What is the significance of a 3mm renal nodule (kidney nodule) that was initially thought to be new on 3-year imaging follow-up after partial nephrectomy (surgical removal of part of the kidney), but was later determined to be pre-existing, having appeared 1 month post-operatively?

From the Guidelines

A 3mm renal nodule that was initially thought to be new but later determined to be pre-existing, having appeared 1 month post-operatively, is most likely a benign post-surgical change rather than a recurrence or new growth, and thus, does not necessitate immediate intervention. This conclusion is based on the understanding that small renal nodules, especially those that are stable over time, are often benign and can represent scar tissue, granulation tissue, or small areas of fibrosis that develop as part of the normal healing process after kidney surgery 1. The European Association of Urology guidelines on renal cell carcinoma emphasize the importance of multiphase contrast-enhanced CT for the diagnosis and staging of renal tumors, but also suggest the use of non-ionizing modalities like MRI for further characterization of small renal masses, especially when the results of contrast-enhanced CT are indeterminate 1.

Given the small size of the nodule (3mm) and its stability over time, it is reasonable to consider it as part of the normal post-surgical healing process. The fact that it was present shortly after surgery but only noticed on the 3-year scan suggests it might have been overlooked on earlier imaging or was initially indistinguishable from expected post-surgical changes. For such small, stable findings, continued routine surveillance is typically recommended rather than additional intervention, aligning with the principle of minimizing harm and avoiding unnecessary procedures unless there is a significant change in the size or characteristics of the nodule 1.

The standard follow-up protocol after partial nephrectomy, which usually involves periodic imaging every 6-12 months for the first few years, should be maintained. This approach allows for monitoring of any changes in the nodule while avoiding unnecessary interventions for what appears to be a benign post-surgical finding. It's also important to consider the patient's overall health status, including any comorbidities or frailty, when deciding on the intensity of follow-up, as treatment decisions should be individualized, weighing the risks and benefits of different approaches 1.

Key points to consider in the management of this patient include:

• The nodule's small size and stability over time suggest a benign nature.
• The presence of the nodule shortly after surgery supports the notion that it is a post-surgical change.
• Continued surveillance rather than immediate intervention is the recommended approach for small, stable renal nodules.
• Patient-specific factors, such as overall health and comorbidities, should guide the intensity of follow-up and any potential interventions.

From the Research

Significance of a 3mm Renal Nodule

The significance of a 3mm renal nodule, initially thought to be new but later determined to be pre-existing, is uncertain and requires careful evaluation.

• The nodule's small size (≤ cT1a, less than 4 cm) suggests it has low malignant and metastatic potential 2.
• However, small renal masses can vary widely in histology and aggressiveness, including benign renal tumors and renal cell carcinomas that can be either indolent or aggressive 3.
• Imaging plays a key role in characterizing small renal masses, but some masses can be indeterminate at imaging and present diagnostic dilemmas 3.
• The fact that the nodule was present 1 month post-operatively and remained stable in size over 3 years suggests it may be benign or have low growth potential.
• Active surveillance is a viable option for small renal masses, with similar outcomes to surgical intervention or ablation, but with varying side effects 2, 4.
• Regular imaging follow-up is essential to monitor the nodule's growth and characteristics, as tumor growth can occur over time 4.

Diagnostic and Treatment Options

• Renal biopsy can be used to help diagnose the nodule before treatment, with a high correlation between biopsy and surgical specimen 4.
• Treatment options for small renal masses include active surveillance, surgery (partial nephrectomy or radical nephrectomy), and thermal ablation, with similar outcomes but varying side effects 2, 5.
• Ablative therapies, such as cryoablation and radiofrequency ablation, are associated with decreased morbidity and excellent preservation of renal function compared to surgical excision 5.
• Contrast-enhanced ultrasound scan (CEUS) and MRI can be used to monitor the nodule's response to treatment and detect any recurrence 6.