Книги по МРТ КТ на английском языке / Advanced Imaging of the Abdomen - Jovitas Skucas

three questions are raised in this setting: Is obstruction indeed present? Where is the obstruction? What is the etiology of an obstruction? From a surgical perspective the first question is most important and generally both the first and often also the second question can be answered by conventional radiography. The underlying etiology is of less interest to the surgeon, except to exclude ischemia and incarceration, etiologies notoriously difficult to detect early by any imaging modality. Bowel obstruction (or the lack of it) can be approached with either an oral barium study or CT, although many radiology departments have evolved to the point where CT is more readily available and is encouraged.

Conventional radiographs aid in differentiating complete or high-grade partial small bowel obstruction from low grade or no obstruction; findings suggesting a high-grade small bowel obstruction include the presence of gas-fluid levels at a differential height in the same loop and presence of a mean gas-fluid level width ≥25mm on upright abdominal radiographs (94).

Barium Study

A small bowel barium study is a viable option in the patient with a suspected small bowel obstruction. Contraindications to barium are few: an acute abdomen, suspected bowel perforation, or distal colonic obstruction. Some surgeons still argue for a water-soluble agent to avoid possible barium spillage into the peritoneal cavity during subsequent surgery, an argument of dubious validity; the surgeon should spill neither barium nor the usually infected intestinal contents proximal to a small bowel obstruction.

A number of studies have documented the advantages of enteroclysis over a conventional small bowel study, yet in most institutions enteroclysis is rarely performed in this clinical setting.

Prior to performing a barium study, be it a conventional small bowel study, enteroclysis, or a CT-enteroclysis study, thought must be given to whether another diagnostic study will be needed that is obviated by the intraluminal retention of barium. Even endoscopists complain if their field of view is obscured by barium.

ADVANCED IMAGING OF THE ABDOMEN

Small bowel obstruction is not a contraindication to an antegrade barium study. Barium proximal to a small bowel obstruction remains in suspension. It does not become more viscous, as happens in the colon, and in the small bowel barium does not influence the degree of obstruction. Contrary to an occasional surgical report (95),barium does not make a small bowel obstruction worse. Likewise, the occasional surgeon’s request to use “thin” barium in a setting of small bowel obstruction is meaningless; marked fluid retention proximal to an obstruction invariably leads to barium dilution.

A barium enema with reflux into the small bowel is a viable study in a patient with suspected distal small bowel or colon obstruction. This study differentiates between obstructive ileus and adynamic ileus in most patients and often provides an etiology for an obstruction.

Computed Tomography

Reported CT sensitivities in detecting small bowel obstruction have ranged up to 100%, with examiner enthusiasm and interest in the technique probably influencing results. Nevertheless, a number of studies over the past decade have shown that CT not only detects a small bowel obstruction but also often identifies a cause. CT can correctly distinguished between small bowel obstruction and adynamic ileus in almost all and established a cause of obstruction in most. In general, CT is more accurate in a setting of a high-grade rather than low-grade obstruction.

Comparing conventional radiography and CT in patients with suspected small bowel obstruction, the positive predictive value of conventional radiography was 80% and of CT 95% (96); of interest is that the false-negative rate was 8% with conventional radiography but only 1.6% with CT. Nevertheless, the authors recommended that conventional radiography still be the initial study of choice. The authors did not evaluate and compare their CT results to barium studies.

A blinded retrospective analysis comparing conventional radiography and CT in patients suspected of having a small-bowel obstruction achieved a similar overall accuracy with both examinations (Table 4.8); CT, however, revealed

a cause of obstruction in 95%, a finding not usually possible with conventional radiography. The authors concluded that conventional radiography should remain the initial imaging study in patients with suspected small bowel obstruction. Comparing enteroclysis and CT in clinically equivocal small bowel obstruction, CT correctly identified 79% of 43 proven intestinal obstructions (98); CT was most accurate with a complex or long narrowed segment and least accurate with short stenotic segments. It was falsely positive in two patients with mesenteric infarction; enteroclysis had no false positives or false negatives. The author concluded that enteroclysis is more accurate in detecting and localizing an obstruction, but CT is superior in determining the cause of the obstruction and in detecting any underlying strangulation.

A retrospective CT study in children achieved a sensitivity of 87% and specificity of 86% for detecting small bowel obstruction (99); the etiology of the obstruction was correctly identified in 47% of scans.

The conclusions of these studies apply to the patient with a suspected small bowel obstruction where an examination is performed to confirm that an obstruction is indeed present and to suggest an etiology. Another large group of patients consists of those hospitalized with an obstruction but due to delays, often erroneous but well-intentioned, the obstruction has now resolved clinically and the radiologist is asked to suggest an etiology for the previous obstruction. The analogy is similar to a chest

radiograph being obtained after pneumonia has cleared. In such a situation enteroclysis appears to be the examination of choice in detecting a subtle underlying tumor, residual adhesion, or similar abnormality; CT is of limited value in such a setting.Also, CT appears to have a limited role in evaluating a partial small bowel obstruction. In such a setting enteroclysis appears superior.

Typical CT criteria for small bowel obstruction consist of a discrepancy between more proximal dilated and more distal nondilated small bowel loops (Fig. 4.23). Distal small bowel obstruction consists of generalized small bowel dilation and a narrowed colon lumen. A CT finding of gas and particulate material in dilated segments of small bowel is considered abnormal, and most of these patients have a more distal small bowel obstruction, although an occasional patient with slow small bowel transit, regardless of etiology, has similar findings. It is, however, an uncommon finding in obstruction.

Thickened bowel wall containing a thin hyperdense component, called a target sign or halo sign, represents fluid within the bowel wall and is seen with bowel ischemia. A somewhat similar appearance is found with small bowel intussusception and with an inflamed loop, such as in Crohn’s disease. This sign is also seen in some normal bowel where it represents fat infiltration and appears related to obesity (100).

Rather than relying on axial images, coronal and sagittal images are often more helpful in

Figure 4.23. An incisional hernia causing small bowel obstruction after laparoscopic surgery. CT identifies both the hernia (arrow) and marked proximal small bowel dilation. (Courtesy of Patrick Fultz, M.D., University of Rochester.)

identifying a point of obstruction and suggesting a possible etiology.

Computed tomography enteroclysis achieves a sensitivity similar to that of conventional enteroclysis in detecting a site of partial small bowel obstruction, assesses the degree of obstruction, and often also identifies a cause of the obstruction. This study is superior to conventional CT, especially in a setting of partial small bowel obstruction. Still, CT enteroclysis should be approached with caution; instillation of large amounts of contrast into a small bowel already distended by an obstruction simply distends it further and risks inducing vomiting and aspiration.

Ultrasonography

Ultrasonography studies of patients with acute abdominal pain have achieved sensitivities of 75% to 95% in detecting an obstruction, yet closer perusal makes it difficult to place these studies in a proper perspective. Ultrasonography is more often employed to study the bowel in Europe rather than the United States or Canada, where it has been supplanted by CT and, to a lesser extent, by MRI.

Conventional US readily identifies extraluminal fluid; such fluid is present in about two thirds of patients with small bowel obstruction.

Duplex Doppler US has been used to differentiate between obstruction and paralytic ileus, with results similar to those obtained during a

physical examination, namely, in the early stages of mechanical obstruction. Doppler US reveals hyperperistalsis proximal to the obstruction; in long-standing obstructions, as expected, a decrease in intensity and duration of peristalsis predominates. Dilated and atonic segments are identified in adynamic ileus, although some bowel motility usually is still present. Fluoroscopic observation of contrast-filled loops of bowel identifies similar peristaltic activity, although most fluoroscopists tend to rely little on these observations.

Magnetic Resonance Imaging

Magnetic resonance imaging is not often employed in suspected small bowel obstruction; rather, obstruction is occasionally detected when a study is performed for other reasons. Preliminary evidence suggests, however, that a MR study dedicated to the small bowel is rather accurate. A prospective study of patients with suspected inflammatory bowel disease or small bowel obstruction found that MR enteroclysis findings were similar to those obtained with conventional enteroclysis or surgery (6).

Adhesions

The most common cause of small bowel obstruction is adhesions, usually secondary to prior surgery. The surgery does not necessarily have to involve small bowel. In one hospital, small bowel obstruction due to adhesions was highest after appendicectomy and colonic resections and lowest after gallbladder and pancreatic surgery (101). Even some urologic procedures lead to small bowel obstruction. Adhesions range from single to multiple. Some adhesions fixate or kink a loop of bowel; others, extrinsic to the bowel, act as a nidus for an internal hernia.

Computed tomography reveals an adhesive obstruction as a sharp bowel angulation at the site of obstruction. A barium study identifies an adhesion as a smooth, extrinsic, linear impression at the point of change in bowel caliber.

Cancer

Not all obstructions in patients with a known cancer are secondary to tumor; about one third

JEJUNUM AND ILEUM

have a benign etiology. At times CT can suggest an etiology for intestinal obstruction. Patients with known intraabdominal malignancy and small bowel obstruction often have other sites of obstruction not detectable by CT (102); additional information altering subsequent treatment is often provided by a contrast enema. In fact, the entire gastrointestinal tract should be studied in cancer patients because multiple sites of obstruction are relatively common.

Surgery relieves most small bowel obstructions. In patients with a malignant obstruction, however, surgical relief of an obstruction usually does not influence survival.

Closed Loop Obstruction/Volvulus

A closed loop obstruction consists of a loop of bowel obstructed at two points. The closed loop refers to bowel lumen and not blood vessels. In time, increasing intraluminal pressure leads to venous stasis, ischemia, and strangulation. Although many closed loop obstructions eventually evolve into strangulation, from an imaging viewpoint the two entities can be distinguished: a closed loop obstruction implies lumen obstruction; strangulation signifies bowel ischemia. Obstruction in a hernia is a type of closed loop obstruction.

A volvulus is due to intestinal twisting and resultant lumen obstruction.A volvulus is a type of closed loop obstruction if the obstruction involves both inflow and outflow to the twisted loop.

Because etiologies of volvulus differ between infants and adults, these populations are best approached separately.

Infants

Small bowel volvulus in infants is almost always associated with midgut malrotation or nonrotation. Malrotation predisposes to a small bowel twist around its mesentery, which contains the superior mesenteric artery and vein; resultant vascular compromise leads to small bowel necrosis unless emergent surgical intervention ensues. The proximal end of malrotation is in the descending duodenum, distal to the papilla of Vater, and resultant luminal obstruction at this level accounts for the common clinical pres-

entation of bilious vomiting, often within first days of life.

Conventional radiographs often reveal partial rather than complete duodenal obstruction. Complete duodenal obstruction and a gasless distal bowel is more common with duodenal atresia. Ischemia developing in a setting of neglected partial volvulus also results in a gasless abdomen. A conventional radiographic finding compatible with duodenal obstruction is seen only in about half of the infants requiring surgical correction. When present, however, a need for further imaging prior to surgery is debatable.

The duodenal corkscrew appearance on a contrast study is familiar to most radiologists. Barium is used by most, with a minority preferring water-soluble low osmolarity contrast agents. Some advocate US using water as a contrast agent, but such an approach is very operator dependent and not widely practiced.

The usual anatomic relationship of superior mesenteric artery and vein is reversed in malrotation. Ultrasonography reveals a whirlpool, with the superior mesenteric vein and mesentery twisted around the superior mesenteric artery. Although this finding is useful in detecting malrotation both with CT and US, falsepositive and false-negative findings do occur. In one study, however, color Doppler US identified a whirlpool sign that rotated clockwise (with caudal movement of the transducer) in 12 of 13 pediatric patients with surgically confirmed midgut volvulus and counterclockwise in three patients without midgut volvulus (103); the sensitivity of this clockwise US whirlpool sign in detecting midgut volvulus was 92% and the specificity 100%, and the authors suggest that color Doppler US should be an initial imaging study in children with suspected midgut volvulus.

Adults

In adults a closed loop small bowel obstruction is most often secondary to adhesions. Small bowel volvulus without a predisposing cause is not common in Western Europe or North America, but in parts of Turkey it represents 13% of small bowel obstruction (104). In some parts of the world volvulus is associated with ingestion of large quantities of milky foods. Ascariasis infestation predisposes to small

bowel volvulus. On a rare occasion a small bowel mesenteric tumor, even a lipoma or lymphangioma, acts as a nidus for a twist, leading to volvulus. A rare cause was a vena cava perforation by a Greenfield filter resulting in smallbowel volvulus (105).

Some adults with chronic small bowel volvulus have few clinical signs and symptoms and some even do not require surgical correction.

The classic conventional radiography description of a closed loop small bowel obstruction is a coffee bean sign, often a late finding caused by the mostly fluid-filled dilated loops. The diagnosis is established with barium studies, CT, MRI, or even angiography. Computed tomography shows radial convergence of stretched mesenteric vessels toward a point of obstruction. The involved small bowel loops taper toward the point of obstruction, and two converging bowel loops, representing the afferent and efferent loops, are identified at the point of obstruction. At times such converging loops are identified even before clinical obstruction is evident. Small bowel loops involved in the closed loop are dilated and have a C or U shape. Veins draining the closed loop are engorged. Eventually bowel and mesenteric folds become edematous and radiate toward the site of torsion.

Computed tomography and US of a volvulus reveal a similar appearance to a closed loop obstruction, but a volvulus also contains a twist or whirl due to rotation of the involved loop of bowel and its mesentery; the radiating folds mimic a spoke wheel. Mesenteric edema and ascites are relatively common findings. In a volvulus involving most of the small bowel, the superior mesenteric artery and vein are reversed in their relative positions.A mesenteric twist is not pathognomonic of volvulus but is also seen with adhesions and prior bowel resection.

Ileosigmoid Knot

A rare cause of both small bowel and sigmoid colon obstruction, the ileosigmoid knot consists of ileal loops wrapping around the base of a redundant sigmoid. Both an elongated small bowel mesentery and a redundant sigmoid colon predispose to this entity. The twisted ileal loops readily become ischemic and gangrenous; thus there is a high prevalence of strangulation.

ADVANCED IMAGING OF THE ABDOMEN

Occasionally conventional radiographs suggest the diagnosis by identifying a small bowel obstruction,a dilated sigmoid colon,and medial displacement of the cecum and distal descending colon. A barium small bowel study simply shows small bowel obstruction, although this study tends to be unsatisfactory due to the often associated peritonitis and superimposed slow bowel transit time. Computed tomography is suggestive by showing a twist, or whirl, of the involved bowel.

Strangulation

In a strangulated obstruction, blood flow to the obstructed loop is compromised, leading initially to ischemia and eventually to bowel necrosis. The diagnostic studies must thus be performed with dispatch.

The most common cause of bowel strangulation is a loop trapped in a hernia, either internal or external. An acute volvulus often also compromises blood supply to the twisted loop and leads to strangulation. Strangulating obstructions are difficult to diagnose both clinically and with conventional radiologic techniques. Enteroclysis should detect a closed loop obstruction, but cannot detect strangulation unless bowel edema or other signs of ischemia are evident. A target sign, mesenteric edema or infiltration by blood, and pneumatosis intestinalis are evidence of ischemia. Strangulation progressing to pneumatosis intestinalis, regardless of how diagnosed, signifies bowel wall necrosis.

Computed tomography of a strangulating loop shows a serrated beak at the site of the bowel obstruction. Intramural edema and hemorrhage develop due to ischemia. Contrastenhanced CT reveals delayed enhancement of diseased bowel loops. Intramesenteric hemorrhage is identified in some patients. Computed tomography findings pointing to a strangulated obstructions rather than a simple small bowel obstruction are poor or no bowel wall enhancement, findings of low sensitivity but high specificity. Less often found are an unusual course for mesenteric vessels and mesenteric vessel engorgement.Ascites develops eventually. Overall,CT identifies about 85% of patients with a strangulated obstruction, keeping in mind that higher sensitivities can be achieved at the expense of lower specificity.

JEJUNUM AND ILEUM

Abnormal US findings are detected in about 90% of patients with bowel strangulation; these consist of small bowel distention, aperistalsis, bowel wall thickening, and intraperitoneal fluid, findings also seen with prolonged simple small bowel obstruction, but with strangulation these findings develop earlier in the course. An US finding of fluid–fluid levels due to intestinal content sedimentation throughout the small bowel is found with small bowel obstruction, regardless of cause, once adynamic ileus ensues. On the other hand, US detection of intraluminal fluid–fluid levels in a segment of adynamic bowel together with peristalsis in other loops suggests a strangulating obstruction (106).

Figure 4.24. Transient jejunojejunal intussusception in a patient with terminal ileal Crohn’s disease, a rare association.

Intussusception

Ileocolic intussusception is discussed in the Chapter 5.

Clinical

The final end point of an intussusception is invagination of one loop of bowel (intussusceptum) into another (intussuscipiens). Almost any segment of the small bowel and colon can be involved. Most intussusceptions are antegrade, with only an occasional one being retrograde. Detected on barium studies or CT, most are transient and cannot be duplicated. Experienced radiologists detect random, transient nonobstructing intussusceptions sufficiently often that these are often considered to be a normal variant (Fig. 4.24). Indeed, whether such transient intussusceptions are of clinical significance in the absence of other findings is debatable. Nevertheless, transient intussusceptions are more common than normal in certain disorders, such as celiac sprue.

It is the longer, more persistent intussusceptions, with the intussusceptum consisting not only of bowel but also its associated mesentery, that cause trouble both in adults and children. Among adults with one or more intussusceptions detected with CT or MR, 30% had a neoplastic lead point (107). Both jejunal and ileal polyps, benign and malignant, act as lead points. A Meckel’s diverticulum or enlarged lymph nodes occasionally serve as a lead point both in adults and children. Hypertrophied Peyer’s patches, a duplication, or even ectopic

pancreas are encountered as a lead point mostly in children. Enteric intussusceptions due to metastases are rare. Rare also is an intussusception due to Crohn’s disease. Small bowel intussusception is a complication encountered after prior abdominal surgery. At times intussusception is obscured by postoperative or chemotherapeutic findings.

Jejunal intussusceptions in children are not common, and although some are idiopathic, more often a polyp, such as a hamartoma, is a lead point. More distal intussusceptions in young children tend to be idiopathic.

In distinction to infants, the signs and symptoms in most adults with intussusception are nonspecific. An obstruction is not even initially suspected in many patients.

Imaging

Jejunogastric intussusception is one of the complications encountered after a hemigastrectomy and gastrojejunostomy (Billroth II operation). A barium study reveals coiled-spring–appearing jejunal loops within the gastric remnant, thus confirming the diagnosis. Computed tomography or US should also establish the diagnosis; a coiled-spring appearance to the jejunal loops (intussusceptum) within the stomach should be evident.

In children with an ileoileocolic intussusception, an air enema tends to identify the intussusceptum as two or more intraluminal polyps

once it has been reduced to the ileocecal valve; this appearance differs from the smooth or somewhat lobulated appearance found with most simple ileocolic intussusceptions to allow differentiation of ileoileocolic from ileocolic intussusceptions.

Computed tomography of an enteroenteric intussusception reveals a characteristic target lesion containing an intraluminal soft tissue tumor (intussusceptum), asymmetric mesentery, and, at times, a dilated intussuscipiens (Fig. 4.25). When imaged along its long axis, an intussusception has more of a sausage-shaped appearance. Occasionally CT also defines an underlying lead point.

The US appearance of an uncomplicated enteric intussusception is that of a target lesion.

Fluid within bowel provides intrinsic contrast for T2-weighted MRI. A bowel-within-bowel or coiled spring appearance is seen on both axial and coronal images.

Gallstone Ileus

Most gallstones impact in the distal ileum (not in the terminal ileum). The next most common site is in the duodenum (discussed in Chapter 3), and the least common is colonic obstruction, where it occurs proximal to a stricture.

A typical clinical scenario is the elderly woman with no previous abdominal surgery presenting with small bowel obstruction. At the other extreme, gallstone ileus has been detected even in a teenager.

ADVANCED IMAGING OF THE ABDOMEN

Gallstone ileus is often suspected from a conventional radiographic examination. The classic Rigler triad consists of small bowel obstruction, biliary tract gas, and a distal small bowel calcification, although all three findings are uncommon in any one patient. Similar findings are also evident with CT, and preliminary data suggest that CT allows a more confident diagnosis.

Abdominal US detects small bowel obstruction and does locate an ectopic gallstone in some patients.

Mortality with gallstone ileus remains high, partly due to an often late diagnosis, aged patient population, and frequently coexisting other medical problems.

Foreign Body

Gastrointestinal foreign bodies are encountered in both children and adults (Fig. 4.26). A majority pass spontaneously without complications.

Small bowel bezoars are less common than gastric ones. Risk for bezoars increases after vagotomy and partial gastric resection. An unusual small bowel obstruction developed during enzymatic treatment for a gastric persimmon bezoar (108). Conventional radiographs simply suggest bowel obstruction without identifying a bezoar. Some bezoars contain sufficient gas to suggest pneumatosis intestinalis. A barium study identifies the intraluminal bezoar. Computed tomography findings consist of an intraluminal heterogeneous soft tissue tumor, often containing focal gas.

JEJUNUM AND ILEUM

Figure 4.26. A swallowed tube-like foreign body contains contrast (arrow). (Courtesy of Algidas Basevicius, M.D., Kaunas Medical University, Kaunas, Lithuania.)

A trichobezoar is an uncommon cause of small bowel obstruction. Most are suggested by conventional radiography or a barium study and further imaging is not warranted.

Retained surgical gauze eventually becomes encased in a fibrotic mass that can lead to small bowel obstruction or a fistula and mimic a neoplasm. In a region of the world endemic for tuberculosis, a retained surgical sponge simulated intestinal tuberculosis (109). Retained surgical staples are generally of little significance, although when incorporated in an adhesion they appear next to an obstruction. Occasionally a severed gastrostomy tube obstructs the small bowel.

The current popularity of a high-fiber diet is also not without risk. Thus in one patient recurrent small bowel ileus was caused by ingestion of high-fiber canned asparagus (110).

Other Obstructions

Acute sigmoid diverticulitis is a not uncommon cause of small bowel obstructions; a loop of small bowel becomes trapped by focal inflammation or simply becomes adynamic.

Any intramural infiltration sufficient to narrow the lumen eventually leads to lumen obstruction. Similar to the duodenum, intramural hemorrhage or a hematoma can obstruct the jejunal or ileal lumen; these obstructions tend to be transient, and they clear as a hematoma resolves.

Small bowel obstruction is a rare but major complication during pregnancy. As in the general population, those women who have had previous abdominal surgery are at increased risk of developing a small bowel obstruction.

Eosinophilic gastroenteritis–associated bowel stenosis is a rare cause of small bowel obstruction.

Therapy

Once appropriate imaging studies are obtained and an obstruction diagnosed, an indwelling catheter is useful in decompressing the small bowel; this should make the patient more comfortable and aid the return of bowel function.

Some surgeons claim a purported therapeutic effect by hyperosmotic water-soluble contrast in relieving small bowel obstructions, but radiologists generally scoff at such claims. A prospective, randomized study of patients with suspected postoperative small bowel obstruction comparing the effect of instilling 100mL of a hyperosmotic water-soluble contrast agent via a nasogastric tube found no difference in length of hospital stay or in the rate of complications, whether a contrast agent was used or not (111).

Traditionally, patients with an unresolving small bowel obstruction underwent a laparotomy. Laparoscopic therapy of small bowel obstruction is also performed, especially in a setting of postoperative adhesions.

Adynamic Ileus

Acute

Peritoneal inflammation, either primary or secondary, leads to bowel paralysis. The resultant adynamic ileus ranges from focal (sentinel loop) to generalized and involves both the small and large bowel. Some surgeons attempt to distinguish between a normal postoperative ileus and adynamic ileus. Most radiologists consider these to be the same entity.

Ingestion of certain raw foods induces adynamic ileus. In Japan, adynamic ileus developed in some patients after eating raw squid (112); the squid contained a specific type of

larva.Acute small bowel angioneurotic edema is also a cause of adynamic ileus.

Acute adynamic ileus can generally be suspected from conventional radiographs; both the small bowel and colon are dilated. Superficially, distal colonic obstruction and an incompetent ileocecal valve mimic these findings.

Chronic (Pseudo-Obstruction)

Chronic adynamic ileus, also called intestinal pseudo-obstruction, is not a single entity but an intestinal condition associated with a number of neuropathies and myopathies. Familial visceral neuropathy results in chronic myenteric plexus destruction leading to poor motility and bowel distention on a chronic basis. Myotonic muscular dystrophy and familial visceral myopathy involve intestinal smooth muscle and lead to small bowel dysmotility and distention (Fig. 4.27). Endoscopic biopsy is generally not helpful in these patients because abnormalities are in the external muscle layers. Barium contrast studies are often necessary to exclude mechanical obstruction.

Figure 4.27. Familial oculo-intestinal myopathy in a 21–year- old patient. Enteroclysis reveals marked bowel hypotonia. The bowel wall is of normal thickness. (Courtesy of Arunas Gasparaitis, M.D., University of Chicago.)

ADVANCED IMAGING OF THE ABDOMEN

At times intestinal pseudo-obstruction is associated with an underlying neoplasms, such as lung carcinoma or carcinoid, with the intestinal dilation presumably secondary to a paraneoplastic process. In some patients intestinal dysmotility resolves after tumor resection. Intestinal pseudo-obstruction and a secretory diarrhea were the initial presentation in a man found to have Crohn’s disease (113).

Infants with fetal alcohol syndrome develop intestinal pseudo-obstruction, probably due to an enteric neuropathy.

Various radiopaque markers have been used to measure small bowel transit time, but they have achieved limited clinical application. Gastric emptying, small bowel transit and colonic transit can be combined into a single scintigraphic whole-gut transit time study. The clinical relevance of such a test, however, is not clear.

Therapy with erythromycin and cisapride are often effective therapies in this condition.

Systemic Sclerosis (Scleroderma)

Systemic sclerosis is readily differentiated from celiac disease. In the latter entity the duodenum tends not to be dilated, close to normal small bowel motility is evident, dilation involves primarily the distal small bowel, and more intraluminal bowel content is present—findings differing from those seen in systemic sclerosis.

Some patients with systemic sclerosis develop pneumatosis cystoides intestinalis and even idiopathic pneumoperitoneum. Although a de novo pneumoperitoneum usually suggests a surgical abdomen, some of these patients are managed medically. Nevertheless, an autopsy study of patients with systemic sclerosis found bowel perforation to be more common than expected (114); these perforations ranged from the esophagus to colon, with some being initially silent. The authors suggest that the bowel wall in these patients is inherently weak, and cautioned physicians performing invasive procedures to keep this in mind.

Other Disorders

Collagenous sprue mimics celiac disease both clinically and radiologically. Duodenal and

JEJUNUM AND ILEUM

jejunal biopsies reveal villous atrophy in both entities, but in collagenous sprue collagen is deposited in small bowel lamina propria.

The small bowel is not a major target organ in Chagas disease. An occasional patient develops marked jejunal dilation due to stasis, bacterial overgrowth, and resultant malabsorption.

The small bowel appearance in dermatomyositis is similar to that seen in sprue, although findings in sprue tend to be more striking.

Ehlers-Danlos syndrome is an inherited connective tissue disorder resulting in skin hyperextensibility, articular hypermobility, and tissue fragility. The bowel is dilated. These patients are prone to developing intestinal hemorrhage and bowel perforation.

Generally a carbon-14 D-xylose breath test is used in patients with suspected small bowel bacterial overgrowth. One limitation of this test is that in individuals with gastrointestinal motor dysfunction, delayed gastric emptying tends to prevent carbon-14 D-xylose from reaching the small bowel loops involved by bacterial overgrowth and thus results in a negative test. A liquid phase gastric emptying test performed at the same time as D-xylose test corrects for gastric stasis.

Perforation/Fistula

Bowel perforation and resultant peritonitis is discussed in Chapter 14.

Migration of a biliary stent into the small bowel is generally of little consequence; rarely, it has led to small bowel perforation.An uncommon cause of bowel perforation is a suction biopsy. A swallowed toothpick or sharp bone can lead to small bowel perforation. Some perforations seal over spontaneously and have few, if any, sequelae; others develop into peritonitis or an abscess.

Pneumoperitoneum is the classic sign of bowel perforation. As is well known, not all perforations result in a pneumoperitoneum; intraperitoneal fluid is more common. Computed tomography visualization of bowel wall discontinuity at a perforation site is rare. Oral contrast extravasation likewise is rarely identified, although renal excretion after oral administration of a water-soluble contrast agent

should raise suspicion of bowel perforation. A caveat: in some patients orally ingested watersoluble contrast is absorbed from normal bowel. Nonabsorbable barium contrast agents are not used in a clinical setting of suspected acute bowel perforation.

A fistula involving the small bowel can develop to any adjacent structure. In adults most fistulas are secondary to either prior surgery or Crohn’s disease. Less often a small bowel malignancy or disorders in adjacent structures lead to a fistula. A small bowel fistula to bone results in osteomyelitis.

Subtle small bowel fistulas and sinus tracts are best studied with enteroclysis.

Most enterocutaneous fistulas are initially managed medically. Fluoroscopically guided fistulous tract and associated bowel catheterization should be considered for those not healing; eventual fistula closure can be achieved in most. Several chronic enterocutaneous fistulas were successfully treated by injecting biologic glue (N-butyl-2-cyanoacrylate-histoacryl) into the fistulous tract (115).

Diverticula

Meckel’s diverticula were discussed earlier (see Congenital Abnormalities).

Jejunal and ileal diverticula are not rare. Most are innocuous and considered to be incidental findings (Fig. 4.28). An occasional diverticulum will bleed (at times massively), perforate, or even obstruct the small bowel. A rare diverticulum evolves into diverticulitis or an intraabdominal abscess, involves extraperitoneum structures, or develops into an abdominal wall abscess. Clinically, ileal diverticulitis mimics appendicitis.

Tumors, including adenocarcinomas and sarcomas, do develop in diverticula; both barium studies and CT detect them, if they are large enough.

Both small bowel and colonic diverticula are more prevalent in patients with connective tissue disorders such as Marfan’s syndrome and Ehlers-Danlos syndrome. These patients also develop diverticula-related complications.

Occasionally detected is extensive diverticulosis of the entire small bowel. Stasis, bacterial