OBJECTIVE.Radiologic findings inSalmonellainfections are not well described. In most patients,Salmonellainfections produce mild and self-limiting clinical manifestations and therefore are treated empirically with antibiotics. Radiologic investigations are usually performed for patients with severe clinical manifestations or complications and for patients with unusual findings.
CONCLUSION.This pictorial essay illustrates various imaging findings in culture-proven cases ofSalmonellainfection, described broadly as common and uncommon manifestations.
Salmonellaspecies are gram-negative facultative intracellular anaerobes that can cause a broad spectrum of clinical manifestations . The clinical spectrum of infection ranges from gastroenteritis, enteric fever (caused by typhoid and paratyphoid serotypes),Salmonellabacteremia, and localized infections to a convalescent lifetime carrier state . The manifestation of disease is dependent on the serotype and various host factors. More than 2500 serovars of genusSalmonellahave been described , some of which, such asS. typhi, are restricted only to human hosts .
Salmonellainfection most commonly begins with ingestion of bacteria in contaminated food and water. Once a person is infected, the organism can spread from person to person via the fecal-oral route . The bacterium proliferates in the intestine and can then penetrate the lymphoid tissue of the gastrointestinal tract, usually in the distal ileal loops and terminal ileum, leading to hematologic dissemination and transmission of the organism to various organ systems .
Salmonellainfection can be endemic, particularly in developing countries. However, an increased incidence of this infection is emerging in developed countries secondary to the prevalence of immunocompromised conditions with the ongoing surge of HIV infection and the evolution of antibiotic resistance. This pictorial essay thus aims to illustrate the various clinical manifestations ofSalmonellainfection, taking into account the changing global environment.
A large inoculum ofSalmonellaspecies is needed to overcome stomach acidity and compete with normal intestinal flora for an established infection of the intestine. The bacterium then proliferates in the small intestine and invades enterocytes in the distal ileum and colon. Elaboration of several toxins by the bacterium contributes to the dysfunction of the intestinal cells .
Small-intestine infection may be seen as symmetric and homogeneous thickening of the ileal wall, which may be focal or diffuse on CT (Fig. 1). A feathery pattern of mucosal thickening may also be seen on ultrasound (Fig. 2). Sometimes colonic involvement can be seen in the absence of ileal involvement and may be patchy or continuous (Fig. 3).Salmonellaenteritis may even simulate pseudomembranous colitis, with toxic megacolon as a known complication . Enlarged mesenteric nodes may be seen adjacent to the involved segment of intestine (Fig. 4).
Gastrointestinal bleeding and perforation are important complications and occur frequently in the terminal ileum . Active bleeding may be visualized in the form of intravascular contrast extravasation on CT angiography studies (Fig. 5).
Hepatobiliary and Splenic
The gallbladder and spleen are common sites of intraabdominalSalmonella infections, and the manifestations can range from nonspecific organomegaly (Fig. 6) to an abscess formation (Fig. 7). Rarely, the spleen may rupture secondary to splenomegaly after trivial trauma.
Acute acalculous cholecystitis is a recognized manifestation ofSalmonella infection . Gallbladder wall thickening, distention, and pericholecystic fluid can be seen on both ultrasound and CT (Figs.8Aand8B). Perforation and empyema of the gallbladder andSalmonellacholangitis are also recognized but rare entities .
Mesenteric and Peritoneal
Ascites, localized or generalized mesenteric stranding, thickening, and adenopathy are frequent manifestations ofSalmonellainfection .Salmonella infections have a predilection for the gastrointestinal tract. Involvement of the terminal ileum or the proximal colon with mesenteric lymphadenopathy may be specific imaging findings.
The manifestations ofSalmonellainfection in the genitourinary tract are nonspecific and do not differ clinically from the manifestations of urinary tract infections secondary to otherEnterobacteriaceae. They range from asymptomatic bacteriuria to cystitis, pyelonephritis, and renal abscess formation (Figs.9Aand9B).Salmonellainfection in a preexisting hydrocele, ovarian cyst, and even epididymoorchitis have been reported .
Pulmonary and Cardiac
Several nonspecific abnormalities are observed on chest radiography, including pleurisy, pleural effusion, bronchopneumonia, and lobar pneumonia (Fig. 10). Endocarditis, myocarditis, and pericarditis also have been described .
Arterial—Although arterial infection due toSalmonellabacteria is unusual, it remains one of the most common causes of infective aneurysms . Most infections occur in preexisting atherosclerotic foci or in an aneurysm, and the risk of infective aneurysms secondary toSalmonellainfection is thereby significantly increased in patients older than 50 years.
The most common site of infection is the abdominal aorta. CT findings may reveal a periaortic gas collection, an interrupted ring of aortic wall, or a rapidly enlarging saccular structure arising from the aortic wall (Figs.11Aand11B). These aneurysms are at risk of causing life-threatening rupture and hemorrhage (Figs.12Aand12B).
Venous—Thrombophlebitis of the veins can also occur, as illustrated by intraluminal filling defects on contrast-enhanced examinations (Figs.13Aand13B).
Salmonellameningitis occurs most commonly in infants . Contrast-enhanced MRI is useful in suspected cases because it reveals meningeal enhancement. Encephalitis in the form of increased signal on FLAIR and T2-weighted sequences and abnormal enhancement may be seen (Figs.14A,14B, and14C). Complications such as hydrocephalus, ventriculitis, and cerebral abscesses can then follow in untreated cases.
The skeletal and soft-tissue infections due toSalmonellainfection occur mostly in patients with preexisting diseases. The association between sickle cell disease andSalmonellaosteomyelitis is well known. Other manifestations include polymyositis, septic arthritis, periosteitis, and abscess formation. MRI plays an important role in the imaging of musculoskeletal complications (Figs.15Aand15B).
Soft-tissue infections are often indolent with a paucity of systemic symptoms. The imaging features are no different from those of abscesses due to any other cause and may not be suspected until culture of a surgically obtained specimen is performed. Superficial abscesses are quite common, with abscesses in the parotid, breast, pancreas, and thyroid having been reported in the literature .
A wide spectrum of radiologic manifestations due toSalmonellainfection may be encountered, especially in endemic areas and immunocompromised patients. However, the imaging findings inSalmonellainfection are not unique and can mimic other infective diseases. Knowledge of radiologic manifestations is important to aid in early diagnosis and timely initiation of appropriate management. In our experience, in the appropriate clinical setting, radiologic findings of thickened terminal ileum or proximal colon with mesenteric lymphadenopathy are specific forSalmonellainfection.