Acute superior mesenteric vein thrombosis
Acute superior mesenteric vein thrombosis is one of the less common causes of intestinal ischaemia. Often despite thrombosis of the SMV, small bowel necrosis does not occur, presumably due to persistent arterial supply and some venous drainage via collaterals.
For a general discussion refer to intestinal ischaemia.
Compared to acute superior mesenteric artery occlusion or ischaemia secondary to small bowel obstruction, acute superior mesenteric vein thrombosis is uncommon, accounting for only 5-15% of all cases of acute mesenteric ischemia 1-3.
Acute superior mesenteric vein thrombosis presents vaguely as an acute abdomen with gradually worsening diffuse, colicky abdominal pain, associated with distention, and symptoms may have been present for a few days 2,3. Haem-positive stool may also be present 3. As ischaemia progresses, eventual necrosis, perforation, sepsis and shock ensue.
As the superior mesenteric vein thrombosis, back pressure builds as arterial supply to the bowel is uninterrupted. This leads to bowel wall oedema (and thus bowel wall thickening) and possible intramural haemorrhage (leading to hyperdense bowel wall) 1. Depending on the how complete occlusion is, and whether or not collateral drainage is available, the combination of back pressure, and bowel wall thickening can lead to inadequate tissue perfusion leading to intestinal ischaemia, infarction and eventual necrosis 1.
The majority of cases are considered secondary to an identifiable underlying condition, including 1-3:
- hypercoagulable states
- recent abdominal surgery
- intra-abdominal or systemic sepsis
- portal hypertension
- mechanical narrowing due to adjacent malignancy
Approximately 20-40% of cases have no clear precipitant and are considered idiopathic 3.
Imaging is the only reliable way of making the diagnosis, especially as clinical presentation is vague. CT is the most accurate test available to us at present, with excellent sensitivity (up to 100%). Ultrasound and catheter mesenteric angiography are reported to have ~70% sensitivity 3 but in practice are infrequently requested as a first line investigation, unless the presentation suggests another diagnosis (e.g. cholecystitis).
For a discussion on CT technique refer to intestinal ischaemia article.
The findings in superior mesenteric vein thrombosis include 1:
- bowel wall
- typically thickened
- most common finding
- 8-9 mm (usually <15 mm)
- normal wall thickness is 3-4 mm
- density (variable)
- hypoattenuating due to oedema
- hyperdense wall on non-contrast images (due to intramural haemorrhage)
- enhancement (variable)
- absent once infarcted (more common in arterial occlusion)
- hyperenhancement or target appearance
- prolonged enhancement
- pneumatosis intestinalis: due to transmural infarction
- typically thickened
- dilated and fluid-filled lumen
- filling defect in the superior mesenteric vein and branches (seen in 90% of cases)
- mesenteric congestion and stranding
Treatment and prognosis
Traditionally management has been surgical, with assessment of the small bowel for necrosis and resection of necrotic bowel, followed by anticoagulation. This has a reported mortality rate of 7-20% 2,3, which, although still high, is much better than 92-100% mortality with conservative management 3.
Surgery is clearly still required in patients with intestinal infarction; however, in patients where this has not yet occurred, endovascular thrombolysis/thrombectomy is a viable option 2,3. Thrombolytic agents can be introduced either via a superior mesenteric artery catheter or a transhepatic transportal retrograde approach, whereas mechanic clot lysis can only be achieved via a retrograde transhepatic venous approach 2.
Probably the safest way to directly access the portal circulation is via a transjugular-transhepatic approach (similar to the initial steps of a TIPS). A direct transhepatic approach has also been performed but is associated with a greater risk of haemorrhage 5.
Complications include 3:
- surgical complications
- anastomosis breakdown
- short bowel syndrome
- recurrent mesenteric thrombosis: 14%, usually within six weeks
If a superior mesenteric vein thrombus/filling defect can be identified, no differential diagnosis exists. In cases where a filling defect cannot be identified, the differential diagnosis is essentially that of bowel wall thickening and includes:
- 1. Furukawa A, Kanasaki S, Kono N et-al. CT diagnosis of acute mesenteric ischemia from various causes. AJR Am J Roentgenol. 2009;192 (2): 408-16. doi:10.2214/AJR.08.1138 - Pubmed citation
- 2. Warshauer DM, Lee JK, Mauro MA et-al. Superior mesenteric vein thrombosis with radiologically occult cause: a retrospective study of 43 cases. AJR Am J Roentgenol. 2001;177 (4): 837-41. AJR Am J Roentgenol (citation) - Pubmed citation
- 3. Goldberg MF, Kim HS. Treatment of acute superior mesenteric vein thrombosis with percutaneous techniques. AJR Am J Roentgenol. 2003;181 (5): 1305-7. AJR Am J Roentgenol (citation) - Pubmed citation
- 4. Shih MC, Hagspiel KD. CTA and MRA in mesenteric ischemia: part 1, Role in diagnosis and differential diagnosis. AJR Am J Roentgenol. 2007;188 (2): 452-61. doi:10.2214/AJR.05.1167 - Pubmed citation
- 5. Sze DY, O'sullivan GJ, Johnson DL et-al. Mesenteric and portal venous thrombosis treated by transjugular mechanical thrombolysis. AJR Am J Roentgenol. 2000;175 (3): 732-4. AJR Am J Roentgenol (citation) - Pubmed citation