What is an obstruction? |

Causes and Symptoms

The
gastrointestinal (GI) tract runs from the mouth to the anus and includes the throat, esophagus, stomach, small intestine, large intestine, and rectum. Accessory glands whose secretions drain into the GI tract include the liver, gallbladder, and pancreas. Because the GI tract is essentially a hollow tube, its inner channel being called its lumen, it is susceptible to being closed off. The same holds true for the biliary tree, which is a series of ducts draining bile from the liver and gallbladder into the duodenum, and the pancreatic duct, which drains secretions from the pancreas into the duodenum.

Obstruction of the gastrointestinal tract is a blockage severe enough to impair the transit of materials through the lumen. Although often caused by narrowing, that term differs from obstruction in that a narrowing may be without consequences. A partial obstruction is one in which there is still some flow through the narrowing; in complete obstruction, there is no flow.

Obstruction of these organs or ducts may be mechanical or functional. Mechanical obstructions result when a problem arises from within the bowel lumen (intraluminal), from within the wall of the organ (mural), or from something outside the organ causing its lumen to be narrowed (extrinsic). Functional obstructions are caused by some motor abnormality, such as spasm or lack of peristalsis, causing impaired transit of materials.

An example of an intraluminal obstruction is a gallstone occluding the cystic duct. The liver produces bile, a fluid that has various functions including excretion of bilirubin, which is a breakdown product of hemoglobin, the protein inside red blood cells that carries oxygen. Bile also contains bile salts and cholesterol, substances that help break down large fat globules in the duodenum into smaller droplets, initiating fat digestion. Bile from the liver flows through tiny ducts that eventually unite to form the common hepatic duct. The gallbladder, a hollow sac that stores bile, joins the common hepatic duct via the cystic duct; these two ducts unite to form the common bile duct, which drains bile into the duodenum.

If there is excess cholesterol in bile, it tends to form gallstones. These stones most often form in the gallbladder, but they may form in other areas of the biliary tree such as in the common bile duct. If the stones are formed in the gallbladder but do not occlude the cystic duct, bile may still flow in and out of the organ. If the stones become impacted in the cystic duct, however, they cause obstruction to the flow of bile, leading to inflammation of the gallbladder, called acute cholecystitis.

With cystic duct obstruction, the impacted stone and some of the components of bile cause the gallbladder to become inflamed. The inflamed lining secretes fluid into the gallbladder; this fluid cannot escape because the cystic duct is occluded by the gallstone. The accumulating fluid causes the gallbladder to become distended.

This inflamed gallbladder causes abdominal pain that often lasts several hours. It is also associated with nausea, vomiting, and a fever. The fever may be attributable to a bacterial infection of the bile: When not flowing well, bile tends to be a good place for bacteria to multiply. The stones may pass through the cystic duct and occlude the common bile duct. In this situation, there is no route for bile to flow into the duodenum. Therefore it backs up, dilating the common bile duct, and is reabsorbed into the bloodstream. This causes jaundice, or a yellowish pigmentation of the skin; it may be associated with dark-colored urine.

There are ways to distinguish between acute
cholecystitis caused by cystic duct obstruction and biliary tract infection (cholangitis) caused by obstruction of the common bile duct. Ultrasonography is excellent for detecting stones in the gallbladder and dilated bile ducts, but it is not as good at detecting stones in the common duct. To detect such stones, endoscopic retrograde cholangiopancreatography (ERCP) may be performed. In this study, an endoscope is passed through the mouth, esophagus, and stomach and into the duodenum. A catheter is inserted into the opening of the common bile duct, and dye is injected. The dye outlines stones in the common bile duct.

An example of a mechanical obstruction caused by a mural process is an esophageal obstruction caused by a cancer which grows from the walls of the
esophagus into its lumen. The most common symptom of esophageal obstruction is dysphagia, or a sensation of food sticking in the throat after being swallowed. If food becomes impacted in the narrowed region, it may cause an aching sensation in the chest wall.

The obstruction is evaluated with a barium esophagram, in which barium is swallowed and an x-ray of the esophagus is taken. It may show findings such as severe narrowing of the lumen of the esophagus. Endoscopy is then performed, which can be used to visualize the area, looking for evidence of cancer, and to take a piece of the lining of the esophagus for evaluation under the microscope.

An example of an extrinsic mechanical obstruction is one caused by scar tissue, or adhesions, compressing a portion of the small intestine. Adhesions may be caused by previous abdominal surgery. If they cause obstruction, the bowel proximal to the obstruction dilates to a diameter that is larger than normal. Its function changes: normally the small intestine absorbs fluid, whereas in obstruction it secretes fluid. Since intestinal contents cannot pass through the narrowing, vomiting occurs.

Normally, the bacterial content of the small intestinal lumen is kept low because of the continuous flow of contents through it. During small bowel obstruction, this flow is partially or completely diminished, enabling bacteria to overgrow in the small intestine. These bacteria may pass through the wall of the small intestine into the bloodstream, causing a systemic infection or even death.

An example of a functional obstruction is a disorder called chronic intestinal pseudo-obstruction (CIP). The prefix “pseudo” means “false”: A pseudo-obstruction is a disorder in gastrointestinal motility that results in diminished peristalsis through the diseased segment of gut, creating an illness similar to a mechanical obstruction but without any occlusion of the lumen. There are a variety of causes of CIP, which can involve the different regions of the gastrointestinal tract. It may occur as part of the spectrum of some systemic diseases, or it may be of unknown cause (idiopathic).

If the esophagus is involved, dysphagia and
heartburn are predominant symptoms, resulting from decreased esophageal peristalsis. Everyone experiences occasional reflux, or the backward flow of stomach acid into the esophagus. Normal esophageal peristalsis keeps this acid in the stomach; if peristalsis is diminished, then the acid may cause heartburn. If the stomach and small intestine are involved, symptoms include nausea, vomiting, bloating, and abdominal discomfort. The abdomen may become extremely distended. Since the flow of small intestinal contents is slowed, overgrowth of bacteria that are normally present only in the colon occurs. These bacteria may take up so much vitamin B12 in the gut that a deficiency results. Bacterial overgrowth may also cause diarrhea. If the colon is extensively involved and exhibits markedly diminished peristalsis, abdominal distension and constipation result. An abdominal x-ray may show that the colon has become very dilated, a condition called megacolon.

Treatment and Therapy

Obstructions caused by
gallstones can be treated in several ways. If the stones are in the gallbladder and are obstructing the cystic duct, surgery is often performed within a day or two. One technique for removing the gallbladder is laparoscopic cholecystectomy, which involves making a small incision in the abdominal wall and inserting an instrument called a laparoscope. The structures of the biliary tree are identified, and dye is injected into the cystic duct to obtain a cholangiogram, an x-ray that helps identify where the stones are located. After cholangiography, clips are placed along the cystic duct, and the duct is cut between the clips (similar to cutting the umbilical cord between the ties). Bile and stones are evacuated from the gallbladder, which is then removed. The advantages of laparoscopic cholecystectomy over other surgical approaches are that the laparoscopic approach is less invasive, causes less scarring and less pain, and allows a more rapid recovery.

If the stones are in the common bile duct, one way to remove them is endoscopically. The endoscope is advanced into the duodenum, and the opening of the common bile duct is visualized. An instrument is passed through the endoscope into the opening of the common bile duct. Electrical current is applied, creating a small incision in the opening of the common bile duct. This enlarges the opening, and sometimes bile and stones come gushing out into the duodenum. If the stone is still in the common duct, a balloon-tipped catheter is passed into the common bile duct and advanced up above the stone. The balloon is inflated, and the catheter is pulled out of the common duct, bringing the stone with it. If this procedure fails, other options include surgery or extracorporeal shock-wave lithotripsy. This involves generating shock waves and focusing them onto the stone, causing it to break into tiny fragments.

Despite progress made in the care of esophageal cancer patients, the overall five-year cure rate did not change from the 1950s to the 1990s. A main treatment goal is to relieve the symptom of dysphagia. This can be done by passing dilators down through the narrowed area, stretching it so that food, saliva, and liquids can pass. Because the tumor is undoubtedly growing, repeated dilations are necessary. This treatment obviously does nothing to reduce the mass of the tumor, but it helps relieve the symptom of dysphagia.

Two treatments aimed at reducing the tumor mass are surgical removal of the tumor and radiation therapy. Before deciding that surgery is a viable option, several factors need to be taken into consideration, including the potential risks of surgery. For example, surgery performed on patients with advanced heart or lung disease has a very high mortality risk. If the tumor involves the lower esophagus, that area can be removed and the stomach can be sewn to the remaining end of the esophagus. This surgery can be dangerous: mortality rates from the operation range from 2.8 to 17 percent.

Another treatment, which is effective if the tumor is of a specific cell type called a squamous cell carcinoma, is to irradiate the tumor, attempting to kill tumor cells by focusing beams of radiation onto the mass. This procedure produces survival rates that are roughly equal to surgical survival rates and avoids the risk of surgery. The most common way to apply radiation is to focus it onto the chest wall using an external source. The radiation energy penetrates into the area on which it is focused—the esophageal tumor. One complication of
radiation therapy is that the radiation, which kills rapidly dividing cells, cannot distinguish between cancer cells and those lining the wall of the esophagus. Therefore the lining of the esophagus may become very inflamed, a condition called radiation esophagitis. Another approach for applying radiation is with a delivery system such as a specialized radioactive device which fits inside the lumen of the esophagus and delivers radiation locally.

Small bowel obstructions can be fatal. Their treatment first consists of generalized care, such as correcting fluid deficits. All oral intake is stopped, and a nasogastric tube, which is a tube inserted into the nose and passed into the stomach, is hooked up to suction to try to decompress the dilated loops of bowel. Since surgery may be imminent, it is important to optimize the functions of various organ systems so that the mortality risk of surgery is minimized. The likelihood of needing surgery depends on whether the obstruction is partial or complete: About 81 percent of partial small bowel obstructions and about 16 percent of complete obstructions resolve without surgery. This likelihood also depends on the cause of obstruction. For example, many partial obstructions resulting from adhesions resolve with conservative treatment, whereas obstructions caused by a loop of intestine twisting at its base, called a volvulus, carry a high probability of needing surgery.

The treatment of CIP is difficult: Nothing is curative, and nothing slows the progression of the diseases causing pseudo-obstruction. The most effective drug for increasing intestinal motility is probably cisapride. Some studies show that it improves symptoms and hastens the transit of material through the gut. Antibiotics to treat bacterial overgrowth in the small intestine are sometimes used in CIP, especially in cases where diarrhea is present. Dietary measures may be somewhat helpful, including lowering fat, lactose, and fiber. Vitamin supplementation may be necessary, especially with injectable vitamin B12.

Occasionally, surgery is helpful in CIP, especially for a localized problem. Because the disease often causes widespread gut involvement, however, surgery will not cure the problem. Nevertheless, when the problem is caused by the lower esophageal sphincter (LES) failing to open properly, creating a distal esophageal obstruction, a myotomy (or cutting of the circular smooth muscle in the LES) may improve dysphagia symptoms. If the stomach or colon is massively dilated, it may need to be removed. Sometimes removal of portions of the small intestine may be helpful. Once abdominal surgery has been performed, it may be difficult to distinguish future attacks of CIP from mechanical bowel obstruction caused by adhesions.

Alternative forms of nutrition may need to be considered. For example, if the disease mainly affects the esophagus and stomach, a feeding tube could be placed into the small intestine. If the gut has such widespread involvement that jejunal feeding would be fruitless, parenteral nutrition, which is the administration of nutrition intravenously, may be necessary.

Perspective and Prospects

Since obstructions of various areas in the gastrointestinal tract can be life-threatening, they served as the sources of some of the most exciting diagnostic and therapeutic advances in medicine during the twentieth century.

The earliest way to diagnose mechanical obstruction, such as small bowel obstruction, was by exploratory surgery. Then came x-ray studies, which were initially able to outline the gastrointestinal tract first by plain-film studies that showed various findings such as loops of small intestine dilated with air that suggested obstruction. Later, the addition of contrast dyes, given either by mouth or by rectum, increased the ability to outline the anatomy of the GI tract and to diagnose obstructions.

Endoscopy has revolutionized the ability to diagnose mechanical obstructions that are attributable to various causes. Developed initially using a rigid endoscope, which was difficult to position and required that the patient be put under general anesthesia, endoscopes now are flexible, only about one centimeter in diameter, and easily passed well into the duodenum. The instruments passed through the endoscope have also been greatly improved. There are instruments for removing coins lodged in the esophagus, inserting feeding tubes through the stomach wall, injecting drugs to stop the bleeding in ulcers, and cutting the opening of the common bile duct for removing stones impacted in it.

Surgical techniques have improved.
Crohn’s disease can cause inflammation and segments of narrowing of the intestine called strictures; these strictures can cause problems such as mechanical small bowel obstructions. Surgeons used to remove the strictured areas, plus a significant margin of small intestine on either side of the stricture, in the belief that such removal would eliminate the diseased segments of the small intestine. The disease tends to recur, however, and a patient needing repeated operations to remove strictures might end up with a small intestine so short that it would be unable to absorb fluids and nutrients. Therefore, the individual could have massive diarrhea and malabsorption of nutrients and need to be fed intravenously. By the 1990s, surgical treatment for Crohn’s disease sought to relieve the stricture but preserve as much small intestine as possible.

In the 1970s, therapy for biliary stones began to move away from traditional surgery and toward the use of stone-dissolving medications, endoscopic techniques, lithotripsy, and laparoscopy.

Manometry, which involves the measurement of pressure inside the GI tract, has been especially useful in helping scientists understand the physiology of functional obstruction and its relationship to emotions. For example, in 1987, L. D. Young and coworkers published an article describing how exposing research subjects to experimental noise and complicated thinking problems would increase the pressure inside the esophagus, in effect concluding that it increased the strength and speed of esophageal muscle contractions.

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