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The Case
A 44 year old female with a Past Medical History of Type 2 Diabetes presents with left lower quadrant and left flank pain. The pain woke her from sleep 5 days ago and was a sharp 10/10 pain and at the time she had one episode of nausea and vomiting. She saw her primary care physician 2 days earlier and had a urinalysis which was reported as negative. Your patient denies fevers, chills, change in bowel movements. Her last menstrual period was 4 weeks ago and she denies any vaginal bleeding or discharge. On physical exam she was well appearing and in no apparent distress. Her abdominal exam revealed a soft abdomen with left lower quadrant and left CVA tenderness, without rebound or guarding. Her pelvic exam was unremarkable. Lab work was normal, including a normal urinalysis. The patient was given Ketorolac IV for pain. At this point, a bedside ultrasound was performed and revealed mild left sided hydronephrosis.
Sounds like a Kidney Stone…
B mode scanning (grey scale scanning) of the ureterovesicular junction was unremarkable but color flow doppler revealed the following image:
[/et_pb_text][/et_pb_column][/et_pb_row][et_pb_row][et_pb_column type=”3_4″][et_pb_image admin_label=”Image” src=”http://theempulse.org/wp-content/uploads/2016/12/twinkle.jpg” show_in_lightbox=”on” url_new_window=”off” animation=”top” sticky=”off” align=”center” force_fullwidth=”off” always_center_on_mobile=”on” use_border_color=”off” border_color=”#ffffff” border_style=”solid”] [/et_pb_image][/et_pb_column][et_pb_column type=”1_4″][et_pb_text admin_label=”Text” background_layout=”light” text_orientation=”left” use_border_color=”off” border_color=”#ffffff” border_style=”solid”]
Note the twinkling artifact at the left ureteral-vesicular junction, suggesting a renal calculus. Repeated B-mode scanning reveals very mild shadowing posterior to the twinkle artifact.
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The Outcome
CT Abdomen/Pelvis confirmed mild left hydroureteronephrosis and also found a 2mm Left Calculus at Ureteral-Vesicular Junction (UVJ). The patient remained pain free and was discharged from the ED with a prescription for analgesia and a follow up with urology.
We Knew It, But How?
Twinkling artifact is a focal area of color uptake during color doppler imaging that falsely depicts movement where there is none. It is theorized that this artifact is due to the splitting of sound waves as they reflect off of a rough, highly reflective object.1 Renal calculi, however, are not the only “highly reflective objects”. These can include biliary calculi, renal stents, vascular calcifications, and even bile duct hamartomas. Because sounds waves move at such high velocities within the calculus, they reach the machine’s upper detection limit – the Nyquist limit. At this point, the machine’s processors compensate by “wrapping around” the color from bright yellow (Nyquist limit in the positive direction) to a light blue (Nyquist limit in the negative direction). To the human eye this looks like a “speckling” or “twinkling” of colors, as seen in the videos below (hit play to start the clip, toggle between the two). The first clip on the left demonstrates the twinkling stone on color doppler mode. The second video is taken in B mode – posterior shadowing is present, though the stone cannot be directly visualized.
[/et_pb_text][et_pb_video_slider admin_label=”UVJ Video Slider” show_image_overlay=”hide” show_arrows=”on” show_thumbnails=”on” controls_color=”light”] [et_pb_video_slider_item admin_title=”Color ” src=”http://theempulse.org/wp-content/uploads/2016/12/twinkling_cropped.mp4″ background_layout=”dark”] [/et_pb_video_slider_item][et_pb_video_slider_item admin_title=”B mode” src=”http://theempulse.org/wp-content/uploads/2016/12/uvjstone_cropped.mp4″ background_layout=”dark”] [/et_pb_video_slider_item] [/et_pb_video_slider][et_pb_text admin_label=”Text” background_layout=”light” text_orientation=”left” use_border_color=”off” border_color=”#ffffff” border_style=”solid”]
So What?
Several studies have investigated whether twinkling artifact has clinical utility in improving the diagnosis of nephrolithiasis. In two single center prospective studies, one in 2012 by Kielar et. al and one in 2013 by Ripollés et al, enrolled 51 and 100 patients respectively who were suspected of having nephrolithiasis and were examined using ultrasonography with Doppler looking specifically at the clinical application of renal ultrasound with twinkle artifact to identify renal calculi.2-3 The Kielar study, they found that standard B-Mode ultrasonography had a Sensitivity of 80.2% and a Positive Predictive Value of 64.9% when looking for renal calculi. However, by adding Doppler and the appearance of twinkle artifact parameters improved to a Sensitivity of 83% and a Positive predictive value of 94%. On the other hand, Ripollés et al found that of the 76 out of 84 stones confirmed by ultrasound, 78% of these also displayed twinkle artifact. Ripollés et al also observed that 16 of the 76 stones were found to have either no findings on standard B-Mode, or twinkling artifact was the first noticed finding before being scrutinized again via B-Mode ultrasound that found an otherwise subtle stone. The authors of this study concluded that in patients with flank pain, renal ultrasound with color doppler showed a sensitivity of 81-95%, specificity of 95-100%, and had a PPV of 95-100%, and NPV of 47-82%. Both studies were limited by small sample size. Also, they were both done by radiologists and not Emergency Physicians (EPs), and only characterized clinical applicability of renal ultrasonography in patients presenting with typical symptoms of nephrolithiasis.
A February 2016 study by Masch et al prospectively examined how renal ultrasound could be used to stratify patients who undergo renal ultrasonography for urolithiasis while excluding those who had known urolithiasis upon presentation.4 This study evaluated 85 patients and found the reported sensitivity (78%), specificity (40%), positive predictive value (68%), and negative predictive value (53%) for isolated twinkling artifact to be much lower than other studies examining twinkling artifact.5 However, when combining twinkling artifact with an echogenic focus, sensitivity, specificity and likelihood ratio improve to 61%, 65% and 1.72 respectively. When combining twinkling artifact with posterior acoustic shadowing the sensitivity, specificity and likelihood ratio became 31%, 95% and 6.81 respectively. Like the previously mentioned research, this study was also limited by its small sample size and participation of Radiologists, not EP’s. Additionally, there was a long lag time to CT confirmation (8 days) and, unlike the previous studies, the Masch paper only looked at the renal parenchyma and pelvis along with the bladder, not the ureteral system.
Conclusion
Twinkling artifact likely does have some clinical utility. Ultrasound examination showing findings of shadowing with twinkle artifact suggest a specificity of 95-100% and a positive predictive value of 92-100% according to the very limited literature. Isolated twinkling artifact has a high false positive rate and low specificity and therefore cannot be used without other findings (such as posterior acoustic shadowing) suggestive of a renal calculus. However, it can help the sonographer further scrutinize that area with B mode, where shadowing might have been missed on the first B-mode scan. The combination of B-mode with twinkling artifact may help to “rule in” a kidney stone in the right clinical context. However, literature of point of care ultrasound (POCUS) by EP’s using twinkling is limited to a case series.5 While the accuracy of POCUS for unilateral hydronephrosis has excellent data for confirming nephrolithiasis, it is possibly that adding an assessment for renal stones may increase the overall accuracy of ultrasound and decrease the need for CT imaging in patients with typical signs and symptoms.6 Further research is required before widespread application can be recommended.
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References:
- Clark A, Ganesh H, Di Santis D. The color comet tail artifact “twinkle sign”. Abdom Imaging. 2015 Aug;40(6):2054-5. doi: 10.1007/s00261-015-0374-3. PubMed PMID: 25676593.
- Kielar AZ, Shabana W, Vakili M, Rubin J. Prospective evaluation of Doppler sonography to detect the twinkling artifact versus unenhanced computed tomography for identifying urinary tract calculi. J Ultrasound Med. 2012 Oct;31(10):1619-25. PubMed PMID: 23011625.
- Ripollés T, Martínez-Pérez MJ, Vizuete J, Miralles S, Delgado F, Pastor-Navarro T. Sonographic diagnosis of symptomatic ureteral calculi: usefulness of the twinkling artifact. Abdom Imaging. 2013 Aug;38(4):863-9. doi: 10.1007/s00261-012-9946-7. PubMed PMID: 23011549.
- Masch WR, Cohan RH, Ellis JH, Dillman JR, Rubin JM, Davenport MS. Clinical Effectiveness of Prospectively Reported Sonographic Twinkling Artifact for the Diagnosis of Renal Calculus in Patients Without Known Urolithiasis. AJR Am J Roentgenol. 2016 Feb;206(2):326-31. doi: 10.2214/AJR.15.14998. PubMed PMID: 26797359.
- Ng C, Tsung JW. Avoiding Computed Tomography Scans By Using Point-Of-Care Ultrasound When Evaluating Suspected Pediatric Renal Colic.J Emerg Med.2015 Aug;49(2):165-71.
- Smith-Bindman R1, Aubin C, Bailitz J, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med.2014 Sep 18;371(12):1100-10.
[/et_pb_text][/et_pb_column][/et_pb_row][et_pb_row][et_pb_column type=”1_2″][et_pb_team_member admin_label=”Person” name=”Kristopher Carbone, MD” position=”Author” image_url=”http://theempulse.org/wp-content/uploads/2015/11/Kristopher-Carbone.png” animation=”off” background_layout=”light” use_border_color=”off” border_color=”#ffffff” border_style=”solid”]
Dr. Carbone is a resident in the combined EM/IM/Critical Care residency program at the LIJ Medical Center.
[/et_pb_team_member][/et_pb_column][et_pb_column type=”1_2″][et_pb_team_member admin_label=”Person” name=”Dr. Josh Guttman, MD, FRCPC” position=”Reviewer and Ultrasound Editor – theEMPulse.org ” image_url=”http://theempulse.org/wp-content/uploads/2015/10/Guttman-e1453253661766.jpg” animation=”off” background_layout=”light” twitter_url=”https://twitter.com/josh_guttman” use_border_color=”off” border_color=”#ffffff” border_style=”solid” saved_tabs=”all”]
Dr. Guttman graduated from the at Mt. Sinai Medical Center Emergency Ultrasound Fellowship and is now an Attending Physician at the NSLIJ Division of Emergency Ultrasound.
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