A patient with a history of chronic kidney disease and nephrolithiasis is seen in the clinic for follow up. Last available serum creatinine is relatively stable compared to baseline. Resident examining the patient finds an anechoic structure in the right kidney and calls it hydronephrosis given the history of stones. However, the patient did not have any renal colic recently, no change in diet, did not need any urologic procedures in the last 3 years. Below are the images:

There is indeed an anechoic area in the mid-kidney, not really clear if there is any branching. We previously saw examples of parapelvic cysts, which appear as well-circumscribed lesions with relatively crisp margins. Below are reminder slides. As I always say, cyst is like a ball and hydronephrosis is like a branching tree.

Our image is a little vague, its difficult to exclude hydronephrosis with certainty. What is the next best step? Compare with prior imaging. It is very likely that a patient with renal stones will have prior ultrasound examinations available. Or patient had several of them over a span of 10 years all of them demonstrate the anechoic structure = parapelvic cyst.

The kidney also had another small cyst and some caliectasis (dilated calyx) adjacent to parapelvic cyst making it appear a little tricky in addition to the fact that it is not very round. If you have not noticed yet, the screen orientation marker is on the right for these images (except for color Doppler) = we used cardiac preset = right side is upper. In some cases, cardiac preset delineates anechoic structures better.

On taking a closer look, it is more toward the lower part of the kidney and not in the center (renal pelvis area), correlating with the CT image. This CT is a non-contrast study from 3 years ago. In general, if you do not have prior imaging to compare and cannot exclude hydronephrosis, consider CT scan with contrast – if it is hydronephrosis, whole thing will light up (collecting system is in continuity). Click here to read our case report illustrating this.