Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

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

Figure 4.8. Multiple fistulas secondary to Crohn’s disease. CT after oral contrast identifies matted loops of small bowel just superior to the bladder (arrow). Fistulas extend between small bowel, colon, and bladder. Other images identified gas within the bladder. (Courtesy of Patrick Fultz, M.D., University of Rochester.)

the two studies in all patients (58); US fistulography was performed using physiologic saline injected through an inserted catheter, with the fistulous tracts appearing as hypoechoic lines extending from the cutaneous opening. One advantage of fluoroscopic guidance is that the amount of contrast injected is easier to estimate by visualizing the extent of the internal communications.

Bowel perforation and peritonitis is infrequent in Crohn’s disease, yet most physicians dealing with this disease sooner or later encounter this complication, at times as an initial presentation. A concurrent small bowel obstruction is often also present.

Bleeding/Thrombosis

Chronic blood loss and iron-deficiency anemia are not uncommon with small bowel Crohn’s disease.A rare patient presents with major hemorrhage even to the point of exsanguination.

Patients with Crohn’s disease are at increased risk of vascular thrombosis. Etiology for thrombosis in these patients is not known; coagulation defects and fibrinolysis have been suggested, although not all patients with thromboembolic complications manifest a coagula-

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tion disorder. Inferior vena caval thrombosis and portal vein thrombosis develop, with the latter being more common with ulcerative colitis than with Crohn’s disease (Fig. 4.9). Inferior mesenteric vein thrombosis is not uncommon.

Arterial occlusive disease is occasionally found in relatively young Crohn’s patients. In some, this appears to be a premature atherosclerosis rather than a vasculitis; these patients often are steroid dependent and have longstanding Crohn’s colitis. Some arterial thrombi are at a remote site, including internal carotid arteries.

These thrombi are readily detected with CT.

Malignancy

The prevalence of small bowel adenocarcinoma, lymphoma, and hematologic malignancies in patients with long-standing Crohn’s disease is greater than in the general population, although the small numbers involved make prediction uncertain. Current evidence suggests that duration of disease and presence of surgically bypassed loops of bowel are factors in carcinoma development. Other potential pathogenetic factors include chromosomal abnormalities, immunologic dysfunction, and medical therapy for Crohn’s disease. These adenocarcinomas develop throughout diseased bowel, including strictureplasty sites and in fistulous tracts.

The imaging appearance of a malignancy in a setting of Crohn’s disease is nonspecific and mimics a benign stricture (Fig. 4.10).

Genitourinary

An extensive phlegmon surrounding the terminal ileum occasionally obstructs the right ureter and results in an eventual loss of the right kidney, at times silently. A rare patient develops left-sided hydronephrosis. Renal US to check for hydronephrosis seems worthwhile in a patient with extensive ileal Crohn’s disease.

Renal tubular damage appears to be an extraintestinal manifestation of disease and not due to therapy (59).

So-called metastatic Crohn’s disease occasionally involves the penis; ulcerations develop and biopsy reveals granulomas.

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Other

Thyroid disease is more common with ulcerative colitis than with Crohn’s disease. Thyroid volume and free thyroxine increase and some patients develop antithyroid antibodies, even in the absence of clinical thyroid disease. Thyroid volume can be calculated by US.

A weak association between Sweet’s syndrome (acute febrile neutrophilic dermatosis), believed to represent a hypersensitivity reaction occurring with parainflammatory and paraneoplastic conditions, and Crohn’s disease appears to exist. Erythematous, ulcerated skin nodules develop in these patients; biopsy revealed noncaseating granulomas.

Mesenteric fibromatosis is a rare complication of Crohn’s disease,almost always associated with previous intestinal resection. Fibromatosis occurs more often after bowel resection in familial polyposis syndrome.

One example of the protean manifestations of Crohn’s disease is a young adult with lung infiltrates, believed to represent sarcoidosis, who also developed peptic ulcer symptoms with gastric outlet obstruction and duodenal stenosis after a Billroth I anastomosis, later thought to be due to Crohn’s disease (60); bronchial biopsy revealed noncaseating granulomas.

Ascites occasionally develops during an acute episode. Ascites is not a feature of chronic Crohn’s disease; if present, another etiology should be sought.

Figure 4.10. Small bowel adenocarcinoma in a setting of longstanding Crohn’s disease.

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Published recurrence rates after surgical resection of diseased bowel vary considerably; the observed symptomatic recurrence rate is lower than endoscopyor biopsy-detected recurrence rate. Also, patients presenting with an acute complication tend to have higher recurrence rates.

The type of surgery performed has little influence on recurrence. Quite often resection margins contain microscopic disease, yet retained disease or length of macroscopic disease-free resection margins probably has little influence on subsequent recurrence.

Strictureplasty avoids a short bowel syndrome developing after an extensive resection and appears useful in managing extensive obstructive Crohn’s disease. It does not alter the natural disease course.

A laparoscopic approach continues to gain ground whenever an ileocecal resection or stoma formation are necessary for Crohn’s disease.

Systemic amyloidosis is a rare but serious complication of Crohn’s disease, with the kidneys being the critical target organ. Scintigraphy using a I-123 serum amyloid component targets body amyloid deposits; preliminary evidence suggests a possible role for this test in patients with suspected Crohn’s amyloidosis (61).

Outcome

Most patients who have Crohn’s disease do not die from it. The Rochester, New York, registry of inflammatory bowel disease patients shows that patient deaths due to Crohn’s disease decreased from 44% in the period 1973–1980 period to 6% in the period 1981–1989 (62).

Serial gray-scale US measurement of bowel wall thickness and Doppler US grading are used by some to follow changes in disease activity during medical management.

Typical indications for surgery are failed medical therapy, small bowel obstruction, enteric fistula, and abscess. The most common site for recurrence after surgery is in the preanastomotic neoterminal ileum.

Surgery does not cure Crohn’s disease. Surgery can, however, control complications.

Chronic Idiopathic Enterocolitis

Also found as an isolated entity, chronic nongranulomatous ulcerative enterocolitis occasionally develops in patients with celiac sprue, lymphoma, hypogammaglobulinemia, and related conditions. Biopsy reveals a chronic inflammatory infiltrate involving small bowel and often also colon. No infection or inflammatory bowel disease is detected during prolonged follow-up. Some patients respond to steroid therapy.

The relationship of chronic granulomatosis syndrome to this condition is conjecture.

Imaging findings in this entity are not established.

Acute Enteritis

In some adults and children acute enteritis causes lymph nodes enlargement. Such enlarged nodes are nonspecific and are found in a number of diseases.

Aside from the two entities discussed, similar clinical presentations are found with Campylobacter jejuni enteritis, Escherichia coli infection, and Clostridium difficile infection. Imaging is often nonspecific and CT simply reveals ileal or cecal wall thickening and enlarged mesenteric lymph nodes. Occasionally marked bowel

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dilation is a prominent feature. Clinically, either acute gastroenteritis or Crohn’s disease are suspected.

Yersinia Enterocolitis

Yersinia enterocolitica, a gram-negative, low temperature growing bacillus, is a common enteric pathogen; in temperate countries gastroenteritis due to yersinia infection usually ranks third after Campylobacter and Salmonella. It often presents as an acute, self-limiting enteritis with symptoms referable to the right lower quadrant mimicking appendicitis or acute Crohn’s disease. Also called mesenteric adenitis, this infection most often is due to either Y. enterocolitica or C. jejuni. Mesenteric lymph node biopsy simply identifies nonspecific follicular hyperplasia.

A number of these patients have been explored for suspected appendicitis; the appendix is found to be unremarkable but terminal ileum is thickened and mesenteric adenopathy identified. Preoperative imaging for suspected appendicitis should differentiate these two conditions. At times Crohn’s disease has a similar clinical presentation and even intraoperative appearance; in patients with Y. enterocolitica infection the clinical and imaging findings revert to normal within several weeks.

At times Y. enterocolitica infection is chronic. Thus CT and US in a woman with weight loss and leukocytosis detected enlarged abdominal lymph nodes. A malignant lymphoma was suspected but bone marrow and lymph node biopsies did not detect a neoplasm (63); serology confirmed a previous Y. enterocolitica infection and in 6 months her enlarged lymph nodes regressed.

Occasionally Y. enterocolitica results in a small bowel intussusception, presumably secondary to enlarged mesenteric nodes.

Salmonella/Shigella (Enteric Fever)

Enteric fever is caused by Salmonella infection, with common serotypes being S. typhi, S. paratyphi, and S. enteritidis. The only reservoir for S. typhi is in humans. Histologically, bowel and mesenteric lymph node involvement mimics Kikuchi-Fujimoto lymphadenitis (see Chapter 14) and infection by some other bacteria. The diagnosis is confirmed by culture.

Salmonella and Shigella infection results in an acute terminal ileitis. A colitis is also often evident and many of these patients cannot tolerate a barium study, especially a barium enema.

A small bowel barium study in a patient with Salmonella ileitis showed terminal ileal spasticity and thickened folds (64); CT revealed a circumferential, homogeneously thickened terminal ileum and mild colonic wall thickening.

A small bowel barium study in a patient with Shigella ileitis identified an irregular narrowed lumen, large nodules, and terminal ileal ulcers, and CT showed thickening of the terminal ileal wall and a target configuration (64). In spite of these anecdotal reports, imaging cannot differentiate between most infective agents. The role of CT in differentiating these infections from Crohn’s disease is not clear.

Giardiasis

Giardiasis is a protozoan infestation endemic throughout large parts of the world. Clinically it presents with gastroenteritis of varying severity. It is commonly diagnosed from duodenal aspirates or biopsies, although a barium study often suggests the diagnosis.

The radiologic changes are best seen in the duodenum and proximal small bowel; small bowel folds are thickened and distorted. Increased intraluminal secretions are common. Some patients develop disordered peristalsis.

Occasionally giardiasis involves most of the gastrointestinal tract and even biopsies of the terminal ileum and colon yield positive results.

Strongyloidiasis

Infestation with the nematode Strongyloides stercoralis leads to vomiting, diarrhea, and rectal bleeding. Disseminated infection is often fatal, especially in the very young and those with diabetes mellitus, malnutrition, and immunosuppression. In others strongyloidiasis smolders for decades, presenting only with occasional relapses.

Imaging reveals thickened valvulae conniventes. With more extensive infestation CT identifies a thickened, poorly marginated bowel wall that enhances postcontrast to varying