Welcome to the Ultrasound Leadership Academy (ULA) summary blog series. This week, we discuss the basics of ultrasound for renal colic. The ULA is essentially an online advanced ultrasound education experience put on by the team from Ultrasound Podcast which brings cutting edge learning to emergency medicine personnel through a variety of interactive platforms including video lectures, google hangouts with experts, simulation, live conferences and real time scanning with a pocket-sized ultrasound device known as a Vscan.
Over the next year I will be posting summaries of the key learning points from my experience. If you want to learn more about the program you can visit Ultrasound Leadership Academy or Ultrasound Podcast to see more from the hosts of this awesome program.
The rate of CT scan use for suspected renal colic has drastically increased, literature citing a jump from 4% to 42 % from 1996 to 2007. Surely this number has continued to rise. Not surprisingly, the absolute number of ureterolithiasis diagnoses has not increased, though other alternative diagnoses have been increasingly found. This makes sense in light of the fact that ED physicians find non contrast CT scans useful for flank pain as it allows rapid diagnosis and location of an obstructing stone as well identification of alternative diagnoses simultaneously. Though new evidence from a recent NEJM article, evaluating US vs CT for initial work up of suspected renal colic, found no difference in adverse outcomes. This suggests that a more conservative imaging strategy, beginning with renal ultrasound, may be the right place to start. Furthermore, ED physicians have been shown to be accurate at identification of hydronephrosis on ultrasound, which is a useful marker for predicting obstructing ureteral stones.
Point of care ultrasound for renal colic will be a more focused assessment of the kidney and our main area of interest will be the collecting system. Unlike assessing the RUQ where we are looking for a hyperechoic stone with posterior shadowing, our goal with renal US is to identify indirect signs of ureterolithiasis such as hydronephrosis.
Probe: Low frequency curvilinear probe to allow for penetration deep into tissue for visualization of the entire kidneys and bladder. If you are having difficulties with significant rib shadowing, consider the phased-array probe for a smaller footprint allowing you to squeeze between th rib spaces.
Positioning: Having the patient lay supine is a good place to start as it will allow you to scan both kidneys and the bladder fairly quickly. I usually stand on the patient's right side with the machine on the patient's left side which gives you a great view of your screen during the entire scan. You can place the patient in alternating lateral decubitus positions if you are not obtaining adequate views of the kidneys supine which is often due to a large body habitus.
Where to Scan: Your scanning positions will be very similar to your FAST, so start as if you were performing this scan, placing the probe with marker towards the patient's head to obtain a long axis view of each kidney. You can try the short axis view as well by rotating the probe 90 degrees, but often the long axis view will be adequate for your evaluation.
- RUQ: Mid axillary line with the middle of the probe over the costal margin, using the liver as your acoustic window.
- LUQ: Start mid axillary line with middle of probe over the costal margin, then move a little more superior and posterior and you should find your kidney here. Use the spleen as your acoustic window.
Hydronephrosis: You will be looking for distention of the collecting system. In a normal kidney the renal pelvis may be minimally visible within the surrounding hyperechoic renal sinus (fat content makes it bright). As obstruction of the ureter occurs, the renal pelvis becomes progressively dilated, leading to enlargement of the calyces and finally thinning of the renal cortex. This can be graded as as mild, moderate or severe and is quite subjective. The above diagram gives you an idea of what you may expect to see on ultrasound when obstruction is present and a general visual grading guideline. Mild hydronephrosis will be difficult to pick up so it is essential to compare it to the opposite side and make sure you are not just appreciating a well hydrated patient.
Ureteral Jets: Assessment of ureterovesicular jet dynamics, including velocity and how frequently they are occurring, as well as asymmetry, has a pretty good sensitivity for assessing for obstruction however this takes time and in the ED may not be that useful. If you are going to take a look, place the probe over a full bladder in a transverse orientation. You will be looking posteriorly at the UVJs. See references for more information on this topic.
The Twinkling Artifact: As we mentioned earlier, most ureteral stones will not be visualized directly on your bedside ultrasound, however color doppler may be useful to identify an obstructing stone that is initially invisible to your eye. You will be looking for the twinkling artifact, which has a 100% specificity for an obstructing stone! I have included 3 great examples of the twinkle artifact below. Note that you can assess for this both when you are performing ultrasound of the kidney as well as when you are assessing for ureteral jets (as the most common location of obstructing stone is at UVJ).
Renal ultrasound is better at identifying indirect signs of ureterolithiasis such as hydronephrosis, and not stone size and location, however we know that the majority of stones are initially managed with medical expulsion therapy. Ultrasound of the renal system is also fast and can be performed at the bedside efficiently and accurately. With this in mind, it is reasonable to start with ultrasound for evaluation of renal colic as long as there are not complicating factors such as infected urine, severe pain or concern for more life threatening alternative diagnosis (be weary in older patients without h/o kidney stones or with multiple co-morbidities). A few more pearls:
- In an elderly patient with acute flank pain, don't forget to perform a simultaneous exam of the aorta as this is a cannot miss diagnosis and may present similarly to renal colic
- A renal cyst can appear as a anechoic structure within the kidney and mimic hydronephrosis. These do not originate from the renal pelvis and usually exist isolated in the renal parenchyma.
- If something looks abnormal or if you are unable to discern the architecture of the kidney well, do not ignore it, work up further with more advanced imaging
THAT'S IT FOR THIS WEEK
If you are interested in learning more about the ULA learning experience, visit their website below:
More on renal ultrasound can be found in "Introduction to Bedside Ultrasound," Volume 1 & 2, from Dr. Mallin and Dr. Dawson. If you are interested in purchasing these ebooks for less than $1, visit Ultrasound Podcast Consumables.
- Kocher K, Meurer W, Fazel R, Scott P, Krumholtz H, Nallamothu B. National trends in the use of computed tomography in the emergency department. Annals of Emerg Med. 2011; 58: 452-462.
- Broder J. Cumulative CT exposures in ED pts evaluated for suspected renal colic: JEM. 2007 Aug; 33(2):161-8.
- Westphalen A, Hsia R, Maselli J, Wang R, Gonzalez R. Radiological imaging of patients with suspected urinary tract stones: national trends, diagnoses and predictors. Acad Emerg Med. 2011; 18: 700-707.
- Chen MY, Zagoria RJ, Saunders HS, Dyer RB. Trends in the use of unenhanced helical CT for acute urinary colic. AJR Am J Roentgenol. 1999; 173:1447-1450.
- Edmonds, et al. The utility of renal ultrasonography in the diagnosis of renal colic in ED patients. CJEM. 2010 May;12(3):201-6.
- Riddell J, et al. Sensitivity of emergency bedside ultrasound to detect hydronephrosis in patients with CT-proven stones. West J Emerg Med. 2014 Feb;15(1):96-100.
- Herbst MK, et al. Effect of Provider Experience on Clinician-Performed Ultrasonography for Hydronephrosis in Patients with Suspected Renal Colic. Ann Emerg Med. 2014 Sep;64:3. PMID: 24630203.
- Dalziel PJ and Noble VE. Bedside ultrasound and the assessment of renal colic: a review.Emerg Med J. 2013;30:3-8. PMID: 22685250.
- Moore CL and Scoutt L. Sonography First for Acute Flank Pain? J Ultrasound Med 2012; 31(11):1703-1711. PMID: 23091240.
- Smith-Bindman R, et al. Ultrasonography versus Computed Tomography for Suspected Nephrolithiasis. N Engl J Med 2014 18;371(12). PMID: 25229916.
Jandaghi A et al. Assessment of ureterovesical jet dynamics in obstructed ureter by urinary stone with color Doppler and duplex Doppler examinations. Urolithiasis 2013, 41 (2): 159-63.
Ripollés T et al. Sonographic diagnosis of symptomatic ureteral calculi: usefulness of the twinkling artifact. Abdominal Imaging 2013, 38 (4): 863-9