CIRCULATON PROBLEM IN THE BOWELS
Acute ischemia of the rectum resulting in full thickness necrosis is an uncommon disease but our doctors wrote the paper on this!
Acute rectal ischemia is rare because the rectum has abundant blood supply and rich collaterals. The superior rectal artery which is the terminal branch of inferior mesenteric artery supplies most of the blood to rectum. Some blood is derived from the middle rectal arteries which are branches of the internal iliac artery or the internal pudendal artery and also from the inferior rectal artery which is a terminal branch of the internal iliac artery. There is extensive intramural anastomosis between the branches of these arteries especially in the lower part of the rectum. Extramural collaterals also occur between the lowest sigmoid and superior rectal arteries. This watershed area (Critical point of Sudeck) is not considered to be critical anymore because adequate collateral are almost always present (2,3). In addition, collaterals also exist between lumbar vessels and branches of the internal iliac arteries which can maintain circulation through the middle and inferior rectal arteries when iliac vessels are compromised (4).
In addition to these named branches rectum also receives blood supply from muscular branches of the levator, and some twigs from the inferior vesical or vaginal arteries. This extensive blood supply ensures that rectum is perfused even in cases where the rest of the bowel is compromised.
Pathophysiology: Unlike ischemic colitis or proctitis, frank gangrene of the rectum is very rare. It is usually described in elderly patients with significant atherosclerotic disease and cardiac risk factors in the presence of hemodynamic instability. It occurs as a result of sudden acute compromise in blood flow in patients with inadequate collateral circulation around the rectum. Most reported cases in literature involve an acute event such as interruption of inferior mesenteric artery during aortofemoral bypass or ligation of internal iliac vessels in patients with atherosclerotic narrowing of major arteries. Hypotensive shock or a low flow state will compound this problem and the rectum becomes ischemic despite the usually excellent collateral circulation. In none of our patients, a preceding surgical event, hemodynamic compromise or low flow state was encountered.
Other rare causes include angiographic embolization of the blood supply of the rectum, infected strangulated hemorrhoids, vasculitis and or immune complex thrombi related to Systemic lupus erythematosis (5,6) or direct necrotizing effect of phosphate enemas on the rectum (7). However, like Reinus et al (8), there was no major precipitating event in any of our three cases.
Clinical presentation & Diagnosis: Most patients will present with diarrhea and rectal bleeding. Abdominal and pelvic pain and distention is also common. Fever, tachycardia along with hypotension is often present. Lower abdominal tenderness is often present but because of the extra peritoneal pelvic position of the rectum these signs may be delayed. Nelson et al has reported loss of anal tone as an early sign of acute rectal ischemia (4).
Leukocytosis and acidosis are reflective of sepsis and shock. CT scan shows rectal wall thickening and peri rectal stranding. Pneumatosis in the rectal wall may also be present in advanced cases as was seen in one of our patients. Later rectal perforation with extra luminal air may be seen. Angiography, though not advisable in acute gangrenous cases, shows diffuse atheromatous disease the aortoilliac vessels with abrupt cut off.
Endoscopic examination of the rectum either using a rigid proctoscope or a bedside flexible scope remains the cornerstone for diagnosis of rectal ischemia. Early findings include erythema, mucosal and sub mucosal hemorrhages, and ulceration. In the setting of lower GI symptoms these changes can be confused with IBD or infectious colitis. With more serious compromise of the blood supply necrosis or frank gangrene of the rectum will be seen. In two of our three cases the rectal wall was black and completely gangrenous.
Management: In early cases or in cases with superficial ischemia conservative management is appropriate but in cases of frank gangrene of the rectum, emergency surgery is the only option. While preparations are being made for surgery patient should be resuscitated and started on broad spectrum antibiotics. In the OR patient should be placed in modified lithotomy position with Lloyd Davis stirrups to allow access to the rectum during surgery. Operation should start with a proctoscopy to evaluate the extent of ischemia. Visual inspection of the rectum during surgery will also help determine the extent and level of ischemia. In most cases a complete proctectomy is required. In the emergency situation this is best accomplished by an APR. The perineal wound is packed in order to avoid infection in a closed space and to expedite the operation. The wound can be closed after a few days when patient is stable and the risk of infection has decreased. Proctectomy may also be achieved with intersphincteric dissection and excision of the rectum but is a longer more complex operation. During an emergency operation every effort must be made to abbreviate the operation and get the patient back to ICU for further resuscitation.
In cases where the lower rectum is spared a low anterior resection of the rectum along with a Hartman’s procedure may be performed. We do not recommend leaving behind a gangrenous or ischemic segment of the rectum as has been suggested by some (9). Rather we support the view of Maun et al that leaving behind a gangrenous rectal segment will be a source of persistent sepsis and should be removed (10). A drain should be left in pelvis and stools be diverted with a colostomy.
Acute full thickness rectal ischemia with gangrene is a rare clinical entity. Immediate bedside proctoscopy should be considered in elderly patients with atherosclerotic disease who present with lower GI symptoms, hypotensive shock and the CT shows an inflamed and swollen rectum. Conservative management is not appropriate in these cases and preoperative resuscitation followed by emergency surgery to resect the frankly gangrenous bowel is necessary.