Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Benign fatty lesion (e.g., lipoma or fibrolipoma): The fact that the radiologist described the nodule as having "matured" over the past three years suggests a benign process. The location in the fat anterior to the psoas muscle and the small size of the nodule also support a benign fatty lesion.
- Other Likely diagnoses
- Reactive lymph node: Although the nodule is small, it could represent a reactive lymph node, especially given its location near the surgical bed.
- Fibrotic nodule: The nodule could be a fibrotic reaction to the previous surgery, similar to the fat necrosis and fibrosis seen in the paranephric space.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Metastatic renal cell carcinoma (RCC): Although the primary tumor was small and low-stage (T1A), there is still a possibility of metastasis, especially given the history of chromophobe RCC.
- Lymphoma: A new lymph node or nodule in the retroperitoneum could be a sign of lymphoma, which would require prompt evaluation and treatment.
- Rare diagnoses
- Soft tissue sarcoma: A rare possibility, but one that should be considered, especially if the nodule grows or changes over time.
- Other rare benign tumors (e.g., schwannoma, neurofibroma): These tumors are uncommon, but could be considered if the nodule has a characteristic appearance or location.