Peritonitis

Published on 19/07/2015 by admin

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Last modified 22/04/2025

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 Ascites may be slightly higher in attenuation (15-30 HU) on CT than simple ascites

image Internal complexity within ascites fluid (septations, debris) is common and easier to appreciate on MR or US
• Smooth thickening and hyperenhancement of peritoneum

image Smooth peritoneal thickening and hyperenhancement does not always suggest peritonitis: Can be iatrogenic (after surgery or other intervention which irritates peritoneal lining) or in earliest stages of carcinomatosis (more commonly nodular and irregular, rather than smooth)
• Infiltration and fat stranding within mesentery/omentum
• Presence of ectopic gas suggests either hollow viscus perforation or gas-forming infection
• Other imaging findings may reveal cause of peritonitis (i.e., diverticulitis, appendicitis, low-attenuation nodes in TB)
• In chronic setting peritoneal lining may be thickened with smooth, curvilinear calcification 

image Most common in sclerosing peritonitis due to chronic peritoneal dialysis: Frequently described as “abdominal cocoon” due to peritoneal thickening and calcification

TOP DIFFERENTIAL DIAGNOSES

• Peritoneal carcinomatosis
• Benign ascites
• Pseudomyxoma peritonei
• Hemoperitoneum

PATHOLOGY

• Innumerable different causes including spontaneous bacterial peritonitis in cirrhotic patients, bowel perforation, gastrointestinal infections, TB, trauma, surgery, etc.
• Peritonitis does not necessarily always imply infection: Sterile peritonitis also possible 

image Sclerosing encapsulating peritonitis: Chronic form of peritoneal inflammation most often due to peritoneal dialysis resulting in severe fibrotic thickening of both visceral and parietal peritoneum
image
(Left) Axial CECT in a cirrhotic patient with spontaneous bacterial peritonitis demonstrates loculated ascites with enhancement and thickening of the parietal and visceral peritoneum image. There are bilateral drains image in place.

image
(Right) Axial CECT in a patient on chronic peritoneal dialysis with constant symptoms of bowel obstruction shows loculated ascites image with thickened, enhancing parietal/visceral peritoneum encasing the small bowel and creating functional obstruction. Note the dilated segments of bowel image.
image
(Left) Axial NECT in a patient with a history of peritoneal dialysis demonstrates extensive calcifications image and thickening of the peritoneal lining.

image
(Right) Axial NECT in the same patient demonstrates even more dramatic calcification image surrounding bowel loops in the pelvis. These findings are classic for sclerosing peritonitis, most typically seen in patients on chronic peritoneal dialysis.

TERMINOLOGY

Definitions

• Infectious or inflammatory process involving peritoneum or peritoneal cavity

IMAGING

General Features

• Best diagnostic clue

image Ascites and omental/mesenteric fat stranding with symmetric, smooth enhancement and thickening of peritoneal lining
• Location

image Peritoneal surface, mesentery, and omentum
• Size

image May be localized or generalized in peritoneal cavity
• Morphology

image Symmetric, smooth thickening and enhancement of peritoneum

CT Findings

• Ascites ± loculated fluid collections or discrete abscess

image Ascites may be slightly higher in attenuation (15-30 Hounsfield units) than simple ascites, but lower in attenuation than hemoperitoneum
• Smooth, regular thickening and enhancement of peritoneum (can be either localized adjacent to site of inflammation or generalized throughout abdomen) 

image Smooth peritoneal thickening and enhancement does not always suggest peritonitis

– Can be iatrogenic (after surgery or other intervention that irritates peritoneal lining) or appear in earliest stages of carcinomatosis (more commonly nodular and irregular, rather than smooth)
• Infiltration and fat stranding within mesentery and omentum (either localized or generalized)
• Presence of ectopic gas suggests either hollow viscus perforation or gas-forming infection
• Other imaging findings may reveal cause of peritonitis (i.e., diverticulitis, appendicitis, low-attenuation nodes in tuberculous peritonitis)
• In chronic setting (usually after multiple bouts of peritonitis) peritoneal lining may be thickened with smooth, curvilinear calcification and encapsulation/tethering of bowel loops

image Classically seen in sclerosing peritonitis as result of chronic peritoneal dialysis

– Extensive peritoneal thickening and calcification may result in frequent small bowel obstructions

MR Findings

• Presence of ascites (low signal on T1WI and high signal on T2WI)

image ± loculated fluid collections or discrete abscesses with peripheral enhancement
image Septations and complexity within ascites fluid may be present and best appreciated on T2WI
• Smooth thickening and enhancement of peritoneal lining on T1WI C+ images

image May be localized or generalized depending on site and extent of infection/inflammation
• Thickening and inflammation of omentum and mesentery (generally high signal on T2WI)

Ultrasonographic Findings

• Peritoneal free fluid ± evidence of loculation or complexity (internal septations, debris, hemorrhage, etc.)
• Omental and mesenteric fat may appear echogenic and hyperemic on color Doppler US as result of inflammation, particularly adjacent to primary source of infection/inflammation
• Ultrasound may be best tool along with MR for diagnosing many pelvic sources of peritonitis

image i.e., dilated fallopian tube with fluid-debris level (pyosalpinx) or complex adnexal cystic masses (tubo-ovarian abscesses [TOAs]) in pelvic inflammatory disease (PID)

Radiographic Findings

• Radiography

image Evidence of ascites: > 500 mL required for plain film diagnosis

– Flank bulging
– Indistinct psoas margin
– Small bowel (SB) loops floating centrally
– Lateral edge of liver displaced medially (Hellmer sign): Visible in 80% of patients with significant ascites
– Pelvic “dog’s ear” present in 90% of patients with significant ascites
– Medial displacement of cecum and ascending colon present in 90% of patients with significant ascites
image ± free air (usually in cases with hollow viscus perforation or gas-forming infection)
image Hydropneumoperitoneum
image Air in lesser sac with perforated gastric ulcer

Imaging Recommendations

• Best imaging tool

image CECT
• Protocol advice

image  

DIFFERENTIAL DIAGNOSIS

Peritoneal Carcinomatosis

• Metastatic disease to omentum, peritoneum, or mesentery (most commonly ovarian cancer and gastrointestinal malignancies)
• Ascites with nodularity, thickening, and induration of omentum (± discrete mass-like peritoneal implants)

image Several patterns possible, including micronodular pattern, nodular pattern (more discrete nodules measuring > 5 mm), and omental caking (coalescence of omental metastases into larger conglomerate masses)
• Frequently associated with other evidence of metastatic disease and lymphadenopathy
• Smooth, regular peritoneal thickening and enhancement on CECT/MR may rarely be present in earliest stages and mimic peritonitis, but more commonly peritoneal lining appears irregular and nodular

Benign Ascites

• No evidence of peritoneal thickening, abnormal peritoneal enhancement, or loculation
• Clinical history usually different from peritonitis, as patients do not appear acutely ill or have abdominal pain
• Multiple different causes of benign ascites

image Cirrhosis, congestive heart failure (CHF), fluid overload, peritoneal dialysis, chronic renal failure, etc.

Pseudomyxoma Peritonei

• Accumulation of gelatinous implants in peritoneal cavity, most commonly due to rupture of mucinous tumor of appendix
• Discrete low density implants scallop contour of liver and spleen and displace loops of bowel centrally
• Implants may demonstrate calcification
• Slowly progressive disorder with relative chronicity of imaging findings (unlike peritonitis)

Hemoperitoneum

• High-attenuation intraperitoneal hematoma 

image Free lysed blood (30-45 HU); clotted blood (60 HU)
image Active arterial extravasation isodense with adjacent major arterial structures
• Typically no evidence of peritoneal thickening or enhancement on CECT

PATHOLOGY

General Features

• Etiology

image Spontaneous: Secondary bacterial infection of chronic ascites 

– Most commonly spontaneous bacterial peritonitis (SBP) in setting of cirrhosis and chronic ascites
image Bacterial infection

– Bowel perforation
– PID, infected intrauterine device (IUD), ruptured TOA
– Gastric or duodenal ulcer
– Ruptured appendicitis, ruptured diverticulitis
image Tuberculous peritonitis: May be associated with other manifestations of abdominal TB
image Traumatic peritonitis

– May result from either frank perforation of bowel or traumatic disruption of peritoneum allowing infection
– Most common sites of bowel injury include duodenum, jejunum, distal ileum

image Bowel injury from deceleration injury
image SB injury may present 4-6 weeks post trauma
– Colonic injuries are rare but result in more rapid clinical onset of peritonitis
image Iatrogenic peritonitis

– Inadvertent bowel injury or perforation during laparotomy or paracentesis
– Postoperative anastomotic leak
– Retained foreign body during surgery
– Dropped gallstones during laparoscopic cholecystectomy
– Infection or chronic sterile inflammation of peritoneum in patients with intraperitoneal dialysis catheters
image Peritonitis does not necessarily always imply infection: Sterile peritonitis also possible

– Sterile peritonitis most commonly iatrogenic, such as foreign body reaction to retained foreign body after surgery or chronic peritoneal inflammation due to peritoneal dialysis catheter
– Sclerosing encapsulating peritonitis: Chronic form of peritoneal inflammation most often due to peritoneal dialysis resulting in severe fibrotic thickening of both visceral and parietal peritoneum

image Frequently described as “abdominal cocoon” due to peritoneal thickening and calcification
image May more rarely be associated with ventriculoperitoneal shunt catheters and certain drugs
image Frequently results in repetitive bowel obstructions

Staging, Grading, & Classification

• Localized: Walled-off infection
• Diffuse: Multiple peritoneal compartments involved

Gross Pathologic & Surgical Features

• Pus in peritoneal cavity
• Inflammatory mesenteric changes and adhesions
• Hyperemia of adherent omentum or mesentery

Microscopic Features

• > 250 leukocytes per mm³ indicates infected ascites

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Fever, abdominal pain, abdominal distension

Demographics

• Age

image Any
• Gender

image No predilection
• Epidemiology

image Increased incidence in patients with chronic ascites (i.e., cirrhosis, peritoneal dialysis)
image Higher incidence of pneumococcal or hemolytic streptococcal infection in younger patients
image Increased incidence in patients with risk factors for PID

– IUD, multiple sexual partners

Natural History & Prognosis

• Prompt treatment necessary to avoid sepsis (if underlying cause is infectious)
• Prognosis determined by primary etiology

image Excellent if inflammation is localized without septicemia, but prognosis more guarded with generalized infection

Treatment

• Etiology determines treatment, and may include antibiotics or surgery

DIAGNOSTIC CHECKLIST

Consider

• Differentiate infectious or inflammatory peritonitis from peritoneal carcinomatosis, which may also result in peritoneal thickening and enhancement on CECT
• Differentiate imaging findings of peritonitis from benign causes of ascites (cirrhosis, renal failure, etc.)

Image Interpretation Pearls

• Smooth thickening and enhancement of peritoneal lining with associated ascites and inflammation of adjacent mesenteric/omental fat

image
(Left) Axial CECT of TB peritonitis shows ascites, enhancement of the parietal peritoneum image, and calcification image within a thickened omentum.
image
(Right) Axial CECT in a patient with peritonitis after necrotizing pancreatitis demonstrates large loculated fluid collections with prominent thickening and enhancement of the adjacent peritoneal lining image.
image
(Left) Axial CECT in a patient who presented with alcoholic cirrhosis and abdominal pain demonstrates a nodular liver and splenomegaly with ascites, findings consistent with the patient’s diagnosis of cirrhosis. Note the loculated ascites and thickened, enhancing parietal peritoneum image.

image
(Right) Axial CECT in the same patient reveals a few foci of ectopic gas image within the ascites fluid, a classic imaging finding of bacterial peritonitis.
image
(Left) Axial NECT in a patient with Crohn disease and bacterial peritonitis shows loculations of ascites throughout the abdomen, including thick-walled collections between bowel loops in the mesentery image. The thickened parietal peritoneum image is further evidence of an inflammatory or exudative etiology for this process.

image
(Right) Axial NECT in the same patient shows infiltration of the omental image and mesenteric fat due to the generalized inflammatory process and peritonitis.
image
Axial CECT of TB peritonitis shows a large amount of ascites image, thickening of the parietal peritoneum image, and nodular infiltration of the omentum image.

image
Axial CECT of the same patient at a more cranial level demonstrates increased vascularity of the omentum image and cystic disease of dialysis image.
image
Axial CECT of acute enteritis and peritonitis from lupus erythematosus shows marked small bowel thickening/prominent submucosal edema image, ascites image, and peritoneal enhancement image.
image
Axial CECT of the same patient at a lower level demonstrates thickening of the descending colon image and peritoneal enhancement image.
image
Axial CECT shows bacterial peritonitis in a patient with cirrhosis. Note the loculated ascites image and the thickened and enhancing parietal peritoneum image.
image
Axial CECT in the same patient shows loculated ascites image and thickened parietal peritoneum image. A gas bubble image is also evident within the fluid.
image
Axial CECT shows pelvic peritonitis from colonic perforation (pseudomembranous colitis). Note the diffuse infiltration of the soft tissue planes image and ectopic gas image adjacent to the thickened sigmoid colon image.
image
Axial CECT of the same patient at a more caudal level demonstrates only a small amount of free fluid image. Diffuse pelvic peritonitis was found at surgery.
image
Axial CECT of perforated appendicitis with peritonitis shows a linear appendicolith image, symmetric thickening of the peritoneum image, and adjacent low-attenuation pus.
image
Axial CECT of perforated appendicitis with peritonitis shows multiple appendicoliths image with a nonenhancing necrotic tip of the appendix image and surrounding soft tissue infiltration.
image
Axial CECT of spontaneous bacterial peritonitis shows marked ascites.
image
Axial CECT of spontaneous bacterial peritonitis shows symmetric thickening of the parietal peritoneum in the left flank image.
image
Axial CECT of TB peritonitis demonstrates ascites and nodular thickening of omentum image and peritoneum.
image
Axial CECT of traumatic bowel perforation with serosal inflammation and peritonitis shows a pneumoperitoneum image and a hyperemic thickened small bowel image.
image
Axial CECT of gallbladder perforation with bile peritonitis and hemoperitoneum shows a clot in the gallbladder image and massive perihepatic low-density fluid.
image
Axial CECT of gallbladder perforation with bile peritonitis and hemoperitoneum shows an interruption of the gallbladder wall image with an adjacent clot image and a large amount of bile in the peritoneal cavity.
image
Axial CECT of subacute peritonitis from a perforated ulcer shows free air anteriorly image and marked serosal thickening and enhancement of the jejunum image.
image
Axial CECT in a patient who had undergone chronic peritoneal dialysis demonstrates ascites with curvilinear calcifications image encasing loops of small bowel.
image
Coronal CECT in the same patient demonstrates similar calcification and thickening of the peritoneal lining of the abdomen. This appearance is classic for sclerosing peritonitis, most commonly seen in patients who have undergone chronic peritoneal dialysis.
image
Axial CECT in a 57-year-old man with chronic renal failure on chronic ambulatory peritoneal dialysis shows end-stage small kidneys image with innumerable cysts and the present of a massive, highly loculated ascites.
image
Axial CECT in the same patient again reveals the massive ascites with mass effect on the small bowel and other abdominal structures. Note the thickened visceral and parietal peritoneum image.

SELECTED REFERENCES

1. Baker, PM, et al. Selected topics in peritoneal pathology. Int J Gynecol Pathol. 2014; 33(4):393–401.

 

Strauss, E. The impact of bacterial infections on survival of patients with decompensated cirrhosis. Ann Hepatol. 2013; 13(1):7–19.

Cakir, B, et al. Complications of continuous ambulatory peritoneal dialysis: evaluation with CT. Diagn Interv Radiol. 2008; 14(4):212–220.

Na-ChiangMai, W, et al. CT findings of tuberculous peritonitis. Singapore Med J. 2008; 49(6):488–491.

Yehia, M, et al. Is computerized tomography useful in identifying abdominal catastrophes in patients presenting with peritonitis? Perit Dial Int. 2008; 28(4):385–390.

George, C, et al. Computed tomography appearances of sclerosing encapsulating peritonitis. Clin Radiol. 2007; 62(8):732–737.

Xu, P, et al. Idiopathic sclerosing encapsulating peritonitis (or abdominal cocoon): a report of 5 cases. World J Gastroenterol. 2007; 13(26):3649–3651.

Alberti, LE, et al. Spontaneous bacterial peritonitis in a patient with myxedema ascites. Digestion. 2003; 68(2–3):91–93.

Brook, I. Microbiology and management of intra-abdominal infections in children. Pediatr Int. 2003; 45(2):123–129.

Cheadle, WG, et al. The continuing challenge of intra-abdominal infection. Am J Surg. 2003; 186(5A):15S–22S. [discussion 31S-34S].

Chow, KM, et al. Indication for peritoneal biopsy in tuberculous peritonitis. Am J Surg. 2003; 185(6):567–573.

Hanbidge, AE, et al. US of the peritoneum. Radiographics. 2003; 23(3):663–684. [discussion 684-5].

Malangoni, MA. Current concepts in peritonitis. Curr Gastroenterol Rep. 2003; 5(4):295–301.

Marshall, JC, et al. Intensive care unit management of intra-abdominal infection. Crit Care Med. 2003; 31(8):2228–2237.

Nishie, A, et al. Fitz-Hugh-Curtis syndrome. Radiologic manifestation. J Comput Assist Tomogr. 2003; 27(5):786–791.

Reijnen, MM, et al. Pathophysiology of intra-abdominal adhesion and abscess formation, and the effect of hyaluronan. Br J Surg. 2003; 90(5):533–541.

Runyon, BA. Strips and tubes: improving the diagnosis of spontaneous bacterial peritonitis. Hepatology. 2003; 37(4):745–747.

Sabri, M, et al. Pathophysiology and management of pediatric ascites. Curr Gastroenterol Rep. 2003; 5(3):240–246.

Shetty, H, et al, Treatment of infections in peritoneal dialysis. Contrib Nephrol. 2003;(140):187–194.

Sivit, CJ, et al. Imaging of acute appendicitis in children. Semin Ultrasound CT MR. 2003; 24(2):74–82.

Troidle, L, et al. Continuous peritoneal dialysis-associated peritonitis: a review and current concepts. Semin Dial. 2003; 16(6):428–437.

Veroux, M, et al. A rare surgical complication of Crohn’s diseases: free peritoneal perforation. Minerva Chir. 2003; 58(3):351–354.

Witte, MB, et al. Repair of full-thickness bowel injury. Crit Care Med. 2003; 31(8 Suppl):S538–S546.

Yao, V, et al. Role of peritoneal mesothelial cells in peritonitis. Br J Surg. 2003; 90(10):1187–1194.

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