Acute Flank Pain in Primary Care: POCUS Alters Management Decisions
This article also appears in the Southern Medical Association News at this link.
Case Presentation
A 47‑year‑old woman with a 3‑day history of dysuria, urinary frequency, and urgency presented to her primary care physician. She noted chills that she treated with acetaminophen. She reports that a colicky pain in her right flank woke her up from sleep this morning. In the clinic, she was afebrile with normal vital signs. Examination revealed right costovertebral angle tenderness. Urine dipstick was positive for leukocyte esterase, nitrites, and microscopic hematuria. The provider suspected uncomplicated pyelonephritis but wanted to exclude an obstructing kidney stone given the colicky nature of her pain, so he performed a bedside renal ultrasound.
What do you see, and what’s the diagnosis?
Figure 1. Coronal view of the right kidney showing moderate hydronephrosis (anechoic dilation of the renal pelvis and calyces) without perinephric fluid.
POCUS Findings in Moderate Hydronephrosis
Figure 2. Side-by-side coronal POCUS images of the right kidney. Left image: Unannotated view showing moderate hydronephrosis with central anechoic dilation extending into the calyces. Right image: Same image with an orange highlight marking the area of hydronephrosis.
Dilation (anechoic fluid) of the renal pelvis and calyces
Preserved Cortical Thickness
Flattened Medullary Pyramids
Normal Renal POCUS
Figure 3. Coronal view of the patient's left kidney showing no dilation of the pelvis or calyces.
Thin anechoic renal pelvis
No calyceal dilation
Preserved corticomedullary differentiation
Normal renal size and echotexture
Absence of perinephric fluid, cysts, or masses
What else can be seen on renal POCUS?
Perinephric abscess: Anechoic or hypoechoic fluid collection with internal echoes, indicating localized infection beyond the collecting system; CT with IV contrast is recommended for definitive evaluation.
Hydroureter: Tubular anechoic structure extending from the renal pelvis along the expected ureter course, signifying obstruction.
Stone visualization: Echogenic foci casting posterior acoustic shadowing; large stones (>5 mm) are more reliably seen.
Pyelonephritis: Renal enlargement, possible perinephric fluid or stranding, and hypoechoic areas of decreased perfusion.
Renal cysts and masses: Well-defined anechoic cysts or solid lesions with internal vascularity, warranting further imaging.POCUS provides high diagnostic accuracy in soft.
Management Guidance
POCUS findings were suggestive of an infected obstructing stone rather than uncomplicated pyelonephritis. The physician immediately referred the patient to the ED for CT confirmation, urologic decompression, and IV antibiotics to prevent sepsis.
Evidence
POCUS sensitivity for hydronephrosis is 84% (range 73–92%) and specificity is 79% (range 59–83%) for suspected renal colic. [1-2] The sensitivity of POCUS increases to 94.4% for moderate to severe hydronephrosis. [3] An ultrasound-first approach reduces time to diagnosis, cumulative radiation exposure, and cost compared with CT. [4-5]
Indications for Renal POCUS in Patients with Acute Pyelonephritis (APN) in Primary Care
Uncomplicated APN is primarily a clinical and laboratory diagnosis and does not require imaging. Renal POCUS should be performed only when there is concern for complications such as urinary obstruction, abscess, or pyonephrosis, or when symptoms persist despite antibiotic therapy. Imaging is also warranted in patients with risk factors for complicated APN—recurrent pyelonephritis, diabetes, immunocompromise, advanced age, vesicoureteral reflux, or pregnancy—due to higher risk of severe sequelae. [6-8] Note that POCUS is the preliminary step, and often more comprehensive imaging is necessary to rule out the above complications.
Limitations of Renal POCUS
Operator and patient dependency: Image quality varies with clinician experience and patient body habitus.
Early or mild obstruction may be missed: Hydronephrosis can be absent if the obstruction is minimal or the patient is dehydrated.
Unknown etiology of obstruction: Renal POCUS confirms urinary obstruction but often cannot identify the cause (stone vs. mass), especially when the obstructing lesion is small (e.g., stone <5mm).
Incomplete anatomy: Focused renal views do not assess the entire ureter or other abdominal/pelvic pathology.
Missed renal pathology: Small perinephric abscesses or cortical changes in pyelonephritis may be missed.
Case Resolution
In the ED, the patient received IV antibiotics and fluids. CT confirmed a 5 mm obstructing stone with moderate hydronephrosis, and she underwent ureteral stent placement alongside a full sepsis workup. She was discharged on oral antibiotics and experienced complete symptom resolution at follow‑up.
Impact of POCUS
Rapid triage: Detected moderate hydronephrosis in minutes
Prevents delay: Avoided empiric outpatient pyelonephritis treatment alone without definitive treatment
Improves safety: Triggered timely ED referral to avoid urosepsis
Cost savings: Reduced imaging and transfer expenses by avoiding unnecessary CT and ED visits
Patient satisfaction: Enhanced patient experience with immediate bedside answers and fewer care delays
Conclusion
Point-of-care ultrasound in primary care provides a rapid, radiation-free first step to distinguish uncomplicated pyelonephritis from obstructing ureterolithiasis. By detecting hydronephrosis at the bedside, clinicians can tailor management—continuing outpatient antibiotics for simple infections or expediting ED referral and urologic intervention for obstructing stones. This approach enhances diagnostic accuracy, improves patient safety and satisfaction, and saves costs.
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Authored by Tatiana Havryliuk, MD
References
Lee S, Kim J, Park Y, et al. Test characteristics of point-of-care ultrasonography in patients with renal colic. Ultrasound J. 2023;15:27.
Pathan SA, Mitra B, Mirza S, et al. Emergency physician interpretation of point-of-care ultrasound for identifying and grading hydronephrosis in renal colic. Acad Emerg Med. 2018;25(10):1129-1137.
Wong C, Teitge B, Ross M, et al. Accuracy and prognostic value of point-of-care ultrasound for nephrolithiasis: systematic review and meta-analysis. Acad Emerg Med. 2018;25(6):684-698.
Smith-Bindman R, Aubin C, Bailitz J, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med. 2014;371(12):1100-1110.
Moore CL, Carpenter CR, Heilbrun ME, et al. Imaging in suspected renal colic: systematic review and consensus. Ann Emerg Med. 2019;74(3):391-399.
Herness J, Buttolph A, Hammer NC. Acute Pyelonephritis in Adults: Rapid Evidence Review. Am Fam Physician. 2020;102(3):173-180.
Weidner W, Ludwig M, Weimar B, Rau W. Rational diagnostic steps in acute pyelonephritis with special reference to ultrasonography and computed tomography scan. Int J Antimicrob Agents. 1999;11(3-4):257-264. doi:10.1016/s0924-8579(99)00026-6
Expert Panel on Urological Imaging, Smith AD, Nikolaidis P, et al. ACR Appropriateness Criteria® Acute Pyelonephritis: 2022 Update. J Am Coll Radiol. 2022;19(11S):S224-S239. doi:10.1016/j.jacr.2022.09.017