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. However, the lack of significant change in size over three years makes this less likely.
- Post-surgical scar or granulation tissue: Given the nodule's proximity to the surgical bed and its appearance shortly after surgery, it could be related to the surgical process itself, such as a small area of scar tissue or granulation tissue.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Metastatic disease (e.g., metastatic RCC): Although the primary tumor was small (T1A) and of a less aggressive subtype (chromophobe RCC), and the nodule has been stable, metastatic disease must always be considered, especially in the context of a history of cancer. The fact that it was not present before surgery but appeared shortly after raises some concern.
- Lymphoma: Unlikely but potentially deadly, lymphoma could present as a small nodule in this location. The stability of the nodule over time makes this less likely, but it should not be entirely dismissed.
- Rare diagnoses
- Soft tissue tumor (e.g., liposarcoma): Although rare, soft tissue tumors could present as small nodules in the fat. The long-term stability of the nodule and its small size make this diagnosis less likely.
- Other rare benign lesions (e.g., schwannoma, neurofibroma): These could present as small, stable nodules but are less common and would be considered only after more likely diagnoses are ruled out.