Differential Diagnosis for the 3mm Nodular Lesion
- Single most likely diagnosis:
- Benign fatty lesion (e.g., lipoma or fibrolipoma): This is likely because the lesion has been stable in size over time and has become more defined, which is consistent with a benign process. The location in the fat anterior to the psoas muscle also supports this diagnosis.
- Other Likely diagnoses:
- Reactive lymph node: Although the lesion is small, it could represent a reactive lymph node that has been present since the patient's partial nephrectomy. The stability in size and increased definition over time could be consistent with a reactive process.
- Fibrotic nodule: This could be a fibrotic reaction to the previous surgery, which has matured over time, becoming more defined.
- Hematoma or seroma: Although less likely given the time frame, it's possible that the lesion represents a chronic hematoma or seroma that has become more organized and defined over time.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Metastatic disease (e.g., from the Chromophobe RCC): Although the primary tumor was low-grade and small, there is still a risk of metastasis. A new lesion, even if small and stable, should prompt consideration of metastatic disease.
- Lymphoma: Although rare, lymphoma could present as a small, stable lesion in the fat, and it's essential to consider this diagnosis to avoid missing a potentially curable malignancy.
- Rare diagnoses:
- Soft tissue sarcoma: This is a rare diagnosis, but it's essential to consider it, especially if the lesion shows any signs of growth or change over time.
- Neurogenic tumor (e.g., schwannoma or neurofibroma): The location near the psoas muscle and the stability of the lesion could suggest a neurogenic tumor, although this is a rare possibility.
- Inflammatory pseudotumor: This is a rare, benign lesion that could present in the fat and mimic a malignant process.