What is the best approach to manage a pregnant patient with right flank pain and a history of kidney stones?

Management of Pregnant Patient with Right Flank Pain and History of Kidney Stones

Start with renal ultrasound as your first-line imaging, proceed to MR urography without contrast if ultrasound is nondiagnostic, and reserve low-dose noncontrast CT as a last resort when diagnosis remains uncertain despite the first two modalities. 1

Initial Diagnostic Approach

First-Line Imaging: Renal Ultrasound

• Ultrasound is the mandatory initial screening examination because it is sensitive and specific for hydronephrosis and avoids ionizing radiation exposure to both mother and fetus 2, 1.
• Ultrasound has nearly 100% sensitivity for detecting large stones (>5 mm) and hydronephrosis, though accuracy drops significantly for small stones (<3 mm) 1.
• This modality receives an appropriateness rating of 8 (usually appropriate) from the American College of Radiology 2.

Critical Diagnostic Pitfall

• Physiologic hydronephrosis occurs in >80% of pregnant patients, more commonly on the right side, typically beginning in the second trimester due to compression of the ureters between the gravid uterus and linea terminalis 2, 1.
• Do not dismiss right-sided hydronephrosis as purely physiologic without considering obstructive urolithiasis as a differential 1.

Second-Line Imaging: MR Urography

When Ultrasound Fails

• If ultrasound is nondiagnostic and the patient remains severely symptomatic despite conservative management, proceed to MR urography (MRU) without IV contrast 1, 3, 4.
• MRU avoids fetal radiation exposure and can detect hydronephrosis and causes of renal obstruction 2, 1.

MRU Limitations to Recognize

• MRU has only 69% sensitivity for identifying the site of stone impaction compared to 100% sensitivity with CT 2, 1.
• Despite this limitation, MRU is preferred over CT in the second and third trimesters when renal calculus is suspected 2.

Third-Line Imaging: Low-Dose Noncontrast CT

Reserved for Diagnostic Uncertainty

• Use noncontrast CT abdomen and pelvis only when diagnosis remains uncertain after ultrasound and MRI, and only when clinical benefit clearly outweighs radiation risks 1, 3, 4.
• Noncontrast CT is sensitive and specific for diagnosing stones in pregnant patients, with the critical principle being dose optimization and minimizing total number of studies 2, 1.
• Most diagnostic CT studies deliver far less than 20 mGy to the uterus 1.

What NOT to Order

• Avoid CT with IV contrast as there is no documented additional benefit for stone detection in pregnancy 2, 1.
• Do not order KUB radiography as there is no relevant literature supporting its benefit in pregnant patients with suspected stones 2, 1.

Management Strategy

Initial Conservative Management

• Offer observation with symptom control as initial therapy when symptoms are well-controlled 3.
• Coordinate all interventions with the patient's obstetrician before proceeding 3, 5.

Pain Management Considerations

• NSAIDs (diclofenac, ibuprofen, metamizole) are contraindicated in pregnancy 3.
• Opioids serve as primary analgesics, with hydromorphine, pentazocine, or tramadol preferred over pethidine 3.

When to Intervene

Emergency Indications

• If infection or sepsis is present, perform emergency decompression (ureteral stent or percutaneous nephrostomy) plus antibiotics immediately 3, 5.

Failed Conservative Management

• If observation fails after 24-48 hours, proceed to ureteroscopy for definitive treatment 3.
• Ureteroscopy is the preferred definitive intervention for pregnant patients who fail observation 2, 3, 6.
• Multiple studies demonstrate successful outcomes with ureteroscopy in pregnant women with very low morbidity and minimal need for long-term ureteral stenting 2, 6.

Alternative Temporizing Measures

• Ureteral stents and percutaneous nephrostomy tubes are options but require frequent exchanges (typically every 6 weeks) due to rapid encrustation during pregnancy 2, 3.
• This temporizing approach is often associated with poor patient tolerance and requires multiple exchanges throughout the remainder of pregnancy 2.

Holmium Laser Advantage

• When intracorporeal lithotripsy is necessary during ureteroscopy, the holmium laser has minimal tissue penetration, theoretically limiting risk of fetal injury 2.

Key Clinical Pearls

• Stone events during pregnancy carry increased risk of maternal and fetal morbidity, including preterm labor, requiring close monitoring even with conservative management 3.
• The most significant risk is induction of preterm labor, which completely resolves once the stone passes or is removed 3.
• A multidisciplinary approach involving urology, obstetrics, anesthesiology, and radiology is essential for optimal outcomes 5, 6, 7.