Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Fat necrosis or a benign post-surgical change: This is the most likely diagnosis given the history of partial nephrectomy and the fact that the nodule has been present since one month after surgery, with no significant change in size over three years. The radiologist's description of the nodule as having "matured" over time also supports a benign process.
- Other Likely diagnoses
- Fibrosis or scar tissue: Similar to fat necrosis, this could be a result of the surgical procedure and the body's healing process.
- A small, benign lipoma or other soft tissue tumor: Although less likely given the post-surgical context, small benign tumors could present as a 3mm nodule.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Metastasis from the original chromophobe RCC: Although the primary tumor was small (1.3 cm) and stage T1A with no sarcomatoid features or necrosis, which suggests a low risk of metastasis, it is crucial to consider this possibility, especially given the new appearance of a nodule in the fat.
- A new primary malignancy (e.g., liposarcoma): Although rare, a new primary malignancy in the fat could present as a small nodule.
- Rare diagnoses
- A small, incidentally found lymph node: While lymph nodes can be found in various locations, a 3mm nodule in the fat anterior to the psoas muscle could potentially be a small lymph node, though this would be unusual without other signs of lymphadenopathy.
- Other rare soft tissue tumors or pseudotumors: There are numerous rare conditions that could present as a small nodule, including but not limited to soft tissue tumors or pseudotumors, though these would be less likely given the context and appearance of the nodule.