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Radiology of Infectious Diseases and
Their Mimics in Critical Care
Jocelyn A. Luongo, Orlando A. Ortiz, and Douglas S. Katz
Department of Radiology, Winthrop-University Hospital, Mineola, New York, U.S.A.INTRODUCTION
Radiologic diagnosis of infection in the critically ill population can be challenging. Various
imaging modalities are usually needed in the workup of infection in these patients to exclude
or diagnose alternate disorders such as malignancy and autoimmune disease. In this chapter,
the radiologic presentation of various abdominal, neurologic, and thoracic infections as well as
the findings in other diseases that may mimic infection on imaging are discussed, as are
potentially helpful differentiating factors.
ABDOMINAL AND PELVIC INFECTIOUS PROCESSES AND THEIR MIMICS
Clinical and Radiologic Diagnosis of Acute Pyelonephritis
Acute pyelonephritis is a bacterial infection involving the renal pelvis, tubules, and
interstitium. The most common pathogen isEscherichia coli. Infection occurs primarily via
ascending spread of a urinary tract infection, although hematogenous spread can occur less
frequently. Uncomplicated disease is rarely, if ever, fatal. However, complications such as
emphysematous pyelonephritis in diabetics, abscess formation, or sepsis increase the
morbidity and mortality substantially. Risk factors for the development of complications
include age greater than 65, bedridden status, immunosuppression, and a long-term
indwelling urinary tract catheter (1).
The diagnosis of acute pyelonephritis is usually made via history and physical exam in
conjunction with positive urinalysis, and imaging is not generally needed except for cases of
atypical presentation or a suspected complication. Contrast-enhanced CT is the imaging method
of choice in adult patients. The classic findings of acute pyelonephritis on CT are wedge-shaped
and striated areas of decreased enhancement (“patchy” nephrogram). There is also usually
stranding of the perinephric fat and thickening of Gerota’s fascia. The kidney involved may also
be enlarged or demonstrate areas of focal swelling in the acute setting and then may become
scarred and contracted if the infection progresses to a chronic state. Ultrasound may be used for
screening, although it is not as sensitive or specific as CT. Findings include a normal or enlarged
kidney with decreased echogenicity and wedge-shaped zones of hypoechogenicity (hyper-
echogenic foci, which are less likely, usually indicate a hemorrhagic component). There is also
blurring of the corticomedullary junction. Anechoic regions are indicative of abscess formation.
A Tc-99m DMSA (nuclear medicine) scan is equally sensitive for the detection of renal infection,
demonstrating decreased uptake at foci of inflammation, and is the diagnostic and follow-up
method of choice in children, to lessen radiation exposure (1–3).
Mimic of Acute Pyelonephritis
Xanthogranulomatous pyelonephritis (XGPN) is a relatively rare form of pyelonephritis
associated with a chronically obstructed kidney, usually in conjunction with a staghorn
calculus. The disease results in destruction of the renal parenchyma and a nonfunctioning
kidney. Unlike conventional bacterial pyelonephritis, which can be treated medically, the
treatment for XGPN is nephrectomy, once the patient is stable. XGPN is most frequently seen
in diabetic or immunocompromised patients (1,2).
The CT findings of XGPN include low-attenuation collections in the kidney involved,
which represent dilated calyces filled with pus and debris, as well as a dilated renal pelvis
(Fig. 1). There is bright enhancement of the rims of the collections secondary to inflammation
and formation of granulation tissue. There is also little to no excretion of IV contrast into the