Man with flank pain

A 48-year-old male with no known past medical history presented to the emergency department with left flank pain of 3 days duration. A urinalysis performed revealed trace blood, which was equivocal for the diagnosis of ureteric colic. A bedside ultrasound performed during assessment revealed a cystic structure within the left renal pelvis (Figure 1A) initially thought to be a renal cyst. Given its unusual location, Doppler ultrasound was utilized with detection of a pulsatile flow (Figure 1B) in the lesion. Computed tomography (CT) urography revealed a ruptured large left renal artery aneurysm (RAA) (Figure 2). The patient subsequently underwent a successful angioembolization of the aneurysm by interventional radiology.

Renal cysts are common incidental findings on imaging. However, they are typically found in the peripheries of the kidney. Parapelvic cysts (PPC) are uncommon, accounting for 1%–2% of all renal cysts.¹ This case exemplified the need to consider differential diagnosis such as RAA when encountering PPC, especially when there is pain involved. The additional utilization of doppler ultrasound can help to differentiate these two entities, of which the latter is a common and rather benign diagnosis while the former is a rare but potentially dangerous diagnosis to miss.

RAA is known to also mimic other diagnoses on ultrasound. Case reports have described them mimicking renal cell carcinoma and even nephrolithiasis.^{2, 3} Once again, the use of doppler may potentially help to differentiate these diagnoses.

The authors declare no conflicts of interest.