Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Benign fatty lesion (e.g., lipoma or fibrolipoma): This diagnosis is likely due to the small size of the nodule, its location in the fat anterior to the psoas muscle, and the fact that it has been stable over three years, with the radiologist describing it as having "matured" over time.
- 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 site of a previous partial nephrectomy.
- Fibrous tissue or scar: Given the history of surgery, it's possible that the nodule represents a small area of fibrous tissue or scar formation.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Metastatic disease: Although the primary tumor was small (T1A) and had no adverse features like sarcomatoid differentiation or necrosis, the possibility of metastatic disease, although low, cannot be entirely excluded without further investigation.
- Local recurrence of chromophobe RCC: Despite the benign appearance and stability of the nodule, the possibility of local recurrence of the primary tumor should be considered, especially since it's located near the surgical bed.
- Rare diagnoses
- Soft tissue tumor (e.g., liposarcoma): Although rare, soft tissue tumors could present as small nodules in the fat, and their consideration is important for comprehensive differential diagnosis.
- Other rare benign lesions (e.g., schwannoma, neurofibroma): These lesions are uncommon but could present in this location and should be considered in the differential diagnosis, especially if other explanations are ruled out.