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 stability over time and the description by the radiologist make this less likely.
- Scar or post-surgical change: Given the nodule's proximity to the surgical bed and its appearance post-operatively, it could be related to the surgical intervention, although the radiologist's description suggests it is a distinct entity.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Metastatic disease: Although the primary tumor was small (T1A) and of a less aggressive subtype (chromophobe RCC), the possibility of metastasis, especially to a location that is not typically screened (like the fat anterior to the psoas muscle), cannot be entirely ruled out without further investigation.
- Local recurrence of RCC: Despite the benign appearance and stability, any new mass in the vicinity of a previous RCC should prompt consideration of local recurrence, especially if there were any concerns about the surgical margins or the biology of the primary tumor.
- Rare diagnoses
- Soft tissue tumor (e.g., liposarcoma): Although rare, soft tissue tumors could present as small, slow-growing masses. The stability and description of the nodule make this less likely, but it remains a consideration in the differential diagnosis.
- Other rare benign lesions (e.g., schwannoma, neurofibroma): These could present as small nodules in the fat, but are less likely given the context and description provided.