What is the recommended management for a 45-year-old female tennis player with a tender, well-circumscribed, hypo-echoic, avascular nodule in her upper left gluteal muscle?

Management of Gluteal Soft Tissue Nodule

This tender, well-circumscribed, hypo-echoic, avascular nodule in the gluteal muscle of an active tennis player should undergo core needle biopsy for definitive tissue diagnosis, as ultrasound characteristics alone cannot reliably distinguish between benign and malignant soft tissue masses. 1

Diagnostic Approach

Initial Imaging Assessment

• MRI is the preferred imaging modality for soft tissue masses in the extremities, trunk, and pelvis, providing superior tissue characterization and surgical planning information compared to ultrasound alone 1, 2, 3
• The ultrasound findings (hypo-echoic, avascular, well-circumscribed) are non-specific and can be seen in both benign lesions (such as hematomas, muscle hernias, or lipomas) and malignant soft tissue sarcomas 1
• MRI should be obtained before biopsy to fully characterize the lesion's size, depth, relationship to fascial planes, and internal characteristics 1, 3

Tissue Diagnosis

Core needle biopsy is the standard diagnostic approach for suspicious soft tissue masses and should be performed under image guidance (ultrasound or CT) 1

Key technical considerations for biopsy:

• Multiple cores should be obtained to maximize diagnostic yield 1
• The biopsy tract should be planned so it can be excised during definitive surgery if malignancy is confirmed 1
• While the risk of tumor seeding along the biopsy tract is very small, proper tract placement remains good surgical practice 1

Clinical Context Considerations

Important factors that increase suspicion for malignancy in this case:

• Size: A golf ball-sized mass (approximately 4-5 cm) exceeds the typical threshold for routine observation 1
• Location: Deep intramuscular location (upper gluteal muscle) rather than subcutaneous 1
• Symptoms: Tenderness could represent either benign inflammation or malignant growth 1

The patient's athletic activity (tennis) raises the possibility of trauma-related lesions such as:

• Intramuscular hematoma (though lack of vascularity on ultrasound makes acute hematoma less likely)
• Muscle herniation
• Post-traumatic myositis ossificans (early stage)

However, these benign diagnoses cannot be assumed without tissue confirmation given the size and deep location 1

Management Algorithm

1. Obtain MRI of the affected region with and without contrast to characterize the lesion fully 1, 2, 3

2. Perform image-guided core needle biopsy with multiple cores for histopathological diagnosis 1

3. If biopsy confirms benign pathology: Clinical and imaging follow-up may be appropriate depending on the specific diagnosis and symptoms 1

4. If biopsy shows malignancy or is non-diagnostic: Refer to a multidisciplinary sarcoma team for definitive management planning, which may include surgical excision 1

5. If biopsy is negative but clinical suspicion remains high: Consider repeat biopsy or excisional biopsy 1

Critical Pitfalls to Avoid

• Do not assume benignity based on ultrasound characteristics alone - the features described are non-specific 1
• Do not perform excisional biopsy as the initial diagnostic procedure - core needle biopsy is preferred to avoid compromising subsequent definitive surgery if sarcoma is diagnosed 1
• Do not delay tissue diagnosis - masses of this size in deep muscular locations require histological confirmation 1
• Ensure the biopsy is evaluated by an expert pathologist familiar with soft tissue pathology, as interpretation can be challenging 1