CT Scan for Blood in Urine: A Detailed Overview

Blood in the urine, or hematuria, can be alarming, with causes ranging from infections to serious conditions like kidney stones or tumors. Identifying the underlying issue is crucial for proper treatment, and imaging tests play a key role.

A CT scan, specifically CT urography, is often recommended for evaluating unexplained hematuria. This imaging technique provides detailed views of the urinary tract, helping doctors detect abnormalities that might not be visible through other diagnostic methods.

Indications for CT Urography

CT urography is primarily used to evaluate hematuria when the cause remains uncertain after initial assessments. While microscopic hematuria—detectable only under a microscope—may sometimes be benign, visible blood in the urine often requires further investigation. The American College of Radiology (ACR) and the American Urological Association (AUA) recommend CT urography for patients at higher risk of urinary tract malignancies, such as those over 35, smokers, or individuals with a history of occupational exposure to carcinogens like aromatic amines or heavy metals.

Beyond cancer concerns, CT urography is also useful for detecting structural abnormalities of the urinary tract. Congenital conditions like ureteropelvic junction obstruction or duplicated collecting systems, as well as acquired issues such as ureteral strictures or bladder diverticula, can contribute to hematuria and may not be adequately visualized using ultrasound or conventional X-rays. The high-resolution imaging of CT urography provides precise anatomical assessment, aiding in management decisions.

CT urography is also critical in trauma cases. Blunt or penetrating injuries to the kidneys, ureters, or bladder can cause vascular damage, leading to hematuria. This imaging helps detect renal lacerations, active bleeding, or urinary extravasation, which may require surgical or interventional procedures. Its ability to identify subtle injuries makes it invaluable in emergency settings, particularly for patients with high-impact injuries from accidents or falls.

Infections and inflammatory conditions of the urinary tract may also necessitate CT urography, especially when complications are suspected. Chronic or recurrent urinary tract infections (UTIs), particularly in patients with diabetes or immunosuppression, can lead to conditions like emphysematous pyelonephritis or renal abscesses. CT urography helps differentiate between simple infections and more severe pathologies requiring aggressive treatment.

Protocol Variations

CT urography uses different imaging protocols, tailored to detect specific abnormalities. The three primary variations include noncontrast imaging, contrast-enhanced phases, and delayed imaging, each serving a distinct purpose.

Noncontrast

The noncontrast phase, typically the first step, is particularly useful for detecting kidney stones, which appear as hyperdense structures against surrounding soft tissues. This phase also identifies hemorrhagic conditions such as renal hematomas or clot formation within the urinary tract, which may be obscured once contrast is introduced.

Beyond stone detection, noncontrast imaging helps assess renal abnormalities, including cysts or solid masses. Cysts appear as well-defined, fluid-filled structures, while solid tumors may have heterogeneous density. This phase is also beneficial for patients who cannot receive iodinated contrast due to severe renal impairment or contrast allergies.

Contrast-Enhanced

The contrast-enhanced phase involves intravenous administration of iodinated contrast material to improve visualization of renal masses, urothelial tumors, and vascular abnormalities. This phase is divided into corticomedullary and nephrographic phases.

The corticomedullary phase, occurring 30–40 seconds after contrast injection, highlights renal perfusion and vascular lesions such as arteriovenous malformations or renal artery stenosis. The nephrographic phase, occurring around 80–100 seconds post-injection, enhances the renal parenchyma, aiding in the detection of small renal masses and infiltrative diseases.

This phase is particularly useful for identifying urothelial carcinomas, which may appear as irregular filling defects or thickened urothelial linings. Additionally, inflammatory conditions such as pyelonephritis or renal abscesses become more apparent due to altered enhancement patterns. Contrast also improves the evaluation of bladder pathology, including tumors or diverticula.

Delayed Imaging

Delayed imaging, or the excretory phase, is performed several minutes after contrast administration to assess the urinary collecting system, ureters, and bladder. This phase is crucial for detecting urothelial malignancies, as contrast outlines the inner lining of the urinary tract, making subtle lesions more visible.

It is particularly useful for detecting transitional cell carcinoma, which appears as irregular filling defects or focal wall thickening. This phase also identifies urinary tract obstructions such as ureteral strictures or extrinsic compressions from adjacent masses. In trauma cases, delayed imaging can reveal contrast extravasation, indicating potential injuries or post-surgical complications.

Additionally, delayed imaging helps assess urinary drainage, relevant in conditions like ureteropelvic junction obstruction or vesicoureteral reflux. In cases of suspected clot-related obstruction, this phase can differentiate between true filling defects caused by tumors and those resulting from blood clots.

Steps During the Examination

Patients are typically advised to fast for a few hours before the scan to optimize image quality and reduce contrast-related complications. Hydration is encouraged to enhance urinary tract visualization and reduce the risk of contrast-induced nephropathy.

During the scan, patients lie supine on the CT table. A preliminary scout image provides an overview of abdominal and pelvic structures, guiding scan parameters. If contrast is required, an intravenous catheter is placed, usually in the antecubital vein, for controlled contrast injection.

The imaging proceeds through multiple phases, beginning with the noncontrast scan, followed by contrast-enhanced acquisitions at specific intervals. Patients may be instructed to hold their breath briefly to minimize motion artifacts. Automated contrast injectors ensure precise timing for optimal image acquisition. If necessary, additional delayed images are obtained to assess urinary excretion patterns.

Key Anatomical Structures Examined

CT urography provides a detailed evaluation of the urinary system, focusing on structures where abnormalities may cause hematuria. The kidneys are closely examined for size, shape, cortical thickness, and any focal lesions. The renal collecting system, including the calyces and renal pelvis, is scrutinized for obstruction, filling defects, or irregular wall thickening.

The ureters are assessed for strictures, stones, or masses that may interfere with urinary flow. Their course from the renal pelvis to the bladder is carefully followed, with contrast-enhanced phases improving the detection of subtle irregularities. Any external compression from retroperitoneal masses or lymphadenopathy is also noted.

The bladder is analyzed for wall thickening, diverticula, or intraluminal lesions. Contrast-filled imaging improves visualization of transitional cell carcinomas, which often appear as mucosal irregularities. Clot formation and post-void residual volume are also assessed in cases of suspected functional abnormalities.

Common Diagnoses Linked to Hematuria

CT urography can reveal various conditions responsible for hematuria. Urinary tract malignancies, particularly urothelial carcinoma of the bladder or renal pelvis, often present as irregular filling defects or focal wall thickening. Renal cell carcinoma may appear as a solid mass with heterogeneous enhancement, sometimes with venous invasion or metastases. Benign tumors like angiomyolipomas, which contain fat, can also be identified.

Urolithiasis is another common cause, with CT urography detecting even small stones. Stones irritate the urinary tract, causing hematuria, and may lead to secondary findings like hydronephrosis. Inflammatory conditions such as pyelonephritis and cystitis can also be identified, often presenting with renal enlargement or bladder wall thickening. Autoimmune diseases like IgA nephropathy or vasculitis may not have direct CT findings but can be suspected when structural causes are excluded.

Result Analysis

Interpreting CT urography findings requires assessing lesion characteristics such as size, shape, and enhancement patterns. A well-circumscribed, non-enhancing renal lesion is likely a simple cyst, whereas an irregular, enhancing mass raises suspicion for malignancy. Vascular invasion or lymphadenopathy further supports an aggressive neoplasm, requiring additional oncologic workup.

For nephrolithiasis, stone composition can often be inferred from attenuation values, aiding in treatment planning. High-density stones, typically composed of calcium oxalate or phosphate, are more visible on noncontrast imaging, while uric acid stones may require specialized CT techniques.

Potential Follow-Up Evaluations

Findings on CT urography often require further testing. Suspicious renal or bladder masses may warrant cystoscopy or biopsy for histopathological analysis. If infiltrative renal disease is suspected, a renal biopsy may be needed.

For non-malignant conditions, follow-up imaging may monitor progression or resolution. Patients with small kidney stones may undergo interval CT scans to track passage or growth. Infections or inflammatory conditions may require repeat imaging after treatment to rule out complications. Functional studies, such as renal scintigraphy or urodynamic testing, may be considered if imaging suggests impaired kidney function or bladder dysfunction.