From the Guidelines
A 3mm lesion in the fat anterior to the psoas muscle, caudal to the lower pole of the left kidney, which has not grown but matured over 3 years, is likely to be benign rather than malignant in a patient with a history of T1a kidney cancer. The location and stability of the lesion over a 3-year period are key factors in this assessment. As noted in the study by 1, the growth rate of renal tumors is low, with a mean of 3 mm/year, and progression to metastatic disease is reported in only 1%-2% of patients. This suggests that the lack of growth in the lesion over 3 years strongly favors a benign process. Furthermore, the fact that the lesion has "matured" over time also supports a benign diagnosis, as metastatic lesions would typically exhibit more aggressive behavior.
The study by 1 highlights that up to 25% of small renal masses are benign, and the location of the lesion in the fat anterior to the psoas muscle could represent post-surgical changes, a small lymph node, or normal fat tissue variation. While the study by 1 discusses the management of clinical T1 renal masses, it does not provide direct evidence regarding the nature of the lesion in question. However, the more recent study by 1 provides guidance on the management of renal cell carcinoma and suggests that active surveillance is an option for patients with small renal masses, particularly those with a low risk of progression.
In this case, given the small size of the lesion, its stable nature over 3 years, and the patient's history of T1a kidney cancer, active surveillance with continued imaging is a reasonable approach, as the risk of malignancy appears to be low. However, if there is significant concern or uncertainty, a biopsy of the lesion could be considered to provide a definitive diagnosis. Ultimately, the decision should be made on a case-by-case basis, taking into account the individual patient's risk factors, overall health, and preferences.
From the Research
Lesion Characteristics
- The lesion in question is a 3mm lesion located in the fat anterior to the psoas muscle, caudal to the lower pole of the left kidney 2.
- The lesion has not grown but has matured over 3 years, which may indicate a benign nature.
Patient History
- The patient has a history of T1a kidney cancer, which increases the risk of developing new renal lesions or metastases 3, 4.
- However, the study by 5 suggests that solid renal masses are often incidentally detected and can be either benign or malignant, with limited ability to differentiate between them using imaging techniques.
Diagnostic Considerations
- The study by 2 highlights the importance of CT-guided core needle biopsy in diagnosing retroperitoneal masses, including those in the psoas muscle.
- The study by 3 found that neoplastic iliopsoas masses are most commonly hypodense lesions and are often associated with primary neoplasms from renal, lung, pharyngeal, ovarian, colorectal neoplasm, and melanoma.
- The study by 5 suggests that MRI can be used to assess renal lesions, especially in situations where CT is limited, and to help guide management in patients who are considered borderline surgical candidates.
Prognosis and Risk Factors
- The study by 4 developed a machine learning model to predict the risk of lymph node metastasis in renal carcinoma, which may be relevant to patients with a history of kidney cancer.
- The study by 6 found that asymmetric cross-sectional area size of the psoas muscle may be a key feature in patients with lumbar disc herniations, but its relevance to the current case is unclear.