B. WOLF*, D.M. NICHOLS# and A. MUNRO*
Departments of *General Surgery and #Radiology, Raigmore Hospital, Inverness, UK
A case is reported where small bowel ischaemia was precipitated by ligation of the inferior mesenteric artery during emergency colectomy. Aetiology and treatment options are discussed.
Keywords: small bowel ischaemia, aortomesenteric graft
J.R.Coll.Surg.Edinb., 45, February 2000, 64-5
The gut is protected from ischaemia by an abundant collateral circulation. As a rule at least two of the three main vessels -coeliac artery (CA), superior (SMA) and inferior mesenteric artery (IMA) - must be compromised to produce symptomatic ischaemia.1
Typically a patient suffering from acute mesenteric ischaemia has certain risk factors and complains of sudden onset of abdominal pain although the presentation can be more insidious.2 In this case small bowel ischaemia was encountered unexpectedly during emergency operation for toxic mega-colon.
A 46-year-old female patient with ulcerative colitis was managed conservatively over a period of five years. At out-patient review there was concern about her general condition. Sigmoidoscopy demonstrated active proctocolitis. She also complained of pain in her left great toe. The toe appeared dusky although it felt warm and there was good capillary refill. She was a non-smoker and pedal pulses were all palpable. She was admitted for assessment. However, her condition deteriorated rapidly necessitating emergency laparotomy.
At operation the typical appearances of a toxic megacolon were confirmed. A total colectomy was carried out with closure of the rectal stump and fashioning of an ileostomy. After removal of the colectomy specimen it was noted that the small bowel appeared ischaemic. The superior mesenteric artery was dissected using an anterior approach. No pulsation was felt in it and no flow observed when an arteriotomy was performed. A Fogarty catheter could not be passed retrogradely into the aorta. There appeared to be a complete occlusion at the origin of the SMA but no thrombus was retrieved. Distally the vessel was patent. A vasculitic process was considered and a frozen section histology was performed on the colonic blood vessels. No vascular abnormality was reported. The inferior mesenteric vein was harvested and used as an interposition graft between the anterior arteriotomy on the SMA and the infrarenal aorta (Figure 1). Although the graft was only a few inches long it tended to kink and had to be revised. The small bowel was slow to reperfuse.
Figure 1: Interposition vein graft between aorta and SMA
She went through a prolonged period of convalescence requiring several weeks of parenteral nutrition. A small bowel enema at four weeks showed normal radiological appearances without evidence of a stricture. Several toes had to be amputated some weeks after the colectomy. Abdominal angiography at four months demonstrated occlusion of both SMA and CA at the origin. The aortomesenteric graft supplied the SMA in its mid-portion and the hepatic, splenic and left gastric arteries retrogradely through pancreaticoduodenal arcades.
Twelve years later the patient remains well with good nutritional status and is actively employed. The aortomesenteric graft has become aneurysmal but remains patent with normal flow (Figure 2).
Figure 2: Duplex scan of aortomesenteric graft showing aneurysmal changes. 1 = IVC, 2 = aorta, 3 = graft, 4 = SMA, 5 = SMV
The mesenteric circulation is characterised by numerous anatomical variations. Nevertheless, there are fairly constant collateral vessels between SMA and IMA, namely the marginal artery of Drummond and the arc of Riolan, as well as communications between CA and SMA through gastroduodenal and pancreaticoduodenal arteries and rarely an arc of B¸hler. As a rule symptomatic ischaemia will only occur if at least two of the three main vessels are compromised.1
In retrospect, there is little doubt that the entire intestinal blood supply pre-operatively in this 41-year-old woman was through the IMA since SMA and CA were both occluded at the origin. It is tempting to propose a common cause for the gut and toe ischaemia in some way related to the inflammatory bowel disease. Mesenteric vasculitis and spontaneous thrombosis at unusual sites have been described in patients with Crohn’s disease.3 However, there was no evidence of vasculitis in the resection specimen of this patient and the vascular disease process involved large vessels at their origin. On the other hand the patient had no risk factors for premature atherosclerosis. The exact aetiology remains therefore obscure.
Owing to the abundant blood supply clinically apparent chronic mesenteric ischaemia is relatively rare. However, significant stenoses of the major mesenteric vessels are a common finding at autopsy. In an unselected autopsy series of 120 patients, 29% had stenosis at the origin of mesenteric arteries and in 15% at least two of the major vessels were involved.4 In this context it seems intriguing that ligation of the IMA can be carried out routinely without ill effects. We know of no other case in which sacrifice of the IMA in a colorectal procedure has resulted in devascularisation of the remaining gut.
Few surgeons have more than anecdotal experience in mesenteric revascularisation.5 Unexpected intra-operative ischaemia of the gut presents a formidable challenge. Treatment options include embolectomy, endarterectomy, selective vasodilation, thrombolysis, angioplasty, re-implantation and bypass grafting. The precise choice depends on the clinical circumstances as well as the expertise of the surgeon. Embolectomy of the SMA is relatively straightforward and worthwhile attempting. With regard to bypass procedures there is controversy in the literature whether antegrade, multi-vessel reconstruction is superior to a retrograde, single vessel bypass.6,7 The former technique uses the supracoeliac aorta as site of origin. Advantages are disease free inflow and relatively anatomical lie of the grafts. The major drawback are the technical difficulties in exposure. A single retrograde bypass from the infrarenal aorta or proximal right common iliac artery onto the SMA is favoured by the relative technical ease and familiar exposure. Autologous vein and externally supported PTFE are described as suitable conduit materials. Serendipity was a major factor in our choice of the inferior mesenteric vein as graft since it was freely available after the colectomy was completed. An appropriately sized, distally bevelled segment is anastomosed in an end-to-side fashion onto the anterior surface of the proximal to mid portion of the SMA. Particular problems with this technique are judgement of graft length and position in order to provide a good lie without kinking and obstruction.
Our isolated experience with a retrograde, single vessel bypass providing a good functional and long-term result seems supported by the literature.7
Copyright date: 14th October 1998
Correspondence: Mr A Munro, Consultant General Surgeon, Raigmore Hospital, Old Perth Road, Inverness IV2 3UJ, UK
©2000 The Royal College of Surgeons of Edinburgh, J.R.Coll.Surg.Edinb.,45; 1: 64-5