Anatomy, Abdomen and Pelvis, Superior Mesenteric Vein


Article Author:
Andrew Broussard


Article Editor:
Navdeep Samra


Editors In Chief:
Kranthi Sitammagari
Mayank Singhal


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Kyle Blair
Trevor Nezwek
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Daniyal Ameen
Altif Muneeb
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes
Komal Shaheen
Sandeep Sekhon


Updated:
8/12/2019 6:07:51 PM

Introduction

The superior mesenteric vein (SMV) is a major venous tributary of the abdominal cavity. Embryologically derived in association with the vitelline vein, the superior mesenteric vein lies lateral to the superior mesenteric artery (SMA) and serves to drain the vast majority of the organs of the abdominal cavity. At the most superior aspect, the superior mesenteric vein joins with the splenic vein, ultimately forming the portal vein. At the mesenteric root, it is of utmost importance that the vascular anatomy is correctly identified to perform complex abdominal surgical procedures. There are several clinical complications involving the superior mesenteric vein that clinicians must readily identify due to their life-threatening nature. This article will serve as a comprehensive review of the anatomy, embryology, function, and clinical significance of the superior mesenteric vein.

Structure and Function

The superior mesenteric vein collects the majority of the venous blood from the jejunum and ileum. According to literature reviewing computed tomography scans of the mesenteric vascular relationships, within the first three 3 cm of their respective origins, the superior mesenteric vein lies lateral to the superior mesenteric artery on the right side. As it ascends, the superior mesenteric vein normally remains on the right side of the superior mesenteric artery. When located to the left of the artery, this can represent either midgut malrotation, a resultant adjacent tumor compression, or a transient phenomenon of a normally rotated midgut.[1][2] The superior mesenteric vein receives many tributaries to drain the various organs of the gastrointestinal system. The superior mesenteric vein drains a portions of the large intestine up to the splenic flexure by the right colic and middle colic veins, the pancreas via the inferior pancreaticoduodenal veins, the transverse colon by means of the middle colic vein, the stomach via the right gastroepiploic vein, the appendix by the ileocolic vein, as well as the small intestine through various venous plexuses.[1][3] The superior mesenteric vein continues to ascend superiorly, until it passes posteriorly to the neck of the pancreas and ultimately anastomoses with the splenic vein to form the portal vein.[3] Via the portal vein, the blood from all of the gastrointestinal organs continues into the liver.

Embryology

When the human embryo is 21 days old, there are three pairs of essential veins supplying and draining the embryo: the vitelline veins, the umbilical veins, and the cardinal veins. Historically, literature has suggested that the superior mesenteric vein remains in the adult human as a remnant of the regressed left vitelline vein. Recent literature has suggested that, although the vitelline vein contributes to the superior mesenteric vein, it is not the sole embryological basis of the vein. This recent 2017 study, which studied serial sections of 5- to 6-week old embryos, suggests that the superior mesenteric vein secondarily develops within the mesentery during or after regression of peripheral courses of the left vitelline vein. [4] This study describes the sequence of mesenteric vasculature development as such. The midgut mesentery contains both the superior mesenteric artery and a long peritoneal fold containing the regressing left vitelline vein. This peritoneal fold was closely associated, but not fused, with the arterial mesentery along its ascension. As the vitelline vein continues to regress within this mesentery, a tissue cleft can appear within the mesentery along the superior mesenteric artery. This tissue cleft is observed to be communicating with the regressing left vitelline vein at the superior end of the peritoneal folds. The superior mesenteric vein is considered to develop from this tissue cleft. [4] Rather than the vitelline vein being the primitive basis for the superior mesenteric vein, this study suggests the only contributions of the vitelline vein is the portion of the portal vein at the conflux of the superior mesenteric and splenic veins. 

Physiologic Variants

Often, surgeons request preoperative CT angiography to assess for any existing anatomical variations as well as accurate imagery of the disease process relative to the mesenteric vasculature in patients undergoing intra-abdominal procedures. Imaging studies have shown that there can be a single main trunk of the superior mesenteric vein, which possesses a variable-length (5 to 50 mm) before dividing into the right and left intestinal branches.[5] A common variation is where the superior mesenteric vein is comprised of two trunks, where the two large mesenteric branches directly drain into the splenoportal confluence. The left superior mesenteric vein trunk frequently runs along the ventral side of the superior mesenteric artery, a relationship that proves important in arterial ligations during pancreaticoduodenectomy surgeries. The variants among the mesenteric tributaries are vast and very complex. Relevant variants to note: the gastrocolic trunk, one of the main tributaries of the superior mesenteric vein composed of the right gastroepiploic vein and the colonic drainage veins, is observed to drain into the main trunk of the superior mesenteric vein or the right intestinal branch of the superior mesenteric vein. The first jejunal branch of the superior mesenteric vein, which drains the duodenojejunal flexure and first jejunal loop, has been observed to drain into either the main trunk of the superior mesenteric vein or into the left intestinal branch.[6] As previously mentioned, the paths of the mesenteric veins draining the colonic tributaries and pancreatic head are very diverse and complex. The utility of preoperative imaging allows appropriate mapping and reduces both operative times and intraoperative complications.

Clinical Significance

There are several clinical implications involving the superior mesenteric vein that clinicians must be vigilant about due to the drastic complications and fatal progression. The most serious of which is pylephlebitis, which is the presence of portal mesenteric venous thrombosis with or without bacteremia within 30 days of an intra-abdominal inflammatory process. Extension into the superior mesenteric vein, termed portomesenteric venous thrombosis, is a subtype of pylephlebitis with an incidence of 2.7 per 100000 person-years. Pylephlebitis was universally fatal before the advent of antibiotics, and now has a reported mortality rate of 10% to 32%. The most common causes of pylephlebitis are diverticulitis, acute appendicitis, inflammatory bowel disease, pancreatitis, and gastroenteritis.[2] Patients commonly present with fever, abdominal pain, hepatic dysfunction, and bacteremia.  Appropriate antibiotic use has proven to be the mainstay of treatment, drastically improving prognosis when initiated early in the disease course. Small bowel resection is also indicated for suspected wide bowel necrosis and peritonitis, which are complications of pylephlebitis. Anticoagulation therapy remains a controversial treatment modality as no randomized control trials have proven its efficacy, but studies have shown anticoagulation to be useful in patients with hypercoagulability, Bacteroides pathogens, or recanalization procedures.[2]

In contrast, isolated superior mesenteric venous thrombosis (SMVT) is reported to have milder disease progression compared to portomesenteric venous thrombosis, due to the extensive venous collateral circulation preventing bowel infarction.[7] SMVT is most commonly the result of malignancy, peritonitis, hypercoagulable state, protein C deficiency, polycythemia vera, recent abdominal surgery, portal hypertension, or sepsis. Post-operatively, post-splenectomy patients are found to have the highest incidence of SMVT.[7] These patients present with a myriad of diffuse, colicky abdominal pain, fever, nausea, hematemesis, melena, and abdominal distension with reported symptom duration averaging 12 days.[2][7] Computed tomography imaging is the gold standard in diagnosis. Before recent improvements in computed tomographic imaging, clinicians commonly mistook SMVT  for superior mesenteric artery ischemia. These improvements in imaging have allowed for more rapid identification, diagnosis, and treatment of SMVT, thus improving clinical outcomes. The appearance of SMVT on CT scan includes enlargement of the thrombosed vein as compared to the normal vein, a distinctly defined vascular wall with a rim of increased density, and a central region of low attenuation of contrast representing the thrombus within the vessel itself.[7] Treatment is determined depending on the severity and duration of disease and consists of appropriate antibiotic use, anticoagulation, surgical thrombectomy or interventional thrombolysis, or small bowel segmental resection.

Traumatic injuries to the superior mesenteric vein account for 0.1% of trauma admissions, but they are associated with a steep mortality rate of 45 to 52.7%. The mechanism of these injuries are often penetrating injuries but increasingly occur due to high-speed motor vehicle collisions. Studies indicate that hemodynamic stability upon presentation, the severity of the vascular injury, and the degree of comorbid injuries are the most important factors that influence mortality rates.[8] These patients present with hemorrhagic shock, hyperthermia, acidosis, and coagulopathy attributed to the superior mesenteric vein injury as well as other injuries at the time of presentation. The most common to least common associated injuries include injuries to the small bowel, pancreas, inferior vena cava, duodenum, stomach, colon, liver, abdominal aorta, and kidney. These patients often warrant an immediate exploratory laparotomy, but a preoperative CT scan can also establish the diagnosis if the patient is hemodynamically stable.[8] The mainstay of initial management for these patients is damage control. There are two approaches to superior mesenteric vein injuries that are continuous topics of debate: repair versus ligation. [9] The ultimate determining factors that guide management are the patient's stability and coexisting injuries. Repair is not suitable for unstable patients as it is more time-consuming when compared to ligation. However, repair has been shown to reduce the postoperative incidence and severity of bowel edema.[8] Superior mesenteric vein ligation is an appropriate management option, especially for hemodynamically unstable patients. To proceed with ligation, adequate collateral flow within the portal system via the inferior mesenteric vein and portosystemic branches is vital.[8][9] If there is a lack of collateral flow, bowel viability becomes a significant concern. Adverse events following ligation include systemic hypotension/splanchnic hypertension syndrome, venous congestion, bowel ischemia, and necrosis.


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Anatomy, Abdomen and Pelvis, Superior Mesenteric Vein - Questions

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A 68-year-old man with confirmed pancreatic cancer within the head of the pancreas undergoes a pancreaticoduodenectomy. During the operation, the attending physician identifies the portal vein. Ligation of which of the following vessels will result in compromise to this vessel?

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During an intra-abdominal procedure, the surgeon notices that the patient’s superior mesenteric vein is located on the left side in relation to the superior mesenteric artery. Which of the following is the most likely explanation for this finding?



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A 48-year-old man is brought to the emergency department following a motor vehicle accident. On presentation, his vital signs reveal a blood pressure of 84/52 mmHg, heart rate 118/min, temperature 39 C, and respiratory rate 22/min. His FAST scan is positive for fluid within the abdominal cavity. Once rush rolled to the operating room, the patient is found to have an injury to the superior mesenteric vein. Collateral vasculature by means of the inferior mesenteric vein as well as the portosystemic branches are intact. Which of the following is the next best step in the management of this patient?



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During an intra-abdominal operation, the surgeon is attempting to locate the superior mesenteric vein (SMV) to ensure collateral blood flow is adequate. Which anatomical landmark is most effective in aiding the identification of this vein?



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A 67-year-old man recovering from a severe bout of diverticulitis reports increased diffuse abdominal pain, nausea, and vomiting over the last two days. His vital signs show a temperature of 101.2 F, heart rate 106/min, blood pressure 94/58 mmHg, and respiratory rate 16/min. On his most recent routine blood work, his white blood cell count, AST, and ALT have all increased from the day prior. Repeat CT scan shows a suspected thrombus within the portal vein that spans to the upper portion of the superior mesenteric vein. Portomesenteric venous thrombosis is suspected. If the patient's treatment continues to be delayed, what is the most likely complication this patient will develop?



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Anatomy, Abdomen and Pelvis, Superior Mesenteric Vein - References

References

Chou CK,Mak CW,Hou CC,Chang JM,Tzeng WS, CT of the mesenteric vascular anatomy. Abdominal imaging. 1997 Sep-Oct;     [PubMed]
Abe H,Yamamoto M,Yanagisawa N,Morimoto R,Murakami G,Rodríguez-Vázquez JF,Abe S, Regressing vitelline vein and the initial development of the superior mesenteric vein in human embryos. Okajimas folia anatomica Japonica. 2017;     [PubMed]
Nesgaard JM,Stimec BV,Bakka AO,Edwin B,Ignjatovic D, Navigating the mesentery: a comparative pre- and per-operative visualization of the vascular anatomy. Colorectal disease : the official journal of the Association of Coloproctology of Great Britain and Ireland. 2015 Sep;     [PubMed]
Cho JW,Choi JJ,Um E,Jung SM,Shin YC,Jung SW,Kim JI,Choi PW,Heo TG,Lee MS,Jun H, Clinical Manifestations of Superior Mesenteric Venous Thrombosis in the Era of Computed Tomography. Vascular specialist international. 2018 Dec;     [PubMed]
Graf O,Boland GW,Kaufman JA,Warshaw AL,Fernandez del Castillo C,Mueller PR, Anatomic variants of mesenteric veins: depiction with helical CT venography. AJR. American journal of roentgenology. 1997 May;     [PubMed]
Sakaguchi T,Suzuki S,Morita Y,Oishi K,Suzuki A,Fukumoto K,Inaba K,Kamiya K,Ota M,Setoguchi T,Takehara Y,Nasu H,Nakamura S,Konno H, Analysis of anatomic variants of mesenteric veins by 3-dimensional portography using multidetector-row computed tomography. American journal of surgery. 2010 Jul;     [PubMed]
Rosen A,Korobkin M,Silverman PM,Dunnick NR,Kelvin FM, Mesenteric vein thrombosis: CT identification. AJR. American journal of roentgenology. 1984 Jul;     [PubMed]
Phillips B,Reiter S,Murray EP,McDonald D,Turco L,Cornell DL,Asensio JA, Trauma to the Superior Mesenteric Artery and Superior Mesenteric Vein: A Narrative Review of Rare but Lethal Injuries. World journal of surgery. 2018 Mar;     [PubMed]
Asensio JA,Petrone P,Garcia-Nuñez L,Healy M,Martin M,Kuncir E, Superior mesenteric venous injuries: to ligate or to repair remains the question. The Journal of trauma. 2007 Mar;     [PubMed]

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