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

Omphalomesenteric Anomalies

Failure of the omphalomesenteric duct to regress results in a residual umbilical sinus, omphalomesenteric cyst, enterocutaneous fistula, or a Meckel’s diverticulum.

Cysts and Fistulas

An omphalocele is the presence of midgut structures in the umbilical cord remnant (Fig. 4.4). A variety of intestinal content may be present within the defect. The midgut is malrotated. Some patients have other anomalies.

An omphalomesenteric cyst is formed when both omphalomesenteric duct ends involute, leaving a persistent central cavity. Most are incidental findings, with an occasional one becoming infected or compressing and obstructing an adjacent structure. A persistent fibrous omphalomesenteric remnant between the umbilicus and midgut is a potential source for small bowel volvulus around the fibrous band.

Meckel’s Diverticulum

Clinical

A Meckel’s diverticulum is the most common congenital gastrointestinal tract abnormality (Fig. 4.5). It results from persistence of the embryonic yolk sac. Most Meckel’s diverticula are asymptomatic but they can be involved in two clinical scenarios: More common is the patient presenting with bleeding suspected

from gastric mucosa in a Meckel’s diverticulum, with bleeding usually being gradual rather than massive. Less often encountered is the patient with sequelae to inflammation or intussusception. Obstruction is more common in patients under the age of 10 years, and perforation is more common in young adults. A rare Meckel’s diverticulum first manifests in the elderly.

Figure 4.5. Meckel’s diverticulum (arrow), detected on a retrograde small bowel examination.

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Meckel’s diverticula vary in size and shape, with an occasional one being very large. A rare one even has a second outpouching, or daughter diverticulum, connected to the main diverticulum. Ultrasonography reveals an uncomplicated, fluid-filled Meckel’s diverticulum as a cyst-like structure. Some of these diverticula mimic an appendiceal mucocele, mesenteric cyst, enteric duplication, or even a cystic ovarian tumor if a separate ovary cannot be identified by imaging.

Complications

Ectopic gastric mucosa is found in 20% to 50% of patients with Meckel’s diverticula and “gastritis” is common in those with gastric mucosa; only an occasional one contains H. pylori. Similar to the stomach, gastric secretions by this ectopic mucosa are stimulated by hormonal factors. As expected, hemorrhage and perforation develop in a setting of ectopic gastric mucosal tissue.

Incidentally, ectopic gastric mucosa is also found at other sites. As already mentioned, ectopic gastric mucosa is not uncommon in gastrointestinal duplications. In some patients, islands of heterotopic gastric mucosa in the jejunum and ileum account for recurrent small bowel bleeding and accumulation of Tc-99m- pertechnetate at these sites. The Tc-99m- pertechnetate concentrates in gastric mucosal mucin secreting cells, and scintigraphy reveals persistent focal activity only if such gastric mucosa is present within the diverticulum. Cimetidine or ranitidine premedication inhibits gastric secretion and helps diminish background activity. Still, both false-positive and false-negative results occur. At times abnormal Tc-99m-pertechnetate uptake is shown with single photon emission computed tomography

scan detects only the presence of gastric mucosa, rather than hemorrhage or other complications.

Gastric mucosa enhances more than any other bowel mucosa on postcontrast MRI, and any gastric mucosa in a Meckel’s diverticulum reveals marked enhancement.

Calculi are not common in a Meckel’s diverticulum. An enterolith consists mostly of calcified food residue (phytobezoar). Some

stones are multiple, calcified in their periphery, or even faceted. Rarely, a milk of calcium suspension forms in a Meckel’s diverticulum (23). Most stones contain enough calcium to be visible with conventional radiography. Computed tomography and US also detect most of these stones.

A stone (or bezoar) passing into the ileal lumen can cause bowel obstruction and mimic gallstone ileus. A rare enterolith within a Meckel’s diverticulum obstructs the diverticular communication with bowel lumen and leads to diverticulitis. Imaging should identify such a calcified enterolith; superficially an appendicolith is in the differential.

Perforation of a Meckel’s diverticulum is commonly ascribed to ulcerated heterotopic gastric mucosa. An 8-day-old boy perforated a Meckel’s diverticulum (24), a highly unusual age for this to occur; no ectopic gastric tissue was found in the resected specimen, and a narrow diverticular neck was believed to have led to poor emptying, subsequent inflammation, and perforation.

Inflammation does result in Meckel’s diverticulitis. A CT scan showing a fluid-filled cavity surrounded by a thickened, contrast-enhancing wall suggests diverticulitis.

There is no reason why a Meckel’s diverticulum should not be involved by Crohn’s disease. Differentiating terminal ileal Crohn’s disease (and possibly involving a Meckel’s diverticulum) from an inflamed and ulcerated Meckel’s diverticulum is another matter; resultant distortion is similar with both.

A Meckel’s diverticulum is a potential point for small bowel fixation. Torsion initially involves only the diverticulum, but a sufficient twist leads to ileal volvulus. Adhesions secondary to an inflamed diverticulum form a site for an internal hernia.

An inverted Meckel’s diverticulum is a potential lead point for a small bowel intussusception, and in the distal ileum most intussusceptions are due to either a polyp or a Meckel’s diverticulum. An inverted Meckel’s diverticulum appears as an intraluminal polyp. A barium study reveals an inverted diverticulum as a solitary, elongated, smoothly marginated, often club-shaped intraluminal tumor. This inverted diverticulum often contains fat along its serosal surface, detected by CT as an intraluminal elongated mass containing central fat surrounded by

soft tissue. Ultrasonography shows a targetlike structure with a hyperechoic center and identifies a blind-ending, thick-walled bowel loop. An intussuscepting inverted Meckel’s diverticulum is difficult to reduce with a barium or air enema.

Conventional radiography detects a perforation or suggests an obstruction; CT and US identify the site of obstruction and any abscesses and often suggest the underlying etiology.

Tumors similar to those found throughout the gastrointestinal tract also develop in Meckel’s diverticula. A number of these are detected incidentally when a diverticulum is resected for unrelated reasons. These tumors range from adenomas and carcinomas to sarcomas, and originate from either ileal or gastric epithelium. A leiomyosarcoma originating in a Meckel’s diverticulum contained a 4-L cystic component, presumably secondary to necrosis (25). A rare neuroendocrine tumor has developed in a Meckel’s diverticulum.

Therapy

If an incidental Meckel’s diverticulum is discovered, some surgeons recommend that a diverticulectomy be performed; others argue that the risk of complications, although low, does not justify a prophylactic resection. A morbidity of 2% and zero mortality was found in a retrospective study of 90 patients who had an incidental diverticulectomy (26); using decision analysis the authors concluded that an incidental diverticulectomy in adults should be abandoned.

Bleeding and obstruction are the primary presentations in patients requiring surgery for symptomatic Meckel’s diverticula. Less frequent indications for surgery are an acute abdomen due to perforation, diverticulitis, or intussusception.

Trauma

Most radiologists administer both oral and IV contrast prior to a CT trauma study. Oral contrast is generally started early on, often in the emergency department. Its use has been questioned by emergency physicians, who point out

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the additional time incurred, the extra need to insert a nasogastric tube in some patients, and the alleged lack of efficacy, yet most radiologists involved in trauma care find oral contrast very beneficial and administer it almost routinely.

Bowel distention is common with significant bowel trauma, yet this finding is nonspecific; it occurs with bowel obstruction and peritoneal irritation due to a number of etiologies.

A review of almost 20,000 blunt trauma patients found that hollow-viscus injury occurred with a similar frequency in both children and adults (27); duodenal injuries, however, were more common in pediatric patients.

Shock Bowel

Shock bowel represents a diffuse bowel abnormality developing in hypotensive patients, often in a setting of blunt abdominal trauma. The CT findings of shock bowel consist of diffuse small bowel wall thickening, with increased and prolonged contrast enhancement. Often fluid-filled, dilated small bowel is also identified. The colon generally is less affected than small bowel. These bowel CT findings are secondary to hypoperfusion and, at least initially, are reversible.

Bleeding/Hematoma

Intramural hemorrhage manifests as a region of bowel wall thickening. It ranges from focal to diffuse. Hematomas also develop adjacent to injured bowel, either intraor retroperitoneal in location. Because of its intraperitoneal location, small bowel trauma often also results in hemoperitoneum rather than a discrete hematoma. Combined bowel wall and mesenteric injury is often present and fluid (blood) between loops of small bowel is a result of trauma to either one.

Intramural hemorrhage is identified as a homogeneous, focal hyperdense bowel wall thickening that does not enhance postcontrast. Unenhanced CT is often helpful in this setting. Generally a bowel wall thicker than 3 or 4mm (as detected with CT) is assumed to be abnormal, although little evidence in the literature provides quantitative guidance. Some authors

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believe that circumferential wall involvement is necessary for bowel to be considered abnormal (28).

A hyperechoic submucosal layer thicker than 2.5mm, detected by US, implies either submucosal edema or hemorrhage (29).

Most bowel wall hematomas resolve without sequelae; some produce transient small bowel obstruction, but in a few bleeding leads to a stricture requiring surgery.

Wall Thickening

Infection/Inflammation

Clinical presentation in a setting of small bowel infection or inflammation varies considerably. Likewise, imaging findings range from minor thickening of valvulae conniventes to marked intramural infiltration. Submucosal edema and hemorrhage, if severe enough, may lead to small bowel obstruction.

Perforation

Isolated small bowel perforation due to acute blunt abdominal trauma is uncommon; a number of these are due to seat belt trauma. More serious injury to adjacent solid organs is often more evident. Small bowel perforation tends to be more common on the antimesenteric border.

A pneumoperitoneum and extraperitoneal gas are specific but insensitive findings of a small bowel perforation. The small bowel normally contains little gas, and a number of these perforations manifest later as an intraabdominal abscess rather than as an immediate pneumoperitoneum.

Direct CT evidence of bowel rupture is uncommon. An indirect postcontrast CT sign of small bowel rupture consists of a streaky density within the related mesentery due to blood and other infiltration along the mesenteric vasculature.

Small bowel perforation after blast injury is not common. Anecdotal evidence in three men injured by the explosion of a terrorist bomb suggests that an eventually proven perforation does occur after a finite time delay rather than being a manifestation of delayed diagnosis (30); the authors suggest that patients exposed to a blast injury be observed for at least 48 hours.

Stricture

In an occasional patient ischemia of a crushed bowel segment leads to an infarct. A less severe insult evolves into an eventual fibrosis and stricture with the patient presenting with small bowel obstruction weeks or even months after trauma.

Crohn’s Disease

Clinical

Epidemiologic data for Crohn’s disease patients suggest the presence of a recessive gene having high penetrance, in distinction to ulcerative colitis where a dominant or additive gene having low penetrance is more likely. Numerous investigators have searched for an infective etiology. Although a superimposed infection is not uncommon, identification of an infective etiology for Crohn’s disease has not been fruitful and currently no convincing infective etiologic agent is established.

Crohn’s disease in two or more members of a family is found in about 10% of patients; similarly, the prevalence among first-degree relatives is about 10 times that of the general population. Conflicting data exist on whether patients with a familial pattern have an earlier age at onset and more extensive disease than those with sporadic disease.

Prevalence of Crohn’s disease has increased during the last several decades in several populations. Considerable variation in relative prevalence of Crohn’s disease still exists. Crohn’s disease is rare in Central and South America. Although rare among the Chinese, prevalence is increasing, at least in Singapore; in 1993, at Singapore General Hospital the prevalence was 27 per 100,000 patients compared with 3.5 per 100,000 patients in 1986 (31). In the United States, distal ileal involvement is most common. In parts of Europe colorectal involvement predominates at the time of diagnosis. In general, colonic involvement is more prevalent in patients with disease manifesting at a later age. The disease is not limited to the bowel, and even extraintestinal sites can be involved.

Crohn’s disease has two age peaks of onset. At the more common younger age, Crohn’s disease tends to develop after puberty, with only an occasional younger child being affected. Almost all present with abdominal pain, with most children also having weight loss and diarrhea. The second age peak is in the elderly. Here one has to exclude bowel ischemia, which in some patients has a similar clinical presentation and imaging appearance. Nevertheless, enough evidence has accrued to establish that a second peak of onset does indeed occur in the elderly. In general, those having an initial diagnosis made before the age of 20 years have a greater prevalence of family history of Crohn’s disease, more small bowel involvement, and they require more frequent surgery than those diagnosed after age 40 years; the older group had more colonic involvement.

Standardized clinical estimates of severity and activity of Crohn’s disease have been developed and these allow comparison of published studies.

Chronic abdominal pain is common, often being insidious in onset and progression. Some children present with growth retardation or simply delayed puberty. In a small minority of patients hepatobiliary or joint abnormalities manifest first. Especially in children, a blood count and erythrocyte sedimentation rate are almost always abnormal, and these tests appear reasonable with suspected Crohn’s disease.

The literature tends to emphasize gradual disease progression, but in reality two patterns predominate: In a minority, Crohn’s disease is unrelenting, progresses rapidly, perforates readily, and relapses after surgery; in a majority a chronic, indolent course marked by periods of exacerbation and quiescence is more common. Clinical evidence suggests that Crohn’s disease patients tend to fall into specific categories such as those primarily with inflammation and fibrosis-stenosis and those forming fistulas. Within families, patients tend to have concordance of sites and types of involvement.

Pregnancy appears to have a mild favorable influence; prevalence of disease relapse after pregnancy is somewhat less than before pregnancy.

Five patients with Crohn’s disease and leukemia received allogeneic bone marrow transplantation (32); four showed no signs or

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symptoms of Crohn’s disease after transplantation; Crohn’s disease relapsed after transplantation in one patient with mixed donor–host hematopoietic chimerism.

Four patients with long-standing Crohn’s disease had a spontaneous clinical improvement after becoming HIV infected, suggesting that immune response integrity has a role in Crohn’s disease (33). These findings are countered, however, by an HIV-infected patient who developed a new onset of Crohn’s disease (34).

Anti–goblet cell autoantibodies are detected in some patients with Crohn’s disease and in their first-degree relatives, suggesting that this marker is of possible use in detecting patients susceptible to inflammatory bowel disease.

Intussusception is rare with Crohn’s disease; presumably the commonly associated fibrosis prevents it. Nevertheless, occasional enteroenteric intussusception has been reported.

Associated Conditions

A family with both familial polyposis and Crohn’s disease, probably a fortuitous association, has been described (35). Several patients have developed synchronous Crohn’s disease and myelodysplastic syndrome, and this association appears to be more than chance. Myelodysplastic syndrome probably should be considered in older patients with Crohn’s disease and peripheral blood cytopenia, and Crohn’s disease should be considered in myelodysplastic syndrome patients developing gastrointestinal symptoms. Isolated associations have been reported with multiple sclerosis, glycogen storage disease, sarcoidosis, rheumatoid purpura, ankylosing spondylitis, Charcot-Marie-Tooth disease, deuteranopia, pachydermoperiostosis, multiple exostosis, and familial ichthyosis.

Remission was induced by chemotherapy in a patient with non-Hodgkin’s lymphoma (36); abdominal pain, diarrhea, and bloody stools 1 year later were found to be secondary to Crohn’s disease.

An occasional pancreatitis is difficult to place in proper perspective; in some patients it appears related to sclerosing cholangitis, in others to azathioprine therapy, and in still others it appears to be fortuitous. Nevertheless,

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pancreatic autoantibodies are detected in some Crohn’s patients, and some have impaired pancreatic function.

Differential Diagnosis

On an acute basis, some infections are indistinguishable both clinically and radiographically from Crohn’s disease (these are discussed below; see Acute Enteritis). On a more chronic basis, other infections, radiation enteritis, ischemia, Behçet’s syndrome, and some neoplasms have a similar appearance. Major venous thrombosis in a young patient or an ischemic stenosis suggests Crohn’s disease.

Close clinical and imaging similarity between Crohn’s disease and Behçet’s syndrome warrants mention (Behçet’s syndrome is further discussed in Chapter 17). Behçet’s syndrome is often not considered in the differential diagnosis in regions of low prevalence, and undoubtedly some patients have been misclassified. Bowel involvement in Behçet’s syndrome manifests as bowel wall thickening enhancing postcontrast, inflammatory polyps, aphthae, or deep ulcers. Deep distal ileal or right colonic ulcers or a frank perforation should suggest Behçet’s syndrome.

A primary ileocecal region lymphoma can mimic Crohn’s disease. A problem exists for the radiologist who detects typical imaging findings of ileal Crohn’s disease in a patient without an established diagnosis. Should lymphoma be mentioned in the differential diagnosis? Although rare in this imaging setting, some radiologists encounter lymphoma mimicking Crohn’s disease in their practice.

Another entity bedeviling radiologists who detect ileal wall thickening on CT and suggest Crohn’s disease is that a minority of right colon cancers result in similar findings (37); in some patients this thickening is due to direct tumor extension, but in others lymphatic obstruction, congestion, and edema are responsible.

The poorly understood chronic granulomatosis syndrome probably is distinct from Crohn’s disease. Whether orofacial granulomatosis is a manifestation of underlying gastrointestinal Crohn’s disease is speculative.

The clinical findings and imaging appearance of diffuse intestinal ganglioneuromatosis, espe-

cially if involving the distal small bowel, mimic Crohn’s disease (38).

Pathologic Findings

Measured intraoperatively, the small bowel in Crohn’s patients is significantly shorter than in controls.

Increased intestinal permeability and presence of antineutrophil leukocyte antibodies are two of several theories proposed to explain the findings in Crohn’s disease; no definitive proof exists for either one.

One of the hallmarks of Crohn’s disease is the presence of noncaseating granulomas. Why these granulomas develop is not clear. Almost half of these granulomas are adjacent to lymphatic vessel. Mucus-secreting cells are found at sites of ulceration and presumably are sequelae of ileal crypt stem cell differentiation.

Ileal ulcers in Crohn’s disease tend to have a longitudinal orientation and predominate along the mesenteric side. The short vessels supplying this region are end arteries, and small vessel ischemia is a possible cause of these ulcers.

Imaging

Barium Studies

Whether a conventional small bowel barium study or enteroclysis is performed in an initial search for Crohn’s disease is controversial. Some enthusiasts consider enteroclysis the primary imaging method in diagnosing small bowel Crohn’s disease, and mild changes, including subtle aphthae and fistulas, are best seen with enteroclysis. With well-established disease a conventional study is generally sufficient and as an initial study is preferred by many investigators due to its simplicity, better patient acceptance, and relatively high yield. A conventional small bowel barium study is often used to follow exacerbation in patients with established disease. A well-performed study detects strictures, obstruction, fistulas, and a phlegmon. It does not differentiate a phlegmon from an abscess. Also, morphologic findings on a small bowel study correlate poorly with clinical activity; scintigraphy achieves better correlation.

A conventional small bowel study reported better mucosal detail, more fistulas, and more

duodenal involvement than enteroclysis performed within 2 weeks (39). Although the authors concluded that if a small bowel study is normal, no need for enteroclysis exists, a number of gastrointestinal radiologists would disagree and recommend enteroclysis, especially when seeking subtle findings.

A peroral pneumocolon or retrograde study evaluates the cecum and distal ileum using a double-contrast technique (Fig. 4.6). It is an underutilized study in select patients with subtle Crohn’s disease suspected at these sites.

The most common site of small bowel involvement is the terminal ileum, yet any site can be involved. The imaging appearance varies considerably with more proximal involvement (Fig. 4.7).

At times normal small bowel proximal to a diseased segment is somewhat dilated, even without evidence of distal obstruction, a finding ascribed to peritoneal irritation and resultant mild adynamic ileus. One interesting observation made by monitoring intraluminal pressure with a double-lumen tube during enteroclysis is that Crohn’s patients have an elevated intraluminal pressure compared to patients with noninflammatory disease and irritable bowel syndrome (40).

Computed Tomography

Computed tomography detects bowel wall thickening, increased enhancement of diseased

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Figure 4.6. Ileal Crohn’s disease (arrows) identified on retrograde small bowel study. Similar diffuse bowel wall thickening is also seen with lymphoma.

bowel, mesenteric infiltration, fistulas, phlegmon, and abscesses in Crohn’s patients. Although some studies have concluded that CT can be an alternative to small bowel barium studies in detecting inflammatory bowel disease (41), but similar to US, it is not sensitive in detecting subtle involvement. Also, one should avoid the trap of simply calling bowel wall thickening in a clinical setting of suspected Crohn’s disease “compatible with Crohn’s disease”; it is not pathognomonic, and a long differential exists. In spite of some enthusiast’s

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advocacy for CT in suspected early Crohn’s disease, the primary role of CT is in more advanced disease, especially in a search for complications. Thus in a setting of exacerbation, CT is the primary imaging test when suspecting an abscess.

Computed tomography achieves a sensitivity of about 70% in identifying abnormal bowel loops, 80% in detecting fistulas, and almost 100% for abscesses; specificities for these findings approach 100%. Computed tomography identifies bowel wall thickening and a homogeneous bowel wall density. A target sign (hypodense submucosal layer), although more common in ulcerative colitis, is also found in Crohn’s disease.

Computed tomography demonstrates submucosal and mesenteric fat deposition. A diffuse fibrofatty mesenteric infiltrate develops, with adjacent small bowel loops separated by this infiltrate. The normal sharp interface seen with CT between the bowel wall and its mesentery is lost, resulting in an irregular bowel contour and periintestinal blurring. Enlarged mesenteric lymph nodes are common. In general, the involved lymph nodes are smaller than 10mm in diameter; larger ones should suggest a malignancy or other complication.

Postcontrast, vasa recta dilation and diseased bowel wall contrast enhancement are evident. The involved mesentery is hypervascular, a finding identified with CT and Doppler US. In some patients with active disease the mesenteric vessels feeding diseased bowel segments are dilated, tortuous, with prominence and wide spacing of vasa recta, a CT finding called the comb sign (42).

Computed tomography enteroclysis is more accurate than conventional CT not only in detecting Crohn’s disease but also in outlining sinus tracts and fistulas. Multiplanar reformatted images aid in image interpretation. A negative contrast agent apears to improve detection of abnormal bowel (43). Whether CT enteroclysis is superior to conventional enteroclysis is not known.

Ultrasonography

Abdominal US achieves sensitivities and specificities of 90% to 95% in detecting Crohn’s disease location.

With established disease, small bowel wall thickness is generally >5mm. Some authors consider an US bowel wall thickness >7mm to be “diagnostic” for inflammatory bowel diseases (44), a generous thickness indeed, which achieves high specificity, but, similar to CT, a thick bowel wall is not synonymous with Crohn’s disease. A stenosis, regardless of etiology, is usually associated with a thickened bowel wall. Effacement of the five bowel wall layers in a thickened bowel wall, as visualized by US, signifies more severe disease activity than if all five wall layers are identified (45). Little data exists on the accuracy of US in detecting mild small bowel abnormalities, such as the presence mostly of aphthae. Likewise, a correlation of bowel wall thickness with disease activity appears rather simplistic.

Doppler US detects significantly greater superior mesenteric artery blood flow in patients with Crohn’s disease than in controls (46).Vessel density in affected bowel loops, measured by Doppler US, reflects disease activity (47). Superior mesenteric artery resistive indices (RI) also reflect disease activity (Table 4.1).Whether such Doppler US blood flow measurements are of clinical relevance in detecting or following disease activity remains to be established. These findings of increased blood flow in diseased bowel should be balanced by laser Doppler flowmetry data from surgery revealing that blood flow in a bowel containing aphthae is slightly less than in normal tissue and with inflammation progression bowel blood flow actually decreases (48).

Ultrasonography probably detects most Crohn’s-associated abscesses, but the yield for stenoses and fistulas is inconstant and sufficiently low to limit the application of US to specific situations.

Magnetic Resonance Imaging

Magnetic resonance imaging is grossly underused in patients with Crohn’s disease. A retrospective comparison concluded that MRI is superior to US in locating affected segments (sensitivity: MRI 98%; US 76%) and in detecting fistulae (sensitivity: MRI 87%; US 31%), stenoses (sensitivity: MRI 100%; US 58%) and abscesses (sensitivity: MRI 100%; US 89%) (49). Its role in pregnant patients is obvious. The use of oral and rectal contrast and bowel distention

aid in visualizing bowel wall thickening. One technique consists of oral contrast using 1000 mL of a 2.5% mannitol solution and imaging in axial and coronal planes using breath-hold T2weighted half-Fourier acquisition single-shot turbo spin echo (HASTE) and contrastenhanced T1-weighted fast low-angle shot (FLASH) sequences (50); diseased bowel wall enhances considerably more than normal bowel. Contrary to some earlier studies, poor correlation exists between bowel wall enhancement and the Crohn’s Disease Activity Index (50). Inflammation, mesenteric involvement, sinus tracts, and abscesses are depicted by MR. It also has a role in the subset of patients with perianal fistulas being evaluated for surgical correction.

Magnetic resonance imaging identified 80% to 85% of abnormal bowel segments, compared with 60% to 65% by single phase helical CT (51); although moderate or marked mural thickening was identified equally by both modalities, MR was superior in mildly thickened bowel.

Scintigraphy

Scintigraphy does not have a role in initial disease detection; its primary application is in following established disease activity. Although scintigraphic findings correlate with clinical activity and this test is thus useful in disease exacerbation, it appears inferior to other imaging modalities in detecting an abscess, fistula, or bowel obstruction.

Technically, labeling of Tc-99m–hexamethyl- propyleneamine oxime (HMPAO) with leukocytes is easier and study acquisition times faster than a corresponding indium-111 examination. A positive scan represents strong presumptive evidence of inflammable bowel disease and scintigraphy appears to be a simple screening test in differentiating these disorders from such entities as irritable bowel syndrome. This test even detects subclinical bowel inflammation. Thus in one study over half of patients with seronegative spondyloarthropathy and no clinical evidence of inflammatory bowel disease had a positive Tc-99m-HMPAO leucocyte scan (52). It is, however, nonspecific and does not differentiate among Crohn’s disease, ulcerative colitis, infectious enteritis, and inflammation due to such entities as appendicitis. Also, its sensitivity decreases in patients receiving steroid therapy.

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Thus in a Crohn’s patient being treated with steroids, Tc-99m–leukocyte scintigraphy failed to detect inflammation but an In-111 leukocyte scan did reveal abscesses (53); the effect of steroid-induced chemotaxis on leukocyte-based scintigraphy is not clear.

Technetium-99m-HMPAO leukocyte scintigraphy appears to have moderate correlation to the Crohn’s Disease Activity Index (54) but currently the impact of scintigraphy on other imaging and endoscopic modalities and its clinical implications are difficult to place in perspective. Potentially combined use of CT and Tc-99m-HMPAO leukocytes scintigraphy appears useful, yet whether the additional information obtained from these two imaging modalities beyond what is available from barium studies does indeed influence clinical management of most patient remains to be established.

Technetium-99m human polyclonal immunoglobulin scintigraphy appears limited in detecting location or extent of disease. Likewise, In-111 polyclonal immunoglobulin scintigraphy appears less sensitive than Tc- 99m-HMPAO both for diagnosis and in evaluating disease extent and has been replaced by the latter. Radioimmunoscintigraphy with Tc99m antigranulocyte monoclonal antibody is also less sensitive than Tc-99m-HMPAO leukocyte scintigraphy

Scintigraphy with gallium-67 citrate and In111 leukocytes are of limited use in Crohn’s disease.

Complications

Hepatobiliary abnormalities of inflammatory bowel disease are discussed in Chapters 7 and 8. Some of these abnormalities, such as subtly abnormal liver function tests or sclerosing cholangitis, are considered to be not complications but rather a direct manifestation of the disease.

Extraintestinal manifestations are part of the spectrum of findings in Crohn’s disease (Table 4.2). Their prevalence varies considerably in different studies.

Musculoskeletal

Arthritis in patients with inflammatory bowel disease ranges from peripheral to axial. Axial

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Table 4.2. Extraintestinal manifestations of Crohn’s disease

Skin

Pyoderma granulosum

Erythema nodosum

Eyes

Conjunctivitis

Iritis

Uveitis

Joints

Ankylosing spondylitis

Hypertrophic osteoarthropathy

Liver

Sclerosing cholangitis

Cholangiocarcinoma

Other

Abscesses

Thrombophlebitis

involvement tends to be similar to that seen with ankylosing spondylitis. Asymptomatic sacroiliitis is not uncommon; conventional radiography identifies asymptomatic sacroiliitis in considerably fewer patients than CT.An interesting study from Korea found that in Crohn’s patients arthritis occurred only in those with colonic involvement (55). Arthritis and erythema nodosum are more frequent in Crohn’s disease than in ulcerative colitis.

Osteoporosis is a known complication of Crohn’s disease. Some adult and pediatric patients have a marked reduction in bone density and develop vertebral compression fractures. Etiologic factors include the use of steroid therapy, superimposed malnutrition and abnormal calcium, vitamin D, and hormone metabolisms. Bone mineral density evaluation of pediatric Crohn’s patients seems reasonable.

Abscess

Abscesses are more common with small bowel or ileocolic Crohn’s than with colonic involvement. An occasional sterile abscess develops. Some abscesses involve not only adjacent structures, including spleen, lymph nodes, psoas muscle, liver, pancreas, and abdominal wall, but also the brain.A Crohn’s fistula led to a presacral abscess and spondylodiscitis (56). A peroneal

abscess in a Crohn’s patient resulted in priapism. In some patients Crohn’s disease is discovered only after the source for an abscess is sought.

From a clinical viewpoint, differentiation of an abscess from a phlegmon is necessary. Computed tomography is usually employed for this purpose.

Successful percutaneous drainage of Crohn’s abscesses has been performed, although the procedure remains controversial. Among percutaneously drained abscessed, 56% were successful (57); successful drainage was associated with fewer fistulas, and the abscesses tended to be first rather than recurrent, spontaneous rather than postsurgical, located in the right lower quadrant, and small. In an acute clinical setting, percutaneous drainage of even a complex abscess is feasible and, if necessary, can be followed by elective surgical drainage. Drainage of an abscess associated with an internal fistula usually does not heal the fistula. A persistent enterocutaneous fistula at the site of catheter insertion is a recognized complication. Perhaps a major consideration for percutaneous drainage of a Crohn’s abscess is that it gains time to stabilize a patient for further, more definitive, therapy.

Some surgeons believe that surgical resection of inflamed tissues, including diseased loops of bowel, leads to faster healing and fewer complications.

Fistula/Perforation

Fistulas are common and extend to another loop of bowel, bladder, or other structure not involved by Crohn’s disease (Fig. 4.8). In the absence of prior surgery or percutaneous drainage, cutaneous abdominal fistulas are uncommon.A fistula almost always is associated with a phlegmon or abscess. Some fistulas bypass an obstructed bowel segment. Unusual sites include rectourethral and even a rare one into a hip joint. Some of these fistulas are associated with prior resection or abscess drainage.

Suspected cutaneous fistulas are typically studied with fistulography using fluoroscopic guidance. A comparison of US-guided and fluoroscopically guided fistulography in eight patients with Crohn’s ileitis and suspected enterocutaneous fistulas found agreement between