Differential Diagnosis for the 3mm Lesion
- Single most likely diagnosis
- Benign fatty lesion (e.g., lipoma or fibrolipoma): The lesion's location within the fat anterior to the psoas, its small size, and stability over time suggest a benign fatty lesion. The fact that it has "matured" over time also supports this diagnosis, as benign lesions can become more characteristic in appearance as they evolve.
- Other Likely diagnoses
- Post-surgical fat necrosis: Given the history of partial nephrectomy, the lesion could represent an area of fat necrosis, which is a benign condition that can occur after surgical trauma.
- Reactive lymph node: Although less likely given the description, a reactive lymph node could be considered, especially if there was any evidence of inflammation or infection in the past.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Metastasis from the Chromophobe RCC: Although the primary tumor was low grade and stage T1a, it is essential to consider the possibility of metastasis, especially given the history of cancer. However, the small size and stability of the lesion make this less likely.
- Lymphoma: Lymphoma can present as a small, stable lesion, and it is crucial to consider this diagnosis, especially if there are any systemic symptoms or other suspicious findings.
- Rare diagnoses
- Soft tissue sarcoma (e.g., liposarcoma): Although rare, soft tissue sarcomas can present as small, slow-growing lesions. The location and appearance of the lesion make this diagnosis less likely, but it should be considered in the differential diagnosis.
- Other rare benign lesions (e.g., schwannoma, neurofibroma): These lesions are rare and can present in various locations, including the retroperitoneum. However, they are less likely given the description and location of the lesion.