Short story of a complex renal cyst
We have previously discussed about distinguishing between autosomal dominant polycystic kidney disease and acquired cystic kidney disease (ACKD). Chronic kidney disease (particularly dialysis-requiring) is frequently associated with the development of multiple and bilateral kidney cysts; a diagnosis of ACKD requires involvement of both kidneys, with > 3 cysts being present. Here is an image obtained from a patient on hemodialysis for 15 years demonstrating ‘egg-shell calcification’ of a complex right renal cyst. A cyst would be normally associated with acoustic enhancement but this one shows acoustic shadowing due to calcification. At first glance, it almost looks like a Foley balloon in the bladder. Note more smaller cysts in the kidney as well as some ascites from liver disease.
CT scan with contrast was reported as highly suspicious for renal cell carcinoma (RCC) with possible necrotic areas. Also, note the calcification on plain X-ray.
Interestingly, renal ultrasound from 12 years ago did not show this lesion. Kidneys just looked diffusely echogenic with loss of cortico-medullary differentiation as you would expect in most ESRD patients. There was a sub-centimeter simple cyst in the right kidney and some small ones on the left.
We also had a right upper quadrant ultrasound available from 3 years ago, which showed this lesion. However, it was more cystic (complex with internal echogenicities) with minimal calcification. You can appreciate prominent acoustic enhancement here as opposed to shadowing (= tells you it initially started as a cyst and the complexity evolved over time with calcium deposition).
While most patients with ACKD are asymptomatic, some develop hematuria, back pain, frequent urinary tract infections etc. In addition, hemorrhagic cysts can be seen in some patients and rarely lead to life-threatening bleeding as in our previous case report. These patients are also at increased risk for renal cell carcinoma though the incidence varies in different studies. There are no clear guidelines on longitudinal screening, but some authors recommend annual screening for patients who have cysts larger than 3 cm and every three years for those with smaller cysts. I believe it is a good practice to perform periodic sonographic assessment in the dialysis unit and obtain CT/MRI if any suspicious lesion is found. After all, POCUS is physical examination.