The Case
The patient was a 23-year-old G3P2 female, approximately 3 months and 12 days pregnant based on her last menstrual period, who presented to the Emergency Department with pelvic pain and vaginal bleeding, as well as dysuria and hematuria for three days. She had not yet established care with an obstetric provider. The pain was described as constant, cramping suprapubic discomfort with associated mild right flank pain. She reported intermittent fevers, dysuria, hematuria, and mild vaginal spotting between episodes of urination. She noted that during one of her prior pregnancies she had experienced similar symptoms when she developed an infected renal stone that required a prolonged hospitalization and ultimately passed spontaneously.
On arrival, she was tachycardic to 112 bpm, afebrile, and hemodynamically stable. Laboratory studies revealed a WBC count of 10.3 K/uL. Point-of-care ultrasound confirmed an intrauterine pregnancy with fetal cardiac activity. Bedside renal ultrasound showed moderate right hydronephrosis (Figure 1). Urinalysis demonstrated 3+ blood, 1+ nitrite, 500 leukocyte esterase, moderate bacteria, 35 RBCs, and 53 WBCs. The patient received an initial dose of intravenous ceftriaxone. Transvaginal ultrasound confirmed a single live intrauterine pregnancy at 18 weeks and 1 day gestation.
Gynecology was consulted and recommended admission to the maternal–fetal medicine service for management of presumed pyelonephritis versus infected obstructing stone. Inpatient renal ultrasound revealed no shadowing renal calculi but mild-to-moderate right hydronephrosis. Urine culture later grew >100,000 CFU/mL of multi-resistant E. coli. The patient completed two days of intravenous ceftriaxone and was transitioned to a 10-day course of oral amoxicillin-clavulanate based on susceptibilities. Her symptoms improved, and she was discharged home with close obstetric follow-up.
Discussion
This case highlights the diagnostic and management challenges of suspected infected kidney stones in pregnancy. While this patient did not ultimately have an obstructing stone, her presentation required careful consideration of imaging strategies that balance maternal and fetal risks. In the emergency setting, differentiating between pyelonephritis and an infected obstructing stone is critical, as delayed recognition of obstruction can result in urosepsis and adverse fetal outcomes.
The American College of Radiology (ACR) recommends that computed tomography (CT) be reserved for pregnant patients with suspected infected urolithiasis only when ultrasound and/or MRI are inconclusive and when there is high clinical suspicion for a complication requiring urgent intervention. CT remains the gold standard for stone detection, offering superior sensitivity and specificity, but its use in pregnancy is limited due to concerns for fetal radiation exposure. When necessary, low-dose or ultra–low-dose CT protocols should be used, with efforts to minimize the number of studies obtained.
Ultrasound remains the preferred initial imaging modality due to its safety and availability, but its accuracy is limited by physiologic hydronephrosis of pregnancy. MRI without contrast serves as a secondary option when ultrasound is nondiagnostic, though it has lower sensitivity for small stones. CT should therefore be considered a last resort when both ultrasound and MRI fail to clarify the diagnosis and when maternal or fetal risk from delayed management outweighs radiation concerns.
This case underscores the importance of multidisciplinary collaboration between emergency medicine, obstetrics and radiology when caring for pregnant patients with suspected infected urolithiasis. Prompt initiation of broad-spectrum antibiotics and timely consultation are essential,
while imaging decisions should be individualized based on clinical stability and diagnostic uncertainty.
In summary, CT imaging should be obtained only when other modalities are nondiagnostic and the patient’s presentation suggests infection, obstruction, or sepsis risk. Emergency physicians play a critical role in balancing diagnostic accuracy with fetal safety and coordinating care across specialties to ensure optimal maternal and fetal outcomes.
References
Gupta RT, Kalisz K, Khatri G, et al. ACR Appropriateness Criteria® Acute Onset Flank Pain–Suspicion of Stone Disease (Urolithiasis). J Am Coll Radiol. 2023;20(11S):S315–S328. doi:10.1016/j.jacr.2023.08.020.
Dai JC, Nicholson TM, Chang HC, et al. Nephrolithiasis in pregnancy: treating for two. Urology. 2021;151:44–53. doi:10.1016/j.urology.2020.06.097.
Deng S, Guo D, Liu L, et al. Preference for diagnosing and treating renal colic during pregnancy: a survey among Chinese urologists. Sci Rep. 2024;14(1):2914. doi:10.1038/s41598-024-53608-w.
Masselli G, Weston M, Spencer J. The role of imaging in the diagnosis and management of renal stone disease in pregnancy. Clin Radiol. 2015;70(12):1462–71. doi:10.1016/j.crad.2015.09.002.
Authored by Kelly Landry MD and Christine Jung MD