Core-Renal Ultrasound

This core didactic session recap is devoted to renal ultrasound. Point-of-care ultrasound uses focused clinical questions to guide management, and our didactic session use focused clinical questions to guide discussions of key literature.

Discussants Vincent Roddy and Phillip Andrus led our group through a series of questions which bring the relevance of renal sonography home.

1. Can the degree of hydronephrosis predict stone size?

In an word, yes. In a retrospective study of 177 patients with documented stones on CT scans, ultrasonographers blinded to the CT results were able to predict stone size (>5mm or <5mm) based on the degree of hydronephrosis observed (1).

Hydronephrosis was defined as mild, moderate, severe

1. Mild: Enlargement of calices with preservation of renal papillae
2. Moderate: Rounding of calices with obliteration of renal papillae
3. Severe: Caliceal ballooning with cortical thinning

Results:

Increasing degree of hydro associated with increasing proportion of ureteral calculi > 5mm (p < 0.001)
Take-home points:

• Stone size is an important predictor of stone passage and clinical outcome; < 5mm likely to pass regardless of location
• Current guidelines recommend triage of “medical expulsion therapy” for calculi between 5 and 10 mm; > 10mm often require surgical removal
• Ultrasound sensitivity for detection of stones greater than 5mm is poor. With severe hydro over one-third had stones over 5mm and one third of THAT group had caliculi larger than 10mm (2)

References:

1. Goertz JK, Lotterman S. Can the degree od hydronephrosis on US predict kidney stone size? Am J Emerg Med 2010; 28:813-6.
2. Preminger GM, Tiselius HG, Assimos DG, et al. 2007 guideline for the mgmt of ureteral calcul. J Urol 2007; 178:2418-34.

2. Should the bladder be included in the renal scan?

Yes – rapid ED renal ultrasound including images of the bladder might exclude distal obstruction and allows clinicians to focus on other diagnoses (1).

Ultrasound of the bladder also allows for the evaluation of the presence of “ureteral jets.”  Although clinically utility is debatable, a unilaterally abnormal ureteral jet can be suggestive of high-grade obstruction on the ipsilateral body side.  Ultrasound is useful in making this determination, though it is limited in its ability to determine stone location.  It is important to note that  normal ureteral jets cannot be used to exclude a diagnosis of renal colic.  (2).

References:

1. Wakins S, Bowra J. Validation of EP Ultrasound in Diagnosing hydronephrosis in ureteric colic. Emergency Medicine Australasia (2007) 19, 188-195.
2. Sheafor D, Hertzberg B, et al. Nonenchanced Helical CT and US in the Emergency Evaluation of Patients with Renal Colic.

3. Can Emergency Physicians accurately diagnosis hydroneprhosis on bedside ultrasonography?

Yes, numerous studies have documented that ultrasound can accurately predict the degree of hydronephrosis as compared to that on CT scans (1-2) and that the degree of hydronephrosis is related to stone size (3).

References:

1. Gaspari RJ, Horst K. Emergency Ultrasound and urinalysis in the evaluation of flank pain. Acad Emer Med 2005; 12:1180-4.
2.  Watkins S, Bowra J, Sharma P, Holdgate A, et el. Validation of EP ultrasound in diagnosing hydronephrosis in ureteric colic. Emerg Med Australas 2007; 19:188-95.
3. Goertz JK, Lotterman S. Can the degree od hydronephrosis on US predict kidney stone size? Am J Emerg Med 2010; 28:813-6.