Search
CTisus CT Scanning CTisus CT Scanning CTisus CT Scanning CTisus CT Scanning CTisus CT Scanning CTisus CT Scanning CTisus CT Scanning Ask the Fish

Everything you need to know about Computed Tomography (CT) & CT Scanning

Kidney: Infection Imaging Pearls - Educational Tools | CT Scanning | CT Imaging | CT Scan Protocols - CTisus
Imaging Pearls ❯ Kidney ❯ Infection

-- OR --

  • Imaging of Acute Pyelonephritis
    - Reniform enlargement
    - Perirenal stranding
    - Hydronephrosis possible due to bacterial neurotoxin
    - Typical CT findings: striations, wedge-shaped defects
    - DDx = Infarcts, infiltrating neoplasms
  • Intrarenal Abscess: CT Findings
    - Fluid containing areas in renal parenchyma
    - Usually co-exists with pyelonephritis findings
    - CT more sensitive than US
    - Debris in fluid may be detectable with US only
    - < 3cm usually not drained
  • Granulomatous Renal Infections
    - Tuberculosis
    - XGP
    - Malacoplakia
    - Fungal infections
  • Renal Tb - Imaging
    - Primary is invisible
    - Usually unilateral
    - Abscess
    - Does not respect fascial planes
    - Urothelial ulcerations
    - Scarring & fibrosis
    - Calcifications
  • Cystitis: Diagnostic Imaging Clues
    - Gas = EC
    - Mural Calcifications = Schistosomiasis
    - Chronic UTIs + focal lesions = CC
    - Alkaline urine + Ca++ = AEC
    - Pear shaped bladder = CG
    - Contracted bladder + chemotherapy = Cytoxan
    - Eosinophilia = EC
  • Key Points: Imaging of UTI per Ron Zagoria
    - Diagnosis requires action: Abscess, Emphysematous pyelo, pyonephrosis, Fournier’s
    - XGP: Classic triad, not hydronephrosis
    - Schistosomiasis: Consider SCC
    - Rapidly changing urethral sx: Think SCC
    - Look for gas where it shouldn’t be!
  • “The most common abdominal manifestation of ECD is retroperitoneal xanthogranulomatosis, with involvement of the kidneys, ureters, and aorta. Perirenal and periureteral manifestations of ECD include a thick rind-like soft-tissue lesion encasing the renal parenchyma and ureters leading to obstruction. This perirenal soft-tissue infiltration has a characteristic, so-called hairy kidney appearance, which is pathognomonic for ECD.”


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, 
Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “ECD is a rare multisystem non–Langerhans cell histiocytotic disorder primarily affecting middle-aged to older adults, with a slight male predominance. Histologically, ECD shows focal fibrosis with foamy histiocyte infiltration. The histiocyte cells are positive for cluster of differentiation (CD) 68 and negative for S-100, CD1a, or Birbeck granules, which differentiates ECD from Langerhans type histiocytosis.”


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, In ammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “FDG PET allows accurate evaluation of the extent of the disease; it also helps in assessing the degree of visceral and vascular involvement. As with all XG processes, ECD exhibits GLUT receptors, and FDG uptake is seen in the organs affected. Retroperitoneal xanthogranulomatosis usually exhibits intense FDG avidity.”


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, In ammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “Another important retroperitoneal structure involved is the aorta, which presents with circumferential soft-tissue-like sheathing, giving a so-called coated aorta appearance. The infiltration may extend into the branching vessels, such as the mesenteric and renal arteries.”


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, In ammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “Xanthogranulomatous processes are un- common. However, they should be considered when an aggressive process is present on abdominal imaging. Although XG processes are nonspecific, recognizing features of XG processes may have a significant impact on patient management, surgical planning, and patient morbidity. Imaging also plays a significant role in assessing disease extension and commonly occurring associated complications. Knowledge of the histopathologic behavior of these processes may aid in consideration of xanthogranulomatous entities in a differential diagnosis.”


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • ”XG pyelonephritis is an unusual variant of chronic pyelonephritis or recurrent bacterial tract infections. It occurs in the setting of chronic obstruction from an infected renal stone and altered immune response. These infections produce a chronic granulomatous 
inflammatory response and eventual destruction of the renal parenchyma, with the renal parenchyma eventually being replaced by lipid-laden (foamy) macrophages.” 


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “Typically, a large staghorn calculus and hydronephrosis are seen. Other associations with XG pyelonephritis include ureteropelvic junction obstruction, ureteropelvic duplication, bladder tumor, chronic interstitial nephritis, and calyceal stones.”


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “XG pyelonephritis typically presents in middle-aged women with a history of recur- rent urinary tract infections, diabetes mellitus, or obstructing renal calculi. Cases in children and in the elderly are also reported. The patient may present with nonspecific complaints such as malaise, fatigue, lethargy, recurrent low-grade fever, and flank pain.”

    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “Clinically, patients may present with a palpa- ble abdominal mass, urinary tract infections, or fistulous tracts. Laboratory studies often show leukocytosis, anemia, elevated C-reactive protein, and erythrocyte sedimentation rate. Positive urine cultures with Proteus mirabillis and Escherichia coli are most frequently seen with XG pyelonephritis, although other pathogens may be found.”

    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “Contrast-enhanced CT shows low-attenuation blown-out calyces replacing the renal parenchyma and cortical thinning, representing the classic “bear paw sign”. These blown-out calyces either signify dilated calyces or renal parenchyma filled with pus, debris, or hemorrhage.” 


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “Peripheral enhancement of the masses is also seen. The remainder of the kidney often shows nonenhancement or lack of excretion, indicating a nonfunctioning kidney. A large staghorn calculus with contraction of the renal pelvis can be seen. Associated hypoattenuation is often seen in the renal pelvis mimicking hydronephrosis, but in most cases this region of hypoattenuation rep- resents an extensive inflammatory process.” 


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “Surrounding perinephric inflammatory changes are common with extrarenal exten- sion. A high rate of complications is reported with diffuse XG pyelonephritis, including perforation with abscess formation involving the spleen, paraspinal muscles, or psoas muscles. Fistula tracts are also common, with case reports of renocutaneous, renocolic, or nephrobronchial fistula tracts.” 


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • “Xanthogranulomatous (XG) processes are rare inflammatory conditions with the characteristic pathologic feature of lipid-laden macrophages or histiocyte cells. Imaging findings are nonspecific and can simulate aggressive neoplastic processes. XG processes can be caused by infection, inflammation, histolytic process, or an inherited lysosomal disorder. XG infectious processes are mainly seen in cholecystitis and pyelonephritis, but several other organs can also be involved. Histiocytic processes can be divided into Langerhans and non–Langerhans cell histiocytosis. The non–Langerhans cell histiocytosis entities include Erdheim-Chester disease, Rosai-Dorfman disease, juvenile xanthogranuloma, and he- mophagocytic lymphohistiocytosis. The inherited lysosomal disorders resulting in XG processes include Nieman-Pick, Gaucher, and other lysosomal storage disorders.” 


    Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses 
Kelsey S. Bourm et al.
AJR 2017; 208:475–484
  • • Hemorrhagic bacterial nephritis: wedge- shaped area of increased attenuation related to an intraparenchymal hemorrhage 

    • Focal pyelonephritis: focal ill-defined infection with a masslike appearance that can mimic a neoplasm.

    • Hematogenousseeding:multiple,bilateraperipheral round low-attenuation lesions in the setting of systemic staphylococcal or streptococcal infection. 

    • Emphysematous pyelonephritis: gas within the renal parenchyma.”


    Acute Urinary Tract Disorders 
Goel RH et al.
Radiol Clin N Am 53 (2015) 1273–1292
  • “Emphysematous pyelonephritis and pyelitis are also diagnoses seen primarily in diabetic patients. About 90% of patients with emphysematous pyelonephritis have diabetes and present with costovertebral tenderness, fever, and rarely crepitus in the flank region or scrotum. The most com- mon causative organism is E coli, followed by Klebsiella pneumoniae. About 50% of patients have bacteremia. CT, the imaging study of choice for emphysematous pyelonephritis, demonstrates gas within the renal parenchyma, asymmetric renal enhancement with delayed contrast excretion, and focal regions of necrosis or abscess.”

    Acute Urinary Tract Disorders 
Goel RH et al.
Radiol Clin N Am 53 (2015) 1273–1292
  • “Gas in the bladder lumen may be from a gas- forming urinary tract infection (typically E coli), a bowel-bladder fistula, or recent instrumentation. Emphysematous cystitis involves gas within the bladder wall and is most commonly seen in middle-aged diabetic women . In contrast to the high mortality rate and surgical management of emphysematous pyelonephritis, 90% of patients are treated with medical management, and the mortality rate is only 7%.”


    Acute Urinary Tract Disorders 
Goel RH et al.
Radiol Clin N Am 53 (2015) 1273–1292
  • “In the setting of relevant risk factors (myocardial infarction, malignancy, aortic aneurysm, and cardiac valvular disease), CT imaging with contrast should be performed when there is an enlarged kidney with surrounding perinephric edema of unknown cause on an initial unenhanced CT. The most common cause for renal infarction is thromboembolism from a cardiac source. Although nonspecific, markedly elevated serum lactate dehydrogenase levels, a serum marker for cell necrosis, is helpful in suggesting the diagnosis.”

    Acute Urinary Tract Disorders 
Goel RH et al.
Radiol Clin N Am 53 (2015) 1273–1292
  • “Acute cortical necrosis is a rare variant (2% of acute renal failure) of global ischemia related to either diffuse vasospasm or injury to the distal arcuate arteries (acute tubular necrosis) in which there is a relative decrease in peripheral cortical enhancement, with sparing of the medulla (F. More than 50% of cases are associated with obstetric-related hemorrhage, most commonly placental abruption. There is bilateral kidney damage due to the systemic causes, resulting in high mortality (>50%).”


    Acute Urinary Tract Disorders 
Goel RH et al.
Radiol Clin N Am 53 (2015) 1273–1292
  • Genitourinary TB : Facts
    - The GU tract is affected by TB in 15-20% of patients with extrapulmonary involvement
    - The interval between initial pulmonary infection and the manifestations of genitourinary disease varies from 5 to 40 years
    - Symptoms are often nonspecific with increased frequency, dysuria and hematuria
    - 20% of patients with GU TB have a negative result at skin testing
  • Genitourinary TB : CT Findings
    - Papillary necrosis
    - Renal calcifications may be amorphous, granular, curvlinear or globular in appearance
    - Fibrosis or stricture may occur
    - Parenchymal scarring with non functioning kidney may occur ( “putty kidney”)
    - Ureter or bladder involvement always seen with renal involvement
  • “ The diagnosis of renal tuberculosis should be considered when a patient has recurrent urinary tract infections that do not fully resolve after conventional antibiotic therapy and when fine urothelial calcifications and caliceal dilatation are seen at imaging.”
    Genitourinary Tuberculosis
    Wong A et al
    RadioGraphics 2012; 32:839-844
  • Pyelonephritis

    - Mimics renal infarcts
    - Mimics renal vein thrombosis
    - Mimics obstruction with striated nephrogram
    - Mimics lymphoma
  • Acute Abdominal Pain

    Siewert et al, AJR 1997;168:173-178

    - 91 patients with acute abdomen
    - CT compared with clinical evaluation
    - CT was superior to clinical evaluation - Sensitivity: CT (90%), Clinical Eval (76%)
    - CT changed management in 25/91 patients
  • Acute Pyelonephritis: CT Findings

    - Enlarged, swollen kidney
    - Perinephric stranding
    - Delay in contrast excretion
    - Loss of corticomedullary differentiation
    - Striated nephrogram: Striations result from stasis of contrast within edematous tubules that demonstrate increasing attenuation overtime
    - Focal pyelonephritis can mimic a mass
  • Erdheim-Chester Disease: Facts

    - Renal and perirenal involvement in up to 29% of cases
    - May encase the thoracic or abdominal aorta (looks like retroperitoneal fibrosis)
    - Cardiac infiltration may be endocardial, myocardial or pericardial
  • Erdheim-Chester Disease: Facts

    - Rare form of non-Langerhans cell histiocytosis
    - Characterized by tissue infiltration by foamy histiocytes
    - Usually in patients over age 40
    - Can be life threatening
  • Perinephric Mass: Differential Dx

    - Proliferative diseases
    - Extramedullary hematopoiesis
    - Retroperitoneal fibrosis
    - Rosai-Dorfman disease
    - Erdheim-Chester disease
  • Perinephric Mass: Differential Dx

    - Fluid
    - Hematoma
    - Urinoma
    - Abscess
    - Pancreatic pseudocyst
  • Papillary Necrosis: Etiologies

    - Diabetes
    - Analgesic abuse
    - Sickle cell disease
    - Renal vein thrombosis
    - Obstructive uropathy
  • "The attenuation coefficient of a cystic renal lesion increased by no more than 10H among the unenhanced, corticomedullary, and parenchymal phase scans."

    Analysis of Changes in Attenuation of Proven Renal Cysts on Different Scanning Phases of Triphasic MDCT
    Chung EP et al.
    AJR 2004; 182:405-410
  • "This study shows that cystic lesions typically reveal a change in attenuation of less than 10HU between the scanning phases of a triphasic MDCT, affirming Bosniaks initial assertion that 10HU is a reasonable cutoff for determining enhancement in renal lesions."
  • "This study shows that cystic lesions typically reveal a change in attenuation of less than 10HU between the scanning phases of a triphasic MDCT, affirming Bosniaks initial assertion that 10HU is a reasonable cutoff for determining enhancement in renal lesions."

    Analysis of Changes in Attenuation of Proven Renal Cysts on Different Scanning Phases of Triphasic MDCT
    Chung EP et al.
    AJR 2004; 182:405-410
© 1999-2018 Elliot K. Fishman, MD, FACR. All rights reserved.