Differential Diagnosis for the 3mm Lesion
- Single most likely diagnosis
- Benign fatty lesion (e.g., lipoma or fibrolipoma): The lesion's stable nature over time, presence in the fat anterior to the psoas, and lack of growth or aggressive features make a benign fatty lesion the most likely diagnosis.
- Other Likely diagnoses
- Post-surgical scar or granuloma: Given the lesion's location near the site of a previous partial nephrectomy, it could represent a benign post-surgical change.
- Lymph node: Although less likely given the small size and stable nature, a small lymph node in the fat anterior to the psoas cannot be entirely ruled out without further imaging or biopsy.
- 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 stage 1 and the lesion has been stable, metastasis to the fat or soft tissues, although rare, is a possibility that should not be missed due to its significant implications.
- Sarcoma (e.g., liposarcoma): Soft tissue sarcomas can present as small, slow-growing lesions and are important to consider due to their potential for malignancy.
- Rare diagnoses
- Neurofibroma or other nerve sheath tumors: These could present as small lesions in the retroperitoneal fat but are less common.
- Extra-adrenal paraganglioma: A rare tumor that could present in this location, although it would typically have more aggressive features or be associated with systemic symptoms.
- Other rare soft tissue tumors (e.g., schwannoma, hemangioma): These are less likely but could be considered in the differential diagnosis of a small, stable lesion in the retroperitoneal fat.