DIGESTIVE SYSTEM PATHOLOGY
Bowel Obstruction This can occur in either the small or large bowel.
Small Bowel Fibrous adhesions caused by previous surgery or peritonitis account for almost 75% of all small bowel obstructions. External hernias (inguinal, femoral, umbilical, incisional) are the second most common cause. Other general causes of mechanical small bowel obstruction include luminal occlusion (gallstone, intussusception) and intrinsic lesions of the bowel wall (neoplastic or inflammatory strictures, vascular insufficiency).
Distended loops of small bowel containing gas and fluid can usually be recognized within 3 to 5 hours of the onset of complete obstruction. On upright or lateral decubitus projections, the interface between gas and fluid forms a straight horizontal margin. The caliber of the air-filled bowel appears as a dilated proximal bowel and a collapsed distal bowel. On upright films, a “string-of-beads sign” appears.
As time passes, the small bowel may become so distended as to be almost indistinguishable from the colon. Small bowel loops generally occupy the more central portion of the abdomen, whereas colonic loops are positioned laterally around the periphery of the abdomen or inferiorly in the pelvis. Gas within the lumen of the small bowel outlines the thin circular folds, which completely encircle the bowel. In contrast, colonic haustral markings are thicker and farther apart and occupy only a portion of the transverse diameter of the bowel.
The presence of a few dilated loops of small bowel located high in the abdomen (in the center or slightly to the left) indicates an obstruction in the distal duodenum or jejunum. The involvement of additional small bowel loops is suggestive of a lower obstruction. As more loops are affected, they appear to be placed one above the other upward and to the left, producing a characteristic “stepladder” appearance
Patients with complete mechanical small bowel obstruction demonstrate little or no gas in the colon. Although a small amount of gas or fecal accumulation may be present at an early stage of a small bowel obstruction the detection of a large amount of gas in the colon effectively eliminates this diagnosis.
Plain abdominal radiographs are occasionally insufficient for a distinction to be made between small and large bowel obstruction. In these instances, a carefully performed barium enema examination will document or eliminate the possibility of large bowel obstruction. If it is necessary to determine the precise site of small bowel obstruction, barium can be administered in either a retrograde (by means of an enema) or an antegrade (by way of the mouth) manner. Orally administered barium (not water-soluble agents) is the most effective contrast material for demonstrating the site of small bowel obstruction. The large amount of fluid proximal to a small bowel obstruction prevents any trapped barium from hardening or increasing the degree of obstruction. The density of barium permits excellent visualization far into the intestine; water-soluble agents, however, are lost to sight because of dilution and absorption. It must be emphasized that if plain radiographs clearly demonstrate a mechanical small bowel obstruction, any contrast examination is unnecessary.
Strangulation of bowel caused by interference with the blood supply is a serious complication of small bowel obstruction. Because venous pressure is normally lower than arterial pressure, blockage of venous outflow from the strangulated segment occurs before obstruction of the mesenteric arterial supply. Ischemia can rapidly cause necrosis of the bowel with sepsis, peritonitis, and a potentially fatal outcome.
CT may aid in demonstrating small bowel obstruction when the plain abdominal radiographs are normal or nonspecific. Surgery is usually required to decompress the bowel as soon as possible to prevent necrosis or bowel perforation from occurring.
Large Bowel About 70% of large bowel obstructions result from primary colonic carcinoma. Diverticulitis and volvulus account for most other cases. Colonic obstructions tend to be less acute than small bowel obstructions; the symptoms develop more slowly, and fewer fluid and electrolyte disturbances are produced.
The radiographic appearance of colonic obstruction depends on the competency of the ileocecal valve. If the ileocecal valve is competent, obstruction causes a large, dilated colon with a greatly distended, thin-walled cecum and little small bowel gas. The colon distal to the obstruction is usually collapsed and free of gas. If the ileocecal valve is incompetent, there is distention of gas-filled loops of both colon and small bowel, which may simulate an adynamic ileus.
The major danger in colonic obstruction is perforation. The cecum is the most likely site for perforation. In the patient with suspected large bowel obstruction, a low-pressure barium enema can be safely performed and will demonstrate the site and often the cause of the obstruction.
Some professionals recommend an abdominal/pelvic CT scan as an initial examination, especially for patients without a surgical history who have symptomatic signs suggesting infection, bowel infarction, or palpable mass. CT can demonstrate causes of an obstruction, such as diverticulitis or appendicitis.
Cholecystitis Acute cholecystitis (inflammation of the gallbladder) in 95% of cases usually occurs after obstruction of the cystic duct by an impacted gallstone.
Either ultrasound or radionuclide scanning can be used. When ultrasound is inconclusive, MR cholangiopancreatography can demonstrate the cystic duct and any obstructing calculi located in the gallbladder neck.
No treatment is necessary for asymptomatic patients. For acute impaction and biliary colic, prompt treatment using an antispasmodic and an analgesic helps alleviate symptoms. Interventional treatments available today include lithotripsy, and stone removal by endoscopic retrograde cholangiopancreatography (ERCP). The most common surgical approach used currently is the laparoscopic cholecystectomy. The radiographer may be requested to obtain images during operative cholangiography to determine ductal blockage and identify remaining stones. Imaging is performed during contrast injection. The contrast agent should be free of air bubbles because this artifact simulates stones.
Colorectal Cancer Carcinoma of the colon is one of the most common malignancies and the second most common cause of cancer mortality. The incidence of colon cancer rises significantly after age 40 and doubles with each decade, reaching a peak at about age 75. Predisposing factors include a family history of familial polyposis and ulcerative colitis. Environmental factors also seem to correlate with colorectal cancer, as countries with higher intakes of sugar and animal fats (Western diet).
Adenocarcinoma is the most common type of colorectal cancer and is derived from the glandular epithelium of the colon. Adenocarcinoma is characterized by infiltration of the colon wall. It begins as a benign adenoma that undergoes a slow malignant transformation. All polypoid lesions larger than 1 cm should be removed from the colon to prevent risk of malignancy.
Fifty percent occur in the rectosigmoid area and are detectable by flexible sigmoidoscopy. Right colon lesions differ considerably from left colon lesions in terms of symptoms produced. Lesions in the right colon, on the one hand, may produce no early symptoms, often becoming quite large, ulcerating, and even bleeding without significant symptoms. They also tend to penetrate and extend into surrounding tissues without causing obstruction. Such patients often present initially with anemia and blood in their stools. Left colon lesions, on the other hand, present more often with obstruction and bleeding, largely because of a smaller lumen and an annular (ringlike) growth pattern.
The evaluation of colon cancer includes fecal blood testing, proctosigmoidoscopy, colonoscopy, CT colonoscopy, and the barium enema. A double-contrast enema has been noted to produce more accurate diagnoses than the traditional single-contrast study. The radiographic appearance of adenocarcinoma has led to its designation as the “napkin-ring” carcinoma or the “apple-core” lesion.
Without treatment, invasion of local tissue spreads the cancer via the lymphatics to the mesenteric nodes and on to the liver and lungs. The primary means of treatment are surgical excision of the primary tumor and its margins and resection of the bowel as possible. A colostomy may be required, depending on the site of the tumor. Radiation therapy is generally given before and after surgery for rectal cancers. For inoperable tumors, the radiation therapy is given to reduce the tumor size and its resultant complications (e.g. obstruction) and also to provide pain relief. Chemotherapy is given when the cancer has metastasized.
Diverticulitis Diverticulitis is a complication of diverticular disease of the colon (necrosing inflammation in the diverticula), especially in the sigmoid region, in which perforation of a diverticulum leads to the development of a peridiverticular abscess. It is estimated that up to 20% of patients with diverticulosis eventually develop acute diverticulitis. Retained fecal material trapped in a diverticulum by the narrow opening of the diverticular neck causes inflammation of the mucosal lining, which then leads to perforation of the diverticulum. This usually results in a localized peridiverticular abscess that is walled off by fibrous adhesions. The inflammatory process may localize within the wall of the colon and produce an intramural mass, or it may dissect around the colon, causing segmental narrowing of the lumen. Extension of the inflammatory process along the colon wall can involve adjacent diverticula, resulting in a longitudinal sinus tract along the bowel wall. A common complication of diverticulitis is the development of fistulas to adjacent organs (bladder, vagina, ureter, small bowel).
Severe spasm or fibrotic healing of diverticulitis can cause a rigidity and progressive narrowing of the colon that simulates annular carcinoma.
Although radiographic distinction from carcinoma may be impossible, findings favoring the diagnosis of diverticulitis include the involvement of a relatively long segment, a gradual transition from diseased to normal colon, a relative preservation of mucosal detail, and fistulous tracts and intramural abscesses. At times, colonoscopy or surgery may be required to make a definitive diagnosis. On a barium enema study, the diverticula appear as barium filled outpouchings of the large intestine.
Noninvasive treatment is the first choice, using dietary modifications (nothing with seeds, nuts, popcorn, etc.) and exercise (to increase peristalsis). If diverticulitis has developed, antibiotics and diet adjustments (liquids) are given until the bowel heals. Perforation requires surgical repair and a regimen of antibiotics.
Esophageal Carcinoma Progressive difficulty in swallowing (dysphagia) in a person older than 40 years must be assumed to be caused by cancer until proven otherwise. Because the symptoms of esophageal carcinoma tend to appear late in the course of the disease, carcinoma of the esophagus has a dismal prognosis. Most carcinomas of the esophagus are of the squamous cell type and they occur most often at the esophagogastric junction. The incidence of carcinoma of the esophagus is far higher in men than in women. There is a strong correlation between excessive alcohol intake, smoking, and esophageal carcinoma.
The earliest radiographic evidence of infiltrating carcinoma of the esophagus appears on a double-contrast barium swallow film as a flat, plaquelike lesion, occasionally with central ulceration, that involves one wall of the esophagus. At this stage, there may be minimal reduction in the caliber of the lumen. Unless the patient is carefully examined in various positions, this earliest form of esophageal carcinoma can be missed. As the infiltrating cancer progresses, irregularity of the wall is seen, indicating mucosal destruction. Advanced lesions encircle the lumen completely, causing annular constrictions with overhanging margins and often some degree of obstruction. The lumen through the stenotic area is irregular, and mucosal folds are absent or severely ulcerated
Luminal obstruction as a result of carcinoma causes proximal dilation of the esophagus and may result in aspiration pneumonia. Extension of the tumor to adjacent mediastinal structures may lead to fistula formation, especially between the esophagus and the respiratory tract.
CT has become a major method of staging patients with esophageal carcinoma (with 90% accuracy), providing information on tumor size, extension, and respectability. Using contrast enhancement improves the detail of tumor delineation.
If the cancerous lesion has not extended into surrounding tissue, surgical resection may result in cure. When the cancerous lesion involves surrounding tissue, treatment becomes palliative surgery together with radiation therapy or chemotherapy. If the esophagus is severely narrowed, a technique known as bougienage can be employed; this is the introduction of a long instrument to dilate and help maintain an adequate lumen
Gastroesophageal Reflux Gastroesophageal reflux disease (GERD) describes any symptomatic condition or structural changes caused by reflux of the stomach contents into the esophagus. Reflux esophagitis develops when the lower esophageal sphincter fails to act as an effective barrier between the stomach and distal esophagus. Alcohol, chocolate, caffeine, and fatty foods tend to decrease the pressure of the esophageal sphincter, allowing reflux to occur. Regardless of the cause, acute esophagitis produces burning chest pain that may simulate the pain of heart disease. Although the reflux of gastric acid contents is the most common cause of acute esophagitis, infectious and granulomatous disorders, physical injury (caustic agents, radiation injury), and medication may produce a similar inflammatory response. Superficial ulcerations are most typical of reflux. The esophagus is often dilated, with a loss of effective peristalsis. Nonpropulsive peristaltic waves, ranging from mild tertiary contractions to severe segmental spasms, are an early finding.
There is a higher-than-normal likelihood of gastroesophageal reflux in patients with sliding hiatal hernias.
Several radiographic approaches can demonstrate gastroesophageal reflux. One procedure is to increase intraabdominal pressure by straight-leg raising or manual pressure on the abdomen, often with Valsalva’s maneuver. Turning the patient from prone to supine or vice versa may demonstrate reflux of barium from the stomach into the esophagus.
The earliest radiographic findings in reflux esophagitis are detectable on double-contrast studies. They consist of superficial ulcerations or erosions that appear as streaks or dots of barium superimposed on the flat mucosa of the distal esophagus. In single-contrast studies of patients with esophagitis, the outer borders of the barium-filled esophagus are not sharply seen but rather have a hazy, serrated appearance with shallow, irregular protrusions indicating erosions of varying length and depth. Widening and coarsening of edematous longitudinal folds can simulate filling defects. In addition to diffuse erosion, reflux esophagitis can result in large, discrete, penetrating ulcers in the distal esophagus or in a hiatal hernia sac.
Surgery as a treatment is the last option for those whose symptoms have failed to respond to medical therapy. It is performed using video-assisted laparoscopic techniques.
Hiatal/Diaphragmatic/Inguinal Hernias A hiatal hernia is a weakness of the esophageal hiatus that permits some portions of the stomach to herniate into the thoracic cavity. Hiatal hernias occur in about half of the population over age 50. In its early stages, a hiatal hernia is reducible. Chronic herniation may be associated with GERD.
A direct, or sliding, hiatal hernia occurs when a portion of the stomach and gastroesophageal junction are both situated above the diaphragm. This type of hernia constitutes the outstanding majority (about 99%) of all hiatal hernias. A Schatzki’s ring is often visible with this condition and consists of a mucosal ring that protrudes into the lumen. Such a ring has traditionally been thought to be congenital but may be related to gastric reflux. It is generally of no clinical significance unless it produces narrowing sufficient to cause dysphagia, usually less than 13 mm in diameter.
A far less common type of hiatal hernia is the rolling, paraesophageal, or diaphragmatic hiatal hernia. This occurs when a portion of the stomach or adjacent viscera herniates above the diaphragm while the gastroesophageal junction remains below the diaphragm. If all of the stomach slides above the diaphragm, an intrathoracic stomach results. Unlike the sliding hiatal hernia, a paraesophageal hernia is potentially life threatening because of the risk of volvulus, incarceration, or strangulation of the hernia.
Most hiatal hernias are asymptomatic, but some are accompanied by reflux. Treatment of hiatal herniation is generally conservative to minimize discomfort. In most cases, a hiatal hernia requires no treatment. If surgical intervention is necessary, the hiatus is tightened and the stomach secured below the diaphragm.
An inguinal hernia, which is common in men, occurs when a bowel loop protrudes through a weakness in the inguinal ring and may descend downward into the scrotum
If a herniated loop of bowel can be pushed back into the abdominal cavity, it is said to be reducible. If it becomes stuck and cannot be reduced, it is called an incarcerated hernia. As described previously, this can result in a bowel obstruction. If the constriction through which the bowel loop has passed is tight enough to cut off blood supply to the bowel, it is called a strangulated hernia. Prompt surgical intervention is required in this case to avoid necrosis of that portion of the bowel. Bowel that has already necrosed can generally be surgically resected.
Ileus Adynamic ileus is a common disorder of intestinal motor activity in which fluid and gas do not progress normally through a nonobstructed small and large bowel. A variety of neural, hormonal, and metabolic factors can precipitate reflexes that inhibit intestinal motility. Adynamic ileus occurs to some extent in almost every patient who undergoes abdominal surgery. Other causes of adynamic ileus include peritonitis, medications that decrease intestinal peristalsis, electrolyte and metabolic disorders, and trauma. Adynamic ileus (or paralytic ileus) occurs more often than mechanical bowel obstruction. The clinical findings in patients with adynamic ileus vary from minimal symptoms to generalized abdominal distention with a sharp decrease in the frequency and intensity of bowel sounds.
The radiographic hallmark of adynamic ileus is the retention of large amounts of gas and fluid in dilated small and large bowel. The entire small and large bowel in adynamic ileus, unlike in mechanical small bowel obstruction, appears almost uniformly dilated with no demonstrable point of obstruction.
There are two major variants of adynamic ileus. Localized ileus refers to an isolated distended loop of small or large bowel (the sentinel loop), which is often associated with an adjacent acute inflammatory process.
Colonic ileus refers to selective or disproportionate gaseous distention of the large bowel without an obstruction. Massive distention of the cecum, which is often horizontally oriented, characteristically dominates the radiographic appearance. Colonic ileus usually accompanies or follows an acute abdominal inflammatory process or abdominal surgery. The clinical presentation and the findings on plain abdominal radiographs simulate those of mechanical obstruction of the colon. A barium enema examination is usually necessary to exclude an obstructing lesion.
Adynamic ileus caused by surgery usually resolves itself spontaneously in 36 to 48 hours if no complications are involved. Treatment includes insertion of a nasogastric tube to aspirate the stomach, decompress the bowel, and allow the intestine to rest. Electrolyte and fluid imbalances are corrected by intravenous (IV) injection.
Irritable Bowel Syndrome The term irritable bowel syndrome refers to several conditions that have an alteration in intestinal motility as the underlying pathophysiologic abnormality. Most consider these conditions to be functional disorders because there is a disruption of the food sequence breakdown in the stomach and intestines. Patients with irritable bowel syndrome may complain primarily of chronic abdominal pain and constipation (spastic colitis), chronic intermittent watery diarrhea, often without pain, or alternating bouts of constipation and diarrhea.
Although there are no specific radiographic findings in irritable bowel syndrome, patients with this condition usually undergo a barium enema examination to exclude another chronic disorder as the cause of the symptoms. When the patient is symptomatic, a barium enema may demonstrate areas of irritability and spasticity and accentuated haustration, although similar radiographic findings may be observed in normal asymptomatic persons, especially those who have received laxatives and enemas.
No cure exists for irritable bowel syndrome. As the precise cause of this functional disorder has not been determined, symptomatic relief is provided. It is necessary to identify trigger foods so that they can be avoided, thus decreasing the spasms and pain. Alternative therapies, relaxation, meditation, and physical exercise have value if the patient can use them to help ease some of the spasms and pain.
Meckel’s Diverticulum Meckel’s diverticulum is a fairly common congenital diverticulum of the distal ileum. It may measure as large as 10 or 12 centimeters in diameter. This saclike anomaly is located within 6 feet of the ileocecal valve and is a remnant of a duct connecting the small bowel to the umbilicus in the fetus. Children with a Meckel’s diverticulum often develop an ulcer in the adjacent bowel, and a common sign is repeated episodes of bleeding from the ulcerated site. Symptoms in adolescents and adults include cramping, vomiting, and bowel obstruction. The symptoms mimic those of appendicitis except for the location of the pain. Diagnosis of a Meckel’s diverticulum is difficult; it is rarely seen on barium studies of the small bowel because of rapid emptying during a barium study. It is best diagnosed with a radionuclide (nuclear medicine) scan. Surgical removal is often recommended to prevent possible diverticulitis, obstruction, or blood loss.
Pancreatitis An inflammation of the pancreatic tissue. It is one of the most complex and clinically challenging disorders of the abdomen and is classified as acute or chronic, according to clinical, morphologic, and histologic criteria. Acute pancreatitis resolves without impairing the histologic makeup of the pancreas and most often results from biliary tract disease. Chronic pancreatitis results when frequent intermittent injury to the pancreas causes increasing damage that produces scar tissue. Chronic pancreatitis does impair the histologic makeup of the pancreas, resulting in irreversible changes in pancreatic function. Its causes include excessive and chronic alcohol consumption, obstruction of the ampulla of Vater by a gallstone or tumor, and even the injection of contrast media during ERCP. Once activated by any of these causes, trypsin, the pancreatic enzyme that is normally excreted through the ducts into the duodenum, begins to autodigest the organ itself. This can be quite serious and carries a high mortality rate. A pseudocyst is a fluid collection caused by pancreatitis. Pancreatic calcifications are a pathognomonic finding in chronic pancreatitis, developing in about one third of patients with this disease. The small, irregular calcifications are seen most frequently in the head of the pancreas and can extend upward and to the left to involve the body and tail of the organ.
Symptoms of pancreatitis vary from mild abdominal pain, nausea, and vomiting to severe pain and shock. Jaundice may develop if inflammatory edema of the head of the pancreas sufficiently obstructs the common bile duct. Three symptoms that help identify chronic pancreatitis are pain, malabsorption causing weight loss, and diabetes.
Radiographic indications of pancreatitis are subtle and previously centered on displacement of the duodenal C-loop or the stomach by the diseased pancreas or calcified stones within the pancreatic or biliary ducts. The infected pancreas is usually enlarged, with a shaggy and irregular contour. In advanced cases, fluid collections are demonstrated within the pancreas, as well as within the retroperitoneum. ERCP is of value in determining the reasons for acute recurrent pancreatitis, chronic pancreatitis, or the complications associated with pancreatitis. Because pancreatic disease is often asymptomatic in the early stages of disease, sonography is good for assessing the texture and size of the organ. Similar information can be obtained less expensively and without ionizing radiation by ultrasound, therefore, CT is usually reserved for patients with chronic pancreatitis in whom technical factors make ultrasound suboptimal. When CT is used as the imaging choice, research has shown that although most CT examinations are performed with the use of IV contrast agents, the use of contrast agents during the onset of acute pancreatitis may cause necrosis in areas with poor blood supply. Pancreatic necrosis increases the mortality and incidence of infection, so patients should be well hydrated before a contrast-enhanced CT examination is performed.
Management of patients with pancreatitis consists of a pain-relieving drug in mild cases and maintaining proper fluid levels to prevent shock, a frequent occurrence in acute pancreatitis. Proper dietary restrictions (e.g., abstinence from alcohol) are also important. Most cases of acute pancreatitis require supportive treatment only (e.g., IV fluids, pain and nausea medications) because the pancreas will self-heal. If acute pancreatitis is caused by stone blockage, procedures to remove the stone (e.g., ERCP) or possibly surgery to remove the gallbladder should be done. In some cases, IV antibiotics are given to help reduce the inflammatory process and prevent infection. The role of surgery in chronic pancreatitis remains controversial with regard to the effectiveness of results. The prognosis is excellent in patients with mild pancreatic inflammation and edema. Chronic pancreatitis also increases the risk of developing pancreatic cancer, so most patients are continuously monitored for malignancy.
Situs Inversus Is a congenital condition in which the major visceral organs are reversed or mirrored from their normal positions. The condition affects all major structures within the thorax and abdomen. Generally, the organs are simply transposed through the sagittal plane. The heart is located on the right side of the thorax, the stomach and spleen on the right side of the abdomen and the liver and gall bladder on the left side. The left lung is trilobed and the right lung bilobed, and blood vessels, nerves, lymphatics and the intestines are also transposed.
Most people with situs inversus have no medical symptoms or complications resulting from the condition. There is no treatment for situs inversus. In the unlikely case that a heart defect is present, it should be treated accordingly by a cardiologist.
Individuals who have situs inversus should be sure to inform all physicians involved in their medical care. In addition to preventing unnecessary confusion, this will reduce the risk of missing a crucial diagnosis that presents with location-specific symptoms (i.e. appendicitis).
Volvulus Volvulus refers to a twisting of the bowel on itself that may lead to intestinal obstruction. Volvulus of the large bowel most frequently involves the cecum and sigmoid colon. A sigmoid volvulus, more commonly found in the elderly, results from a bulky high-residue diet causing constipation.
There are 2 types of volvulus – cecal volvulus and sigmoid volvulus. Only a few patients with an extremely mobile cecum ever develop cecal volvulus.
A long, redundant loop of sigmoid colon can undergo a twist on its mesenteric axis and form a closed-loop obstruction. In sigmoid volvulus, the greatly inflated sigmoid loop appears as an inverted U-shaped shadow that rises out of the pelvis in a vertical or oblique direction and can even reach the level of the diaphragm. The affected loop appears devoid of haustral markings and has a sausage or balloon shape.
A barium enema examination demonstrates an obstruction to the flow of contrast material at the site of volvulus and considerable distention of the rectum. The lumen of the sigmoid tapers toward the site of stenosis, and a pathognomonic bird’s-beak appearance is produced.
Surgical detorsion is usually required, although a water-soluble enema may be therapeutic and resolve the obstruction.