatment of nutcracker syndrome using individualized three-dimensional printed extravascular titanium stents

BACKGROUND

This study was designed to evaluate the clinical and radiographic outcomes of patients with nutcracker syndrome (NCS) who were treated with three-dimensional printing (3DP) extravascular titanium stents (EVTSs). The 3DP EVTS was expected to release the hypertension of the left renal vein (LRV) produced by its compression between the superior mesenteric artery (SMA) and the aorta without causing any complications.

METHOD

The pre-operative kidney model of each patient was printed out to enable surgical planning. After that, the EVTS was designed based on the LRV's primitive physiologic structure using computer-aided design software, and each stent was printed out with a precision setting of 20 μm. Seventeen patients who had been suffering from NCS underwent laparoscopic 3DP EVTS placement. The surgical procedure was designed for the placement of EVTS, taking great care in positioning and fixing the stent. Surgical data, which included patient demographic characteristics as well as pre- and post-operative test results, were collected and analyzed.

RESULTS

The mean duration of surgery was 75 ± 9 min, and the mean blood loss was 20 ± 5 mL. Computed tomography examinations revealed that the pre- and post-operative angle between the SMA and the aorta ranged from 18.7° ± 4.3° to 48.0° ± 8.8° (P < 0.05); in patients with left varicocele, the mean diameter of the left spermatic vein ranged from 3.7 ± 0.5 to 1.3 ± 0.2 mm (P < 0.05). Moreover, Doppler ultrasound examinations showed that the peak velocity of blood flow at the hilar area ranged from 12.4 ± 3.3 to 18.5 ± 3.4 cm/s (P < 0.05). No side effects were observed in the 24 to 42 months following surgery.

CONCLUSION

The findings after 2 years of follow-up suggest that the 3DP EVTS is a safe and effective minimally invasive alternative for the treatment of NCS.

Superior gluteal vein syndrome: an intrapelvic cause of sciatica

The role of malformed or dilated branches of iliac vessels in causing pelvic pain is not well understood. Such vessels may entrap nerves of the lumbosacral (LS) plexus against the pelvic sidewalls, producing symptoms not typically encountered in gynecological practice, including sciatica and refractory urinary and/or anorectal dysfunction. We describe cases of sciatica in which laparoscopy revealed compression of the LS plexus by variant superior gluteal veins (SGVs). In demonstrating an improvement in patient symptoms after decompression, we identify this neurovascular conflict as a potential intrapelvic cause of sciatica. This study is a retrospective case series (Canadian Task Force Classification II-3). Nerve decompression laparoscopies were performed in São Paulo, Brazil. Thirteen female patients undergoing laparoscopy for sciatica with no clear spinal or musculoskeletal causes were included in this study. In all cases, we identified LS entrapment by aberrant SGVs, and performed decompression by vessel ligation. The average preoperative visual analog scale score of 9.62 ± 0.77 decreased significantly to 2.54 ± 2.88 post-operatively (P < 0.001). The success rate (defined as ≥ 50% improvement in visual analog scale score) was 92.3%, over a follow-up of 13.2 ± 10.6 months. Our case series demonstrates a high success rate and significant decrease in pain scores after laparoscopic intrapelvic decompression, thereby identifying pelvic nerve entrapment by aberrant SGVs as a potential yet previously unrecognized cause of sciatica. This intrapelvic neurovascular conflict—the SGV syndrome—should be considered in cases of sciatica with no identifiable spinal or musculoskeletal etiology.

Maternal Venous Hemodynamic Dysfunction in Proteinuric Gestational Hypertension: Evidence and Implications

This review summarizes current knowledge from experimental and clinical studies on renal function and venous hemodynamics in normal pregnancy, in gestational hypertension (GH) and in two types of preeclampsia: placental or early-onset preeclampsia (EPE) and maternal or late-onset (LPE) preeclampsia, presenting at <34 weeks and ≥34 weeks respectively. In addition, data from maternal venous Doppler studies are summarized, showing evidence for (1) the maternal circulation functioning closer to the upper limits of capacitance than in non-pregnant conditions, with intrinsic risks for volume overload, (2) abnormal venous Doppler measurements obtainable in preeclampsia, more pronounced in EPE than LPE, however not observed in GH, and (3) abnormal venous hemodynamic function installing gradually from first to third trimester within unique pathways of general circulatory deterioration in GH, EPE and LPE. These associations have important clinical implications in terms of screening, diagnosis, prevention and management of gestational hypertensive diseases. They invite for further hypothesis-driven research on the role of retrograde venous congestion in the etiology of preeclampsia-related organ dysfunctions and their absence in GH, and also challenge the generally accepted view of abnormal placentation as the primary cause of preeclampsia. The striking similarity between abnormal maternal venous Doppler flow patterns and those observed at the ductus venosus and other abdominal veins of the intra-uterine growth restricted fetus, also invites to explore the role of venous congestion in the intra-uterine programming of some adult diseases.

Robot-Assisted Laparoscopic Left Renal Vein Transposition for the Treatment of Nutcracker Syndrome: A Preliminary Experience

BACKGROUND

The aim of this study was to describe our robot-assisted laparoscopic left renal vein (LRV) transposition experiences for nutcracker syndrome treatment.

METHODS

From August 2016 through May 2017, three patients with nutcracker syndrome underwent robot-assisted laparoscopic LRV transpositions. The patient demographics, surgical outcomes, and postoperative morbidities were reviewed.

RESULTS

Successful surgical procedures were performed in all three patients. The operative times for the three cases were 150, 175, and 162 minutes, respectively, while the LRV anastomosis times were 19, 22, and 13 minutes, respectively. No major perioperative complications were encountered, and the hematuria and flank pain were resolved in all three cases. At the 6-month follow-up, the computed tomography scan showed that the LRV narrowing had disappeared in two of the patients. Although one patient still exhibited LRV flattening, his symptoms were also relieved, and the varicose tributaries spontaneously ceased.

CONCLUSIONS

Robot-assisted laparoscopic LRV transposition can be a viable minimally invasive treatment option for patients with nutcracker syndrome.

Hematuria and Proteinuria in Children

Practice Gap

Pediatricians must be aware of screening indications and the evaluation

and management of a child with hematuria and/or proteinuria.

Objectives

After completing this article, readers should be able to:

1. Understand the common causes of proteinuria and hematuria and be able to differentiate between benign and serious causes.

2. Describe screening techniques for initial evaluation of hematuria and proteinuria.

3. Recognize the criteria for diagnosis of proteinuria and hematuria.

4. Plan the appropriate initial evaluation for hematuria and proteinuria and interpret laboratory findings essential for diagnosis.

5. Recognize serious causes of hematuria and proteinuria that warrant immediate referral.

Surgical Treatment of a Patient With Nutcracker Syndrome via Transposition of the Left Renal Vein

Introduction

Nutcracker syndrome (NCS) is caused by compression of the left renal vein (LRV) between the aorta and the superior mesenteric artery (SMA) where it passes in the fork formed at the bifurcation of these arteries. NCS leads to LRV hypertension, resulting in left flank and abdominal pain, with or without haematuria and pelvic ureteral varices.

Report

The patient was a young female with diagnostic criteria of NCS, with severe clinical manifestations. The patient underwent transposition of the LRV approximately 3.0 cm below the original anatomic site and was anastomosed to the inferior vena cava (IVC) outside the meso-aortic compression zone.

Conclusion

Although NCS is not as common as other clinical scenarios, it may be encountered by physicians in a variety of disciplines, and can cause substantial morbidity and mortality rates. This report addresses the surgical approach used in a particular case, as well as the possible complications and outcomes if not treated in due time.

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A young female patient with diagnostic criteria of NCS, with severe clinical manifestations.

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The patient underwent transposition of the LRV approximately 3.5 cm below the original anatomic site.

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She was then anastomosed to the inferior vena cava (IVC) outside the meso-aortic compression zone.

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The symptoms were masked for an extended period of time, while the patient deteriorated at a rapid pace.

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At 36 months of follow-up the patient remained symptom free.

Evaluation of posterior nutcracker phenomenon using multisection spiral CT

AIM

To prospectively evaluate the epidemiological, anatomical classification, clinical importance, and radiological features of posterior nutcracker phenomenon (PNP) in patients examined with multisection spiral computed tomography (MSCT).

MATERIAL AND METHODS

Patients who underwent abdominal enhanced MSCT from January 2012 to July 2016 were evaluated retrospectively. Combined with the blood, normal biochemistry, and urine tests, patients were assessed retrospectively for renal vein diameter measurements, the compression ratio of blood vessels, gender differences, anatomical classification, percentage of proteinuria and haematuria, and clinical symptoms.

RESULTS

The study included 6,225 consecutive patients, PNP was observed in 2.06% involving the CLRV in 1.22% and retro-aortic left renal vein in 0.84%. The proportion of posterior nutcracker syndrome (PNS) was lower in PNP (17.2%). There was no difference by sex and age in the prevalence of PNP (p>0.05). In patients with urological symptoms, the number of type II abnormalities was more frequent than type Ia and type Ib abnormalities. Meanwhile, the number of type II abnormalities was frequent than the other two types. There was a significant difference between PNS and asymptomatic PNP (aPNP) in all measured values (p<0.001), the ratio was >4, especially in type II abnormalities (ratio >5.0).

CONCLUSIONS

PNP is a type of left renal vein entrapment. It is exceptionally rare and might be underdiagnosed. MSCT and measured values can be useful in diagnosis and recognition.

Co-occurring superior mesenteric artery syndrome and nutcracker syndrome requiring Roux-en-Y duodenojejunostomy and left renal vein transposition: a case report and review of the literature

BACKGROUND

The duodenum and the left renal vein occupy the vascular angle made by the superior mesenteric artery and the aorta. When the angle becomes too acute, compression of either structure can occur. Each type of compression is associated with specific clinical symptoms that constitute a rare disorder. If clinical symptoms are mild, conservative treatment is implemented. However, surgery is often the only solution that can improve quality of life and/or avoid life-threatening complications. This report describes a case of a patient with both types of aortomesenteric compression that required two separate surgeries to alleviate all symptoms.

CASE PRESENTATION

A 20-year-old white woman presented to the Emergency Room complaining of sudden onset severe left flank and lower left quadrant abdominal pain, nausea, and vomiting. A clinical work-up revealed elevated white blood cells and hematuria. She was discharged with a diagnosis of urinary tract infection. Symptoms continued to worsen over the subsequent 2 months. Repeated and extensive clinical work-ups failed to suggest evidence of serious pathology. Ultimately, an endoscopy revealed obstruction of her duodenum, and barium swallow identified compression by the superior mesenteric artery, leading to the diagnosis of superior mesenteric artery syndrome. She underwent a Roux-en-Y duodenojejunostomy. Six weeks later she continued to have severe left-sided pain and intermittent hematuria. Venography revealed compression of the left renal vein, extensive pelvic varices, and significant engorgement of her left ovarian vein. A diagnosis of nutcracker syndrome was made and a left renal vein transposition was performed. Significant improvement was seen after 8 weeks.

CONCLUSIONS

The disorders associated with aortomesenteric compression can lead to serious symptoms and sometimes death. Diagnosis is challenging not only because of the lack of awareness of these rare disorders, but also because they are associated with symptoms that are similar to those seen in less serious diseases. Guidance for health care professionals with respect to relevant radiological and clinical markers needs to be reconsidered in order to clarify the etiology of the diseases and create better diagnostic protocols.