27.6: Imaging Studies III: Computed Tomography

Definition

Computed Tomography (CT) of the genitourinary (GU) tract is a non-invasive imaging modality that utilizes X-rays and computer processing to generate detailed cross-sectional images of the urinary system, encompassing the kidneys, ureters, bladder, and adjacent structures such as the adrenal glands.

Purpose

CT scans of the GU tract serve several diagnostic and therapeutic purposes, including:

• Diagnosis of Urinary Tract Diseases: Detects kidney stones, tumors, cysts, and congenital anomalies in the kidneys, ureters, and bladder.
• Evaluation of Trauma: Assesses injuries to the kidneys, ureters, bladder, and adrenal glands.
• Staging and Monitoring of Cancers: Guides treatment plans and monitors response to therapy for cancers like renal cell carcinoma and bladder cancer.
• Evaluation of Infections: Identifies complicated urinary tract infections (UTIs) and conditions such as pyelonephritis and abscesses.

Pre-Procedure

Preparation before a CT scan of the GU tract involves several steps to ensure safety and accuracy:

• Patient Assessment: Review the patient’s medical history, including allergies (especially to iodine or contrast agents), current medications, and renal function status. Verify that the patient is not pregnant, as radiation exposure can be dangerous to a fetus.
• Informed Consent: Explain the procedure, its purpose, and any potential risks (such as contrast reactions or radiation exposure) to the patient. Obtain written informed consent once the patient understands the procedure.
• NPO Status: Patients are typically instructed to take nothing by mouth (NPO) for 4-6 hours before the scan to reduce the risk of aspiration and improve the clarity of images, particularly when IV contrast is used.
• Preparation of the Scan Area: Before imaging, it is essential to instruct the patient to eliminate any metallic items, such as jewelry, garments with metal components, or removable dental prosthetics, to mitigate potential image distortion.

Intra-Procedure

During the CT scan, several steps ensure accurate imaging and patient safety:

• Positioning: The patient lies on their back (supine) on the CT table.
• Administration of IV Contrast: If required, a contrast agent is injected through an IV line to enhance visualization of blood vessels and soft tissues. The patient may feel a warm sensation or metallic taste during the injection. The need for contrast depends on the specific clinical scenario.
• Image Acquisition: The patient is asked to hold their breath briefly during the scan to prevent motion artifacts and ensure high-quality images. The scanner rotates around the patient, capturing several images of the GU tract within a few seconds or minutes.
• Monitoring: The patient is observed throughout the procedure using a camera and intercom system to ensure safety.

Post-Procedure

After the CT scan, specific steps are taken to ensure patient safety and follow-up:

• Observation for Contrast Reactions: Monitor the patient for 15-30 minutes after using IV contrast, watching for delayed reactions such as rash, nausea, or difficulty breathing. Patients with impaired renal function may require closer monitoring to ensure proper elimination of the contrast agent, as it can potentially worsen kidney function.
• Encourage Hydration: Advise the patient to drink fluids to help flush the contrast medium out of their urinary system.
• Discharge Instructions: Inform the patient when to expect their results and schedule any follow-up appointments as needed.
• Documentation: Document the procedure, including the type and volume of contrast used, any reactions observed, and instructions provided to the patient.