Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Fat necrosis or a benign fibrofatty nodule: This is the most likely diagnosis given the patient's history of partial nephrectomy and the presence of a similar benign lesion (fat necrosis, mild chronic inflammation, and fibrosis) in the paranephric space. The fact that the nodule has "matured" over time and become more defined without growing also supports a benign etiology.
- 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 previous surgery, raises the possibility of a post-surgical scar or granuloma.
- Benign lymph node or lymphoid tissue: Although the nodule is small, it could represent a benign lymph node or a focus of 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 tumor was chromophobe RCC with favorable features (T1A, no sarcomatoid differentiation, 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 a small nodule could be an early manifestation of such a tumor.
- Other rare benign tumors (e.g., lipoma, schwannoma): The nodule could represent a rare benign tumor, although this is less likely given the patient's history and the nodule's appearance on imaging.