Is nephrolithiasis (kidney stones) present?

From the Guidelines

I strongly recommend a non-contrast CT scan of the abdomen and pelvis to confirm the presence of nephrolithiasis (kidney stones). This imaging modality is the gold standard for diagnosing kidney stones as it can detect stones of all compositions with approximately 97% sensitivity and specificity, as reported in the most recent study 1. The scan should be performed with thin slices (1-3mm) to optimize stone detection.

Key Points to Consider

• Ultrasound is an alternative option, particularly for pregnant patients or children, though it has lower sensitivity (around 60-80%) especially for smaller stones or those in the ureter 1.
• X-ray (KUB) has limited utility as it only detects radiopaque stones.
• When ordering the CT, specify "CT abdomen/pelvis without contrast for suspected nephrolithiasis" to ensure the appropriate protocol is used.
• Intravenous contrast is not needed and actually makes stones harder to visualize.
• The scan will not only confirm the presence of stones but also provide critical information about stone size, location, and degree of hydronephrosis, which guides management decisions regarding medical expulsive therapy versus urological intervention 1.

Rationale

The use of non-contrast CT scans for diagnosing nephrolithiasis is supported by recent studies, including a 2023 study published in the Journal of the American College of Radiology 1, which reported a high sensitivity and specificity for detecting kidney stones. Another study published in 2024 1 also highlighted the utility of non-contrast CT scans in evaluating patients with symptomatic hydronephrosis and suspected urolithiasis.

Additional Considerations

• Low-dose non-contrast CT scans can be used to reduce radiation exposure, especially in young patients, while still maintaining high diagnostic accuracy 1.
• The presence of hydronephrosis on ultrasound can increase the likelihood of detecting a ureteral stone on CT, making it a useful supportive finding in the diagnosis of nephrolithiasis 1.

From the Research

Diagnosis of Nephrolithiasis

• Nephrolithiasis, also known as kidney stones, can be diagnosed using various imaging modalities, including renal bladder ultrasound (RBUS), non-contrast computerized tomography (NCCT), and magnetic resonance imaging (MRI) 2, 3, 4.
• According to a study published in 2021, RBUS should be the initial diagnostic study for suspected nephrolithiasis in pregnant patients, followed by a non-contrast CT scan if diagnostic uncertainty still exists 2.
• Another study published in 2014 compared the use of ultrasound and non-contrast helical CT for diagnosing nephrolithiasis in children, and found that non-contrast helical CT is essential for confirming the diagnosis and ruling out other extrarenal causes of symptoms 3.

Imaging Modalities

• NCCT is considered the gold standard for diagnosing nephrolithiasis, but it exposes patients to radiation 5.
• A study published in 2024 found that limiting the cranial extent of CT KUB imaging to the T10 vertebral level can reduce radiation exposure while maintaining diagnostic accuracy 5.
• Ultrasound is a cost-effective and radiation-free modality that can be used to monitor interval stone development and evaluate for hydronephrosis 4.
• MRI and Kidney Ureter Bladder plain film radiography (KUB) also have unique roles in the management of urolithiasis, although their use may be more limited in certain clinical settings 4.

Clinical Presentation

• Nephrolithiasis can present with a range of symptoms, including flank pain, hematuria, and urinary frequency 2, 3.
• A case report published in 2008 described a patient who presented with left flank pain that was initially suspected to be nephrolithiasis, but was later diagnosed with perforated appendicitis 6.
• The clinical presentation of nephrolithiasis can be variable, and a thorough diagnostic workup is necessary to confirm the diagnosis and rule out other causes of symptoms.