Dr Graham Exelby January 2024
Looking closely at causes for autonomic dysfunction, there are quite a number of areas where compression of the arteries, veins and the accompanying autonomic nerves can occur. These include in the legs, at the origin of the Adductor Canal, some 12 cm above the femoral condyle of the knee, and the Popliteal Compression Syndrome, a common problem in the hypermobile patients that lock their knees back when standing. In the arms and neck, the Thoracic Outlet Syndrome and Jugular Outlet Syndrome. These are dealt with in Thoracic Outlet Syndrome and Internal Jugular Vein Dysfunction- Jugular Outlet Syndrome, Internal Jugular Vein Stenosis and Obstruction. The Popliteal Vein Compression Syndrome is well-described in Dr David Grosser’s blog: https://www.arteries-veins.com/single-post/2017/01/07/popliteal-vein-compression-syndrome-the-main-cause-of-dvt-unrecognised
POTS clinics internationally have made the association of POTS with pelvic congestion (20). Ehlers-Danlos syndrome, POTS, and May-Thurner may interact synergistically to exacerbate symptoms. Ormiston et al (12) found that left common iliac vein stenting for May-Thurner Syndrome can mitigate POTS symptoms by decreasing lower extremity venous pooling. But it is far more complex than this single area of vascular compression.
Within the abdomen the most important we have found while looking at POTS and Dysautonomia are the Median Arcuate, Superior Mesenteric Artery, Nutcracker, Pelvic Congestion and May-Thurner Syndromes. There are often multiples of these, and the symptoms that result from these are varied, and more complex than just arterial or venous obstruction, involving the autonomic pathways and co-morbidities secondary to the compressions.
Even the side of the pelvic congestion is important, the left usually reflective of left renal vein compression (probably with accompanying Azygous system dysfunction). The right sided congestion, usually thought to be secondary to left sided congestion, may be more reflective of Azygous dysfunction, an overloaded spinal venous system (or as research into embryonic vein remnants accelerates, the Cardinal veins.)
Bowdino, Owens and Shaw (23) describe that in 3% of people, the retroperitoneal venous vessels, such as lumbar or hemiazygos vessels, drain into the right renal vein before it enters the inferior vena cava. Scholbach (2) describes blood from an overloaded spinal venous plexus being able leave the spinal canal via intervertebral veins on the right side of the spine, potentially complicating the Azygous system dysfunction.
Does this provides the link to right sided pelvic congestion and fatty liver that is a common co-morbidity in POTS? The common association of POTS with fatty liver has made this a target for future research. NAFLD has now been linked to autonomic dysfunction, and fatigue is a well-known symptom of this.(18) I believe the underlying causes are linked with the vascular compression and autonomic instability that typifies the POTS-like conditions and co-morbidities.
Each compression can affect the autonomic nerves that envelop the vessel affected. These can be sympathetic or parasympathetic, and in renal arteries and veins, the sympathetic innervation regulates blood pressure as well as baroreceptors responses to blood flow and control of NaCl concentration.(19) But there is a “hydraulic” effect as well, that has been seen particularly by Scholbach (2) that can have far-reaching effects as pressure in the valveless spinal vein system increases, with potential effects on intracranial pressure.
Nicolaides, Zambone et al (8) described “the cerebrospinal venous system is usually asymmetric and having a more variable vessel pattern than the arterial system, with the intracranial part mainly composed of parenchymal veins draining into the dural sinuses. Two main systems are responsible for blood collection, the superficial (cortical) system (blood reaches the dural sinuses by cortical veins and drains blood mainly from the cortex and part of the subcortical white matter), and the deep cerebral venous system, composed of internal cerebral veins, the basal vein of Rosenthal and the great cerebral vein of Galen and their tributaries. They drain the deep “periventricular” white and central grey matter “basal ganglia and thalamus” surrounding the lateral and third ventricles, the brainstem and anterior cerebellum which drains into the straight sinus.” (8)
“The vertebral venous system is a valveless system stretching the length of the entire spinal column and it comprises three parts: the internal intraspinal part, the epidural veins, and the extraspinal paravertebral part. The extraspinal part in the neck consists of the vertebral veins (VVs) which accompany the vertebral artery and drain into the innominate vein on the right and into the subclavian vein on the left.”(20)
“Venographic studies have shown that valves may be present at the junction of the vertebral and subclavian veins. The rest of the vertebral venous system, which is a rich plexus, communicates with the deep thoracic and lumbar veins, intercostal veins, the azygos (AZ) and hemiazygos veins. The lumbar hemiazygos arch is connected with the left renal vein representing a major outflow route for shunting blood into the inferior vena cava. The AZ vein represents the final collector and drains into the superior vena cava with an outlet on the posterior aspect just one cm below the brachiocephalic trunks.”(8)
Figure 1. Vertebral Venous Plexus
Figure 2: Enlarged Paraspinal Veins from Left Renal Vein Compression (Nutcracker)
Source: courtesy Dr Zane Sherif. Mermaid Beach Radiology
The origin of venous anomalies is still not completely understood. The answer appears to lie in the evolving research into the Cardinal veins. Kumar, Neyaz and Gupta (22) describe: “Variations of the renal veins and IVC are related to the developmental processes in the foetus. The renal venous collar is made up laterally by the paired dorsal and ventral primitive renal veins on each side, which are linked to the centrally paired ventral subcardinal and dorsal supracardinal veins, and anastomoses of these four craniocaudally oriented subcardinal- supracardinal veins. Different anatomic presentations of the renal veins are encountered depending on the persistence or regression of different components of this primitive circumaortic venous network.”(22)
Figure 3: Anterior Cardinal Veins
Courtesy of Craig Hacking, <a href="https://radiopaedia.org/?lang=gb">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/93162?lang=gb">rID: 93162</a>
From Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body
To try to understand this complex area, start with the Azygous venous system, and its connection to the spinal veins, and where so many of the problems seem to be involved with. The AZ vein represents the final collector and drains into the superior vena cava with an outlet on the posterior aspect just one cm below the brachiocephalic trunks. The lumbar hemiazygos arch is connected with the left renal vein representing a major outflow route for shunting blood into the inferior vena cava.(8)
Figure 4. The Azygous System
Source: OpenStax College, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons. https://upload.wikimedia.org/wikipedia/commons/2/28/2132_Thoracic_Abdominal_Veins.jpg
Figure 5: The Azygous System (schematic)
Source: By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 480, Public Domain, https://commons.wikimedia.org/w/index.php?curid=567249
Piciucchi et al (17) describes “ The azygos system creates an important connection between the superior and inferior venae cavae. The azygos and hemiazygos systems create vital collateral pathways that become a vital shunt in cases of obstruction of the major pathways. The azygos vein, normally measuring about 0.9 cm, can be seen in 75 % of normal chest X-rays. Variations in the size of the azygos vein were described by Milne and co-workers,(21) who identified an azygos enlargement in the supine position or in case of overhydration, renal failure or being in the mid-trimester of pregnancy.”
They also describe that in “Inferior Vena Cava obstruction, intrahepatic venous, portocaval and spider web collateral vessels develop to decompress the liver parenchyma. Extrahepatic collateral vessels include the ascending lumbar veins, which drain into the azygos vein on the right side and into the hemiazygos vein on the left.”
The azygos vein is a unilateral vessel that ascends in the thorax to the right of the vertebral column, carrying deoxygenated blood from the posterior chest and abdominal walls, carrying deoxygenated blood forming a collateral pathway between the superior vena cava and the inferior vena cava, forming part of the azygos venous system. While there is the hemiazygos vein and its accessory on the left side of the body, they are considered tributaries of the azygos vein rather than its left-side equivalent.
The azygos vein is formed by the union of the right ascending lumbar vein and right subcostal veins at around the T12-L2 vertebral level. In addition to receiving the right posterior intercostal veins, the azygos vein communicates with the vertebral venous plexus that drains the back, vertebrae, and structures in the vertebral canal. The azygos vein also receives the mediastinal, oesophageal, and bronchial veins, the hemi-azygos vein, and the accessory hemi-azygos vein.
The hemi-azygos and accessory hemi-azygos veins cross the midline at T9 and T8, respectively, posterior to the aorta, thoracic duct, and oesophagus. In some instances, the hemi-azygos and the accessory hemi-azygos veins combine to form a shared vein crossing the midline at T9 to empty into the azygos vein. The azygous vein enters the thorax through the aortic hiatus in the diaphragm just to the right of the cisterna chyli.(10)
In a clinical situation, “trigger areas” in POTS dysautonomia are commonly seen at the T7-8 region. Case studies have demonstrated tachycardia with rotational stress in this area. T7 has the uppermost diaphragmatic attachment point and this area is the narrowest part of the central canal. As the patients seen with this almost always have scoliosis in this region, it asks the question if this area has a greater susceptibility to venous congestion and activation of the sympathetics that accompany the Azygous system.
In the linking of the Azygous system to POTS, the research by Nicolaides, Zamboni et al (8) into Multiple Sclerosis must be considered, despite the redaction of their management in 2017. They found using venography, multilevel involvement of the Azygous and lumbar venous system (18%), as well as head and neck compression areas as described in Cervical Spine Abnormality, Ehlers-Danlos Syndrome and Vertebral Vascular and Lymphatic Dysfunction.
Inside the spinal canal it fills a vast network of veins, the epidural plexus, that lies on the on the dural sac, a sheath of connective tissue enveloping the spinal cord that swims within this sac in the cerebrospinal fluid. Blood entering the epidural plexus from the left side, via the collaterals of the left renal vein, fill the plexus which may become engorged. Its pressure rises so that the blood is diverted more or less, depending on the actual pressure, up and down the spine and heads to exits with a pressure less than in the left renal vein. (2)
Within the spinal canal, blood can move up or down as the system is valveless. Veins at the level of the intervertebral discs communicate with veins that enter the spinal canal. In the case of nutcracker phenomenon the hemiazygos vein and the ascending lumbar vein are subject to considerably increasing pressure. The blood flow changes its direction into the intervertebral veins, so that eventually renal vein blood is injected into the spinal canal. (2)
Scholbach describes that while blood may leave the spinal canal via intervertebral veins on the right side of the spine, if the pressure is high enough the cerebrospinal fluid is shifted towards the skull and causes a slight but perceptible rise of the pressure inside the skull. This he reports causing dizziness, headache, and exacerbating the Chronic Cerebrospinal Venous Insufficiency documented by Zamboni (8) and others.
Scholbach (2) describes that more frequently the surplus blood inside the epidural plexus and of the other collateral pathways follows simply the force of gravity and flows to veins of the pelvis, mostly via the left ovarian/gonadal vein. This vein often enlarges substantially, becomes painful and meandering and bring renal blood to the left ovary and via its ovarian tube to the uterus and in males to the left testis, where a varicocele develops, and the prostate), leading to Pelvic Congestion Syndrome.
When there is left renal vein compression and no ovarian vein dilatation or pelvic congestion what collaterals are involved?
The kidney is the most vascularized, blood filled organ of the body, second only to the brain. Even at minor flow impediments a substantial amount of blood has to be carried away from the left kidney across the above mentioned collaterals. These collateral vessels are actually the feeder to the renal vein and thus have a much smaller and weaker calibre. The backflow of renal blood to these organs produces a high pressure within these vessels since the congestion pressure from the left renal vein is directly transferred to these organs due to their open communication. An important but not well known collateral vessel, which exists in many people, Scholbach (2) describes a short but large vein to the spinal column, called the réno-rachidien. The other bypasses are the left ovarian or spermatic vein, the ascending lumbar vein, the veins of the ureter, the hemiazygos vein and other veins of the retroperitoneum.
The left renal vein often communicates with the retroperitoneal veins, including the adrenal, lumbar, gonadal and hemiazygous veins. In many cases, the gonadal vein is joined by a lumbar branch before eventual insertion into the left renal vein. Multiple left adrenal veins are seen in 2% of patients and multiple left gonadal veins are seen in 7% of patients.(22)
Figure 6: The Autonomic Nervous System
Source: Carter,H, Gray, H. Anatomy of the Human Body, 1918. Bartleby.com.
Figure 7: Intra-abdominal Autonomic Pathways
Source: Carter,H, Gray, H. Anatomy of the Human Body, 1918. Bartleby.com.
Nutcracker Syndrome
The Nutcracker phenomenon is an entrapment of the left renal vein between the aorta and the superior mesenteric artery. The syndrome is when there is compression plus haematuria and left flank pain. Seen frequently in young girls, young and slender women, pregnant women, people with soft connective tissue and overweight people. Within this angle between the aorta and the superior mesenteric artery runs the left renal vein and the duodenum.
Figure 8: Compression of Left Renal Vein between Superior Mesenteric Artery and Aorta (Nutcracker)
Source: courtesy Dr Zane Sherif. Mermaid Beach Radiology
The blood flow in the left renal vein becomes obstructed, blocking the outflow from the left kidney. Its blood is then forced into tributaries that normally bring blood from their organs towards the left renal vein. This sets these organs under pressure, they swell, their vessels become engorged and the walls of these vessels react with an inflammation. These so called collateral vessels enlarge and go baggy, become varicose veins, which are painful. As Schonbach describes, these fill other collateral vessels, including the spinal venous plexus, thus linking the head and neck to the abdominal “drivers” in POTS and chronic fatigue.
Common accompaniments include abdominal pain and headaches, with symptoms often worse with exercise. Pain is often exacerbated by sitting, standing, walking or riding in vehicles. Males often develop varicocoeles.
Severe orthostatic intolerance associated with left renal vein occlusion may occur.(2) Chronic fatigue associated with high left renal vein/ interior vena cava pressure gradients occur, with relief of fatigue in some patients following surgery to correct the obstruction.(2) Unfortunately surgery does not consistently produce relief of symptoms, implicating the neural compression as being more important in symptom causation than the venous compression itself.
Pelvic Congestion Syndrome
In pelvic congestion, pain in the lower abdomen or in the left testicle results from the diversion of blood from the left kidney to the organs of the pelvis. This additional volume needs to be transported to the inferior vena cava, which runs at the right side of the spine. Within the pelvis a vast network of veins fills the space between the organs, mainly the uterus (prostate), rectum, urinary bladder and vagina. This network takes up the renal blood from the left kidney but may soon be overfilled. If so, symptoms may be present including abdominal pain, increased menstrual cramps, genital pain, pain during bowel movements, urinary discomfort, congestion in the genital region and vulval varicosities. Thrombosis of the deep veins of the left leg, mainly of the calf, and varices of the left leg may develop.(2)
Figure 9: Pelvic Congestion Syndrome
The blood from the left kidney runs into the compressed renal vein then turns downwards via the left ovarian vein into the vast pool of retroperitoneal veins in the pelvis.
Courtesy of Nicolin Hainc, <a href="https://radiopaedia.org/?lang=gb">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/42219?lang=gb">rID: 42219</a>
May-Thurner Syndrome
May-Thurner syndrome is increasingly recognized as a frequent source of leg swelling and a precipitating factor for venous thromboembolism due to an anatomical variant in which the right common iliac artery overlies and compresses the left common iliac vein against the lumbar spine. This variant has been shown to be present in over 20% of the population.(3)
Figure 10: May-Thurner Syndrome
Source: Sudheendra,D. The 5 Vascular Causes of Chronic Pelvic Pain. Get Heathy Veins. https://www.gethealthyveins.com/2021/05/26/the-5-vascular-causes-of-chronic-pelvic-pain-what-every-primary-care-provider-should-know/
Left iliac vein compression from the right common iliac artery, against the posterior fifth lumbar vertebral body, is estimated to comprise 49% to 62% of cases of left lower extremity venous disease. There is some degree of iliac vein compression present as a normal anatomic variant in otherwise healthy patients (>50% compression) in up to 25% of patients.(4) Retrograde flow is sometimes noted in the internal iliac vein.
Symptoms include left-sided abdominal pain radiating into the left thigh, left-sided flank pain. Left leg swelling and increased tendency to varicose veins and thrombosis left leg.(2)
Once again, patients with this compression suffer similar autonomic symptoms, again asking the question of venous microtrauma and microemboli, sympathetic or vagal activation through the coeliac plexus, just as appears likely in the renal vein compression. Once again, it is likely to be a combination of all three.
Median Arcuate Ligament Syndrome (MALS)- also known as Coeliac Artery Compression Syndrome, Dunbar Syndrome, Coeliac Axis Syndrome or Harjola-Marable Syndrome
The median arcuate ligament is the fibrous arch that unites the diaphragmatic crura forming the anterior arc of the aortic hiatus. The coeliac trunk is a major branch of the abdominal aorta, originating anteriorly near the level of the diaphragm and usually in close proximity to the median arcuate ligament.(14)
There is considerable variation in positioning of both the coeliac trunk and the diaphragm. In some, the ligament is positioned more inferiorly relative to the coeliac artery, resulting in compression. The degree of compression typically varies with respiration, most accentuated during end-expiration when the two structures move closer together.(14)
Median Arcuate Ligament Syndrome is caused by compression of the coeliac ganglion, a web of nerves in the upper abdomen located immediately below the diaphragm. Arching over the aorta is the arcuate ligament. Movement of the diaphragm while breathing may irritate the coeliac ganglion leading to pain and autonomic symptoms.(2)
Symptoms may include, and not always associated with intake of food, are clearly related to autonomic dysfunction. It is very commonly misdiagnosed as an eating disorder, but a sound history will usually elucidate the problem. The pain can often be relieved by positional changes, eg standing, and aggravated by lying.
Abdominal pain below the sternum which sometimes radiates like a belt or even into the chest
Loss of appetite
Rapid fullness while eating
Weight loss
Syncope and pre-syncope
Sweating
Tachycardia
Short-lived bouts of diarrhoea.(2)
The Coeliac Artery (or Coeliac Axis or Coeliac Trunk) is a major artery in the abdominal cavity supplying the foregut. Arising from the Aorta, it branches into the Left Gastric Artery, Splenic Artery and Common Hepatic Artery. When visualized on ultrasound, which would show displacement and variable narrowing of the Coeliac Axis, it is an indirect sign of compression of the over-riding Coeliac Ganglion.
Figure 11: Coeliac plexus and Sympathetic Chain
Source: S. Jacob. Human Anatomy, 2008
The Coeliac Plexus
The coeliac plexus is the largest sympathetic plexus and surrounds the coeliac trunk. The plexus receives the greater and lesser splanchnic nerves and also a branch from the right vagus. The two coeliac ganglia, in which the preganglionic fibres of the splanchnic nerves synapse, lie on the crura of the diaphragm. Each ganglion is about 2cm in diameter. A large contribution of preganglionic fibres from the plexus supply the adrenal medulla. The rest of the plexus descends over the abdominal aorta and is distributed to the abdominal viscera as plexuses accompanying the branches of the aorta.
Figures 12, 13, 14: Median Arcuate Ligament Compression
Courtesy of Dr Matt Skalski, <a href="https://radiopaedia.org/?lang=us">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/36837?lang=us">rID: 36837</a>
Courtesy of Domenico Nicoletti, <a href="https://radiopaedia.org/?lang=gb">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/45205?lang=gb">rID: 45205</a>
Courtesy of Sami Elhinnawi, <a href="https://radiopaedia.org/?lang=gb">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/55455?lang=gb">rID: 55455</a>
Traditionally the aetiology of abdominal pain is hypothesized to be ischaemic, due to impaired flow in the coeliac axis secondary to compression by the median arcuate ligament. However, the contribution of a neuropathic component related to the effect on the coeliac plexus has been proposed and described by Weber et al.(15) Kim et al (24) propose a change of name to better explain the pathology involved, to Nutcracker Coeliac Ganglion Abdominal Pain Syndrome.
Figure 15: MALS and Compression of Coeliac ganglion
Source: Kim, J, Kang, M, Jeong,O, Rhee, P. A Median Arcuate Ligament Syndrome Could Be Re-termed as a Nutcracker Celiac Ganglion Abdominal Pain Syndrome.
From this compression of the coeliac plexus causes inflammation and fibrosis, resulting in further compression and neuropathy of the coeliac plexus. This neuropathy triggers aberrant pain in response to eating.
Secondly it may cause remodelling and injury from arterial compression. The coeliac axis can develop post-stenotic dilatation, and may become aneurysmal. It can damage the intimal lining of the artery and could cause dissection. Aneurysmal segments may develop thrombosis and be the source of thromboembolism usually affecting the spleen.
The selection of patients for surgical management is difficult. A study from Queensland in 2017 provided valuable information on patient selection for surgery. Ho et al (25) found patients more likely to respond to decompression if the patients had post-exertional pain. Patients who presented with vomiting and unprovoked pain were unlikely to respond to surgery. In contrast with previous studies, postprandial pain was not found to be predictive of outcome. (14)
They described how surgical management has evolved during the past five decades, but long-term outcomes remain variable, with symptom relief occurring in 65% to 87% of treated patients. In clinical practice, selection of appropriate patients for surgical treatment remains difficult because both clinical and radiographic features of MALS are nonspecific.
In management of nonoperatively treated patients, options included dietary alteration, medical therapy (analgesia, laxatives, and antacid therapy).
Superior Mesenteric Artery Syndrome (SMA, Wilkie Syndrome)
The Superior Mesenteric Artery Syndrome (SMA) is compression of the 3rd part of the duodenum between the abdominal aorta and the superior mesenteric artery, and is an unusual cause of proximal intestinal obstruction. Duodenal compression is usually due to the loss of the intervening mesenteric fat pad between the aorta and SMA, which in turn, results in a narrower angle between the vessels. The fat pad cushion functions to hold the SMA off the spine and protect it from duodenal compression.(16)(86)
Figure 15: Compression of Left Renal Vein and Duodenum in Superior Mesenteric Artery Syndrome (SMA)
Source: courtesy Dr Zane Sherif. Mermaid Beach Radiology
Symptoms are usually vague and non-specific, and can be acute or gradual and is commonly misdiagnosed as an eating disorder. Recent advances in radiology has shown a high incidence of left renal vein compression associated with Superior Mesenteric Artery Syndrome (SMA), providing a potential explanation for intra-abdominal venous (and spinal vein plexus) dysfunction in SMA, previously unable to be explained.
Initial treatment is usually conservative, when acute IV fluid resuscitation and nasogastric tube feeding may be required. Conservative treatment is aimed at restoring the fat pad. Symptoms may include:
Epigastric pain
Nausea
Vomiting
Abdominal distension
Weight loss
Early satiety
Post-prandial pain worse in supine position
Figure 16: SMA Syndrome coexisting with Nutcracker Syndrome.
Angle between abdominal aorta (A) and SMA (B) less than 35 deg.
Source: Shi, Y., Shi, G., Li, Z. et al. Superior mesenteric artery syndrome coexists with Nutcracker syndrome in a female: a case report. BMC Gastroenterol 19, 15 (2019). https://doi.org/10.1186/s12876-019-0932-1
References:
1. Kurklinsky, A., Rooke, T.: Nutcracker Phenomenon and Nutcracker Syndrome
2. Scholbach, T.: Diagnosis and treatment of vascular compression syndromes of the abdomen based on the anatomical features of man and gender-specific characteristics after puberty. https://scholbach.de/wp-content/uploads/2017/09/20170917-vascular-compression-syndromes-website.pdf
3. Peters, M., Syed,R., Katz,M.,Moscona., Press,C., Nijjar,V., Bisharat,M., Baldwin,D.: May-Thurner syndrome: a not so uncommon cause of a common condition, Proc (Bayl Univ Med Cent). 2012 Jul; 25(3): 231–233.
4. Rajachandran, M.,Schainfeld,R.: Diagnosis and Treatment of May-Thurner Syndrome, Vascular Disease Management 2018. https://www.vasculardiseasemanagement.com/content/diagnosis-and-treatment-may-thurner-syndrome
5. Median Arcuate Syndrome: University of Chicago MALS Program http://www.ucmals.com/uploads/1/6/6/7/16670080/1847895_orig.jpg
6. Wikipedia: Median Arcuate Ligament Syndrome. https://en.wikipedia.org/wiki/Median_arcuate_ligament_syndrome
7. Mylankal, K.: Venous Compression. http://www.vascularcareadelaide.com.au/vein-compression.html
8. Nicolaides AN, Morovic S, Menegatti E, Viselner G, Zamboni P. Screening for chronic cerebrospinal venous insufficiency (CCSVI) using ultrasound: recommendations for a protocol. Funct Neurol. 2011 Oct-Dec;26(4):229-48. PMID: 22364944; PMCID: PMC3814564
9. Shin MS, Ho KJ. Clinical significance of azygos vein enlargement: radiographic recognition and etiologic analysis. Clin Imaging. 1999 Jul-Aug;23(4):236-40. doi: 10.1016/s0899-7071(99)00141-2. PMID: 10631900.
10. Donohue, J. Anatomy, Thorax, Azygous Veins. StatPearls. 2023. https://www.ncbi.nlm.nih.gov/books/NBK554430/#:~:text=The%20azygos%20vein%20is%20a,top%20of%20the%20thoracic%20vertebrae.
11. POTS Syndrome. Cardiovascular Health Clinic. https://cvhealthclinic.com/conditions-treated/postural-orthostatic-tachycardia-syndrome/#:~:text=We%20have%20found%20that%20many,brain%20difficult%2C%20causing%20associated%20symptoms
12. Ormiston CK, Padilla E, Van DT, Boone C, You S, Roberts AC, Hsiao A, Taub PR. May-Thurner syndrome in patients with postural orthostatic tachycardia syndrome and Ehlers-Danlos syndrome: a case series. Eur Heart J Case Rep. 2022 Apr 9;6(4):ytac161. doi: 10.1093/ehjcr/ytac161. PMID: 35620060; PMCID: PMC9131024.
13. Weber JM, Boules M, Fong K, Abraham B, Bena J, El-Hayek K, Kroh M, Park WM. Median Arcuate Ligament Syndrome Is Not a Vascular Disease. Ann Vasc Surg. 2016 Jan;30:22-7. doi: 10.1016/j.avsg.2015.07.013. Epub 2015 Sep 10. PMID: 26365109.
14. Gaillard F, Alhusseiny K, Hacking C, et al. Celiac artery compression syndrome. Reference article, Radiopaedia.org. https://doi.org/10.53347/rID-1143
15. Weber JM, Boules M, Fong K, Abraham B, Bena J, El-Hayek K, Kroh M, Park WM. Median Arcuate Ligament Syndrome Is Not a Vascular Disease. Ann Vasc Surg. 2016 Jan;30:22-7. doi: 10.1016/j.avsg.2015.07.013. Epub 2015 Sep 10. PMID: 26365109.
16. Van Horne, N, Jackson, J. Superior Mesenteric Artery Syndrome. StatPearls. 2023. https://www.ncbi.nlm.nih.gov/books/NBK482209/#:~:text=Superior%20mesenteric%20artery%20(SMA)%20syndrome,and%20the%20superior%20mesenteric%20artery.
17. Piciucchi S, Barone D, Sanna S, Dubini A, Goodman LR, Oboldi D, Bertocco M, Ciccotosto C, Gavelli G, Carloni A, Poletti V. The azygos vein pathway: an overview from anatomical variations to pathological changes. Insights Imaging. 2014 Oct;5(5):619-28. doi: 10.1007/s13244-014-0351-3. Epub 2014 Aug 30. PMID: 25171956; PMCID: PMC4195836.
18. Frith J, Newton JL. Autonomic dysfunction in chronic liver disease. Hepat Med. 2011 Aug 23;3:81-7. doi: 10.2147/HMER.S16312. PMID: 24367224; PMCID: PMC3846459.
19. Joshua J. Kirkpatrick; Spencer Foutz; Stephen W. Leslie. Anatomy, Abdomen and Pelvis: Kidney Nerves, 2023. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK459339/
20. Ormiston CK, Padilla E, Van DT, Boone C, You S, Roberts AC, Hsiao A, Taub PR. May-Thurner syndrome in patients with postural orthostatic tachycardia syndrome and Ehlers-Danlos syndrome: a case series. Eur Heart J Case Rep. 2022 Apr 9;6(4):ytac161. doi: 10.1093/ehjcr/ytac161. PMID: 35620060; PMCID: PMC9131024.
21. Bass JE, Redwine MD, Kramer LA, Huynh PT, Harris JH Jr. Spectrum of congenital anomalies of the inferior vena cava: cross-sectional imaging findings. Radiographics. 2000 May-Jun;20(3):639-52. doi: 10.1148/radiographics.20.3.g00ma09639. PMID: 10835118.
22. Kumar S, Neyaz Z, Gupta A. The Utility of 64 Channel Multidetector CT Angiography for Evaluating the Renal Vascular Anatomy and Possible Variations: a Pictorial Essay. Korean J Radiol. 2010 May-Jun;11(3):346-354. https://doi.org/10.3348/kjr.2010.11.3.346
23. Cole S. Bowdino; Justin Owens; Palma M. Shaw. Anatomy, Abdomen and Pelvis, Renal Veins, 2023. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK538298/
24. Kim, J, Kang, M, Jeong,O, Rhee, P. A Median Arcuate Ligament Syndrome Could Be Re-termed as a Nutcracker Celiac Ganglion Abdominal Pain Syndrome. J Neurogastroenterol Motil 2023 https://doi.org/10.5056/jnm22158
25. Ho KKF, Walker P, Smithers BM, Foster W, Nathanson L, O'Rourke N, Shaw I, McGahan T. Outcome predictors in median arcuate ligament syndrome. J Vasc Surg. 2017 Jun;65(6):1745-1752. doi: 10.1016/j.jvs.2016.11.040. Epub 2017 Feb 8. PMID: 28189355.
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