Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Benign fatty lesion (e.g., lipoma or fibrolipoma): The fact that the radiologist described the nodule as having "matured" over the past three years suggests a benign process. The location in the fat anterior to the psoas muscle and the small size of the nodule also support a benign fatty lesion.
- Other Likely diagnoses
- Post-surgical scar or granuloma: Given the nodule's proximity to the surgical site and its appearance one month after partial nephrectomy, it is possible that the nodule represents a post-surgical reaction.
- Lymph node: Although the size of the nodule is small, it could potentially represent a lymph node, especially given its location near the kidney.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Metastasis: Although the primary tumor was small and low-stage (T1A), and there was no sarcomatoid differentiation or necrosis, metastasis is still a possibility, especially in the context of a new nodule appearing after surgery.
- Recurrent renal cell carcinoma: Similarly, recurrence of the primary tumor, even if small and low-grade, is a critical diagnosis not to miss.
- Rare diagnoses
- Soft tissue sarcoma: This would be an unusual occurrence, especially given the lack of any suspicious features on imaging, but it is a rare possibility that should be considered.
- Other rare benign tumors (e.g., schwannoma, neurofibroma): These tumors can occur in the retroperitoneum but are less likely given the clinical context and imaging appearance.