Is a small lesion in the fat anterior to the psoas (musculus psoas) muscle below the lower pole of the left kidney shortly after a partial nephrectomy concerning for a metastatic (mets) lymph node?

From the Guidelines

A small lesion in the fat anterior to the psoas muscle below the lower pole of the left kidney shortly after a partial nephrectomy is concerning for a metastatic lymph node and requires further evaluation with imaging and potentially tissue sampling. This location, in the retroperitoneal space near the renal hilum, is a common site for metastatic lymph nodes from renal cell carcinoma, as lymphatic drainage from the kidney typically follows the renal vasculature, and nodes in this para-aortic region are often the first echelon of nodal metastasis 1. To determine if this lesion is truly a metastatic lymph node, additional imaging such as a contrast-enhanced CT or MRI would be recommended, potentially with comparison to pre-operative imaging to assess for interval change, as suggested by the NCCN clinical practice guidelines for kidney cancer 1. Some key points to consider in the evaluation of this lesion include:

• The size, shape, and enhancement pattern of the lesion are important characteristics to evaluate, as they can help differentiate between a metastatic lymph node and other potential causes of the lesion.
• PET/CT might also be helpful if there is diagnostic uncertainty, as it can provide additional information on the metabolic activity of the lesion.
• If the lesion is concerning based on imaging, tissue sampling through CT-guided biopsy could provide definitive diagnosis, as recommended by the ESMO clinical practice guidelines for renal cell carcinoma 1.
• Close surveillance imaging is typically warranted in this scenario, regardless of initial impression, to monitor for any changes in size or characteristics of the lesion, as suggested by the NCCN clinical practice guidelines for kidney cancer 1. It's worth noting that the role of surgery in the management of metastatic renal cell carcinoma is evolving, and cytoreductive nephrectomy may be recommended in select patients with a potentially surgically resectable primary tumor mass, as suggested by the NCCN clinical practice guidelines for kidney cancer 1. However, the management of oligometastatic disease is also an important consideration, and metastasectomy or ablative techniques may be recommended for select patients with solitary or easily accessible metastases, as suggested by the ESMO clinical practice guidelines for renal cell carcinoma 1.

From the Research

Concerns about a small lesion in the fat anterior to the psoas muscle

• A small lesion in the fat anterior to the psoas muscle below the lower pole of the left kidney shortly after a partial nephrectomy may be concerning for a metastatic lymph node, as metastatic renal cell carcinoma can occur in various locations, including unusual visceral metastases 2.
• The presence of a lesion in this location may indicate the spread of cancer, and further evaluation is necessary to determine the nature of the lesion.

Relevance of partial nephrectomy in metastatic renal cell carcinoma

• Partial nephrectomy can be considered in the setting of metastatic renal cell carcinoma, particularly in patients with localized disease or those who are not candidates for radical nephrectomy 3, 4.
• However, the role of partial nephrectomy in the management of metastatic disease is still evolving, and more research is needed to determine its efficacy and safety in this context.

Lymph node dissection in renal cell carcinoma

• Lymph node dissection (LND) may not provide a therapeutic benefit in patients with metastatic renal cell carcinoma, although it can yield independent prognostic information 5.
• The decision to perform LND should be individualized based on patient factors, such as the presence of high-risk features or isolated nodal metastases.

Implications for patient management

• Patients with a history of renal cell carcinoma who develop a new lesion in the fat anterior to the psoas muscle should undergo further evaluation, including imaging studies and possibly biopsy, to determine the nature of the lesion.
• The management of metastatic renal cell carcinoma should be tailored to the individual patient, taking into account factors such as the location and extent of disease, as well as the patient's overall health and preferences.