Differential Diagnosis for the 3mm Nodule
- Single most likely diagnosis
- Benign fatty lesion or a small lymph node: This diagnosis is likely due to the small size of the nodule and its stable appearance over three years, with the radiologist noting that it has "matured" over time. The location in the fat anterior to the psoas muscle also supports a benign fatty lesion.
- Other Likely diagnoses
- Post-surgical change or scar: Given the nodule's appearance one month after partial nephrectomy, it could be related to the surgical procedure, such as a small hematoma or inflammatory reaction that has since resolved and appears stable.
- Small angiomyolipoma or other benign renal or extrarenal lesion: Although less likely due to the small size and location, it's possible that this could be a small, benign tumor. However, the lack of growth over three years makes this less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Metastasis from the original chromophobe RCC: Although the primary tumor was small (T1A) and had no adverse features, metastasis is always a concern in the post-operative period. The fact that this nodule appeared after surgery and has been stable is somewhat reassuring, but metastasis should always be considered.
- Lymphoma: A small lymph node could potentially represent lymphoma, which would be a critical diagnosis to make. However, the stability of the nodule over time makes this less likely.
- Rare diagnoses
- Primitive neuroectodermal tumor (PNET) or other small round cell tumor: These are rare tumors that could present as small nodules, but they are extremely uncommon and would typically show more rapid growth.
- Other rare soft tissue tumors: There are numerous rare soft tissue tumors that could present in this location, but they are unlikely given the stable appearance of the nodule over time.