What is the significance of a 3mm nodule in the fat anterior to the psoas muscle, below the lower pole of the left kidney, initially thought to be new on 3-year imaging follow-up after partial nephrectomy for T1a chromophobe renal cell carcinoma (RCC), but later determined to be present 1 month post-operatively?

From the Guidelines

The 3mm nodule found in the fat anterior to the psoas below the lower pole of the left kidney is most likely a benign finding, possibly representing a small lymph node, fat necrosis, or post-surgical change. Since it was present one month after surgery but initially misinterpreted as new on the 3-year follow-up imaging, this represents a common scenario of a previously overlooked small finding rather than a new development. For a nodule of this size and location following partial nephrectomy for T1a chromophobe renal cell carcinoma, continued routine surveillance is appropriate without need for immediate intervention. The standard follow-up protocol for post-nephrectomy patients should be maintained, typically consisting of imaging every 6-12 months for the first few years, then annually thereafter, as suggested by the American College of Radiology guidelines 1. The small size (3mm) and stable appearance since the post-operative period are reassuring features. Chromophobe RCC generally has a favorable prognosis with low metastatic potential, especially for small (T1a) tumors that have been surgically removed, as noted in the guidelines for post-treatment follow-up and active surveillance of clinically localized renal cell carcinoma 1. Post-surgical changes including small nodularities in the operative field are common findings that can persist for years after kidney surgery and should not automatically raise concern for recurrence when stable over time, as discussed in the context of CT abdomen and pelvis for surveillance after localized RCC ablation 1. Key points to consider in the management of this patient include:

• The nodule's stability since the post-operative period
• The lack of contrast enhancement, which is a hallmark of successful treatment, as noted in the guidelines for CT abdomen after RCC ablation 1
• The low metastatic potential of chromophobe RCC, especially for small (T1a) tumors
• The importance of continued routine surveillance to monitor for any changes in the nodule or the development of new findings. Given the available evidence and guidelines, continued routine surveillance without immediate intervention is the most appropriate course of action, prioritizing the patient's quality of life and minimizing unnecessary interventions, as supported by the guidelines for post-treatment follow-up and active surveillance of clinically localized renal cell carcinoma 1.

From the Research

Significance of a 3mm Nodule

• The provided studies do not directly address the significance of a 3mm nodule in the fat anterior to the psoas muscle, below the lower pole of the left kidney, in a patient with a history of T1a chromophobe renal cell carcinoma (RCC) 2, 3, 4, 5, 6.
• However, studies on incidental nodules in other contexts, such as pulmonary nodules, suggest that small nodules (<4mm) are unlikely to grow or be malignant in a short period (<12 months) 3.
• The American College of Radiology Incidental Findings Committee's recommendations for managing incidental lymph nodes may not be directly applicable to this case, but they do emphasize the importance of follow-up and consideration of multiple factors in assessing the risk of malignancy 4.
• In the context of hepatocellular carcinoma, a nodule's characteristics, such as arterial hypervascularity and washout, are crucial in determining its likelihood of being malignant 2.
• The management of pulmonary nodules, as outlined in guidelines from the Fleischner Society and American College of Chest Physician, emphasizes risk stratification, patient involvement, and consideration of biopsy or surgical options 5.

Relevance to the Current Case

• The fact that the nodule was initially thought to be new but later determined to be present 1 month post-operatively suggests that its significance may be uncertain 2, 3, 4, 5, 6.
• The location of the nodule, in the fat anterior to the psoas muscle, below the lower pole of the left kidney, may be relevant in determining its likelihood of being related to the patient's history of RCC.
• Further evaluation, such as imaging or biopsy, may be necessary to determine the nature and significance of the nodule 2, 3, 4, 5, 6.