From the Guidelines

Hemorrhagic or proteinaceous renal cysts are typically benign.

These cysts can be differentiated from renal cell carcinoma (RCC) based on their appearance on MRI, with homogenous high T1 signal intensity lesions and smooth borders being more indicative of benign cysts 1.
A lesion to renal parenchyma signal intensity ratio of >1.6 on MRI can also predict a benign cyst 1.
Diffuse and marked T1 hyperintensity on MRI can achieve accuracies of 73.6% to 79.9% for the diagnosis of T1-hyperintense cysts, which are often benign 1.

MRI without and with IV contrast is optimal for renal lesion characterization, but MRI without IV contrast can also provide diagnostic information, especially for simple cystic lesions or those with thin septations 1.
Noncontrast T2-weighted imaging can characterize lesions based on their homogeneous and very high T2 signal intensity, and an angular interface with the renal parenchyma on T2-weighted imaging can help differentiate benign exophytic renal masses from malignant masses 1.
New and specialized MRI sequences, such as arterial spin labeling, may also be used to characterize the vascularity of renal lesions in patients with renal dysfunction 1.

From the Research

Renal cysts can be classified as simple or complex, with simple cysts being typically benign and asymptomatic 2, 3.
Complex cysts, on the other hand, may be malignant or benign and often require further characterization 2, 3.
The Bosniak Classification of Cystic Renal Masses is used to determine the likelihood of a cyst being malignant or benign 3.

Hemorrhagic renal cysts are usually benign, but can be difficult to distinguish from malignant tumors 2, 4, 5.
Proteinaceous renal cysts are also typically benign, but can have a similar appearance to malignant tumors on imaging 4.
Both hemorrhagic and proteinaceous cysts can have irregular borders and echogenic material within their walls and within the cyst 2.

Computed tomography (CT) and magnetic resonance imaging (MRI) can be used to further characterize complex renal cysts and distinguish them from malignant tumors 2, 3, 4.
Percutaneous biopsy may be necessary in some cases to confirm the diagnosis 4, 6.
The management of complex renal cysts depends on the likelihood of malignancy, with benign cysts often being followed with serial ultrasounds and malignant cysts requiring surgical excision 2, 3, 6.

There can be overlap in the diagnosis of complex renal cysts, particularly between Bosniak II and III lesions 6.
Interobserver variability can also make it difficult to accurately diagnose complex renal cysts 6.
Regular surveillance and percutaneous biopsy may be necessary to confirm the diagnosis and guide management 6.