Imaging

Pyelonephritis

Preliminary Diagnosis: Pyelonephritis (Acute)

I. What imaging technique is first-line for this diagnosis?

Pre- and post-contrast CT (Uro-CT) is the first line imaging study of choice in complicated patients. Imaging adds little to the clinical management if the patient responds to therapy within 72 hours. Best if used in complicated patients, (e.g., those with diabetes or who are immunocompromised, have a history of stones, have had prior renal surgery, or who are not responding to therapy).

II. Describe the advantages and disadvantages of this technique for diagnosing pyelonephritis.

Advantages

  • CT scan without contrast is able to localize a radiopaque obstructive renal collecting system and urinary bladder calculi.

  • Dynamic CT study may demonstrate alterations in renal parenchymal enhancement and focal lesions of the kidneys, ureters, or bladder, causing urinary flow obstruction.

Disadvantages

  • Exposure to ionizing radiation.

  • Exposure to iodinated contrast.

III. What are the contraindications for the first-line imaging technique?

  • Contraindicated in pregnant women, especially within the first two trimesters.

  • Relative contraindication in patients with renal failure.

  • Relative contraindication in patients with contrast allergy.

IV. What alternative imaging techniques are available?

  • Kidney and bladder ultrasound.

  • MRI of the abdomen and pelvis, with and without contrast.

V. Describe the advantages and disadvantages of the alternative techniques for diagnosing pyelonephritis?

Kidney and bladder ultrasound

Advantages

  • May diagnose proximal or distal obstructions to urine flow.

  • May demonstrate renal morphological alterations and focal lesions of the kidneys.

  • May detail secondary signs of collecting system obstruction, such as hydroureter and hydronephrosis.

  • Relatively inexpensive and portable imaging modality that does not use ionizing radiation.

Disadvantages

  • Unable to visualize the entire course of the collecting system due to overlying bone, bowel gas, and depth of structures.

  • There is limited evaluation in obese patients.

MRI of the abdomen and pelvis with and without contrast

Advantages

Dynamic MRI exam may demonstrate alterations in renal parenchymal enhancement and presence of focal lesions of the kidneys, ureters, or bladder, causing urinary flow obstruction.

Disadvantages

  • Expensive.

  • Time consuming.

  • Requires significant patient cooperation to minimize motion artifact.

VI. What are the contraindications for the alternative imaging techniques?

Kidney and bladder ultrasound

  • No significant contraindications exist.

MRI of the abdomen and pelvis with and without contrast

  • Contraindicated in patients with non-MR compatible metallic (ferromagnetic) hardware or foreign bodies, and those who are uncooperative or claustrophobic.

  • Gadolinium contrast is contraindicated in patients with a GFR ≤ 30.

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