What are the initial steps for testing a suspected myofibroblastic mass in the thigh?

Initial Diagnostic Approach for Suspected Myofibroblastic Mass in the Thigh

For a suspected myofibroblastic mass in the thigh, the initial diagnostic steps should include radiographs followed by ultrasound, with MRI reserved for further characterization, and a core needle biopsy for definitive diagnosis. 1

Initial Imaging Studies

• Radiographs should be the first imaging study performed for any suspected soft tissue mass in the thigh to identify calcifications (present in 27% of cases), bone involvement (22%), or intrinsic fat (11%) 1
• Although often considered unrewarding, radiographic evaluation has demonstrated positive results in 62% of cases with proven soft tissue masses 1
• Radiographs may provide information on the type and scope of mineralization, presence of foreign matter, or changes in adjacent bone that can help determine treatment approach 1

Ultrasound Evaluation

• Ultrasound is highly appropriate as the next step, particularly for small superficial lesions, with reported sensitivity of 94.1% and specificity of 99.7% for superficial soft tissue masses 1, 2
• Ultrasound can help differentiate solid from cystic lesions and demonstrate the relationship between a mass and adjacent neurovascular structures 2
• For inflammatory myofibroblastic tumors (IMTs), ultrasound typically detects non-homogeneous solid formations and may identify calcifications in some cases 3

Advanced Imaging

• MRI without and with IV contrast is essential if initial evaluation is nondiagnostic or for deep masses in the thigh 4
• For IMTs, MRI typically shows low signal intensity on T1-weighted sequences and intermediate-low signal intensity on T2-weighted sequences in most cases 3
• Both contrast-enhanced CT and MRI for IMTs often show precocious enhancement with multiple peripheral hypertrophic blood vessels 3
• MRI provides the most accurate information for diagnosis, surgical planning, and radiotherapy planning for soft tissue tumors of the extremities 5, 4

Tissue Sampling

• Core needle biopsy is the standard approach for suspicious soft tissue masses that require histopathological diagnosis 2, 4
• Multiple core samples should be taken under image guidance to maximize diagnostic yield 2, 4
• The biopsy should be planned carefully so that the biopsy tract can be safely removed during definitive surgery 4
• For IMTs specifically, histopathological examination with immunohistochemistry for smooth muscle actin and anaplastic lymphoma kinase 1 (ALK1) is crucial for diagnosis 6

Specialist Referral

• Any patient with imaging findings suggestive of a suspicious soft tissue mass should be referred to a specialized sarcoma multidisciplinary team 4
• For suspected IMTs, referral is particularly important as these tumors are classified as lesions of intermediate biological potential with risk of local recurrence 7

Common Pitfalls to Avoid

• Relying solely on physical examination is insufficient, as it correctly identifies only about 85% of soft tissue tumors 1
• Radiographs have limitations and may be unrewarding when a mass is small, deep-seated, non-mineralized, or in an area with complex anatomy 1
• IMTs can be misdiagnosed as other entities such as nodular fasciitis, requiring molecular analysis in cases with unusual presentation 7
• For IMTs in the thigh, it's important to note that they may present with clear boundaries in soft tissues but can be invasive, showing features similar to both benign and malignant tumors 8

Special Considerations for Inflammatory Myofibroblastic Tumors

• IMTs of the thigh without bone involvement are extremely rare but have been reported 9
• Molecular testing for ALK gene rearrangement should be considered, as it may have therapeutic implications if systemic disease is present 6
• IMTs may show radiological features that mimic both benign tumors (in shape) and malignant tumors (peritumoral edema, invasive rim) 8