From the Guidelines
A hemorrhagic cyst in the kidney identified on non-contrast MRI is typically not worrisome, as it usually represents a benign, complicated cyst (Bosniak category II or IIF) with a high specificity for small cysts on MRI [ 1 ]. These cysts contain blood products and appear hyperintense on T1-weighted images due to the presence of methemoglobin in the blood products, which helps distinguish them from simple cysts.
Key Characteristics of Hemorrhagic Cysts
- Appear hyperintense on T1-weighted images
- Usually represent benign, complicated cysts (Bosniak category II or IIF)
- High specificity for small cysts on MRI While non-contrast MRI can identify these cysts, contrast-enhanced imaging may be recommended for complete characterization, especially if there are concerning features like irregular walls, septa, or solid components.
Recommendations for Follow-Up
- Periodic imaging follow-up every 6-12 months to ensure stability
- Further evaluation with contrast-enhanced studies or possibly biopsy may be warranted if the cyst shows complex features like enhancing solid components, nodularity, or growth on follow-up imaging Most hemorrhagic renal cysts are benign and require no treatment. Patients with hemorrhagic renal cysts typically remain asymptomatic, but occasionally may experience flank pain if the cyst is large or bleeding is acute. According to a retrospective study, homogenous high T1 signal intensity lesions with smooth borders and lesion to renal parenchyma signal intensity ratio of >1.6 predicted the lesion as a benign cyst [ 1 ]. Another study of 144 T1-hyperintense lesions demonstrated that diffuse and marked T1-hyperintensity achieved accuracies of 73.6% to 79.9% for the diagnosis of T1-hyperintense cysts [ 1 ].
From the Research
Hemorrhagic Cyst Kidney on Noncon MRI
- A hemorrhagic cyst kidney can be worrisome, but its appearance on non-contrast MRI (noncon MRI) can help differentiate it from other conditions, such as renal cell carcinoma (RCC) 2, 3, 4.
- On T1-weighted MRI, hemorrhagic cysts typically appear as homogeneous medium- to high-signal intensity regions, which can be distinguished from simple cysts and RCCs 2, 3.
- The intensity and pattern of T1 hyperintensity on MRI can be used to differentiate hemorrhagic renal cysts from RCCs, with marked and diffusely homogeneous T1 hyperintensity being more characteristic of hemorrhagic cysts 4.
- A study found that a T1-weighted lesion-to-muscle signal-intensity ratio of 1.39 or higher can be used to differentiate hemorrhagic cysts from RCCs, with a sensitivity of 91.2% and specificity of 74.6% 3.
- Another study found that diffuse T1 hyperintensity, particularly when marked, strongly indicates a hemorrhagic cyst rather than an RCC, and deferral of follow-up imaging may be considered when this imaging appearance is encountered at unenhanced MRI 4.
Diagnostic Considerations
- MRI can be useful in differentiating between simple cysts, hemorrhagic cysts, and neoplasms when CT and sonography are indeterminate 5, 2.
- The presence of fluid-iron levels within the cyst, which can be evident on MRI as dependent high-intensity layering, can also help distinguish hemorrhagic cysts from RCCs 2.
- However, it is essential to note that some RCCs can exhibit similar imaging characteristics to hemorrhagic cysts, and further evaluation may be necessary to confirm the diagnosis 3, 4.