Abdomen and Gastrointestinal System

Anatomy and Physiology

Abdomen

The abdomen is composed of the abdominal and pelvic cavities and is often divided into nine anatomic regions: (1) right hypochondriac, (2) epigastric, (3) left hypochondriac, (4) right lumbar, (5) umbilical, (6) left lumbar, (7) right iliac, (8) hypogastric, and (9) left iliac (Fig. 5-1). It may also be described in terms of quadrants: right-upper (RUQ), right-lower (RLQ), left-upper (LUQ), and left-lower (LLQ) (Fig. 5-2). The abdominal cavity contains organs of the digestive system (stomach and intestines), the hepatobiliary system (liver, gallbladder, and pancreas), the urinary system (kidneys and ureters), and the circulatory system (spleen). The pelvic cavity contains the bladder, portions of the intestines, and the reproductive organs.

The abdominal cavity is lined by the peritoneum, a serous membrane (Fig. 5-3, A). The serous lining attached to the abdominal organs is the visceral peritoneum. The peritoneum attached directly to the abdominal wall is the parietal peritoneum. The mesentery is a double fold of parietal peritoneum projecting from the posterior abdominal wall in the lumbar region (see Fig. 5-3, B). Most of the small bowel is attached to the outer edge of the mesentery.

FIGURE 5-3 A, A cross-sectional drawing of the abdomen demonstrates the peritoneum. B, A cross-sectional drawing of the lower abdomen demonstrates the mesentery.

The greater omentum is a double fold of peritoneum that attaches to the duodenum, stomach, and transverse colon. It hangs loosely over the intestines. The lesser omentum is a fold of peritoneum that attaches the liver to the lesser curvature of the stomach and the duodenum (Fig. 5-4).

FIGURE 5-4 A cross-sectional drawing of the abdominal cavity demonstrates the omentum.

Gastrointestinal System

A major portion of the gastrointestinal (GI) system is the alimentary tract, which serves to digest and absorb food. Extending from the mouth to the anus, the alimentary tract consists of the mouth, pharynx, esophagus, stomach, small bowel and large bowel, and rectum.

The esophagus is the first part of the GI system. It is approximately 10 to 12 inches long and extends from the posterior pharynx to the stomach (Fig. 5-5). The upper esophagus is midline, but it courses to the left to pass behind the aortic arch, which indents the esophagus. Other indentations occur at the level of the left main stem bronchus and at the gastroesophageal junction. As it passes downward, the esophagus follows the curvature of the thoracic spine and thoracic descending aorta.

FIGURE 5-5 The esophagus in the mediastinum.

The stomach occupies the body’s LUQ, with the cardiac orifice at the level of the tenth or eleventh thoracic vertebra and the pyloric canal just to the right of the first or second lumbar vertebra (Fig. 5-6). Peristalsis churns the gastric content and propels it toward the pylorus. Gastric emptying of liquids is accounted for by the peristalsis initiated in the fundus of the stomach; gastric emptying of solids requires a to-and-fro action of the antrum and pylorus. In the presence of masses, inflammation, or diabetes, the peristaltic activity may be diminished. When the stomach is filled with barium, its curvatures are visible as generally smooth contours. The rugae appear as longitudinal ridges within the stomach.

FIGURE 5-6 The stomach depicted in its average orientation when empty.

The small bowel includes the duodenum, jejunum, and ileum. It arises from the stomach at the duodenal bulb and courses to the ileocecal valve (Fig. 5-7), over a length of nearly 21 feet. The duodenal C-loop moves posteriorly from the gastric antrum to its ending at the ligament of Treitz. The jejunum begins here and coils in the LUQ before terminating at the ileum in the RUQ. The ileum then courses through the RLQ and LLQ to terminate at the ileocecal junction. When filled with barium the segments of the small bowel are distinguishable by their appearance. The duodenal mucosa is indicated by its transverse rigid appearance. The jejunal mucosa appears delicate and feathery. Ileal folds look like those of the duodenum, although not as large.

FIGURE 5-7 The small bowel and its divisions.

The large bowel extends from the terminal ileum to the anus for a length of about 6 feet (Fig. 5-8). Its distinct regions are the cecum, orifices for the terminal ileum and the appendix, ascending colon and hepatic flexure, transverse colon and splenic flexure, descending colon, sigmoid, rectum, and anus. The cecum is usually retroperitoneal and anterior and lies against the abdominal wall. The ascending colon is also retroperitoneal and becomes more posterior as it ascends to lie adjacent to the undersurface of the liver. The hepatic flexure, transverse colon, and splenic flexure are all intraperitoneal. They lie more anteriorly and are attached to the posterior abdominal wall by the mesocolon, a double layer of peritoneum. The descending colon is retroperitoneal, moving posteriorly as it descends. The peritoneal sigmoid colon lies in the pelvis and is quite mobile. Structures located anterior to it include the bladder and, in women, the uterus. Posterior structures include the iliac arteries and sacral nerves. The rectum is extraperitoneal, beginning at the third sacral segment and following the sacrococcygeal curve to the anus. The valves of Houston are prominent transverse folds in the distal rectum, where it dilates. The anus forms the distal 1 to 2 inches of the large bowel and contains no peritoneal covering.

FIGURE 5-8 The colon and its four parts.

Imaging Considerations

Radiography

Abdomen.

Abdominal radiography is often performed for survey purposes, without contrast agents. The usual starting point is a supine radiograph taken to include the kidneys, ureters, and bladder (“KUB”). The frequency of abnormal findings on a conventional abdominal radiograph is fairly low and nonspecific, but it is of most value for patients complaining of severe abdominal tenderness and to rule out bowel obstructions and perforations. In addition, abdominal radiographs are invaluable in assessing the placement of various tubes and catheters, as discussed later in this chapter.

Anteroposterior (AP) projections of the abdomen are generally taken in the supine position. An AP radiograph allows examination of air distribution within the bowels and of the size of the viscera, serves to evaluate vascular and other types of calcifications and body or soft tissue trauma, and, finally, serves as a preliminary radiograph for other procedures.

On initial inspection of the abdominal radiograph, the technologist should verify that the technique chosen is correct or diagnostic, motion is nonexistent, and the anatomy under consideration has been properly visualized. As with other body areas, evaluation of the abdomen should be done systematically. This should include inspection of the renal outlines, ureters, psoas muscles, spleen, liver, gallbladder, and peritoneal fat stripes.

In a normal abdomen (Fig. 5-9), varying amounts of gas and fecal material are always present in an unprepared patient. The liver, kidney, spleen, and psoas muscle shadows are variably outlined because of the lucent layer of fat surrounding them. Properitoneal fat stripes are visible as radiolucencies extending laterally from the costal margins down to the iliac crests. The aorta and pancreas are not normally seen unless they are calcified, as might be expected in an older patient in the case of the aorta or in a patient with chronic calcific pancreatitis. The inferior margin of the liver should lie at or above the level of the right twelfth rib. The left kidney is usually slightly higher than the right kidney because of the presence of the liver superior to it. The top of the left kidney generally lies at the vertebral level of T11-T12, whereas the top of the right kidney is approximately 1 cm lower in position. In terms of renal size, the kidneys are generally the length of three vertebrae in children over 1 year of age. By adulthood, the kidneys reach the length of approximately two and a half vertebrae.

FIGURE 5-9 Radiographic appearance of a normal abdomen, demonstrating kidney shadows, liver shadow, psoas muscles, and transverse processes of the lumbar spine.

Few, if any, air–fluid levels are present in the normal patient who is radiographed in the erect position. Limited fluid levels in the small bowel and large bowel, however, may be considered normal. Fluid levels are abnormal when they are seen in dilated bowel loops or when they are numerous. The intestinal gas pattern may be confusing to the diagnostician. In infants and children, gas may be scattered throughout the bowel, but in adults gas is normally seen only in the stomach and colon. Small bowel gas in an adult, therefore, may indicate a pathologic process. In some patients, gas may be recognizable only on erect radiographs because of the presence of intraluminal fluid. Free air should not be visible in the peritoneal cavity and is indicative of a bowel perforation or other pathologic entities that introduce air into the peritoneum. Erect abdominal radiographs must include the diaphragm to assess for free air, and in instances in which the patient is unable to stand, a left lateral decubitus abdomen should be obtained (Fig. 5-10).

FIGURE 5-10 A left lateral decubitus abdomen demonstrating free air over the dome of the liver.

A series of images are obtained during or after fluoroscopy, with the projections differing from one institution to another. Typical patient positions include recumbent posteroanterior (PA) projection to demonstrate the entire stomach and duodenal bulb, right anterior oblique (RAO) to highlight the pyloric canal and duodenal bulb (Fig. 5-11), right lateral to show the duodenal bulb, duodenal loop, and retrogastric space, and left posterior oblique (LPO) to demonstrate the gastric fundus. Proper positioning relates significantly to the patient’s body habitus. Generally, the more hypersthenic a patient is, the higher and more transverse the stomach tends to lie. For other body habitus (i.e., sthenic, hyposthenic, and asthenic), the stomach is more J-shaped, lying lower and closer to the spine.

FIGURE 5-11 Normal stomach as seen on this radiograph of an 18-year-old man.

Small Bowel.

In some instances, the barium sulfate mixture may be followed as it progresses through the small intestines. Radiographs are exposed at set intervals to determine GI motility and to demonstrate abnormalities within the small bowel. Once the contrast agent reaches the ileocecal valve, the small bowel study is complete, typically within 2 to 3 hours (Fig. 5-12).

FIGURE 5-12 A, Small-bowel radiograph demonstrating barium filled terminal ileum. B, Spot image demonstrating ileocecal junction.

The small intestines may also be studied radiographically by means of enteroclysis, a small-bowel enema. This is accomplished by advancing an intestinal tube through the patient’s mouth to the end of the duodenum at the ligament of Treitz. Contrast agents, both positive and negative (barium sulfate and methylcellulose, respectively), are directly injected into the small bowel.

Large Bowel.

The lower GI tract is examined by administering a barium enema through the rectum. This examination demonstrates abnormalities of the large bowel and intraluminal neoplasms. The barium enema is performed in a single-contrast fashion with only barium or as a double-contrast study using barium sulfate in combination with a negative contrast agent (e.g., air). The negative contrast agent distends the lumen, allowing improved visualization of the mucosal lining (Fig. 5-13), especially small polyps and intraluminal tumors. In either case, the radiologist typically obtains a series of images during fluoroscopy, with the patient in various positions to highlight certain areas of the colon (e.g., flexures). The radiographer may also expose a series of radiographs of the contrast-enhanced large bowel per the radiologist’s instructions (Fig. 5-14). After evacuation of the barium sulfate mixture, the radiographer will obtain a “postevacuation” radiograph to visualize colon contraction and to demonstrate the mucosa.

FIGURE 5-13 Normal air-contrast enema as demonstrated on this anteroposterior projection.

Abdominal radiography may often depict abnormalities in patients with known inflammatory bowel disease (IBD). Since negative findings will rarely preclude the need for further imaging studies, radiography typically is reserved for evaluating the presence of obstruction, perforation, or toxic colon distention associated with advanced disease. Although small bowel barium studies were, at one point, the primary method for diagnosing suspected IBD cases, the introduction of capsule endoscopy is playing an increasingly larger role in making the initial diagnosis.

If a patient has had a surgical enterostomy procedure, the contrast medium may be administered through the opening in the abdominal wall to the specific area of the GI system. A colostomy is a procedure in which a stoma is surgically created on the abdominal wall to allow drainage of bowel contents into a closed pouch hung outside the body. Those in the sigmoid and descending colon are most frequently placed because of rectal or sigmoid cancer. Those placed in the transverse or ascending colon are often for indications that allow the colostomy to be placed for temporary purposes for diversion of flow of colonic contents (e.g., sigmoid diverticulitis, rectovaginal fistula, colon obstruction).

An ileostomy is a similar opening but is placed from the ileum, with the most common indication being ulcerative colitis. As with colostomies, patient problems with ileostomies include proper skin protection and odor control. Proper fit of the appliance for drainage is essential to prevent problems caused by excoriating digestive enzymes. Other enterostomies (i.e., jejunostomies and duodenostomies) are more rarely used, and only under very specific circumstances because of the loss of electrolytes that occurs before their absorption through the small bowel. Affected patients often require total parenteral nutrition to maintain life.

If a patient has had a surgical enterostomy procedure, the contrast agent may be administered through the opening in the abdominal wall to the specific area of the GI system (Fig. 5-15). Special care needs to be taken when imaging the patient with some types of stoma because this area can be particularly sensitive.

FIGURE 5-15 A, Barium enema via a colostomy demonstrating enema tip within the ostomy. B and C, Spot images demonstrating administration of barium sulfate via the ostomy.

Computed Tomography

CT is an important modality in abdominal survey as well as in the examination of the GI system. Because CT can visualize small differences in tissue density, it clearly demonstrates abdominal organs, which are normally not apparent on conventional abdominal radiographs without the use of contrast, resulting in good visualization of structure in the upper abdomen close to the diaphragm.

On CT examination, the liver, spleen, pancreas, and kidneys appear as homogeneous soft tissue densities, making any alteration in the density resulting from pathologic conditions readily visible, even without contrast media. Abscesses and solid and cystic masses all have a respective range of densities between that of water and normal soft tissue densities. CT is also quite useful in the evaluation of retroperitoneal pathologies such as lymph node enlargement resulting from neoplastic disease or infection. In combination with conventional abdominal radiography, CT of the abdomen is recommended when a bowel obstruction is suspected. Finally, it has become the accepted modality for following the progress of GI malignancies and also plays a role in the diagnosis of inflammatory conditions (e.g., abscess). CT of the colon is commonly performed to evaluate neoplastic disease, diverticulitis, and appendicitis. It has the capability of locating the exact site of neoplasms and allowing the clinician to measure the size of the tumor and the presence of infiltration into surrounding tissues. It is also useful in planning radiation therapy protocols. An increase in the availability of CT dose reduction techniques is resulting in a decrease in associated radiation exposure levels.

Routine CT examination of the abdomen requires good opacification of the bowel and vascular structures because poorly opacified bowel loops may be mistaken for abdominal masses. Patients must be given an oral contrast agent approximately 45 minutes to 1 hour before abdominal CT scanning. This time allows the contrast agent to reach the distal ileum before examination. Contrast agents may also be administered rectally, depending on the anatomic structures to be imaged.

Multidetector CT (MDCT) units, in combination with oral contrast and gas distention of the colon, have the capability to perform a noninvasive endoscopic procedure called virtual colonoscopy (or CT colonography). This technique produces two-dimensional (2-D) and three-dimensional (3-D) images of the colon, thus enabling the radiologist and endoscopist to view anatomic landmarks and structures that may not be seen with conventional colonoscopy. This, in turn, can reduce risk and discomfort to the patient. This application is a benefit to those who may not be able to or choose not to have a traditional colonoscopy procedure, which remains the gold standard for detection of smaller polyps. Additionally, virtual colonoscopy has a high sensitivity for detection of polyps greater than 10 mm as well as lesions that may be missed with fecal blood tests, barium enemas, and sigmoidoscopy. However, it is important to note that residual stool may cause problems with accuracy of image reconstruction, potentially simulating pathology such as polyps or masses.

CT enterography is also an increasingly used technique, in which optimal visualization of the small bowel mucosa is attained through use of MDCT scanners. For these examinations, patients are given large volumes (approximately 1350 mL) of 0.1% barium sulfate prior to imaging. Additionally, for certain indications such as obscure GI bleeding, small bowel tumors, and chronic ischemia, a biphasic contrast-enhanced study may be performed. Because of the ability to acquire both intraluminal and extraluminal information of the entire GI tract in a noninvasive manner, techniques such as CT enterography and CT colonography are quickly supplanting the standard small bowel series and barium enema examinations.

Magnetic Resonance Imaging

The role of magnetic resonance imaging (MRI) in the abdomen has expanded as a result of faster sequences and shorter scan times. Evaluation of the GI tract is still limited by bowel motion; however, MRI is useful in demonstrating the presence of retroperitoneal masses impinging on the GI system. Breath-hold imaging in MRI allows the technologist to visualize abdominal organs in a matter of seconds (Fig. 5-16). A few different imaging sequences are used to differentiate between normal tissue and pathology. The most common of the imaging sequences are T1-weighted images for optimal visualization of anatomic structures and T2-weighted images for optimal visualization of diseased tissues. Three-dimensional contrast-enhanced magnetic resonance angiography (MRA) is also used in imaging of the arterial vessels of the abdomen.

FIGURE 5-16 A T2-weighted coronal breath-hold magnetic resonance image of the abdomen.

For imaging of the small bowel, magnetic resonance enterography (MRE) is gradually being incorporated into routine clinical practice as published literature highlighting the benefits of its use are becoming more prevalent. Because of its ability to display both intraluminal and extraluminal information, similar to that of CT, MRE is often the preferred imaging modality for pediatric populations as well as pregnant women, in whom radiation exposure is of high concern. MRE has the ability to demonstrate areas of active bowel inflammation as well as complications such as bowel obstruction, fistulas, and abscesses. Furthermore, MRE sequences have the ability to depict bowel motility, which is a potential advantage when attempting to distinguish between fixed and transient segments of luminal narrowing. Subsequently, sequences can be repeated to capture various vascular phases, reassess abnormal bowel segments, or improve image quality without increasing the radiation risk to the patient. The examination is performed by having the patient ingest 1 to 2 liters (L) of a 0.1% barium suspension containing sorbitol, prior to MRE of the abdomen. Use of this agent produces high signal intensity in the bowel lumen on T2-weighted images and low signal intensity in the lumen on T1-weighted images. The “dark lumen” appearance that results with the administration of the contrast is critical for the detection of mural enhancement on postcontrast T1-weighted images, which rarely can be achieved through use of water alone.

Sonography

Sonography is occasionally useful in imaging the GI system, although successful examination is highly dependent on the skill of the operator. When water is used as a contrast agent, it can be highly successful in imaging gastric emptying, gastroesophageal reflux disease (GERD), and duodenal abnormalities. More commonly, however, it is used to image the retroperitoneum because of the flexibility of angling the transducer to image that region. The aorta, kidneys, lymph nodes, and adrenal glands are subject to a variety of abnormalities, and with ultrasound it is possible to image behind the bowel and assess for abnormalities.

Most commonly used in the evaluation of appendicitis, graded compression ultrasonography is a technique performed using a 5 or 7 megahertz (MHz) linear transducer to firmly compress the anterior abdominal wall, displacing normal bowel loops in an effort to locate a potentially inflamed appendix.

Nuclear Medicine Procedures

In nuclear medicine, GI bleed scans, which are quick, noninvasive procedures useful in demonstrating GI bleeding, direct angiographers to the site of bleeding if therapeutic intervention is to be performed. This is accomplished by labeling either using technetium-99m (Tc-99m) to label red blood cells (RBCs) or Tc-99m–labeled colloid to identify the origin of the bleed. Tc-99m is a short-lived (half-life of about 6 hours) nuclear isomer that emits β-rays, enabling its use as a contrast agent. Active bleeding sites are identified through evaluation of focal areas of the tracers that conform to the bowel anatomy, increase with time, and move with peristalsis. This study is typically performed in patients with significant hemorrhage and an unprepared bowel, in whom endoscopic evaluation is not optimal.

Gastric emptying scans are used to assess the rate food exits the stomach into the duodenum. The examination is performed by having the patient consume either a solid or liquid radiolabeled meal and then observed via a gamma camera as it passes out of the stomach. Typically, a high level of radioactivity maintained within the stomach after an extended period would indicate poor gastric emptying (Fig. 5-17). In addition, the test may also be used to monitor the response of promotility drug treatments such as that of metoclopramide or erythromycin. One drawback of the test is that it cannot differentiate between physical obstruction and gastroparesis; that is, further diagnostic studies will often need to be ordered if the patient exhibits a delay in gastric emptying.

FIGURE 5-17 A nuclear medicine gastric emptying scan demonstrates a marked delay in emptying of the stomach.

Urea breath tests are performed on patients with gastric ulcers to identify the presence of Helicobacter pylori. Infection with this bacterial species is a common cause of gastric ulcers and can be treated quite effectively with antibiotic therapy. The procedure begins by having the patient drink radioactive urea. If the bacteria are present in the stomach, they will break down the urea, and the patient will release radioactive carbon dioxide. This is captured in the breath test.

Meckel scans can also be utilized in identifying ectopic gastric mucosa as in a Meckel diverticulum. This is accomplished through injection of Tc-99m pertechnetate, which is taken up by mucus-secreting cells of the gastric mucosa. Focal uptake outside of the stomach and in the small bowel would be positive for the pathologic condition.

Positron emission tomography (PET) may be used to evaluate and stage GI cancers (Fig. 5-18). PET has been proven to demonstrate approximately 20% of esophageal cancerous lesions (Fig. 5-19) undetected by CT.

FIGURE 5-18 A positron emission tomography (PET) scan for staging of colon cancer demonstrates new hypermetabolic activity of metastatic disease in the liver and right hemithorax.

Endoscopic Procedures

As noted earlier, endoscopy is the use of tubular fiberoptic devices to look inside the GI tract and other hollow organs or cavities of the body. As its sophistication and specificity have increased, it is assuming a greater role in diagnosis and therapy of the GI tract. Upper endoscopy is capable of seeing down into the esophagus, stomach, duodenum (including the ampulla of Vater), and even the proximal jejunum. Colonoscopy allows retrograde visualization of the rectum as far as the terminal ileum. The small bowel is still largely out of reach through endoscopy; however, the advent of capsule endoscopy, which involves the ingestion of a small camera pill, has resulted in its increased use in the diagnosis of small bowel tumors. The capsule encases a digital camera that transmits images to a recording device worn on a belt. The capsule has a gastric transit time of approximately 1 hour and small-bowel transit time of 3 to 4 hours. This technology is indicated in diagnosis of obscure GI bleeding, which is often caused by a lesion. This technology, however, has several drawbacks such as inability to identify the precise location of pathology, inability to biopsy or treat located pathology, and lack of reimbursement by insurance companies. The only contraindication to performing capsule endoscopy is a bowel obstruction. Photographic views of the interior of the body provide readily diagnosable information (Figs. 5-20 and 5-21). Therapeutic applications of endoscopy are numerous. They include polyp removal, injection and thermal methods to stop hemorrhaging, sclerosing and banding of esophageal varices, lesion biopsy, sealing of tracheoesophageal fistulas, stone removal, esophageal prosthesis insertion, and laser tumor removal (both generally for palliative purposes). In addition, enteric wall stents have been used to open the lesions in nonoperative malignancies of the colon.

FIGURE 5-20 Endoscopic image of a sigmoid colon mass in a 72-year-old woman; the mass is seen bulging into the lumen of the colon.

Abdominal Tubes and Catheters

As with the chest, a variety of tubes and catheters can be placed within particular portions of the abdomen. The technologist must be familiar with each type of tube and exercise great caution in attempting to move patients with abdominal tubes in place. The technologist should also ask the patient’s nurse or consult the chart before altering the patient’s position. In addition, some abdominal tubes and catheters allow entry into body systems that are normally sterile and require special care to avoid infection.

Gastric tubes may be placed (generally through the nose) for a variety of diagnostic and therapeutic purposes. They may be indicated for aspiration of gastric contents to help control nausea and vomiting, for decompression and removal of gastric contents because of bowel dysfunction or surgery, and for nutritional support tube feedings (gastric gavage) or medication administration. The Levin tube is the most common nasogastric (NG) tube. It is a fairly small, single-lumen tube with a plain tip, and it may be visualized radiographically. Proper placement is commonly assessed through aspiration of gastric juices and listening for proper placement within the stomach via a stethoscope. If an NG tube is placed for feeding, the patient’s head must remain elevated to prevent the tube from becoming displaced, leading to aspiration of the gastric contents. If an emergent condition exists that requires large amounts of gastric contents to be aspirated quickly (gastric lavage), the Ewald tube or the Edlich tube may be used. These tubes are placed through the mouth, are wider than the Levin tube, and contain several openings that allow quicker aspiration. The Levacuator tube may also be used for evacuation of gastric contents. This is a wide, double-lumen tube placed through the patient’s mouth. The larger lumen is used for gastric lavage, and the smaller lumen allows instillation of an irrigant.

An enteral tube is a small-caliber tube used to deliver a liquid diet directly to the duodenum or jejunum. It most commonly has a weighted end to hold the tube in the proper placement. The Dobhoff tube is a common radiopaque enteral tube (Fig. 5-22). Other common types of prolonged enteral tubes include the Corpak tube and the Entriflex tube.

FIGURE 5-22 A, Supine abdominal radiograph demonstrating Dobhoff tube reaching to the fourth segment of the duodenum (ligament of Treitz). B, Semierect abdominal radiograph demonstrating Dobhoff tube placement in same patient.

Nasoenteric decompression tubes are used to remove gas and fluids in the prevention and treatment of abdominal distention. At one end, these tubes have a balloon or rubber bag filled with air, mercury, or water to stimulate peristalsis and facilitate passage through the pylorus into the intestinal tract. The Miller-Abbott tube is a common type of double-lumen decompression tube. It is passed through the nose, pharynx, and esophagus with the balloon uninflated. Once the end of the tube reaches the stomach, the balloon is inflated and the tube is pulled back until it stops at the cardiac sphincter. The patient is then placed on his or her right side in the semierect position, and the air is withdrawn from the balloon and replaced with mercury. Progress of the tube is assessed by taking abdominal radiographs at regular intervals. The Harris and Cantor tubes are other types of decompression tubes. Unlike the Miller-Abbott tube, however, the Cantor tube (Fig. 5-23) and the Harris tube contain a single lumen.

FIGURE 5-23 Radiographic appearance of the Cantor tube in this 50-year-old man with a mechanical bowel obstruction. Approximately 4 hours after placement, it has advanced into the second portion of the duodenum.

The Levin tube or the Foley catheter may also be surgically placed in any portion of the GI system. A gastrostomy tube, as the name indicates, is a tube placed through the wall of the stomach, whereas a duodenostomy tube or jejunostomy tube is specific to that portion of the small intestine. A percutaneous endoscopic gastrostomy tube is frequently placed endoscopically. These tubes provide a direct route for administering liquid feedings.

Congenital and Hereditary Anomalies

Esophageal Atresia

Atresia is a congenital absence or closure of a normal body orifice or tubular organ. Esophageal atresia is a rare congenital anomaly in which the esophagus fails to develop past some point, resulting in discontinuation of the esophagus (Fig. 5-24). This anomaly is caused by a defect in cell differentiation of the trachea and esophagus during the fourth to sixth week of embryonic development. The symptoms of esophageal atresia are visible soon after birth and include excessive salivation, choking, gagging, dyspnea, and cyanosis. Diagnosis of this congenital anomaly may be established by inability to pass an NG tube into the stomach. If a radiopaque NG tube is used, the terminal end of the pouch may be demonstrated radiographically with a chest radiograph without the use of a contrast agent. Immediate surgery is required to alleviate the problem, and preoperative care must be taken to prevent aspiration pneumonia. The infant may not receive oral feedings, and continuous suction is necessary to prevent aspiration. Under most circumstances, this increased risk of aspiration contraindicates the use of a contrast agent to visualize the extent of the atresia.

Usually, a tracheoesophageal fistula is coincident with atresia (Fig. 5-25). This consists of an atresia at the level of the fourth thoracic vertebra with a fistula—an abnormal tubelike passage from one structure to another—to the trachea (Fig. 5-26). In addition, a gastrostomy tube may be placed in the infant’s stomach to prevent reflux of gastric secretions into the trachea through the fistula. Such a condition is incompatible with life for more than 2 to 3 days, but the prognosis is good if the infant is handled appropriately before surgery to prevent aspiration.