What is the clinical significance of a 1.5 cm soft tissue mass and a 3 mm nodule in the fat anterior to the psoas muscle in a patient with a history of partial nephrectomy for chromophobe renal cell carcinoma (RCC)?

From the Guidelines

The 1.5 cm soft tissue mass and 3 mm nodule in the fat anterior to the psoas muscle are likely benign and not concerning for recurrence of chromophobe renal cell carcinoma (RCC), given the patient's history of partial nephrectomy and the stability of the lesions over time. The patient's history of partial nephrectomy for chromophobe RCC and the presence of a 1.5 cm soft tissue mass and a 3 mm nodule in the fat anterior to the psoas muscle can be evaluated based on the latest guidelines for follow-up and active surveillance of clinically localized RCC 1. According to the American College of Radiology, the standard of care for clinically localized RCC includes surgical resection with curative intent, such as radical nephrectomy or partial nephrectomy, and radiologic imaging is the most useful component of surveillance for detecting relapses and disease progression 1. The guidelines recommend that patients undergo cross-sectional abdominal scanning (CT or MRI) within six months of active surveillance initiation to establish a growth rate, and continued imaging (US, CT, or MRI) at least annually thereafter 1. Given the patient's history and the stability of the lesions, I recommend continuing with routine surveillance according to standard post-nephrectomy protocols, typically involving imaging every 6-12 months for the first few years, then annually thereafter. No additional intervention is needed for either lesion at this time, as the stability of the small nodule over time is reassuring, and malignant lesions would typically grow during this timeframe 1. The patient's original tumor was likely small and low stage with favorable histology, which carries an excellent prognosis, and these post-surgical changes are common after partial nephrectomy and represent normal healing processes rather than disease recurrence 1. Key points to consider in the patient's follow-up include:

• The use of imaging modalities such as CT, MRI, or US for surveillance
• The timing and frequency of follow-up imaging
• The patient's overall health and tumor-specific characteristics
• The potential benefits and limitations of each imaging modality 1. By following these guidelines and considering the patient's individual characteristics, we can ensure that the patient receives appropriate surveillance and follow-up care to detect any potential recurrence or disease progression.

From the Research

Clinical Significance of Soft Tissue Mass and Nodule

The clinical significance of a 1.5 cm soft tissue mass and a 3 mm nodule in the fat anterior to the psoas muscle in a patient with a history of partial nephrectomy for chromophobe renal cell carcinoma (RCC) can be assessed based on the following factors:

• The size and location of the soft tissue mass and nodule
• The patient's history of RCC
• The imaging characteristics of the mass and nodule

Imaging Characteristics

According to 2, MRI is the most important and sensitive imaging modality in the differentiation of unclear soft tissue tumors. A systematic approach helps to narrow down the large number of possible differential diagnoses.

• MRI characteristics of the major soft-tissue masses can help differentiate between benign and malignant masses
• A systematic approach may differentiate benign from unclear lesions
• In cases of doubt, a biopsy should be performed to rule out malignancy

Benign vs Malignant Soft Tissue Masses

3 states that the overwhelming majority of soft tissue masses encountered on routine imaging are incidental and benign.

• Typical imaging features can point to a single diagnosis or limited differential diagnosis
• Many lesions are nonspecific and may require contrast administration, evaluation with other imaging modalities, follow-up imaging, or biopsy for diagnosis

Differentiating Benign and Malignant Soft Tissue Masses

4 found that there is a variable degree of accuracy in discriminating benign from malignant soft tissue masses based on signal intensity and morphologic characteristics by magnetic resonance imaging (MRI).

• Detailed component pattern assessment, in addition to morphologic study, can help differentiate benign from malignant soft tissue masses by MRI
• Parameters favoring malignancy include large lesion size, peritumoral edema, necrosis, and absent calcification, absent fibrosis, and lack of fat rim

Lung Nodule Malignancy

5 tested the hypothesis that a model including clinical and computed tomography (CT) features may allow discrimination between benign and malignant lung nodules in patients with soft-tissue sarcoma (STS).

• The combination of clinical and CT features has the highest predictive value for detecting the malignancy of pulmonary nodules in patients with soft tissue sarcoma
• CT nodule features such as size ≥ 5.6 mm, well-defined margins, increased size from baseline CT, and new onset at preoperative CT can increase the likelihood of malignancy

Thin-Section CT Findings

6 evaluated thin-section computed tomographic (CT) characteristics of malignant nodules on the basis of overall appearance in comparison with the appearance of benign nodules.

• Recognition of certain characteristics at thin-section CT can be helpful in differentiating small malignant nodules from benign nodules
• A round shape, mixed ground-glass opacity (GGO) with GGO in the periphery and a high-attenuation zone in the center, and a polygonal shape or smooth margin can be indicative of malignancy or benignity.