Differential Diagnosis
- Single most likely diagnosis
- Reactive change or fat necrosis: This is the most likely diagnosis given the biopsy results of the 1.5 cm soft tissue adjacent to the surgical bed, which showed fibroadipose tissue with focal macrophages and chronic inflammation, consistent with a reactive process or fat necrosis possibly related to the prior partial nephrectomy.
- Other Likely diagnoses
- Benign retroperitoneal lesion: The 3mm retroperitoneal nodule's appearance and stability over time, described as "maturing," could suggest a benign nature, such as a benign cyst or a small lymph node.
- Fibrosis or scar tissue: The new soft tissue in the left perinephric space could also represent fibrosis or scar tissue formation as a result of the surgical procedure.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Local recurrence of Chromophobe RCC: Although the biopsy of the soft tissue adjacent to the surgical bed did not show malignancy, the presence of a new nodule in the retroperitoneal space, which was not present before the surgery but appeared post-operatively, necessitates careful consideration of tumor recurrence.
- Metastatic disease: The new retroperitoneal nodule, despite its small size and stable appearance, could potentially represent a metastasis, especially given its appearance post-surgery.
- Rare diagnoses
- Retroperitoneal sarcoma: Although rare, sarcomas can occur in the retroperitoneum and could present as a new nodule or mass in this area.
- Other rare benign or malignant tumors: Other rare tumors, either benign or malignant, could potentially explain the findings, including but not limited to lymphangiomas, hemangiomas, or other soft tissue tumors.