Air in the portal and the superior mesenteric vein (SMV) due to acute bowel ischaemia, demonstrated using CT

Clinical History

A 73-year-old female presented with paraoxysmal A fibrillation, high BP, and asthma. She had undergone a cholecystectomy 20 years ago, and had had pseudocoarcation. She had been on arfarin since November 2002. On examination, her blood pressure was 150/90; temperature, 38.5; heart rate, 128 (irregularly irregular); sat 96% on 28% oxygen; pulse, 110/min. The patient was found to be very dehydrated, anuric, pale and was unresponsive. The four quadrant pain tenderness, guarding (voluntary/involuntary), and bowel sounds were absent.

Imaging Findings

A 73-year-old female patient presented to her General Practitioner with dysuria and was given trimethoprin 200 mg. Within 24 h, she was admitted to A&E with a 24-h history of vomiting and diarrhoea. Her vomiting and diarrhoea were reported to be frequent, episodes of 20–30 times; initially her vomit was greenish in colour and then changed to a coffee ground colour. She then developed a severe constant abdominal pain. Laboratory tests done revealed the following: International Normalized Ratio (INR) = 2.7, HB = 19.8, haematocrit = 57.9%, WCC = 25.5 normal (4–10) 10⁹/L, neutrophils 92%, pH = 7.323, clac = 4.1 mmol/L, ABEc = 4.7 mmol/L, Hco3- = 30.7 mmol/L, urea and electrolyte analysis showed a slightly elevated urea and creatinine level. Ur = 10.2 (normal range 2.8–6.8), CR = 109 (normal range 62–97); troponin was negative; amylase, 229 (normal range 0–1000 IU/L); liver function tests were found to be normal. On ECG, were found ST depressions C2C3C4C5C6, Chaotic atrial tachycardia T wave inversion in precordial lead II. IMAGING: A chest/abdomen X-ray showed normal findings and there was no free air, and later a CT scan of the abdomen was also taken. Differential diagnosis includes mesenteric ischaemia; secondary to chaotic arterial tachycardia or perforated abdominal viscus. The CT findings demonstrated the presence of gas in the portal and superior mesenteric vein (SMV). Also, a few matted loops of small bowel were seen in the right iliac fossa (RIF). No fluid retention was identified, and there was no pneumatosis and the bowel wall was not thickened. The patient was given fluids, four units of fresh frozen plasma, antibiotics, and prompt laparoscopy with/without laparotomy. The CT examination showed infarction of the small bowel from 10 cm distal to the duodenojejunal flexure to the hepatic flexure and SMA thrombosis. The outcome was only palliative care was given as it was felt that surgical intervention would be of no avail as her prognosis was grave. The patient died within 48 h of performing laparotomy.

Discussion

The superior mesenteric artery (SMA) supplies blood to a part of the colon. Blood is supplied to the colon by the inferior mesenteric artery (IMA). The superior mesenteric artery originates at the level of the first lumbar vertebra posterior to the body of the pancreas and the splenic vein and its branches are inferior pancreaticoduodenal, middle colic artery, right colic artery and the ileocolic artery. The jejunal and ileal branches include 12–15 branches which arise from the left side of the SMA i.e. supplying the midgut. The IMA supplies the hindgut (distal colon and the rectum) and its branches include the left colic artery, sigmoid artery, the superior rectal artery. It is uncommon for an embolus to lodge in the IMA because it has a smaller lumen. The superior mesenteric vein (SMV) accompanies the SMA and drains the jejunum and ilium. It then unites with the splenic vein to form the portal vein. Acute bowel ischaemia is believed to be a rare condition in elderly patients. The diagnosis is often made late because the clinical signs, laboratory results and the radiological findings are non-specific. Bowel ischaemia has been shown to have a poor prognosis with a mortality rate of 75%–95%. Based on the literature, the extent of portal venous gas is not a predictor of mortality. Advanced imaging based on CT contrast has greatly improved the detection limit of SMV gas. SMV gas is characterized by tubular or branched areas of a decreased attenuation in the liver, more common in the left lobe and extends within 2 cm of the liver capsule. This is differentiated from the air in the bilary tree which does not extend to within 2 cm of the liver capsule and is central in location. Moreover, the SMV in our patient had a tubular appearance with an area of decreased attenuation (Figs. 1, 2). The CT findings of bowel ischaemia may include occlusion of splanchnic vasculature, bowel distension, bowel wall thickening, a marked or absent enhancement of the bowel wall and the presence of portomesenteric gas. In our patient, the only feature seen was SMV gas. Causes of mesenteric ischaemia are extensive and they can be either intra-vascular or extra-vascular. Intra-vascular can be arterial or venous. Arterial disease can be thrombus or embolus,that is, acute mesenteric arterial thrombosis (AMAT) or acute mesenteric arterial embolus (AMAE), nonocclusive mesenteric ischaemia (NOMI) or occlusive mesenteric arterial ischaemia (including both AMAE and AMAT), while the venous disease is caused by thrombosis. Insufficient blood perfusion is caused by arterial occlusion by an embolus or thrombosis, thrombosis of venous system, nonocclusion caused by vasospasms or a low cardiac output. Arterial insufficiency causes hypoxia, leading to bowel spasms, vomiting and diarrhoea. Bowel necrosis occurs in a matter of 8–12 h from the onset of pain. If the ischaemia persists, it will lead to the disruption of the mucosal barrier, bacteria, toxins, and vasoactive substances are released into the systemic circulation and to the portal vein through the mesenteric venous drainage system. Portal venous gas develops as a result of the disruption in the gastrointestinal mucosa, permitting the passage of intraluminal gas into the portomesenteric venous system.

Differential Diagnosis List

Final Diagnosis

Necrotic small bowel and superior mesenteric artery (SMA) thrombosis.

URL:	https://eurorad.org/case/3349
DOI:	10.1594/EURORAD/CASE.3349
ISSN:	1563-4086