Point-of-care ultrasound in suspected renal colic. Recognising extrarenal pelvis as a rare anatomical variant mimicking hydronephrosis
Dr Himanshu Gul Mirani
Case Presentation:
A patient presented to the emergency department with acute left-sided flank pain concerning for renal colic. At first clinical contact, point-of-care ultrasound (POCUS) was performed by a trainee clinician to assess for hydronephrosis. Initial interpretation suggested possible left hydronephrosis based on the presence of a hypoechoic fluid-filled area near the renal pelvis.
However, senior review identified several atypical features that challenged this assumption. There was no branching or interconnected calyceal dilatation, no “bear claw” or claw-like appearance, no calyceal ballooning, and no cortical thinning. The bladder was not significantly distended, and no hydroureter was visualised. These findings raised suspicion for an extrarenal pelvis rather than true obstructive hydronephrosis.
Given persistent clinical concern for renal colic, computed tomography of the kidneys, ureters and bladder (CT KUB) was arranged for definitive assessment.
Extrarenal pelvis is usually a normal anatomical variant
Management and Outcome:
CT KUB demonstrated an extrarenal pelvis without evidence of obstructive uropathy or current ureteric calculus. Mild perinephric stranding was noted, raising the possibility of a recently passed stone. No hydronephrosis, hydroureter, or obstructing lesion was identified.
Inflammatory markers and renal function were within normal limits, reducing concern for infective or significant obstructive pathology. The patient was managed conservatively with analgesia and safety-netting advice.
This case emphasised the importance of correlating POCUS findings with sonographic morphology rather than relying solely on the presence of pelvic fluid. Recognition that isolated pelvic prominence without calyceal involvement may represent an anatomical variant prevented unnecessary escalation or misdiagnosis of obstructive renal pathology.
Key Learnings and Points:
Extrarenal pelvis is an anatomical variant that may mimic hydronephrosis on ultrasound and can lead to overcalling, particularly for novice sonographers.
Key distinguishing features of extrarenal pelvis include: isolated central or medial pelvic dilatation, absence of branching calyceal dilatation, no “bear claw” appearance, preserved renal cortex, no cortical thinning, no calyceal ballooning, and absence of hydroureter.
In contrast, hydronephrosis typically demonstrates dilatation of both the renal pelvis and calyces, branching interconnected fluid spaces, progressive calyceal ballooning, and, in severe cases, cortical thinning. A structured ultrasound approach assessing pelvis, calyces, cortex, ureter, and bladder can reduce diagnostic error.
This case highlights the educational value of recognising normal variants in emergency ultrasound practice to avoid unnecessary investigations, inappropriate management, and diagnostic anchoring.