Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Fat necrosis or a benign fatty lesion: This is the most likely diagnosis given the patient's history of partial nephrectomy and the presence of a similar benign lesion (fat necrosis with mild chronic inflammation and fibrosis) in the paranephric space. The fact that the nodule has "matured" over time and became more defined also suggests a benign process.
- Other Likely diagnoses
- Post-surgical scar or granuloma: The nodule's location in the fat anterior to the psoas muscle, near the site of the partial nephrectomy, raises the possibility of a post-surgical scar or granuloma.
- Benign lymph node or lymphoid tissue: Although no lymph nodes were submitted during the partial nephrectomy, it is possible that the nodule represents a benign lymph node or lymphoid tissue.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Recurrent renal cell carcinoma (RCC): Although the patient's previous RCC was chromophobe type with favorable characteristics (T1A, no sarcomatoid features, no necrosis), recurrence is still a possibility, especially given the proximity of the nodule to the surgical bed.
- Metastatic disease: Although the patient's surveillance scans have been negative for distant metastases, it is essential to consider the possibility of metastatic disease, especially if the nodule exhibits suspicious features on imaging.
- Rare diagnoses
- Soft tissue sarcoma: Although rare, soft tissue sarcomas can occur in the retroperitoneum, and the nodule's location in the fat anterior to the psoas muscle raises this possibility.
- Other rare benign tumors (e.g., lipoma, schwannoma): These tumors are rare but can occur in the retroperitoneum and may present as small nodules.