Differential Diagnosis for the 3 mm Nodule
- Single most likely diagnosis
- Post-surgical granuloma or scar: The nodule's appearance and evolution over time, becoming more defined and solid, could be consistent with a post-surgical granuloma or scar, especially given its proximity to the surgical site and the fact that it was first visible one month after surgery.
- Other Likely diagnoses
- Benign fatty lesion (e.g., lipoma or fibrolipoma): The location within the fat anterior to the psoas muscle and the small size could suggest a benign fatty lesion, which would be consistent with the lack of growth or other concerning features.
- Reactive lymph node: Although no adenopathy was mentioned, a small reactive lymph node could present as a solid nodule, especially in the context of post-surgical changes.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Metastatic disease (e.g., from the chromophobe RCC): Despite the small size and the fact that the primary tumor was stage T1a with favorable histology, metastatic disease must be considered, especially given the history of cancer.
- Local recurrence of chromophobe RCC: Although less likely given the small size and location outside the kidney, local recurrence must be considered, especially if the nodule shows any growth or suspicious features on follow-up.
- Rare diagnoses
- Soft tissue sarcoma: This would be an unusual occurrence, especially given the small size and the post-surgical context, but it cannot be entirely ruled out without further evaluation.
- Other rare benign or malignant soft tissue tumors: Various other soft tissue tumors could present as a small nodule, although they would be less common and might require biopsy for diagnosis.