Is MRI indicated for a 1.6 cm cystic lesion in the right upper pole of the kidney with a new 0.5 cm mural (mural) nodule?

From the Guidelines

Yes, an MRI is recommended for a 1.6 cm cystic kidney lesion with a new 0.5 cm mural nodule. The presence of a new mural nodule within a renal cyst is concerning as it may represent a complex cyst (Bosniak category III or IV) or possibly a cystic renal cell carcinoma. MRI provides superior soft tissue contrast compared to CT and can better characterize the internal architecture of the cyst, the enhancement pattern of the nodule, and any additional concerning features, as shown in a study published in the Journal of the American College of Radiology 1.

The MRI should be performed with and without contrast (unless contraindicated) to evaluate for enhancement of the nodule, which would increase suspicion for malignancy. While waiting for the MRI, no specific intervention is needed, but prompt scheduling (within 2-4 weeks) is advisable. The finding of a new mural nodule represents a significant change that warrants further evaluation, as simple renal cysts (Bosniak I) do not contain solid components, and the development of a nodule may indicate progression to a potentially malignant lesion requiring urological consultation and possible surgical intervention depending on the MRI findings.

Some key points to consider when evaluating renal masses include:

• The use of high-quality, multiphase, cross-sectional abdominal imaging to characterize and clinically stage the renal mass, as recommended by the American Urological Association 1
• The importance of assessing tumor complexity, degree of contrast enhancement, and presence or absence of fat in the renal mass, as outlined in the AUA guideline 1
• The potential benefits of MRI in characterizing renal lesions, including its high specificity for small cysts and its ability to detect enhancement in renal masses with indeterminate enhancement on CT, as discussed in a study published in the Journal of the American College of Radiology 1.

Overall, the recommendation for an MRI is based on the need for further evaluation of the new mural nodule and the potential benefits of MRI in characterizing renal lesions, as supported by the evidence from recent studies 1.

From the Research

Cystic Lesion with Mural Nodule

• A 1.6 cm cystic lesion in the right upper pole of the kidney with a 0.5 cm genic mural nodule is a complex renal cyst that requires further evaluation.
• The presence of a mural nodule is a concerning feature, as it is associated with an increased risk of malignancy 2.
• A study on complex renal cysts found that mural masses or nodules were present in 4 out of 55 lesions, and 3 of these 4 lesions were malignant (75%) 2.

Imaging Evaluation

• MRI is a useful imaging modality for evaluating complex renal cysts, as it can provide detailed information about the cyst's internal structure and the presence of any solid components 2.
• However, the appearance of benign and malignant lesions may overlap, and distinct separation of these entities is not currently possible in all cases with MR imaging 2.
• Other imaging modalities, such as CT scans, may also be useful in evaluating cystic lesions with mural nodules, particularly in other organs such as the pancreas 3 or retroperitoneum 4.

Mural Nodule as a Predictor of Malignancy

• The presence of a mural nodule is a strong predictor of malignancy in certain types of cystic lesions, such as pancreatic mucinous cystic neoplasms 3.
• In one study, the presence of a mural nodule on CT scan had a sensitivity and specificity of 100% and 98%, respectively, for diagnosing malignant pancreatic mucinous cystic neoplasms 3.
• However, the predictive value of a mural nodule may vary depending on the specific type of cystic lesion and its location 2, 5, 4, 6.