Twinkle Twinkle Little Stone: Identification of Nephrolithiasis Using Color Doppler

CASE

25-year-old male with history of nephrolithiasis (prior right UVJ stone, 4x6mm visualized on CT a year ago) presenting with acute onset severe L sided flank pain that woke him from sleep. He endorsed associated chills, two episodes of emesis, and increased urinary frequency.  He denied measured fevers. He described pain as similar to, but less severe, than what he experienced with a prior stone, which he passed spontaneously.

His physical exam was unrevealing. He was normotensive, had a heart rate in the 60s and was afebrile. His abdominal exam was benign without tenderness. He had no CVA tenderness.

Bedside renal ultrasound was performed at initial presentation and notable for possible left UVJ stone, no hydronephrosis. Urinary jets were not visualized.

Notably, he had poor oral intake and multiple episodes of emesis on the day he presented for which he received IV fluid hydration, pain control with oxycodone, and antiemetics while labs and urinalysis were pending.

Urinalysis: 3+ blood, trace leukocyte esterase, negative nitrates with >180 RBC and 7 WBC on microscopy, moderate squamous epithelial cells

Basic Metabolic Panel: no significant electrolyte abnormalities, no evidence of AKI with BUN 15 and Serum Creatinine 1.06

Repeat Renal and Bladder POCUS after 1L fluid resuscitation was notable for mild hydronephrosis of the left kidney, twinkle artifact consistent with stone at the left UVJ, and absence of left urinary jets.

Image 1: Bladder ultrasonography with color doppler demonstrating a right ureteral jet and twinkle sign at left ureterovesciular junction representing an obstructive UVJ stone.

DIAGNOSIS

Left obstructive ureterovesicular junction stone with mild hydronephrosis

DISCUSSION

Imaging of Choice

The American Urological Society currently recommends noncontrast-enhanced computed tomography as the standard imaging modality and the preferred initial imaging study for most patients with suspected ureteral stone. It is strongly recommended that any patient with fever or solitary kidney, or any patient in which renal stone is less likely or as likely as other acute intraabdominal or retroperitoneal pathologies receive immediate CT imaging [1]. While noncontrast CT imaging holds the highest sensitivity (98%) and specificity (97%) for diagnosis of nephrolithiasis, it does carry significant radiation exposure. Renal ultrasound, however,  maintains relatively high specificity (94%) for ureteral stones with no radiation exposure and as such, is the preferred diagnostic imaging tool for pregnant patients particularly in the first trimester [2]. The European Association of Urology also recommends ultrasound as the first-line imaging modality in patients with acute flank pain and a high suspicion for nephrolithiasis [1]. Ultrasound avoids radiation, is inexpensive, and is easily reproducible. A 2019 multispecialty consensus supports avoidance of CT in younger patients ( <35 years old) with a presentation typical for kidney stones or in middle aged patients (<55 years old) with a prior history of kidney stones [3]. Ultrasound first approach is also supported by findings of a large, multicenter study comparing point-of-care ultrasonography, radiology ultrasonography, and CT that showed no significant difference in identification of high-risk diagnoses with complications, serious adverse events, emergency department bounce-backs, or hospitalization [5].  

Though ultrasound can be operator dependent, the use of Color Doppler has been shown to facilitate the detection of urinary stones, specifically the presence of a “twinkling artifact”. Compared to non-contrast CT, the detection sensitivity of gray scale ultrasonography is relatively low, approximately 45% as it is dependent on the echogenicity of the stone and its ability to produce a posterior acoustic shadow [5].   Studies have shown that the use of color doppler may improve diagnostic confidence in sonographic practice, and specifically the “twinkling sign” is suggestive of urinary stones that may not demonstrate echogenicity on gray scale ultrasonography or a posterior acoustic shadow [5,6].  

Ultrasound Findings

  • Hydronephrosis

    • Mild – dilation of the renal pelvis while calices and pyramids appear normal

    • Moderate – “bear claw”, entire renal pelvis and calices dilated

    • Severe – obliteration of normal renal architecture, thinning of the cortex

  • Ureteral jets – normal physiological periodical efflux of urine (≥ 2 in 60 seconds) from the distal end of each ureter into the bladder visualized on transverse plane; absence or shortening of duration (normal: 6+ seconds) suggests ureteric obstruction

  • “Twinkle Artifact” – focus of alternating colors on Doppler signal behind a reflective object such as stone

CASE RESOLUTION

Given the absence of infection on urinalysis and only mild hydronephrosis visualized on ultrasound, patient was discharged home with supportive care including pain control with naproxen, tamsulosin, and Urology referral.

 

TAKE-AWAYS

  • “Twinkling Artifact” or “Twinkle Sign” is a color doppler phenomenon that facilitates the identification of urinary stones on renal/bladder ultrasonography, including stones that may not demonstrate posterior acoustic shadowing or difference in echogenicity

  • Presence of “Twinkling Artifact” improves confidence in identifying stone location in the urinary tract

  • If patient is under-resuscitated you may not visualize findings of obstructive nephropathy (hydronephrosis, urinary jets) secondary to nephrolithiasis. If signs and symptoms are consistent with nephrolithiasis, consider volume resuscitation and re-performing renal ultrasonography.

  • Consider ultrasound as a first-line diagnostic modality in non-pregnant, healthy, and afebrile patients with high suspicion for ureteral or renal stone as cause for acute onset flank pain

Author: Cristina M. Marsocci, DO, is a second-year emergency medicine resident at Brown Emergency Medicine Residency.

Faculty Reviewer:

Jennifer Rogers, MD is an attending emergency medicine physician at Rhode Island Hospital

REFERENCES

1.        Skolarikos A, et al. EAU guideline on urolithiasis [Internet]. European Association of Urology. 2020 [accessed 2024 Oct 16]. Available from: https://uroweb.org/guidelines/urolithiasis.

2.        Pearle MS, Goldfarb DS, Assimos DG, et al. Medical management of kidney stones: AUA guideline. J Urol. 2016 Oct; 196(2):316-24.

3.        Moore CL, Carpenter CR, Heilbrun ME, et al. Imaging in suspected renal colic: Systematic review of the literature and multispecialty consensus. Journal of the American College of Radiology. 2019 Sep; 16(9):1132-1143. https://doi.org/10.1016/j.jacr.2019.04.004

4.        Smith-Bindman R, Aubin C. Ultrasonography versus computed tomography for suspected nephrolithiasis. New England Journal of Medicine. 2014 Sept; 37:1100-1110.  https://doi.org/10.1056/NEJMoa1404446

5.        Ahmad SK, Abdallah MM. The diagnostic value of the twinkle sign in color Doppler imaging of urinary stones. Egyptian Journal of Radiology and Nuclear Medicine. 2014 Jun; 45(2):569-574. https://doi.org/10.1016/j.ejrnm.2014.01.013

6.        Mitterberger M, Aigner F, Pallwein L, et al. Sonographic detection of renal and ureteral stones: value of the twinkling sign. Int Braz J Urol. 2009 Oct; 35(5):532-541. https://doi.org/10.1590/S1677-55382009000500004  

Emergency Medicine, GU, Radiology, UltrasoundCristina MarsocciEmergency Medicine, Ultrasound, NephrologyComment