What is the significance of a 3mm nodule, identified as a potential local recurrence, in the fat anterior to the psoas muscle, in a patient with a history of Chromophobe Renal Cell Carcinoma (RCC) status post partial nephrectomy, given its presence on previous imaging and recent characterization as likely post-surgical change?

Differential Diagnosis

• Single most likely diagnosis:
  • Post-surgical change or scar tissue: This is the most likely diagnosis given the location of the 3mm nodule, its stability over time, and the radiologist's opinion that it has "matured" and become more defined. The improved imaging quality likely made the nodule more visible.
• Other Likely diagnoses:
  • Reactive lymph node: Although the location is not typical for a metastatic lymph node, it's possible that the node is reactive to the prior surgery or other inflammatory processes.
  • Benign fatty lesion: The nodule's location in the fat anterior to the psoas muscle and its small size make a benign fatty lesion a possible diagnosis.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Metastatic lymph node: Although the urologist/oncologist and radiologist consider this unlikely, it's essential to rule out metastasis, especially given the patient's history of renal cell carcinoma.
  • Local recurrence of renal cell carcinoma: Although the nodule's location is not typical for a metastatic site, it's possible that it represents a local recurrence, which would require prompt attention.
• Rare diagnoses:
  • Other malignant tumors: It's possible, although rare, that the nodule represents a new primary malignancy or a metastasis from an unknown primary site.
  • Inflammatory or infectious process: A rare possibility is that the nodule represents an inflammatory or infectious process, such as a granuloma or an abscess, although this would likely be associated with other symptoms and laboratory findings.