Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

Figure 14.7. Psoas abscess. Transverse CT image reveals an enlarged, mostly hypodense right psoas muscle (arrow) displacing kidney anterior. (Source: Paley M, Sidhu PS, Evans RA, Karani JB. Retroperitoneal collections—aetiology and radiological implications. Clin Radiol 1997;52:290–294, with permission from the Royal Collage of Radiologists.)

more common. In distinction to intraabdominal abscesses, surgical psoas abscess drainage appears to result in a shorter patient hospitalization than with percutaneous drainage. On the other hand, serious complications are more common after surgical drainage than after percutaneous drainage (21). Imaging confirms abscess resolution.

Peritonitis

Peritonitis either is primary or develops secondary to an infected adjacent structure. It ranges from localized to diffuse. In the elderly, peritonitis tends to manifest initially in a more advanced or severe form than in a younger patient. At times both peritonitis and ascites coexist. Conditions presenting primarily with ascites are discussed in a later section.

Gastrointestinal perforation is a common cause of acute peritonitis and occurs both in the very young and very old. Peritonitis can develop after inadvertent gallbladder puncture during a liver biopsy or percutaneous nephrostomy. Occasionally encountered is aseptic peritonitis, usually in association with a peritoneal malignancy.

Primary peritonitis is rare in children, but more common in girls. Some of these

children are clinically suspected to have appendicitis, and the diagnosis is made only during surgery.

Imaging has a limited role in detecting acute peritonitis. Some degree of ascites is common. Contrast-enhanced CT and MR reveal increased peritoneal enhancement.

Infectious Peritonitis

Discussed here are only some of the more unusual organisms associated with infectious peritonitis.

Patients undergoing peritoneal dialysis are at increased risk of cryptococcal peritonitis. Cryptococcal peritonitis also occurs in patients with cirrhosis and end-stage renal disease.

Listeria is a rare cause of spontaneous bacterial peritonitis. About two thirds of reported patients have chronic liver disease or an underlying malignancy, or the patient was undergoing peritoneal dialysis.

Actinomycosis is a chronic infection by an anaerobic gram-positive commensal bacterium present in body orifices. Typically involved are the genitourinary tract and occasionally bowel. Rarely, it involves the peritoneum or greater omentum. Needle biopsies do not always provide a diagnosis; at times only inflammatory tissue is obtained and only an open biopsy provides the organisms.

Fitz-Hugh–Curtis syndrome, or venereal perihepatitis, is a complication of genital gonococcal or chlamydial infection. In Europe and the United States infection by Chlamydia trachomatis is more frequent. A majority of patients are women. Clinically, acute right upper quadrant symptoms mimic those of biliary disease, but liver function tests are normal. Likewise, US of the gallbladder and bile ducts is normal yet gallbladder wall thickening develops in some and multislice CT can detect transient liver attenuation abnormalities (22). Pathologically, perihepatitis consists of adhesions and peritoneal inflammation. Perihepatic fluid is often present. A biopsy should be diagnostic. The diagnosis is confirmed by finding Neisseria gonorrhoeae or

C. trachomatis organisms in perihepatic tissues. Some of these patients have undergone laparoscopy before the true diagnosis is suspected.

A rare cause of peritonitis is acute ascaris peritonitis due to bowel perforation. This con-

PERITONEUM, MESENTERY, AND EXTRAPERITONEAL SOFT TISSUES

dition, more common in children and occurring mostly in China, has a high mortality; on a more chronic basis, ascaris peritonitis leads to peritoneal granuloma formation.

Vernix Caseosa–Induced Peritonitis

An occasional woman develops unexplained abdominal pain after a cesarean section. An exploratory laparotomy reveals an organizing peritonitis, which includes a foreign-body granulomatous reaction. It is believed that this peritonitis most likely is induced by spillage of keratinous material (vernix caseosa) derived from amniotic fluid during the cesarean section.

In Cirrhosis

Most spontaneous bacterial peritonitis is encountered in patients with cirrhosis and ascites. Antecedent gastrointestinal bleeding is common in these patients. The clinical presentation is often subtle, and thus evaluation of ascitic fluid should be performed promptly, realizing that ascitic fluid culture is positive only in about half. Most common organisms involved are Enterobacteriaceae species and Gram positive cocci. Detection of these and other, less common infectious agents should lead to a search for either underlying cirrhosis or AIDS. Rarely, Streptococcus pneumoniae results in primary peritonitis without underlying disease.

Lupus

Acute lupus peritonitis is a rare manifestation of systemic lupus erythematosus. Imaging detects marked bowel wall thickening, intraluminal fluid, and ascites.

Meconium

Meconium peritonitis is a result of intra-utero bowel perforation, spill of meconium, and a resultant sterile chemical peritonitis. These perforations are often associated with congenital bowel obstruction such as small bowel atresia, volvulus, or meconium ileus. At times peritoni- tis-induced adhesions result in further obstruction. Although usually considered a benign condition, meconium peritonitis can be associated with infarcts secondary to intravascular dissemination of meconium emboli. Meconium

in the peritoneal cavity induces an exuberant fibrosis,leading to a multiseptate ascites appearance, which eventually calcifies. In some infants these calcifications are detected as an incidental finding, with the intra-utero bowel perforation having healed.

Imaging shows characteristic calcifications in the peritoneal cavity. These calcifications can extend into the scrotum through an intact processus vaginalis. Ultrasonography identifies these calcifications as hyperechoic linear or irregular abdominal foci, suggesting a cystic appearance.

Sclerosing Peritonitis/Mesenteritis

Clinical

Some authors treat mesenteritis and sclerosing peritonitis as separate entities, although recent thought suggests that these represent different manifestations of the same condition—an acute form (generally a mesenteritis or panniculitis) and a chronic form (often called sclerosing peritonitis). Diffuse mesenteric infiltration consists of inflammation (mesenteritis and panniculitis), fatty dystrophy, fluid, neoplasms, fibrosis, or even amyloid. Some patients develop a combination of inflammation, fatty dystrophy, and fibrosis, although usually one of these predominates. The terminology for this condition(s) is inconsistent and includes mesenteric panniculitis, mesenteric fibromatosis, retractile mesenteritis, sclerosing mesenteritis, mesenteric lipodystrophy, mesenteric WeberChristian disease, and inflammatory pseudotumor. The terms mesenteritis and sclerosing peritonitis are used here only for description of the primary sites involved. In some patients a sclerosing peritonitis appearance develops during peritoneal dialysis or use of certain drugs, such as practolol and beta-blocking agents. Occasionally mesenteritis is associated with estrogen use. Interestingly, retractile mesenteritis has resolved with progesterone therapy. Intraperitoneal hemorrhage is suggested as a possible link in forming sclerosing peritonitis. The older literature ascribed this condition in some patients to chronic repetitive abdominal trauma caused by vibrations of a pneumatic jackhammer. Mesenteritis has developed in a setting of Crohn’s disease, realizing that the clinical and radiologic features of both

are similar. A role for ischemia is occasionally postulated. Its relationship to extraperitoneal fibrosis (discussed below) is uncertain. Retractile mesenteric is associated with a number of neoplasms and immunosuppression therapy. Numerous reports describe sclerosing peritonitis developing in association with a luteinizing thecoma. A rare association exists between retractile mesenteritis and a mesothelioma.

Excessive fatty infiltration of the mesentery, or lipomatosis, may be idiopathic, part of generalized obesity, or associated with steroid therapy. Most lipomatosis is diffuse and tends to infiltrate rather than displace adjacent structures. It is the occasional focal collections of fat that suggest a fat-containing neoplasm in the differential diagnosis.

Mesenteritis presents either as an acute abdomen or, more often, evolves as a chronic condition of diffuse abdominal pain, at times intermittent. Large fibrofatty tumors develop in the abdomen. Histology reveals a fibrofatty infiltrate containing inflammation, fat necrosis, and fibrosis. Multiple mesenteric lymphatic cysts develop in this entity. Mesenteric fat necrosis, or lipodystrophy, also occurs with pancreatitis and some infections. Mesenteric infiltration has led to a protein-losing enteropathy; in fact, enteropathy can be the first manifestation of this condition.

Exuberant small bowel mesenteric fibrosis predominates in some individuals. This variant, often called retractile mesenteritis, also leads to some degree of inflammation, but the primary finding is mesenteric foreshortening and resultant mesenteric and small bowel distortion. Less often the mesocolon or sigmoid mesentery are affected. Normally little omental involvement is found. Rarely, a similar inflammatory process involves primarily the omentum rather than mesentery.

The differential diagnosis of retractile mesenteritis includes mesenteric and other peritoneal neoplasms. In some patients an open biopsy is necessary for diagnosis and to exclude a malignancy.

Imaging

Usually the small bowel mesentery is involved and ranges from a diffuse infiltrate, a focal soft tissue tumor, to discrete inflammatory nodules. The infiltrate typically also involves adjacent small bowel and results in a spiculated, irregu-

ADVANCED IMAGING OF THE ABDOMEN

lar outline to contrast-filled bowel. Valvulae conniventes are thickened and distorted but not destroyed, thus differentiating this condition from most malignant infiltrations. At times the appearance mimics Crohn’s disease, which also results in mesenteric inflammation and fibrosis. Occasionally mesenteric calcifications develop, probably within necrotic tissue.

Primarily retractile mesenteritis and panniculitis have separate and distinct CT appearances (23): patients with retractile mesenteritis show a mostly homogeneous soft tissue infiltrate denser than fat that distorts bowel loops. Those with panniculitis have a heterogeneous fat-density infiltrate typically involving the mesenteric root but with preserved fat around the greater vessels (fat ring sign), and a loss of the usual sharp outline of enclosed arteries; at times soft-tissue nodules are evident.

Ultrasonography identifies hypoechoic mesenteric tumors, occasionally containing a cystic component.

Magnetic resonance of lipomatosis reveals a fat signal intensity with all imaging parameters. T1-weighted fat-suppressed SGE images are useful to confirm that a focal collection is indeed fat. T1-weighted images of panniculitis (inflammation) reveal hypointense stranding traversing the hyperintense fat.

Sclerosing peritonitis manifests by thickening of the peritoneal lining, diffuse or loculated fluid collections, peritonitis and resultant small bowel obstruction, or simply disordered small bowel motility. Dense adhesions develop. Extensive fibrosis can involve the liver capsule. Peritoneal calcifications develop eventually. Imaging of patients on chronic ambulatory peritoneal dialysis and sclerosing peritonitis detects peritoneal thickening and calcifications; most also have loculated fluid collections and small bowel tethering or dilation.

Aside from calcifications, the imaging appearance of sclerosing peritonitis is similar to that of ovarian carcinoma with carcinomatosis. Both tend to develop adnexal tumors. In carcinomatosis, however, only the peritoneal surface is involved and it has an irregular outline due to malignant nodules; in sclerosing peritonitis not only does the peritoneal thickening have a smooth outline, but also the small bowel and colon walls are thickened. The differential for sclerosing peritonitis also includes diffuse mesothelioma, some chronic infections, and primary and secondary amyloidosis.

PERITONEUM, MESENTERY, AND EXTRAPERITONEAL SOFT TISSUES

Abdominal Cocoon

An abdominal cocoon, also called sclerosing encapsulating peritonitis, is a descriptive term for a variant of sclerosing peritonitis consisting of the small bowel being encased by a membrane and displaced centrally. It is a rare condition. Associated soft tissue tumors are evident in some patients. It is not uncommon to see small bowel obstruction.

The etiology of this condition is unknown. Most reported patients have been from the tropics or subtropical zones, with only an occasional report from temperate zones. One group of patients consists of young adolescent girls. Another group includes cirrhotic patients treated with a peritoneovenous shunt for ascites; autopsy in some of these patients simply identifies generalized peritoneal fibrosis. It has developed in a liver transplant recipient (24). A diagnosis of an abdominal cocoon as a separate entity probably is not appropriate if an infectious organism is recognized; peritoneal tuberculosis has resulted in a similar appearance, and this diagnosis should be excluded if an idiopathic abdominal cocoon is encountered.

Once established, a barium small bowel study is diagnostic. Occasionally, a barium study shows the small bowel to have a cauliflower-like configuration. Computed tomography reveals most or all of the small bowel encased by a thick membrane. Obstruction tends to develop at the site where the proximal small bowel enters its cocoon. Superficially, the condition mimics a large paraduodenal hernia.

Tuberculosis

Clinical

An increasing prevalence is evident not only for pulmonary tuberculosis but also for its extrapulmonary manifestation. Isolated abdominal involvement is not uncommon in endemic regions. Fatigue, prolonged fever, weight loss, nonspecific bowel symptoms, and a chronic wasting illness are common clinical findings.An erroneous initial diagnosis is common in parts of the world with a low prevalence of abdominal tuberculosis.

Hypercalcemia developed in patients with tuberculous peritonitis without pulmonary involvement. Elevated serum CA 125 tumor

marker levels are found in some of these patients; levels decrease after antituberculous therapy.

Tuberculosis ranges from disseminated disease to abdominal involvement only.Abdominal tuberculosis varies in organ involvement considerably, with ulcerative ileocecal involvement not uncommon. Peritonitis, mesenteric and extraperitoneal lymphadenopathy, and genitourinary involvement can occur as separate findings or together; multiorgan involvement, including ulcerative ileocecal involvement is not uncommon. Bowel perforation and obstruction lead to an acute abdomen. Presence vascular and perivascular granulomas, intraluminal thrombi and subintimal fibrosis suggest that bowel ischemia is a common pathway.

A diagnosis of peritoneal tuberculosis is difficult; in spite of clinical, endoscopic, and radiologic evaluation, peritoneal tuberculosis, especially if it involves the ileocecal region, is readily misdiagnosed as Crohn’s disease. Differentiating peritoneal tuberculosis from advanced ovarian cancer is difficult. Malignant lymphoma is also often in the differential diagnosis.

Tuberculous ascitic fluid acid-fast stains tend to be negative and not all Mycobacterium tuberculosis cultures are positive. Biopsy in some patients reveals epithelioid giant-cell granulomas containing caseous necrosis. At times diagnostic laparotomy and culture of tissue biopsy specimens are necessary for diagnosis.

Imaging

Imaging identifies intraand extraperitoneal lymphadenopathy. At times these enlarged nodes are focal in location and mimic a malignancy. Nevertheless, CT lymph node location and specific node appearance provide clues aiding the differentiation of these two entities.

Tuberculosis tends to involve more superior para-aortic lymph nodes, while lymphoma more often involves the inferior para-aortic lymph nodes (25). An exception is with disseminated tuberculosis, which affects nodes diffusely and involves the hepatoduodenal and hepatogastric ligaments and mesenteric and extraperitoneal lymph nodes; nondisseminated tuberculosis can involve similar node chains, except the inferior extraperitoneal lymph nodes are mostly spared. The large, confluent lymph nodes found in lym-