Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Fat necrosis or benign post-surgical change: This is the most likely diagnosis given the patient's history of partial nephrectomy and the presence of a similar benign lesion (fat necrosis, mild chronic inflammation, and fibrosis) in the paranephric space. The fact that the nodule has been present since one month after surgery and has "matured" over time also supports a benign etiology.
- Other Likely diagnoses
- Reactive lymph node: A small reactive lymph node in the fat anterior to the psoas muscle could be a possible explanation, especially given the patient's history of surgery and potential for chronic inflammation.
- Benign soft tissue tumor (e.g., lipoma, fibroma): Although less likely, a small benign soft tissue tumor could be present in this location.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Metastatic disease (e.g., RCC recurrence): Although the primary tumor was small and low-stage (T1A), and the nodule has been present for three years, it is essential to consider the possibility of metastatic disease, especially given the patient's history of RCC.
- Lymphoma: A small lymphomatous deposit in the fat anterior to the psoas muscle could be a possible, although unlikely, explanation.
- Rare diagnoses
- Soft tissue sarcoma: A primary soft tissue sarcoma in this location would be rare, but it is essential to consider this possibility, especially if the nodule were to grow or change over time.
- Other rare benign or malignant tumors (e.g., schwannoma, neurofibroma): These tumors are rare and would be unlikely explanations for the 3mm nodule, but they should be considered in the differential diagnosis.