Case

A 35-year-old man presents to the Emergency Department with sudden onset severe right flank pain radiating towards the groin. He reports intermittent “niggles” of pain over the previous week and now has microscopic haematuria on urine dipstick.

After receiving NSAIDs and opioids, his pain settles and a focused renal point-of-care ultrasound (POCUS) is performed.

The ultrasound demonstrates:

  • Mild right hydronephrosis
  • Dilatation of the proximal ureter (hydroureter)
  • A small calculus at the vesicoureteric junction (VUJ)
  • Reduced right ureteric jet on colour Doppler

These findings are highly suggestive of an obstructing distal ureteric stone.

Transverse view right kidney:

There is mild hydronephrosis and the proximal ureter is dilated   (1.18cm).

Bladder in the transverse plane:

A small stone is visible at the VUJ. Note that it does not cast an acoustic shadow.

A larger stone, >3- 5 mm will cast an acoustic shadow as seen in this different case below.

Using Doppler, a reduced jet is visible in our patient on the right compared to the left  indicating partial obstruction of the right ureter. Note that reduced or absent ureteric jets are a highly specific (85–100%) but moderately sensitive (73–95%) indicator of renal colic obstruction. They provide reliable functional data, but are primarily used as adjunctive, supportive evidence rather than a standalone diagnostic tool. They also can take a long time to obtain – up to 10 minutes.  The visualisation of ureteric jets is therefore not an essential imaging modality to obtain in the setting of renal colic in the Emergency Department.

The right ureter is also visible and dilated indicating mild hydroureter.

If you suspect a renal stone what should you look for on ultrasound?

1. Hydronephrosis

Hydronephrosis is the most important indirect sign of ureteric obstruction.

It appears as dilatation of the renal collecting system and is graded as:

  • Mild – dilated renal pelvis and calyces
  • Moderate – increasing calyceal dilatation
  • Severe – marked dilatation with cortical thinning

The degree of hydronephrosis does not always correlate with stone size, and very early obstruction may produce no hydronephrosis.

2. Stones

Ultrasound can directly identify many renal and distal ureteric stones but this requires practice.

Typical appearances include:

  • Bright hyperechoic focus
  • Posterior acoustic shadowing (particularly stones >5 mm)
  • Twinkling artefact on colour Doppler

Small stones (<3–4 mm) frequently do not shadow and may be missed.

The mid ureter remains the most difficult location to visualise because of overlying bowel gas

3. Ureteric Jets

Colour Doppler evaluation of the bladder can assess ureteric jets.

A reduced or absent jet on the symptomatic side suggests partial or complete obstruction.

4. Hydroureter

Follow the proximal ureter whenever possible.

A dilated ureter supports the diagnosis of distal obstruction and can occasionally lead you directly to the obstructing stone. Although not essential for diagnosis, ureteric jets can increase confidence when combined with hydronephrosis and the clinical presentation.

What are the advantages of Point-of-Care Ultrasound?

POCUS offers several important advantages:

  • No ionising radiation
  • Rapid bedside diagnosis
  • Repeatable examinations
  • Useful for monitoring resolution
  • Identifies hydronephrosis and larger stones
  • May demonstrate alternative diagnoses such as abdominal aortic aneurysm, biliary disease or urinary retention

What are the limitations of USS ?

Ultrasound is not a replacement for CT in every patient.

Limitations include:

  • Operator dependent
  • Small stones may be invisible
  • Mid-ureteric stones are difficult to detect
  • Normal ultrasound does not exclude renal colic
  • Hydronephrosis may be absent early in obstruction

Ultrasound or CT – which modality would you use and why?

Modern practice increasingly supports using ultrasound as the initial imaging modality in selected low-risk patients while reserving CT for patients in whom the diagnosis is uncertain or complications are suspected. Low-dose non-contrast CT remains the most accurate imaging test when CT is required.

Ultrasound is appropriate when:

  • Young patient with classic renal colic
  • Previous history of stones
  • Symptoms improve with analgesia
  • Radiation exposure should be minimised
  • Follow-up of known stone disease

CT should be considered when:

  • First presentation with diagnostic uncertainty
  • Fever or suspected infected obstruction
  • Solitary kidney or renal transplant
  • Acute kidney injury
  • Persistent uncontrolled pain
  • Concern for an alternative diagnosis
  • Pre-operative planning

Practical Emergency Department Approach

For uncomplicated renal colic:

  • Provide adequate analgesia.
  • Perform focused renal POCUS.
  • Assess for hydronephrosis, hydroureter, visible stones +/- ureteric jets
  • If findings match the clinical picture and the patient is low risk, outpatient management may be appropriate.
  • Obtain low-dose CT when complications or diagnostic uncertainty exist.

This selective imaging strategy can reduce radiation exposure without compromising patient outcomes.

Key Teaching Points

  • Hydronephrosis is the most useful indirect ultrasound sign of ureteric obstruction.
  • Absence of hydronephrosis does not exclude renal colic.
  • Distal ureteric stones near the VUJ are visible with bladder scanning but this requires a certain amount of USS expertise to identify.
  • Colour Doppler can improve stone detection through the twinkling artefact.
  • Point-of-care ultrasound complements clinical assessment and helps determine which patients require CT rather than replacing CT in every case.

 

Some more facts about renal colic

  • Prevalence ranges between 2 and 8%.
  • Peak presentation for men age 40 -50, for women late 20’s
  • 80% contain calcium crystals
  • Risk factors for stone formation include warm climates (due to dehydration), patients producing less than 1 L of urine a day, obesity, family history, any abnormality of the renal tract medical disorders (hyperparathyroidism, chronic diarrhoeal disorders, myeloprolipherative disorders and renal tubular acidosis)
  • 90% of stones will pass spontaneously.
  • 50% of patients with stones will have a recurrence within 10 years.

Urinalysis

  • 90% of patients with renal colic will have microscopic haematuria
  • 40% of patients with flank pain and haematuria do not have renal colic. Consider other diagnoses (UTI, pyelonephritis, AAA, diverticulitis, pneumonia, small bowel obstruction, cholecystitis, pelvic inflammatory disease)

Location of stones

  • Pelvi ureteric junction (10%)
  • Proximal ureter (23%)
  • Mid ureter where the ureter crosses the iliac vessels (2%)
  • Vesico ureteric junction (60%)

Which stones are likely to pass?

  • overall 90% of stones will pass spontaneously
  • 70% of stones < 5 mm will pass spontaneously
  • 47% of stones between 5-10 mm will pass spontaneously
  • the smaller the stone the faster the passage over time. Larger stones may take up to 3 weeks to pass.

 

 

References 

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  12. Acad Life Emerg med: Top 10 reasons NOT to order a CT scan for suspected renal colic April 10th, 2014 | Expert Peer Reviewed (Clinical), Genitourinary, Radiology |9 Comments
    By: Daniel Firestone, MD RDMS