Management of Anechoic Milk of Calcium Cyst in Kidney on Ultrasound

Classification and Risk Stratification

Simple cysts, such as anechoic milk of calcium cysts, are round/oval-shaped, anechoic with sharp smooth borders, thin walls, and strong posterior acoustic enhancement, and have a 0% risk of malignancy, according to the American College of Radiology 1
The American College of Radiology confirms that simple cysts have approximately 0% risk of malignancy 1
Simple cysts on ultrasound do not require further characterization with CT and MRI once diagnosed 2

For premenopausal women and men <40 years, cysts ≤5 cm require no additional management 3
For postmenopausal women and men ≥40 years, cysts ≤3 cm require no further management 3
Cysts >3 cm but <10 cm in postmenopausal women and men ≥40 years require one-year follow-up showing stability, then consider annual follow-up for up to 5 years if stable 3

MRI with T2-weighted sequences can confirm simple cystic nature by demonstrating homogeneous very high T2 signal intensity 4
If diagnostic uncertainty exists, non-contrast CT or MRI may be considered to exclude wall abnormalities or confirm simple cystic nature 3, 4

The distinction between milk of calcium cysts and other renal lesions, such as angiomyolipoma, polycystic kidney disease, and complex cysts, is crucial for proper management 1, 7, 8
Angiomyolipomas are hyperechoic and homogeneous on ultrasound but contain macroscopic fat on CT, whereas polycystic kidney disease shows multiple bilateral cysts with progressive renal dysfunction 7, 8
Complex cysts, such as Bosniak IIF, III, or IV cysts, require surgical evaluation due to malignancy risk 1

Patients with a family history of renal cell carcinoma or genetic renal tumor syndrome should undergo upper tract imaging regardless of cyst appearance 5
Wall irregularities or nodularity suggest Bosniak IIF or higher, requiring different management 6, 1
Associated symptoms, such as hematuria, flank pain, or constitutional symptoms, warrant complete evaluation 5