Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Benign fatty lesion (e.g., lipoma or fibrolipoma): The fact that the nodule has been present since one month after the partial nephrectomy and has "matured" over the past three years, without significant growth, suggests a benign nature. Its location in the fat anterior to the psoas muscle also supports this diagnosis.
- Other Likely diagnoses
- Reactive lymph node: Although less common in this context, a reactive lymph node could present as a small nodule in the fat. However, the stability of the nodule over time makes this less likely.
- Post-surgical scar or granuloma: Given the nodule's appearance shortly after surgery and its stable nature, it could be related to the surgical procedure itself, such as a scar or granuloma.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Metastatic chromophobe RCC: Although the primary tumor was small (1.3 cm) and of low stage (T1A) with no adverse features like sarcomatoid differentiation or necrosis, the possibility of metastasis, however small, cannot be entirely ruled out. The early appearance of the nodule post-surgery raises some concern, but its small size and stable nature over three years make this less likely.
- Rare diagnoses
- Soft tissue sarcoma: Extremely rare and unlikely given the nodule's small size and stable nature over three years, but it cannot be ruled out without further investigation.
- Other rare benign tumors (e.g., schwannoma, neurofibroma): These could present as small nodules in the fat but are less likely given the clinical context and the nodule's behavior over time.