What is the significance of a 3 mm nodule found in the fat anterior to the psoas muscle, below the lower pole of the left kidney, on imaging 3 years after a partial nephrectomy for a 1.3 cm exophytic Chromophobe renal cell carcinoma (RCC)?

From the Guidelines

The 3 mm nodule found anterior to the psoas muscle below the left kidney is likely not concerning for recurrent cancer, given the small size of the original tumor (1.3 cm), the chromophobe subtype, and the lack of aggressive features, as well as the fact that it has been 3 years since the partial nephrectomy 1. The patient's original cancer was completely removed (T1a stage) and had an excellent prognosis with low recurrence rates. Chromophobe RCC typically has a favorable outcome, especially when it lacks aggressive features like sarcomatoid differentiation or necrosis, which this patient's cancer did not have. Some key points to consider in this case include:

• The size of the nodule is small, which reduces the likelihood of it being a recurrent cancer
• The location of the nodule is anterior to the psoas muscle, which is not a typical location for recurrent RCC
• The patient has been asymptomatic since the partial nephrectomy, which suggests that the nodule is likely benign
• The follow-up imaging has shown no significant change in the size or appearance of the nodule, which further suggests that it is likely benign Standard follow-up would include periodic imaging (usually CT or MRI) every 6-12 months for the first few years, then annually for at least 5 years, as recommended by the ESMO clinical practice guideline for diagnosis, treatment, and follow-up of renal cell carcinoma 1. No specific medication is needed at this time, but continued surveillance is important. If the patient notices any symptoms like flank pain, blood in urine, or unexplained weight loss, they should contact their urologist promptly rather than waiting for their next scheduled appointment. It is also important to note that the risk of local recurrence is greater than the risk of distant metastases in this patient population, and surveillance strategies should prioritize evaluation of the treatment bed, as recommended by the ACR appropriateness criteria for post-treatment follow-up and active surveillance of clinically localized renal cell carcinoma 1.

From the Research

Nodule Significance

The provided studies primarily focus on pulmonary nodules, which may not be directly relevant to a 3 mm nodule found in the fat anterior to the psoas muscle, below the lower pole of the left kidney. However, some general information about nodules can be applied:

• Nodules are commonly identified on imaging studies, with approximately 1.6 million patients per year in the US having pulmonary nodules detected 2.
• The majority of nodules are benign, with at least 95% of all pulmonary nodules identified being benign 2.
• The probability of malignancy is less than 1% for all nodules smaller than 6 mm and 1% to 2% for nodules 6 mm to 8 mm 2.

Nodule Management

The management of nodules depends on their size, location, and patient risk factors:

• Small nodules (<6 mm) are more likely to be benign and can be followed with repeat imaging 2, 3.
• Larger nodules (≥8 mm) have a higher risk of malignancy and may require further evaluation, such as biopsy or surgical resection 2, 4.
• The Fleischner Society provides recommendations for measuring pulmonary nodules at CT, including technical requirements for accurate nodule measurement and directions on how to report nodule size and changes in size 5.

Extrapolation to the Given Scenario

While the provided studies focus on pulmonary nodules, the general principles of nodule management can be applied to other types of nodules:

• A 3 mm nodule found in the fat anterior to the psoas muscle, below the lower pole of the left kidney, is likely to be benign, given its small size.
• However, the patient's history of a partial nephrectomy for a 1.3 cm exophytic Chromophobe renal cell carcinoma (RCC) may increase the risk of malignancy, and further evaluation may be necessary.
• The management of this nodule would depend on various factors, including the patient's overall health, the presence of any symptoms, and the results of any additional imaging or diagnostic tests.

Key Points

• The majority of nodules are benign, but the risk of malignancy increases with nodule size.
• Nodule management depends on size, location, and patient risk factors.
• Further evaluation may be necessary for a 3 mm nodule in a patient with a history of RCC, despite its small size.