Opportunistic Intestinal Infections

Published on 19/07/2015 by admin

Filed under Radiology

Last modified 22/04/2025

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 Favors distal small bowel (SB) and colon

image Mucosal hyper- or hypoenhancement; submucosal edema
image Infiltration of mesenteric fat
image Lymphadenopathy is very uncommon
• Mycobacterial

image Mycobacterium avium-intracellulare  (MAI): Thickened SB folds with relatively little submucosal edema
image Tuberculosis (TB): Favors ileocecal distribution
image Mesenteric lymphadenopathy, often with low density (caseation)
image Exudative ascites (may mimic peritoneal carcinomatosis)
• Protozoan (Cryptosporidium, Microsporidia, and  Giardia) 

image Duodenum and jejunum, sparing distal SB and colon
image Fold thickening without much submucosal edema
image Excess fluid (luminal distention) of proximal small bowel
image No ascites; uncommon lymphadenopathy
• Bacterial (Clostridium difficile colitis, Campylobacter, and others)

image Segmental or, more commonly, pancolitis
image Striking mucosal hyperenhancement and submucosal edema
image Ascites (present in 40% of cases)
image May progress to toxic megacolon or perforation

TOP DIFFERENTIAL DIAGNOSES

• Gastrointestinal lymphoma

CLINICAL ISSUES

• Prevalence of opportunistic GI infections in HIV patients has markedly decreased with potent antiretroviral therapy

DIAGNOSTIC CHECKLIST

• Specific diagnosis can be suggested by CT
• Diagnosis depends on microbiological confirmation by analysis of bowel content or even biopsy
image
(Left) This young woman has cystic fibrosis and lung transplantation, with new onset diarrhea. Axial CECT shows hyperenhancement and submucosal edema image affecting most of the small bowel (SB).

image
(Right) Coronal CECT in the same patient shows the widespread enteritis with engorged mesenteric vessels image. The colon image is spared. Endoscopy and biopsy confirmed cytomegalovirus (CMV) enteritis.
image
(Left) This 35-year-old man with AIDS developed profuse diarrhea and abdominal pain. Axial CECT shows pancolitis with marked submucosal edema image but no hyperenhancement of the mucosa.

image
(Right) Coronal CECT in the same patient shows more evidence of pancolitis image, proven to be due to CMV, which may induce ischemic injury to both the SB and colon in immunocompromised patients.

TERMINOLOGY

Abbreviations

•  

Synonyms

 

Definitions

• Symptomatic gastrointestinal (GI) infection of immunocompromised host by organisms that usually cause no or minor illness in immunocompetent individuals

IMAGING

General Features

• Best diagnostic clue

image Cytomegalovirus (CMV): Mucosal hyper- or hypoenhancement; submucosal edema

– Distribution: Small bowel (SB), colon >  stomach, esophagus, rectum

image Favors distal small bowel and colon
– Pattern CECT: Mucosal hyper- or hypoenhancement

image Reflects active inflammation vs. ischemic necrosis
image Deep ulcers may be transmural, causing mesenteric infiltration
– Pattern on upper GI series, small bowel series, or barium enema

image Aphthoid erosions in earlier stages
image Deep ulcers, even sinus tracts in later stages
– Barium studies and CT findings may mimic Crohn disease or ulcerative colitis
– Associated findings

image Lymphadenopathy is very uncommon
image Infiltration of mesenteric fat by transmural, deep ulceration
image Mycobacterial

– Mycobacterium avium-intracellulare (MAI): Thickened SB folds with relatively little submucosal edema

image Micronodular fold thickening on SB follow-through
– Tuberculosis (TB)

image Favors ileocecal distribution
image Wall thickening, luminal narrowing, ± obstruction
– Associated findings

image Mesenteric lymphadenopathy, often with low density (caseation)
image Exudative ascites (peritonitis)
image Peritoneal and omental thickening (may mimic peritoneal carcinomatosis)
image Most affected patients do not have overt lung disease
image Protozoan (Cryptosporidium and Giardia)

– Distribution

image Duodenum and jejunum
image Ileum and colon are spared
– Pattern

image Fold thickening without much submucosal edema
image Excess fluid (luminal distention) of proximal small bowel
– Associated findings

image No ascites nor lymphadenopathy
image Bacterial (Clostridium difficile colitis, Campylobacter, and others)

– Distribution

image Segmental or, more commonly, pancolitis
image Terminal ileum affected uncommonly
– Pattern

image Striking mucosal hyperenhancement
image Marked submucosal edema (target or accordion sign)
– Associated findings

image Ascites (present in 40% of cases)
image May progress to toxic megacolon or perforation
image No lymphadenopathy
• Location

image  

CT Findings

• CECT

image  

Imaging Recommendations

• Best imaging tool

image Multiplanar CECT
• Protocol advice

image IV contrast at > 3 mL/sec; image at 60 seconds; view in multiple planes
image Oral contrast is rarely useful (makes determination of mucosal enhancement impossible)

DIFFERENTIAL DIAGNOSIS

Gastrointestinal Lymphoma

• Most commonly non-Hodgkin lymphomas, high-grade large cell or immunoblastic cell types

image Burkitt more common in pediatric patients
• Most common symptoms: Abdominal pain, weight loss, fever, anemia

image Not diarrhea
• Soft tissue density wall thickening

image Without luminal obstruction or submucosal edema
• May be multifocal; SB and colon
• Often with bulky, widespread lymphadenopathy
• Ascites is rare

PATHOLOGY

General Features

• Etiology

image CMV

– Occurs in severely immunocompromised patients

image e.g., HIV patients with CD4 counts < 50 cells/μL
image Prevalence has deceased markedly with use of potent antiretroviral therapy (HAART)
– Causes vasculitis leading to GI ulceration, ischemia, bleeding, perforation
image Mycobacteria

– Atypical MAI and TB
– May be newly acquired in immunocompromised patient

image Or reactivation of prior quiescent infection
– Macrophages infiltrate lamina propria of SB, distending villi
image Cryptosporidium, Microsporidia, and Giardia

– May affect immunocompetent individuals, usually less severely
– Protozoan organisms attach between microvilli of small intestine
– Leads to mucosal damage and secretory enteritis and diarrhea
image Infectious colitis

– May affect immunocompetent patients as well

image Usually nosocomial infection
image Often preceded by antibiotic use
– C. difficile is most common

image Campylobacter, Escherichia coli, and others may occur

Microscopic Features

• CMV

image Cytoplasmic inclusion bodies in enterocytes, macrophages, fibroblasts, and endothelial cells
image May induce ischemic necrosis of bowel mucosa
• MAI

image Coarsely granular mucosa
image Sheets of foamy macrophages infiltrate lamina propria
image Positive acid-fast or Fite stain for organisms
• Cryptosporidiosis

image Organisms proliferate from apex of enterocyte
image Villous atrophy
image Crypt hyperplasia
image Inflammatory infiltrate

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Abdominal pain, nausea, diarrhea, fever, GI bleeding
image Symptoms are often masked by medications or suppressed immune status

– May be simulated by coexisting infections and neoplasms

Demographics

• Age

image Any age but elderly are more prone
• Gender

image M = F
• Epidemiology

image HIV or immunocompromised patient (e.g., transplant recipient, aggressive chemotherapy)
image Patients with Crohn disease or ulcerative colitis

– Treatment with biological agents, immune modulators  (e.g., antitumor necrosis factor), corticosteroids
– High prevalence of opportunistic infections in patients with inflammatory bowel disease

Natural History & Prognosis

• Many opportunistic intestinal infections clear spontaneously with recovery of functional immune competence
• MAI in AIDS patients often difficult to treat

Treatment

• CMV: Antiviral therapy with acyclovir or ganciclovir
• Mycobacterial: Antituberculous chemotherapy
• Cryptosporidiosis: Chemotherapy with nitazoxanide
• Microsporidiosis: Albendazole, metronidazole, and others
• Bacterial: Antibiotics

image “Stool transplantation” in refractory cases to repopulate normal colonic biome

DIAGNOSTIC CHECKLIST

Consider

• Specific diagnosis can be suggested by CT
• Diagnosis depends on microbiological confirmation by analysis of bowel content or even biopsy

Image Interpretation Pearls

• CMV: Deep ulcerations and focal enteritis or colitis
• Mycobacterial infection: Enteritis and low-attenuation lymphadenopathy
• Cryptosporidiosis: Thickened bowel wall and edematous folds

image
(Left) Axial CECT in a 34-year-old HIV-positive man presenting with diarrhea shows the typical appearance of CMV colitis. Note the diffuse thickening of the colon wall and mucosal hyperenhancement image.
image
(Right) Coronal CECT in the same patient illustrates the global nature of this colitis with involvement of the ascending and descending colon, as well as sigmoid image. CMV colitis infects an immunocompromised host with a virus that causes vasculitis.
image
(Left) Axial CECT in a 28-year-old man with HIV and intractable diarrhea shows the typical appearance of Mycobacterium avium-intracellulare (MAI) enteritis. Note the diffuse small bowel wall thickening image and mesenteric adenopathy image.

image
(Right) This young woman is HIV-positive with new onset diarrhea. Axial CECT shows fluid distention of both small image and large bowel image, along with mesenteric lymphadenopathy image. Cryptosporidium was the causative organism and typically causes diarrhea.
image
(Left) This man has a functioning renal allograft and developed acute bloody diarrhea due to Clostridium difficile. Axial NECT shows massive submucosal edema of the entire colon (pancolitis) with some segments having an “accordion” appearance image.

image
(Right) Axial NECT in the same patient shows ascites image and mesenteric edema. Note the atrophic native kidneys image. In spite of prompt diagnosis and treatment, the colitis progressed to perforation and emergency colectomy.
image
Small bowel follow-through shows marked mural narrowing and extensive fold thickening image in this patient with advanced cryptosporidiosis of the small bowel.

image
Small bowel follow-through demonstrates mild fold thickening image in this patient with early cryptosporidiosis of the small bowel.
image
Axial CECT in a patient with MAI shows a low-attenuation mesenteric lymph node image.
image
Axial CECT in a patient with MAI demonstrates mural thickening of the cecum and terminal ileum image.
image
Small bowel follow-through in a patient with gastrointestinal CMV demonstrates enteritis with thickened folds image.
image
Lateral view of the stomach from an upper GI series in a patient with gastrointestinal CMV shows marked antral narrowing and thickened folds image from antral CMV gastritis.
image
Axial CECT shows CMV colitis. Note the edematous right colon image with pericolonic soft tissue stranding image.
image
AP compression spot film from a barium enema demonstrates deep cecal ulcer image from CMV colitis.

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