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Perspectives on large bowel obstruction

Weledji, Elroy P

doi: 10.4103/2468-7332.200556
Review Article
Free

Large bowel obstruction (LBO) is a serious and costly medical condition, indicating often emergency surgery. The main clinical issue is to determine whether the obstruction affects the small bowel or the colon since the causes and treatments are different. Delay in operative intervention may lead to an unnecessary bowel resection, increased risk of perforation, and overall worsening of patient morbidity and mortality. With the advent of colonic endoluminal stent, the treatment of distal colonic obstruction should be individually tailored to each patient. This article discussed LBO and emphasized the importance of history taking, examination, and basic imaging in the early diagnosis of its cause, thus facilitating appropriate management.

Department of Surgery, University of Buea, Buea, Cameroon

Address for correspondence:Elroy Weledji, Department of Surgery, University of Buea, Buea, Cameroon elroypat@yahoo.co.uk

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Introduction

Intestinal obstruction remains a common and difficult problem encountered by the abdominal surgeon. Although large bowel obstruction (LBO) presents less frequently (15%) than its small bowel counterpart (85%), it remains nonetheless a common surgical emergency. 1 Following resuscitation, a precise history may indicate the pathology and physical examination supported by basic imaging may indicate where the pathology is. These would determine which patient may require immediate surgery, urgent surgery, semi-elective surgery, or a trial of conservative management. The consequences of bowel obstruction are progressive dehydration, electrolyte imbalance, and systemic toxicity due to migration of toxins and bacteria translocation either through the intact but ischemic bowel or through a perforation. Appreciation of fluid balance, acid–base–electrolyte disturbance, and importance of preoperative resuscitation decrease the morbidity and mortality from intestinal obstruction. 2 , 3 , 4

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Discussion

LBO may be mechanical (lumen partly or completely blocked) or paralytic (no peristalsis). It may be chronic, acute-on-chronic, acute, or pseudo obstruction (nonmechanical). In fact, there is a complete spectrum of clinical presentation and patients may present with acute LBO without a preexisting history of obstructive symptoms. 5 , 6 The visceral pain of intestinal obstruction is due to increased gut peristalsis against the obstruction and is usually referred toward the midline rather than being localized as the gut has a midline origin of development. The visceral sensory fibers are carried by the sympathetic nerves on their way to the spinal cord. Thus, mid-gut (mid second part of duodenum to proximal two-thirds of transverse colon) colicky pain is carried by the lesser splanchnic nerve (T10–T11) and referred to the umbilicus while hindgut (beyond the distal third of transverse colon) colicky abdominal pain being carried by the least splanchnic nerve (T12) is referred to the suprapubic area. The other sources of pain are somatic (localized) from abdominal distension and peritoneal irritation when ischemia or perforation supervenes. 7 , 8

The main causes of LBO are malignancy and volvulus of the sigmoid colon /1. The prevalence of both is subject to a wide geographical variability. 5 , 6 Colorectal cancer is particularly prevalent in the west, accounting for at least 50% of LBO. This proportion alters in Africa and Eastern Europe where sigmoid volvulus is the cause of obstruction in up to 40% of cases. 9 , 10 The most common site of LBO is the sigmoid colon, accounting for 50% of all cases. This is not only because the sigmoid colon is a common site for colonic carcinoma but also because the lumen is relatively narrow and the feces are firm rather than liquid. The second most common site is the splenic flexure (10%), where the combination of a sharp kink in the colon together with luminal narrowing by the tumor and relatively firm stools leads to blockage. The features of a right-sided LBO may be less obvious than those of left-sided colonic lesions because only a small proportion of the colon is distended. However, an obstruction at the ileocecal valve will produce features of a low small bowel obstruction. 5 , 11 A closed loop obstruction may follow an acute-on-chronic LBO from a distally obstructing colonic lesion. In cases where the ileocecal valve forms one end of a closed loop strangulation obstruction is not a problem here, but a similar problem to look for is intramural ischemia of the cecum due to stretching causing patchy necrosis. Right iliac fossa tenderness in a patient with LBO may indicate cecal distension and imminent perforation which is a disastrous complication of LBO. According to the law of Laplace (2T = PR wherePis the transmural pressure, T is the wall tension and is the radius of a sphere), tension (in this case in the wall of the colon) is proportional to the radius and is therefore higher in the cecum which is the widest point of the colon than elsewhere. Thus, the cecum takes the brunt of the distension with imminent perforation if the cecal diameter is >15 cm. When there is distal obstruction, the ileocecal valve often becomes incompetent and both small and large bowel become distended. If left untreated, the patient will start to vomit, but ischemia or perforation of the bowel is unlikely. 5 With regard to colonic intussusception in adults, the leading point is invariable; a colonic pathology and laparotomy are indicated. 12 {Table 1}

Sigmoid volvulus is the most common form of volvulus in the gastrointestinal tract. The anatomic defect is the narrow attachment of the root of the mesentery to the posterior abdominal wall and a long mesenteric axis. Predisposed by very high fiber diet and long redundant sigmoid colon in Africans, chronic constipation and laxative abuse, psychiatric and senile disorders, the sigmoid colon rotates around its mesenteric pedicle usually more than 180° counterclockwise resulting in partial or complete LBO. There is a palpable tympanic mass and with the risk of ischemia from venous obstruction. 9 , 11 Because of its high recurrence rate, sigmoid colectomy is the definitive treatment as compared to sigmoidoscopic decompression. 13 , 14 Less common causes of LBO are diverticular disease, either as a result of stricture or acute inflammation with edema, and obstructed groin hernia. Inflammatory bowel disease is a very unusual cause of obstruction, but strictures from any cause may precipitate obstruction by proximal fecal impaction. Fecal impaction alone rarely causes obstruction. 5

The four cardinal clinical features of intestinal obstruction are colicky abdominal pain, vomiting, constipation, and abdominal distension. The clinical history may establish other features indicative of the likely etiology of the obstruction. A thorough history of the obstruction would include the patient's age, duration of symptoms, history and nature of the pain, history of similar symptoms or surgery. A history of colorectal or other intra-abdominal malignancy, recent alteration in bowel habit, or the passage of blood is suggestive of neoplasm. Patients who are institutionalized and have cognitive impairment have a high incidence of sigmoid volvulus and severe constipation, and pseudo-obstruction tends to occur in patients with a history of recent nongastrointestinal surgery or severe concurrent medical illness. 6 , 15 Chronic symptoms will be associated with weight loss and anorexia, and the general premorbid state (cardiovascular and respiratory) is assessed for a patient with a known diagnosis and the possibility of surgical intervention. Clinically, it is extremely difficult to distinguish with any certainty between simple obstruction and strangulation. 4 Simple obstruction presents with colicky (visceral) pain, but there is mild generalized abdominal tenderness from the distension with gas and fluid. Strangulation (closed loop) obstruction usually has an acute onset. The pain is most marked and the condition very serious if overlooked. There is localized tenderness with pain on coughing (rebound tenderness) as peritonism develops from stimulation of pain receptors in the parietal peritoneum or abdominal wall. The pain is constant rather than colicky and abdominal rigidity is more marked. There is a tender mass even with associated erythema of the skin. The patient is obviously ill, toxic and may have a leukocytosis. Thus a tense, tender, irreducible lump with no cough impulse, especially over hernia orifice, for example, femoral or inguinal, is a strangulation until proven otherwise. Occasionally, hernia is internal and not palpable. 1 , 4 , 5 In colon obstruction, vomiting occurs much later if at all especially if the ileocecal valve remains competent and implies a state of severe volume depletion. In LBO, the lesion is very distal within the intestine and constipation and distension are the earliest and most predominant symptoms. Absolute constipation occurs when there is complete luminal obstruction and the patient is unable to pass either feces or flatus. Patients with partial obstruction may develop spurious diarrhea because fluid feces are all that can pass through a stenosed segment.

The physical findings include dehydration, abdominal distension, and sometimes, visible peristalsis. Dehydration assessed by examination of the mucous membranes and skin turgor is an indication of severe fluid depletion. In colonic obstruction, distension is mainly in the flanks and upper abdomen. Abdominal distension is usually evident and more marked the more distal the obstruction, but it is more an indication of the site than the extent of obstruction. 5 Swallowed air, gas from bacterial fermentation, and nitrogen diffusion from the congested mucosa are all responsible for the increased intestinal gas. The cause of the obstruction may be may be evident (e.g., scars from previous surgery, tender irreducible hernia, abdominal mass, e.g., intussusception or carcinoma of the bowel). Percussion produces a tympanic note and auscultation high-pitched tinkling bowel sounds. If the obstruction is advanced, there may be signs of bowel strangulation (worsening constant pain, toxic patient, tachycardia, hypotension, and pyrexia) with absent bowel sounds (paralytic ileus). 1 , 5 , 16 The examination findings will depend on the stage at which the patient presents. The patients with complete obstruction are at substantial risk of strangulation (20%–40%), but a patient with chronic obstruction may appear generally quite well with normal vital signs. 4 On the other hand, the patient who has an acute large bowel volvulus or an acute closed loop small bowel obstruction may be profoundly ill at the time of presentation. Abdominal distension may be so marked as to render further assessment of the intra-abdominal contents impossible. Rarely a mass be felt, or an irregularly enlarged liver may suggest a malignant lesion as the cause of obstruction. Hernia orifices must be examined in all cases of intestinal obstruction although hernias are unusual cause of LBO. 5 , 16 Although rectal examination will rarely provide a diagnosis as a true rectal lesion rarely causes LBO, it must always be performed in bowel obstruction. Symptoms such as rectal bleeding and Tenesmus herald its discovery before obstruction ensues. The rectum will be empty unless the cause of the problem is impacted feces. A pelvic mass may be palpable, and the presence of blood and mucus on the glove is suggestive of a distal neoplasm. Assessment of the cardiovascular and respiratory systems is necessary as most of these patients will require surgery. 5 , 16

A plain abdominal X-ray (AXR) will show the distribution of gas and its distal limits, and it can thus distinguish small from LBO. AXR features of LBO include distended colon (over 5 cm) proximal to the obstructing lesion, collapsed colon distally (“cutoff” sign). Distended large bowel tends to lie peripherally and to show the haustrations of the taenia coli, which does not extend across the whole width of the bowel. Distended small bowel may also be seen if the ileocecal valve is incompetent. 17 Only rarely is the cause of obstruction detectable on plain films of the abdomen. The advent of modern, fast multidetector computed tomography (MDCT) scanners has changed management strategies for acute abdominal conditions including suspected LBO in all groups of patients, especially the elderly infirm, and those on intensive care/high dependency unit (ITU/HDU). MDCT was shown to be more accurate in the diagnosis of LBO. It is usually available on a 24-h basis, and in many institutions, it has replaced the urgent water-soluble contrast enema X-ray indicated in all cases of apparent LBO but contraindicated in the presence of peritonitis and in toxic megacolon. 18 It also has the advantage of excluding incidental findings and in staging malignant disease.

The management of LBO depends on its presentation. If intervention is not forthcoming following progressive symptoms of chronic obstruction over a period, acute-on-chronic obstruction may supervene. These acute presentations are managed as an emergency to prevent imminent perforation and fecal peritonitis. 6 , 16 , 18 Following resuscitation, a water-soluble gastrografin contrast enema X-ray may show the level of obstruction and importantly exclude a pseudo-obstruction if a CT scan is not available. 16 The penalty of misdiag nosis in pseudo-obstruction is an unnecessary laparotomy in a poor-risk patient. 15 Obstructing carcinomas of right colon are treated by right hemicolectomy and of splenic flexure by extended right hemicolectomy. This removes cancer and obstructed right colon and results in a well-vascularized ileocolic anastomosis. Postoperative diarrhea is rarely problematic as the sigmoid and rectum are preserved. The surgical treatment of sigmoid and rectosigmoid junction lesions depends on the general status of the patient, findings at operation, and preference of the operating surgeon. Perhaps, the most common procedure performed for acutely obstructed left-sided colonic cancer is Hartmann's operation (left-sided segmental resection without primary anastomosis). The advantages have no anastomosis, limited mobilization required, resection of obstructing lesion, and preservation of proximal colon. The disadvantages are stoma formation, high morbidity of reversal, and up to 50% are not reversed. More recently, surgical practice has moved toward one-stage procedures for LBO. The advantages are avoiding stoma, resecting the lesion, and preserving the proximal colon. The disadvantages are the potential for anastomotic leakage and the possibility of a synchronous proximal lesion. A subtotal colectomy with ileosigmoid or ileorectal anastomosis is indicated if, in the obstructed colon, the quality of the proximal bowel is poor with respect to anastomosis because of edema, fecal loading, shutdown of the splanchnic blood supply, and an inconsistent marginal vessel. The anastomosis has a good blood supply from the ileum and proximal diversion is unnecessary. As the whole of the proximal colon is removed, undetected synchronous lesions, which may be missed in the absence of preoperative imaging, are removed and subsequent colonoscopic surveillance can be avoided. The main perceived disadvantage is postoperative bowel frequency of twice per day with ileosigmoid anastomosis increasing to three per day after ileorectal anastomosis. Subtotal colectomy is of course inadvisable in patients with sphincter dysfunction or fecal incontinence. 5 , 6 , 11 , 16 On-table lavage is most appropriate for obstructing rectal lesions amenable to primary resection, where preservation of colon above a low anastomosis is desirable. 17 A chronic LBO can be admitted electively for colonoscopic investigations before definitive elective surgery. 4 , 5 , 6 , 16 Self-expandable metal stents are now being used more widely in the management of malignant low (distal to the splenic flexure) left-sided LBO. These stents are placed endoscopically under fluoroscopic control through the obstructing lesion and can remain in place for a prolonged period where the stent is definitive palliative treatment or alternatively can decompress the colon, and after staging and a complete workup, a definitive one-stage resection and anastomosis may be possible. 19 The stents are expensive, but they appear to be cost-effective. Colonic stenting as a bridge to surgery provides surgical advantages, as higher primary anastomosis rate and a lower overall stoma rate, without increasing the risk of anastomotic leak or intra-abdominal abscess. 20 However, these results should be interpreted with caution because of few studies reported data on these outcomes. 21 Further randomized controlled trials are needed including a larger number of patients and evaluating long-term results (overall survival and quality of life) and cost-effectiveness. 22 Optimal treatment in advanced disease remains controversial. Complications of perforation and bleeding are possible but uncommon, and it is likely this technique will be used more widely in the future. At present, the treatment of distal colonic obstruction is individually tailored to each patient. 20 , 21

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Conclusions

LBO remains a common and difficult problem encountered by the abdominal surgeon. It is important to distinguish simple from strangulation obstruction, following resuscitation. A precise history may indicate the pathology and physical examination supported by basic imaging may indicate where the pathology is. Appreciation of fluid balance, acid–base–electrolyte disturbance, and importance of preoperative resuscitation decrease the morbidity and mortality from intestinal obstruction. In distal obstruction, optimal treatment in advanced disease remains controversial, particularly after the appearance and use of colonic endoluminal stents.

Financial support and sponsorship

Nil.

Conflicts of interests

There are no conflicts of interest.

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    Keywords:

    Examination; history; large bowel; obstruction; resuscitation; treatment

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