Management of Incidentally Found Renal Cysts

Initial Characterization Strategy

The American College of Radiology recommends that homogeneous masses <20 HU on unenhanced CT are benign and require no further evaluation 1, 2, 3
The American College of Radiology suggests that homogeneous masses >70 HU on unenhanced CT are benign and require no further evaluation 1, 2, 3
Homogeneous cysts measuring 10-20 HU on contrast-enhanced CT are considered benign and do not require further evaluation, according to the American College of Radiology 1, 2
The American College of Radiology states that homogeneous cysts measuring 21-30 HU on portal venous phase contrast-enhanced CT may also be considered benign and do not require further evaluation 1, 2, 3

The American College of Radiology recommends that any mass with density 20-70 HU on unenhanced CT warrants further evaluation 1, 2, 3
The American College of Radiology suggests that any heterogeneous mass on unenhanced CT is considered indeterminate and requires additional imaging 1, 2, 3

The American College of Radiology recommends performing multiphase CT or MRI with IV contrast to assess for enhancement and complexity in cysts that cannot be definitively characterized as benign 1, 2, 4
Initial follow-up within 6 months is recommended to establish growth rate, according to the American College of Radiology 5
Annual imaging thereafter with CT, MRI, or ultrasound is suggested by the American College of Radiology 5

Contrast-enhanced ultrasound (CEUS) is valuable for patients with contraindications to iodinated CT contrast or gadolinium-based MRI contrast, according to the American College of Radiology 1, 2, 3
Unenhanced MRI has advantages over unenhanced CT for characterizing cysts when contrast is contraindicated, as stated by the American College of Radiology 6, 7

The American College of Radiology recommends proceeding to biopsy or treatment when growth rate accelerates or mass demonstrates interval change in complexity 5
Enhancement pattern suggesting malignancy (>15% enhancement on MRI or >10-20 HU enhancement on CT) is a reason to proceed to biopsy or treatment, according to the American College of Radiology 4
Development of solid nodules, thick septations, or irregular walls is a reason to proceed to biopsy or treatment, as stated by the American College of Radiology 1, 2

Multiple cysts in the absence of known family history require clinical workup for cystic kidney diseases including genetic testing, according to the American College of Radiology and Kidney International 8, 9
Solitary cysts in children with positive family history are likely signs of ADPKD and require follow-up imaging, as stated by Nature Reviews Nephrology 9