WrongDoctors

Introduction

Mesenteric venous thrombosis (also known as visceral venous thrombosis) is a rare but lethal form of mesenteric ischemia (see the image below). Antonio Hodgson first described mesenteric ischemia in the latter part of the 15th century. In 1895, Elliot first described mesenteric venous thrombosis as a cause of mesenteric ischemia. By the turn of the 19th century, many review articles and texts were describing the recent advances in the characterization and treatment of mesenteric ischemia, particularly venous thrombosis. In 1935, Warren and Eberhard reported that intestinal infarction resulted from ischemia due to venous thrombosis, and they reported a mortality rate of 34% in patients with venous thrombosis after resection. Unfortunately, despite improvements in therapy, this mortality rate still holds.

Problem

Mesenteric venous thrombosis is an insidious disease with a high mortality rate typically attributed to the long delay in diagnosis. Patients with this condition benefit from rapid diagnosis and expedient surgical therapy.

Mesenteric venous thrombosis is one of many causes of mesenteric ischemia, and the mechanism has been well described. Once treated, patients with this condition have a fairly good prognosis, and long-term outcomes are good if patients receive long-term anticoagulant therapy.

Frequency

Mesenteric venous thrombosis accounts for approximately 10-15% of all cases of mesenteric ischemia. This accounts for 0.006% of hospital admissions. Venous thrombosis is found in approximately 0.001% of patients who undergo exploratory laparotomy.

Etiology

The risk of acute mesenteric venous thrombosis increases in patients with hypercoagulable states (eg, polycythemia vera, protein C and S deficiencies¹ ), visceral infection, portal hypertension, perforated viscus, blunt abdominal trauma, malignancy, previous abdominal surgery (open or laparoscopic), or pancreatitis and in patients who smoke. Women taking oral contraceptives are also at increased risk of venous thrombosis. Patients who have undergone splenectomy,^2,3 colectomy, and Roux-en-Y gastric bypass^4,5 are at increased risk of subsequent portal venous thrombosis, which rarely results in bowel infarction. A CT scan demonstrating mesenteric venous thrombosis is shown below. Malignancy may cause thrombosis because of a hypercoagulable state or by direct extension of the tumor. The most common cause seems to be intra-abdominal sepsis. No underlying cause is found in 25-50% of patients diagnosed with mesenteric venous thrombosis.

Pathophysiology

While the mesenteric arterial system may carry 25-40% of the cardiac output at one time, the venous system typically carries 30%. The mechanism that causes ischemia is a massive influx of fluid into the bowel wall and lumen, resulting in systemic hypovolemia and hemoconcentration. Resulting bowel edema and decreased outflow of blood secondary to venous thrombosis impede the inflow of arterial blood, which leads to bowel ischemia. While bowel ischemia is detrimental to the patient, the resulting multiple organ system failure actually accounts for the increased mortality rate.

In a study of mortality factors in 31 patients with mesenteric venous thrombosis, Abu-Daff et al determined that 30-day mortality in these patients was strongly linked to colonic involvement in ischemia and to short-bowel syndrome.⁶ Lack of anticoagulation also may have been a factor. Five-year mortality, according to the investigators, was primarily related to short-bowel syndrome.

Presentation

Patients with mesenteric venous thrombosis have an insidious onset of symptoms described as vague abdominal discomfort that typically evolve over 7-10 days.

Patients may have a condition that predisposes them to a hypercoagulable state, which may be elicited by taking a thorough history. Cancer, polycythemia vera, or a history of deep vein thrombosis or pulmonary embolus are important risk factors that should be elicited from the history. Patients presenting with pancreatitis or signs of intra-abdominal infection should be considered predisposed to developing mesenteric venous thrombosis.

Patients may have a distended abdomen and guaiac-positive stool samples. If the patient has an underlying intra-abdominal infection, peritoneal signs may be elicited and a palpable abdominal mass may be felt. As with acute mesenteric ischemia, patients may report pain disproportionate to that normally elicited during a physical examination.

Paracentesis may demonstrate bloody peritoneal fluid; however, this occurs after bowel infarction and, therefore, is a late sign.

Unfortunately, laboratory examinations are not much help for confirming the diagnosis of venous thrombosis. Laboratory studies help more to suggest, rather than exclude, the diagnosis. Requisite laboratory studies include prothrombin time (PT), activated partial thromboplastin time (aPTT), complete blood count (CBC, which may reveal leukocytosis and/or hemoconcentration), and chemistries (which may show metabolic acidosis). Leukocytosis and acidosis are the most specific laboratory findings in patients with ischemia. Unfortunately, they are late findings. Evaluate patients for protein C and S deficiencies; antithrombin III deficiency; and abnormalities in lupus anticoagulant, anticardiolipin antibody, and platelet aggregation.

Obtain chest films and electrocardiograms (ECGs). Additionally, computed tomography (CT) scanning and angiography have proven equally reliable in helping confirm the diagnosis of acute venous occlusion, although some researchers consider CT scanning to be the diagnostic test of choice. A CT scan of the abdomen may show an enlarged mesenteric or portal vein with sharp definition of the venous wall and low density within the vein. An arteriogram may show vasospasm, contrast in the bowel lumen, nonvisualized venous system, reflux of contrast into the aorta, and finally, absent flow to necrotic bowel areas. A duplex scan of the mesenteric vessels is beneficial only if used early.

Despite all of these diagnostic indicators, the diagnosis of venous thrombosis is usually confirmed during laparotomy or autopsy. Only after other causes of a hypercoagulable state have been excluded can a patient be considered to have idiopathic venous thrombosis.

Indications

Indications for surgery in patients with acute mesenteric venous thrombosis include signs of peritonitis, possible bowel infarction,⁷ and hemodynamic instability.

Relevant Anatomy

Mastery of the anatomy of the mesenteric vessels is key to understanding and treating patients with mesenteric ischemia. The endless array of vascular variations can make this difficult. The celiac axis, the superior mesenteric artery, and the inferior mesenteric artery supply the foregut, midgut, and hindgut, respectively.

The anatomy of the arterial system is described in detail in the eMedicine topics Mesenteric Artery Ischemia andMesenteric Artery Thrombosis.

The venous system, for the most part, parallels the arterial system. The superior mesenteric vein (SMV) is formed by the jejunal, ileal, ileocolic, right colic, and middle colic veins, which drain the small intestine, cecum, ascending colon, and transverse colon. The right gastroepiploic vein drains the stomach to the SMV, while the inferior pancreaticoduodenal vein drains the pancreas and duodenum. The inferior mesenteric vein drains the descending colon, the sigmoid colon, and the rectum through the left colic vein, the sigmoid branches, and the superior rectal vein, respectively. The inferior mesenteric vein joins the splenic vein, which then joins the SMV to form the portal vein, which enters the liver.

Contraindications

If bowel infarction is probable, acute mesenteric thrombosis is a surgical emergency and should be treated without hesitation.

Laboratory Studies

• Unfortunately, laboratory studies are not much help in confirming the diagnosis of venous thrombosis. Laboratory studies help more to suggest, rather than exclude, the diagnosis.
  • Obligatory studies include PT, aPTT, CBC (which may reveal leukocytosis and/or hemoconcentration), and chemistries (which may show metabolic acidosis).
  • Evaluate patients for protein C and S deficiencies; antithrombin III deficiency; and abnormalities in lupus anticoagulant, anticardiolipin antibody, and platelet aggregation.

Imaging Studies

• Plain radiographs may show nonspecific findings, such as dilated loops of bowel with air-fluid levels. Air in the portal system may also be observed on plain radiographs, although this is rare.
• CT scanning (see the image below) is the diagnostic test of choice in patients stable enough to undergo the procedure.¹
  • 
    

    

    Computed tomography (CT) scan demonstrating cavernous change of the superior mesenteric vein, a consequence of venous thrombosis.

  • CT scans may show an enlarged mesenteric or portal vein with sharp definition of the venous wall and low density within the vein (thrombus).
  • Other findings, such as gas in the wall of the bowel, fat streaking, and thickened bowel wall, have been described.
• Magnetic resonance imaging (MRI) is also very sensitive, but because of cost and the time required for the examination, it is not as practical as CT scanning.
• In a few studies, duplex ultrasonography of the visceral system has been found to be as effective as CT scanning.
  • Duplex scans of the mesenteric vessels are beneficial only if used early.
  • Some researchers believe that duplex scans should be used as a first-line diagnostic tool in any patient thought to have this diagnosis.

Other Tests

• Perform an ECG to evaluate cardiac status.

Diagnostic Procedures

• An arteriogram may show vasospasm, contrast in the bowel lumen, nonvisualized venous system, reflux of contrast into the aorta, and, finally, absent flow to necrotic bowel areas.
• CT scanning and angiography have proven equally reliable in helping confirm the diagnosis of acute venous occlusion, although some researchers consider CT scanning to be the diagnostic test of choice.
• CT angiography and gadolinium-enhanced MR angiography enable volumetric acquisitions with the patient holding only a single breath, and they offer excellent diagnostic capabilities for patients with venous thrombosis.

• Treatment

  Medical Therapy

  • The goals of the initial treatment of venous thrombosis are defining the underlying cause of the patient's hypercoagulable state and treating it appropriately.¹
  • Patients with polycythemia should undergo phlebotomy, while those with clotting abnormalities should receive anticoagulation therapy with heparin.
  • After achieving appropriate anticoagulation, start patients on long-term warfarin.
  • Lytic therapy with urokinase, streptokinase, or tissue plasminogen activator has been found to be beneficial in some cases. Mechanical transhepatic thrombectomy has been described in one patient.⁸
  • Other supportive measures, such as nasogastric decompression, fluid resuscitation, and bowel rest, should be instituted.

  Surgical Therapy

  • Surgery is required only in patients with signs of bowel infarction or peritonitis.¹
  • When laparotomy reveals acute venous thrombosis, surgically remove the involved bowel and reanastomose the remaining bowel.
  • Direct venous surgery to remove the clot is usually unsuccessful and is best reserved for patients with portal or superior mesenteric vein involvement.
  • Reports of diagnostic laparoscopy in patients with venous thrombosis suggest this modality may have some use in preventing fruitless laparotomies in these patients; however, the decreased mesenteric blood flow that occurs with laparoscopy may worsen bowel ischemia.
  • Patients with severe intestinal loss due to mesenteric venous thrombosis may be considered for intestinal transplantation in specialized centers.
  • Seriously consider a second-look laparotomy, especially in patients with significant bowel involvement, to minimize the amount of bowel loss.

  Preoperative Details

  • Immediately replete fluids in patients with acute ischemia, and correct any acid-base abnormalities; then, operate without delay.
  • Because of the massive amount of blood lost from the circulatory system to the bowel, provide patients with blood transfusions without hesitation. Type and crossmatch 4 units of packed red blood cells before surgery.
  • Start all patients on broad-spectrum antibiotic therapy before the operation.
  • Immediately begin anticoagulation therapy.
  • Vasodilators have not proven effective in the treatment of venous thrombosis.

  Intraoperative Details

  • Establish viability during direct visualization of the bowel. Look for peristalsis, and observe the color of the bowel. Hemorrhagic, edematous bowel suggests visceral thrombosis as the cause of ischemia.
  • One gram of intravenous fluorescein followed by bowel examination under Wood lamp illumination can delineate poorly perfused bowel. Intraoperative Doppler studies are not as effective as fluorescein studies in determining venous thrombosis.
  • Anticoagulation therapy with intravenous heparin should be continued intraoperatively.

  Postoperative Details

  • Postoperative care includes close monitoring of blood pressure and hemoglobin parameters to evaluate for sepsis or hemorrhage.
  • Patients should have heparin anticoagulation continued postoperatively to reduce thrombotic events. Studies have shown that 60% of cases of rethrombosis of the mesenteric vein occur at the site of reanastomosis, probably because of local thrombotic factors. This finding demonstrates the importance of maintaining the patient on postoperative heparin therapy.⁹
  • Patients require a workup for a hypercoagulable state if this was not accomplished preoperatively.
  • A patient can be expected to have a postoperative ileus due to bowel reperfusion.
  • Unlike patients with arterial ischemia, patients with venous thrombosis do not require a second-look laparotomy unless progression of the disease is possible, which typically occurs in 40% of patients.

  Follow-up

  • Because of the high incidence of concomitant vascular disease, patients require close monitoring.
  • Perform routine evaluations of the PT, aPTT, and international normalized ratio to ensure the adequacy of anticoagulation therapy.

  Complications

  Because patients with venous thrombosis are typically in a hypercoagulable state, the incidence of deep venous thrombosis is increased. Proper anticoagulation therapy and liberal use of sequential compression stockings can help prevent this postoperative complication.

  Patients should have a Swan-Ganz catheter kept in place postoperatively to monitor cardiac and pulmonary status.

  Because patients become acutely hypovolemic, acute renal failure may occur. Keeping the patient well hydrated and administering mannitol before the aorta is cross-clamped can prevent acute renal failure.

  Inform patients of other possible complications, including bleeding, infection, bowel infarction, and prolonged ileus.

  Outcome and Prognosis

  Acute venous thrombosis has a 30% mortality rate with a 25% recurrence rate without anticoagulant therapy. Anticoagulant therapy combined with surgery is associated with the lowest recurrence rate (~3-5%). Patients presenting with peritonitis and infarcted bowel have a prolonged and complicated course. Of all etiologies of mesenteric ischemia, venous thrombosis carries the best prognosis.¹⁰ Survival has improved over the last 4 decades.

  Multimedia

  (Enlarge Image)

  Media file 1: Computed tomography (CT) scan demonstrating thrombosis of the superior mesenteric vein.

  (Enlarge Image)

  Media file 2: Computed tomography (CT) scan demonstrating thrombosis of the portal vein.

  (Enlarge Image)

  Media file 3: Computed tomography (CT) scan demonstrating cavernous change of the superior mesenteric vein, a consequence of venous thrombosis.