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

COLON AND RECTUM

Some chronically hospitalized or bedridden patients have a chronic megacolon or megarectum, generally of idiopathic etiology. Manometry in these patients reveals abnormal colonic tonicity. Histology of resected specimens from patients with idiopathic megarectum and megacolon reveals hypertrophy of muscularis mucosae and muscularis propria; those with an idiopathic megarectum tend to have decreased innervation density of the longitudinal muscle.

Recurrent acute colonic pseudo-obstruction in a young patient with no evident risk factors was eventually ascribed to toxoplasmosis infection (197); adrenergic bowel denervation was believed to be caused by toxicity or crossreaction between a toxoplasma antigen and the patient’s immune system.

Imaging

The conventional radiographic appearance of Ogilvie’s syndrome mimics distal colonic obstruction. Thus if the diagnosis is in doubt, a limited barium enema is indicated and should differentiate between these conditions.

Instead of a barium enema, two additional conventional radiographs often suffice: a right lateral decubitus view of the abdomen followed by a prone lateral view of the pelvis. With these two additional views gaseous distention of the rectum can be achieved in most patients with pseudo-obstruction, while in patients with mechanical obstruction such distention is not found.

Although the cecum is generally most dilated in Ogilvie’s syndrome, occasionally some other colonic segment is involved. The rectum tends to be collapsed.

Therapy

Ogilvie’s syndrome has been treated successfully with a parasympathomimetic drug such as neostigmine. The success of such therapy suggests that Ogilvie’s syndrome is a result of excessive parasympathetic suppression rather than sympathetic overactivity. Colonoscopic decompression has a high success rate, although some patients required multiple decompressions. A decompression tube positioned in either the right colon or transverse colon appears to be equally successful.

Untreated, Ogilvie’s syndrome has progressed to perforation and an acute abdomen.

Chagasic

Chagas’ disease is a chronic infection caused by the parasite Trypanosoma cruzi, which is endemic in rural regions of Latin America. A chronic phase develops several decades after initial infection, most often manifesting through cardiac abnormalities. Colonic abnormalities consist of decreased motility and tonicity, identified as a megacolon. These patients develop small bowel bacterial overgrowth with resultant complications.

Systemic Sclerosis (Scleroderma)

Colorectal dysfunction is common in patients with systemic sclerosis. Hypotonia and stasis develop in some. Constipation is common, but, paradoxically, incontinence is also not uncommon.

T1and T2-weighted SE MRI magnetization transfer contrast-weighted and dynamic gadolinium-enhanced images in 11 of 14 patients with scleroderma and fecal incontinence revealed forward deviation of an atrophied internal sphincter that had decreased contrast enhancement (198); for comparison, patients with incontinence alone showed no internal sphincter deviation or decreased vascularity but did have significant reduction in external sphincter mass.

Diverticula

Colonic

Colonic diverticula represent outpouchings in the bowel wall. In the past, a distinction was made between true and false diverticula (pseudodiverticula), but common indiscriminate usage has made any such distinction moot.

Prevalence of colonic diverticula varies considerably throughout the world. Their prevalence is increasing in some populations. Right-sided colonic diverticula are more common in Asia than in the West.

Occasionally encountered are calcified stones within a diverticulum. Presumably these stones form as a result of stasis. Superficially such

right-sided diverticular stones mimic gallbladder stones or renal stones.

In rare instances a diverticulum intussuscepts or inverts into colonic lumen and simulates a polyp. Some of these patients have undergone surgery or colonoscopy because the diverticulum could not be distinguished from a polyp. Some of these inverted diverticula have an umbilication that represents the en face diverticular opening. Computed tomography of these inverted diverticula reveal a central contrast collection within the lumen, presumably within the diverticulum.

Ultrasonography does not readily identify colonic diverticula. When seen, diverticulitis rather than diverticulosis should be suspected.

Rectal

Rectal diverticula are uncommon and, in general, tend to be larger than the corresponding sigmoid ones. These diverticula tend to be more common in scleroderma patients.

Giant Diverticula

Giant colonic diverticula are sufficiently rare that individual reports are still being published. Most occur in the sigmoid colon. Their etiology

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is unknown, although several theories are postulated: First, a check-valve mechanism in the diverticular neck allows colonic content to enter but not exit. Or,a localized diverticular infection results in an abscess that eventually communicates with colonic lumen. Although less likely, such a cavity may also represent sequelae of a communicating duplication cyst. In either case, some of these cavities enlarge to giant proportions. Histologically, these giant diverticula do not have a mucosal lining, with the wall consisting mostly of fibrotic tissue, thus suggesting a contained perforation as their etiology.

Patients range from asymptomatic to those presenting with bleeding or an acute abdomen. An occasional giant colonic diverticulum perforates and results in a pneumoperitoneum. Other rare complications include an associated carcinoma, small bowel obstruction, or even volvulus.

These uncommon lesions can be suspected with conventional radiography and are diagnostic with a barium enema when barium flows into the diverticulum, thus establishing its colonic communication (Fig. 5.40). Imaging shows a large gas collection, usually close to the sigmoid colon. The diverticular wall tends to be thin and smooth. Horizontal x-ray beam radiographs often reveal a gas-fluid level. The diverticular wall shows no CT contrast enhancement,

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except if surrounding inflammation is present. Some rare chronic diverticula contain calcifications within their wall.

A thick-walled cavity or any nodularity should suggest a necrotic tumor rather than a giant diverticulum. A communicating duplication is rare in the sigmoid, usually is on the mesenteric side, is seen in a younger patient population, and histology should reveal an epithelial lining containing all layers of the colonic wall.

Most giant colonic diverticula are resected.

Evacuation Disorders

Lax pelvic floor muscles and an abnormal pelvic floor descent are evident in some patients with evacuation disorders, leading to multiorgan interrelated abnormalities; these complex pelvic floor abnormalities, found mostly in women, are discussed in Chapter 12.

Discussed here are primarily evacuation disorders, which in themselves are a diverse and complex group of conditions manifesting mostly by rectal pain and difficulty in evacuation. Rectal incontinence is the other extreme. The nomenclature for various abnormal findings is still evolving, and authors often describe these conditions based on the primary abnormality detected.

Traditionally, proctography evaluated both structural and function, although dynamic MRI is assuming a primary role in evaluating evacuation disorders.

Enterocele

One of the causes of a widened rectovaginal space is a peritoneocele, defined as herniation of the posterior-inferior peritoneal space (cul-de- sac) into a recess between the rectum posteriorly and vagina or bladder anteriorly. Any adjacent intraperitoneal structures can be involved, although most often small bowel is involved and is then called an enterocele. Prolapse of redundant sigmoid (sigmoidocele) is less common. Some of these are capable of partially obstructing the rectum. A distended rectum may conceal a peritoneocele and an enterocele; a radiograph taken with the rectum collapsed should detect this condition.

An anterior enterocele, or anterior vaginal wall hernia containing small bowel, develops in some women who undergo a cystectomy for intractable interstitial cystitis.

Evacuation proctography is the examination of choice to detect the more common posterior enterocele consisting of prolapsed small bowel interposed between vagina and rectum. Small bowel and vaginal opacification are needed during this study. Some enteroceles become evident only at the end of evacuation or on postevacuation radiographs. Of interest is that physical examination detects only half of enteroceles found on proctography (199); the reverse is also true—some enteroceles detected by physical examination are not identified at proctography.

Vaginal US is helpful to detect a posterior enterocele; if one is present, bowel is visualized in the rectovaginal space, especially when bearing down. This examination is highly sensitive and specific in detecting these enteroceles and is an alternative to evacuation proctography.

Rectocele

Although constipation is common in patients with a rectocele, in some patients even a large rectocele is not associated with impaired evacuation. Also, placing rectoceles in clinical perspective can be difficult; constipation is not always relieved after rectocele repair.

Anterior Rectocele

An anterior rectocele consists of a bulge in the anterior wall of the rectum during straining. Although a mild bulge is a normal finding, a typical definition is that the bulge should be >2cm in extent to be considered a rectocele. Most rectoceles are reduced at rest. They are more common in women, probably due to a weakness of the rectovaginal septum.

Some investigators subdivide anterior rectoceles into two groups: distention and displacement. Manometry in patients with each type revealed a significantly higher anal pressure and a more impaired rectoanal inhibitory reflex in the distention group than in controls or the other group (200); patients in the displacement group have a lower anal pressure, and proctog-

raphy at rest and during evacuation show a significantly higher anorectal angle and a more abnormal pelvic floor descent than in the distention group or in controls. Overall, distention rectoceles have pelvic floor dyssynergia, while displacement rectoceles show a descent in the pelvic floor.

Currently a suspected rectocele or sigmoidocele is most often studied with evacuation proctography. Whether a rectocele is detected or not is mostly independent of contrast agent viscosity. Pelvic MRI, including MR proctography, often provides additional information. Proctography detects most rectoceles, although a majority are also detected on physical examination (201); whether barium is trapped in a rectocele depends mostly on its size.

A rectocele tends to bulge only during straining. Among patients with rectocele shown by proctography, 60% also had paradoxical anal sphincter relaxation (202).

In addition to enteroceles and rectoceles, widening of the rectovaginal space on straining is occasionally due to a peritoneocele. Sigmoidoceles are uncommon.

Posterior Rectocele

Posterior rectal outpouchings include posterior rectoceles and ischiorectal hernias. Posterior or perineal rectoceles are outpouchings of the lower posterior rectal wall through a levator ani muscle defect, usually present only during straining. An ischiorectal hernia is seen as a posterolateral outpouching; these are present at rest.

Posterior rectal herniation also develops after resection of sacral tumors, such as a chordoma.

Rectal Prolapse/Solitary Rectal

Ulcer Syndrome

Clinical

Abnormal puborectalis muscle contraction and rectal wall prolapse or intussusception are often implicated in the pathogenesis of solitary rectal ulcer syndrome, a benign condition found mostly in adults. Prolapse ranges from internal to external; the term intussusception is appropriate if it is circumferential. Complete rectal prolapse is a clinical diagnosis and generally needs surgical correction. Whether this

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condition is one syndrome or encompasses a number of disorders is conjecture. Diffuse pelvic floor weakness involving genitourinary structures is found in some women. Chronic constipation, evacuation abnormalities, and rectal prolapse are typical presentations. Confusing the issue, some authors find rectal bleeding to be common, but others believe it is an uncommon finding.

Pressure necrosis and mucosal injury during rectal prolapse and intermittent intussusception appear to play a role, although the pathophysiology is probably multifactorial. Typical histopathologic findings consist of focal mucosal distortion, muscularis mucosa proliferation, and obliteration of lamina propria. An ulcer, accompanied by granulation tissue, is usually located anterior in the rectum but at times extends circumferentially.

Sigmoidoscopy is generally noncontributory in these patients, aside from providing a biopsy and excluding other abnormalities. In some patients manometry reveals decreased external sphincter tone during straining, a nonspecific finding.

Biopsy in patients believed to suffer from solitary rectal ulcer syndrome revealed a solitary ulcer in 78%, multiple ulcers in 11%, granular proctitis in 7%, and rectal inflammation in 4% (203); although voiding proctography missed some ulcers, it identified rectal intussusception in 41%, rectoanal intussusception in 26%, external rectal prolapse in 22%, and mucosal prolapse in 30%. Only one patient had a rectocele. In a majority of patients videoproctography showed that the ulcer wall was first to invaginate.

Solitary rectal ulcer syndrome and an inflammatory cloacogenic polyp have similar histopathologic findings; both are located anterior in the rectum and both tend to be associated with rectal prolapse.

Previous therapy for intractable symptoms included rectocolic resection, a procedure rarely performed today. After elastic binding for rectal mucosal prolapse, follow-up voiding proctography revealed prolapse remission in most patients.

Imaging

A double-contrast barium enema, with emphasis on the anterior rectal wall, is useful to detect

COLON AND RECTUM

an ulcer and the sequelae of inflammation, but an evacuation study is necessary to evaluate functional abnormalities. Imaging is also often requested prior to surgical repair to evaluate the rest of the large bowel.

In spite of its name, solitary rectal ulcer syndrome does not always present with an ulcer, nor is it always solitary. A common imaging appearance is that of nodularity or an anterior rectal wall irregular polyp. Similar findings are

A

seen with an inflammatory cloacogenic polyp; some mimic a rectal adenocarcinoma.

Voiding videoproctography is the imaging modality of choice for suspected rectal prolapse. Prolapse originates in the midrectum as an intussusception varying in length. Proctography reveals rectal mucosal prolapse as a soft tissue bulge into the rectal lumen, more evident during straining and evacuation than during rest (Fig. 5.41). Mucosal prolapse is more

B

common than intussusception (204). Associated other abnormalities are common and include rectocele, perineal descent syndrome, puborectalis muscle syndrome, and levator ani diastasis, the latter identified with dynamic CT.

At times endorectal US is helpful. Ultrasonography reveals an inhomogeneous and thickened submucosa in the internal and external sphincter regions; the ratio of external to internal anal sphincter thickness is reduced in these patients and muscle hypertrophy identified by US appears useful in some in suggesting the diagnosis.

Puborectalis Syndrome

Puborectalis syndrome is used to describe incomplete relaxation or paradoxical contraction of the puborectalis muscle during evacuation, often with resultant outlet obstruction. At times an isolated finding, it is one of a spectrum of abnormalities detected in constipated patients. The term pelvic floor dyssynergy is used by some to encompass a more complex set of findings.

Primary symptom of puborectalis syndrome consists of incomplete or intermittent evacuation. Voiding proctography reveals an abnormal puborectalis muscle impression along the posterior rectal wall, a reduced change in anorectal angle during straining, and prolonged barium pooling in the rectal ampulla; manometry detects an increase in external anal sphincter pressure under straining in about two thirds of these patients (Fig. 5.42). Some patients also have associated rectal mucosal prolapse and a rectocele.

Anismus/Incontinence

Whether anismus and puborectalis syndrome are the same entity is conjecture. Many authors discuss them together. Some patients with functional outlet obstruction have a megarectum, rectocele, rectal intussusception, mucosal prolapse, or abnormal perineal descent. Reduced change in anorectal angle between rest and evacuation is used by some as a criterion for defining functional outlet obstruction. Although the anorectal angle does change during straining and voiding (and viscosity of the contrast medium used influences the

Figure 5.42. Nonrelaxing puborectalis muscle (arrow). This is a contributing factor in solitary rectal ulcer syndrome. (Courtesy of Arunas Gasparaitis, M.D., University of Chicago.)

results), the importance of a particular amount of change is questionable. Anorectal angle measurements provide conflicting data, with some studies revealing no significant difference between patients with anismus and controls and others concluding that in most patients with incontinence the anorectal angle is increased at rest.

One study found that 90% of patients with impaired proctographic evacuation had anismus at subsequent anorectal physiologic testing (205).

Endoanal US identifies anal sphincter defects in approximately two thirds of incontinent patients (206); these findings are difficult to place in the proper perspective because in this same study the prevalence of anal sphincter defects in continent patients was 43%. Endovaginal US appears to be as reliable as endoanal US in evaluating the anal sphincter but endovaginal US is more accurate for perianal inflammatory disease (207).

Whether endoanal US or MR is superior is not clear. A retrospective study in women with fecal incontinence concluded that in detecting external and internal sphincter lesions

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endoanal MRI agreed better with subsequent surgical findings than did endoanal US (208); endoanal US was not accurate in identifying external sphincter thinning, a finding confirmed in another study (209). Yet another study found not only endoanal US and MRI to be equivalent in detecting external anal sphincter defects, but also US was superior for internal anal sphincter defects (210).

Often a combination of studies is helpful in these patients. As one example, proctography in 38 patients with incontinence identified rectal mucosal prolapse (n = 12), rectocele (n = 10), perineal descent syndrome (n = 8), and external rectal prolapse (n = 3); endoanal US identified 15 sphincter ring interruptions (12 hypoechoic, two mixed, and one hyperechoic) and internal anal sphincter thinning in five; perineography revealed a cystocele in five and a cystourethrocele in one; and manometry showed sphincter hypotonia at rest in 15 (211). Placing these findings in a proper perspective, however, is often challenging.

A separate group of patients with fecal incontinence consists of those with congenital anomalies, such as spina bifida. Some of these often young patients are successfully treated with percutaneous cecostomy tube placement, a procedure having few complications.

Table 5.7. Conditions associated with colonic perforation

Mechanical obstruction (obstructive ileus)

Neoplasm

Benign stricture/obstruction

Volvulus

Herniation

Intussusception

Fecal impaction

Adynamic ileus

Inflammation/infection

Ogilvie’s syndrome

Toxic megacolon

Necrotizing enterocolitis

Typhlitis

Ischemic ileus

Severe malacoplakia

Instrumentation

Endoscopy

Barium enema

Biopsy

Foreign body

Toothpick

Other sharp objects

Drug therapy

Ehlers-Danlos syndrome

Perforation

Some of conditions associated with colonic perforation are listed in Table 5.7. Among common etiologies for colonic perforation, patients with a perforating carcinoma have a high mortality. An unusual cause is due to paclitaxel therapy; these perforations appear to be a direct drug effect causing mitotic arrest of the gastrointestinal epithelium. The prevalence of such perforation is not known, although it is associated with a high mortality rate.

Ehlers-Danlos syndrome type IV consists of an inherited collagen disorder. The syndrome can be confirmed by culture of skin fibroblasts. These patients have a defect in either the synthesis or structure of type III procollagen and are prone to spontaneous aortic, small bowel, and colonic rupture. Recurrent colon perforations develop in patients with this syndrome.

A number of reports describe colonic perforation by an ingested sharp bone or toothpick,

generally in the sigmoid colon. Among ingested bones, chicken bones seem to predominate.

Spontaneous rectal perforation is rare; one unusual rectal rupture led to small intestine evisceration through the anus (212).

In distinction to upper gastrointestinal perforation from peptic ulcer disease, which tends to result in small amounts of intraperitoneal gas, colonic perforations more often lead to a large pneumoperitoneum. Exceptions, however, are common. Also, some colonic perforations manifest with an abscess rather than pneumoperitoneum.

Nonspecific Ulcer

Grouped under this heading are those colonic ulcerations believed not to be associated with other diseases. Some of these ulcers presumably are ischemic in etiology. Few publications exist on this topic.

Fistula

Diagnostic modalities to evaluate fistulas include fistulography for cutaneous fistulas, CT, MRI using an endorectal coil, and proctosigmoidoscopy, with endorectal US having a major role in perirectal fistulas. Nevertheless, MRI has gradually achieved preeminence.

At times a two-part CT study is found advantageous when searching internal communication for cutaneous fistulas; first, conventional CT is obtained after filling the appropriate bowel with contrast, followed by concentrated contrast injection into any visible fistulas and rescanning using wide window settings.

Colonoscopy is insensitive in identifying colonic fistulas.

Perianal Fistulas

Perianal fistulas are either anovaginal, associated with Crohn’s disease, or cryptoglandular in origin. Most perianal infections originate in intersphincteric anal glands located close to the dentate line and spread from there. The Parks classification of perianal fistulas is based on a fistula track relationship to anorectal musculature and consists of four main types: (1) superficial or low, (2) intersphincteric, (3) transsphincteric, and (4) suprasphincteric or high fistula. A horseshoe fistula extends circumferentially.

Almost all external sinus tracts and fistulas located close to the posterior midline are associated with a simple superficial or intersphincteric fistula; on the other hand anterior and posterolateral external sinus tracts and fistulas tend to be complex and often extend transsphincteric or are suprasphincteric in their course. These fistulas must be differentiated from necrotic tumors, infections such as actinomycosis, pilonidal cysts, and similar disorders. Any associated abscesses also need be identified by imaging.

What are the relative roles of US and MRI? No obvious answers have emerged, although current evidence suggests that, overall, MR is superior to US; also, MR is the more active current research front.

Fistulography is traditionally used to study sinuses and external fistulas. Few studies have

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compared US and MR against fistulography, preferring to use surgical findings as their gold standard. Yet the reliability of surgery as a standard has been questioned; using long-term patient outcome as a gold standard, preoperative contrast-enhanced MR grading achieves higher sensitivity and specificity than surgical exploration in predicting patient outcome (213); in this study surgery was performed without knowledge of MR findings, and outcome was considered unsatisfactory if additional surgery was necessary.

Is endoanal US superior to a transperineal US approach? Some patients cannot tolerate anal coil insertion. In some patients, such as those with Crohn’s disease, fistulas tend to extend beyond the field of view of an endoanal coil. Gray-scale US identifies fistulas as a thin hypoechoic line. Endocavitary US is more sensitive in detecting intersphincteric than transsphincteric fistulas (214). Overall, however, transperineal US in men and both endovaginal and transperineal US in women appear preferable to endoanal US when evaluating perianal inflammation. Hydrogen peroxide introduced into the fistula tract through the external opening appears of limited additional value except in assessing an internal opening (215).

Although some studies concluded that endorectal US detects more fistulas than MRI, a prospective study of MRI [1.0-T axial and coronal T2-weighted turbo spin echo (TSE) and turbo-STIR sequences] and US (10-mHz rotating endoanal probe) of patients with perianal fistulas achieved an 84% sensitivity for MRI and 60% for US, and specificities of 68% and 21%, respectively, in detecting and classifying these fistulas (216).

An MR endoanal coil was superior to a pelvic phased array coil in evaluating most fistulas, the exception being supralevator fistulas and in evaluating subcutaneous extensions where a phased array was superior (217); sagittal and coronal plane images are very helpful. MR using rectal contrast identifies more pelvic and perirectal fistulas than precontrast imaging.

As an example of the optimistic results achievable with MR, high-spatial-resolution MRI using a quadrature phased-array coil reached 100% sensitivity and 86% specificity for detecting fistulous tracks; 96% and 97%, respectively, for associated abscesses, 100% and 100%, respectively, for horseshoe fistulas, and 96% and

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90%, respectively, for internal openings (218). Even when using a low field (0.1-T) MR unit, results have agreed with the final diagnosis in over 95% (219). Nevertheless, some MR studies are more pessimistic when evaluating the site and extent of a fistula; for instance, in patients with subsequently confirmed fistula-in-ano, MRI detected only 42% to 50%, depending on the radiologist’s experience (220).

Genitourinary Tract Fistulas

Renocolic Fistula

Renocolic fistulas are usually secondary to renal inflammation or neoplasms. An occasional patient with xanthogranulomatous pyelonephritis and ureteric obstruction develops a renocolic fistula. An antegrade or retrograde pyelogram should identify these fistulas. Computed tomography usually reveals a complex air-fluid collection within either the kidney or the adjacent soft tissues.

Urethrorectal Fistula

Rare urethrorectal fistulas consist of fistulas communicating between the prostate or bulbomembranous urethra and rectum. Trauma from missiles is a not uncommon cause of these fistulas. A number of these patients have had prior surgery or complex anoperineal suppuration.

Detection of urethrorectal fistulas is straightforward, either via a urethrogram or a contrast enema.

Some of these fistulas close spontaneously after a more proximal-sigmoid colostomy and suprapubic cystostomy; others require surgical correction.

Colorectal Vesical Fistula

Most enterovesical fistulas are secondary to inflammatory bowel disease or diverticulitis, with an occasional one originating from a colon carcinoma, bladder carcinoma, or other neoplasms. Pneumaturia is common but not universal in patients with a colovesical fistula.At times cystitis is the primary presentation.

Most colovesical fistulas can be identified by barium enema, cystography, or cystoscopy. In some patients a one-way check valve mecha-

Figure 5.43. Rectovaginal fistula (arrow) secondary to lymphomatous infiltration.

nism presumably exists, and in any one patient not all three studies identify a fistula.

Rectovaginal Fistula

Most rectovaginal fistulas are secondary to birth trauma, gynecologic surgery, or pelvic radiation. A rare cause is pelvic amebiasis or actinomycosis. Diverticulitis predominates as a cause of colovaginal fistulas.

Either a barium enema or vaginogram identifies these fistulas (Fig. 5.43). Pelvic MRI is useful to define involved tissue planes. T2weighted images identify rectovaginal fistulas as hyperintense linear defects. Most internal opening can be identified.

A nitinol-silicone double-disc device was inserted transrectally into a rectovaginal fistula and the fistula occluded (221). Such an occluding device appears useful in a setting of tumor, pelvic radiation, and reluctance for repeat surgery in someone with limited life expectancy.

Other Fistulas

Some iatrogenic gastrocolic fistulas are created due to inadvertent transverse colon puncture during percutaneous gastrostomy. An occa-

sional duodenocolic fistula is secondary to colonic Crohn’s disease or a neoplasm. A peptic ulcer–induced fistula to the colon is rare. Most cholecystocolic fistulas are secondary to cholecystolithiasis. Resulting inflammation and fibrosis, generally involving the hepatic flexure or proximal transverse colon, mimics the barium enema appearance of a primary colon adenocarcinoma.

One complication of interleukin-2 therapy is bowel perforation.

Pneumatosis Coli

Pneumatosis cystoides intestinalis is discussed in more detail in Chapter 4.

Pneumatosis coli represents pneumatosis cystoides intestinalis limited primarily to the colon. Similar to small bowel, pneumatosis coli can be subdivided into ischemic and nonischemic (benign) causes. It is characterized by multiple gas-filled cysts within bowel wall. Pneumatosis most often affects the left colon; a redundant sigmoid colon is a common ancillary finding. An occasional colonic intussusception is associated with pneumatosis cystoides intestinalis.

Pneumatosis coli is readily diagnosed with conventional radiography. A barium enema or CT confirms the intramural location for these gas collections. Endosonography reveals hyperechoic collections with acoustical shadowing.

Body Packer

Smuggling of cocaine or heroin concealed in the gastrointestinal tract is not new. The drugs are typically wrapped in cellophane or condoms and swallowed. In general, rupture of a single package is above the toxic dose and is fatal. At times these packages also obstruct the bowel. Most of these “mules” are treated conservatively, although an occasional one requires surgery.

Both US and conventional abdominal radiographs readily detect swallowed drug packages. Conventional radiographs and CT identify cannabis and cocaine packages as wellmarginated, rectangular, high-density structures surrounded by a gas halo, called the double condom sign; heroin packages are seen as poorly outlined structures resembling stool and are

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difficult to identify on conventional radiographs. Ultrasonography of cannabis packages reveals round hyperechoic structures.

Vascular Lesions (Bleeding)

Discussed here are those entities manifesting primarily by bleeding. Ischemic colitis has been discussed in a previous section.

The etiologies of rectal bleeding in adults are wide-ranging (Table 5.8) and differ between pediatric patients and adults; in pediatrics it is worthwhile to consider causes of rectal bleeding by age (Table 5.9).

Detection

Contrast-enhanced CT is at times worth-while in a patient with suspected lower gastrointestinal bleeding. Contrast extravasation is obviously diagnostic, but bowel wall contrastenhancement or presence of a focal lesion also point towards a bleeding site.

Technetium-99m–red blood cell scintigraphy is often employed as a screening examination for patients with suspected colonic bleeding. Should a nuclear medicine bleeding scan be obtained and mesenteric arteriography per-

Table 5.8. Etiologies of rectal bleeding in adults

Colonic Diverticulosis

Inflammatory bowel disease Ischemic colitis

Infectious colitis Neoplasms Hemorrhoids

Angiodysplasia/arteriovenous malformations Portal hypertension—colonic varices

Small bowel

Inflammatory bowel disease Angiodysplasia/arteriovenous malformations Diverticular causes

Meckel’s diverticulum related Neoplasms

Proximal to ligament of Treitz Peptic ulcer disease

Angiodysplasia/arteriovenous malformations Dieulafoy lesions

Portal hypertension—gastroesophageal varices