What are the odds that a 1.5 cm single solid kidney lesion that enhances with contrast on Magnetic Resonance Imaging (MRI) is malignant?

From the Guidelines

The odds that a 1.5 cm single solid kidney lesion that enhances with contrast on MRI is malignant are moderate to high, approximately 40-60%. Small enhancing renal masses of this size have a significant chance of being renal cell carcinoma, though they could also represent benign lesions such as oncocytomas or angiomyolipomas with minimal fat. The enhancement pattern on MRI is particularly important, as malignant lesions typically show rapid enhancement during the arterial phase followed by washout in later phases, as noted in a study published in the Journal of the American College of Radiology 1. The size of 1.5 cm places this lesion in a category where malignancy is a serious concern, though smaller than the traditional 4 cm cutoff that has historically guided management decisions.

Further evaluation with additional imaging or biopsy would be recommended to characterize the lesion more definitively, as suggested by the American Society of Clinical Oncology clinical practice guideline 1. The location within the kidney, the patient's age, gender, and medical history would also influence the specific risk assessment. While many small renal masses are found incidentally and may grow slowly, proper evaluation is essential as early detection of renal cell carcinoma significantly improves treatment outcomes. The use of MRI without and with IV contrast is optimal for renal lesion characterization, and the diagnostic accuracy of contrast-enhanced MRI for predicting RCC has been shown to be high, with a sensitivity of 88.1% in one study 1.

Some key factors to consider in the evaluation of this lesion include:

• The enhancement pattern on MRI, with rapid enhancement during the arterial phase followed by washout in later phases being more suggestive of malignancy
• The size of the lesion, with larger lesions being more likely to be malignant
• The presence of any other suspicious features, such as irregular borders or heterogeneous enhancement
• The patient's overall health and medical history, including any history of cancer or other kidney disease. Given the potential for malignancy, further evaluation with additional imaging or biopsy is strongly recommended to characterize the lesion more definitively and guide management decisions, as emphasized by the American College of Radiology 1.

From the Research

Solid Kidney Lesions and Malignancy

• The odds of a 1.5 cm single solid kidney lesion that enhances with contrast on MRI being malignant are difficult to determine without a biopsy or further diagnostic testing 2, 3.
• Renal cell carcinoma is the most common solid lesion of the kidney, and the treatment is typically surgical removal 4.
• However, there are also rare solid benign primary kidney neoplasms, such as renal leiomyoma, reninoma, and metanephric adenoma, that can present as solid lesions 4.
• The use of cross-sectional imaging has increased the detection of renal lesions, especially in asymptomatic patients, making it important to consider the possibility of benign lesions 4, 2.
• Percutaneous biopsy of the kidney has been shown to be a safe and accurate diagnostic procedure, with a high diagnostic yield and a low rate of complications 2, 3.
• The incidence of false diagnoses with biopsy is low, around 1.2% 2.
• In some cases, biopsy may not provide enough material to establish a diagnosis, highlighting the need for careful consideration of the diagnostic approach 2.

Diagnostic Approaches

• Imaging-guided biopsy can provide a definitive diagnosis in many cases, but may not always be able to determine the etiology of the lesion with acceptable confidence 2.
• The choice of diagnostic approach will depend on the individual patient and the specific characteristics of the lesion 3.
• Renal mass biopsy now plays an important role in selected patients with renal masses, particularly with improvements in biopsy technique and advancements in pathologic evaluation of biopsy samples 3.

Malignant Solid Neoplasms

• Malignant kidney neoplasms are the most frequently encountered solid kidney masses, with renal cell carcinoma being the major renal malignancy 5.
• However, other solid malignant renal masses, such as primitive neuroectodermal tumor, primary liposarcoma, and leiomyosarcoma, should also be considered in the differential diagnosis of solid renal masses 5, 6.
• Leiomyosarcoma of the kidney is a rare entity with poor prognosis, highlighting the importance of accurate diagnosis and timely treatment 6.