Non-obstructive nephrolithiasis with twinkling artifact
Daily-practice case showing a non-obstructive stone in the lower third of the left kidney, with a Doppler twinkling artifact.
Case discussion
CLINICAL AND PATHOPHYSIOLOGICAL DISCUSSION:
The identification of a hyperechogenic formation in the lower calyceal group of the left kidney, associated with a faint posterior acoustic shadow, reflects a stone with lower crystallization density (lower sonic attenuation). The "twinkling artifact" in color Doppler acts as a crucial diagnostic refinement tool, as the fluctuation of the phase noise of the sound beam when interacting with the rough surface of the stone confirms lithiasis, even in the absence of a frank acoustic shadow.
The presence of mild ipsilateral hydronephrosis with an inferior calyceal stone — which, due to its anatomical position, is intrinsically non-obstructive to the rest of the kidney — establishes an essential clinical-radiological paradox: the cause of the pelvic dilation is not the visualized stone. Pathophysiologically, this imposes the suspicion of a downstream (ureteral) obstruction, often from a second, smaller, impacted stone in the ureter that may not be visible on ultrasound due to gas interposition, or from other extrinsic/intrinsic etiologies (such as ureteropelvic junction stenosis or compressions). Therefore, the inferior calyceal finding is an "adjuvant" and the true cause of hydronephrosis should be actively investigated.
DIFFERENTIAL DIAGNOSIS (ordered by probability):
1. Left inferior calyceal nephrolithiasis associated with occult ureteral obstruction due to stones not visualized downstream (main hypothesis).
2. Left inferior calyceal nephrolithiasis concomitant with another cause of hydronephrosis (e.g. chronic decompensated ureteropelelic junction stenosis or vesicoureteral reflux).
3. Calcification of the renal parenchyma/papilla (Randall's plaque) with pelvic dilatation of hypotonic or extrarenal origin (false positive for real obstruction).
How to report it
In the topography of the lower calyceal group, a hyperechoic image measuring approximately [insert size, e.g. 0.4] cm is noted, determining a faint posterior acoustic shadow, but showing a marked twinkling artifact when studied with color Doppler, compatible with calyceal calculus.
Mild dilation of the left collecting system is observed (mild hydronephrosis). It is noteworthy that the lower calyceal stone described does not justify the aforementioned pelvic dilation, suggesting the possibility of an obstructive process downstream (in the ureteral path), not characterized by the method.
CONCLUSION:
1. Image compatible with non-obstructive calculus in the inferior calyceal group of the left kidney.
2. Mild left-sided hydronephrosis, with no obvious obstructive factor to the method in the ureteropyelic transition or in the accessible ureteral segments, suggesting the presence of obstruction downstream (e.g., occult ureteral lithiasis).
REPORT TO THE ASSISTANT AND RECOMMENDED CONDUCT:
It is recommended to actively report the finding to the attending physician, warning that mild hydronephrosis is not justified by the lower calyceal stone seen. There is imminent suspicion of a second stone impacted in the left ureter, which may be hidden by intestinal meteorism. It is suggested to correlate it with clinical symptoms (search for classic nephretic colic) and, if clinically indicated, perform a Computed Tomography (CT) of the abdomen and pelvis without contrast (Urotomography) to map the entire ureteral path and define the exact cause and level of obstruction.
How to explain it to the patient
NOTE TO PATIENT:
During your ultrasound exam, two important findings were noted in your left kidney:
1. A small stone (microstone) located on the underside of the kidney. It was confirmed by a special effect on the device called "Doppler flicker" (which glows in color on the screen).
2. A slight swelling (dilation) in the duct that collects urine inside the kidney, a condition called mild hydronephrosis.
Special attention: As the stone is located in the lower part of the kidney, it is not to blame for this swelling. This means that there may be another cause for the urine to be accumulating slightly, such as a second, smaller stone that has already left the kidney and is passing through the channel that takes urine to the bladder (the ureter), which may not appear on the ultrasound due to the gases blocking the vision of the device.
What should you do next:
This exam is complementary and does not replace the assessment of your attending physician (who requested the exam). It is essential that you schedule a return appointment with him as soon as possible to present this result. He may order a more detailed examination (such as a CT scan) to investigate the exact cause of the swelling. If you experience severe pain in your back or side, fever, nausea or blood in your urine before your appointment, seek emergency medical care immediately.