Synovial Sarcoma of Foot

Clinical Scenario

A 15-year-old male presents with a slowly enlarging lump on the lateral border of his right foot that he first noticed 6 months ago. It has been gradually increasing in size and has recently become mildly painful. He is otherwise fit and well with no significant medical history.

History:

• 6-month history of painless lump, now mildly tender
• No history of trauma
• Gradual increase in size (initially marble-sized, now golf ball-sized)
• No constitutional symptoms (no weight loss, night sweats, fevers)
• No previous skin lesions or radiation exposure
• No family history of malignancy
• Full-time student, plays football recreationally

Examination Findings:

• 4 x 3 cm firm, non-fluctuant mass on lateral border of right foot
• Located over 5th metatarsal region
• Not attached to skin, moves slightly with underlying tissues
• Non-tender to palpation
• No overlying skin changes
• No palpable regional lymphadenopathy (inguinal nodes)
• Full range of motion of ankle and foot
• Normal neurovascular examination distally
• Contralateral foot normal

Investigations

Laboratory Results

Imaging

Plain X-ray Right Foot:

• Soft tissue mass visible adjacent to 5th metatarsal
• Calcification within the mass (~30% of synovial sarcomas show calcification)
• No bone destruction or periosteal reaction
• No obvious bone involvement

MRI Right Foot with Gadolinium:

• 4.2 x 3.1 x 2.8 cm heterogeneous soft tissue mass
• Located in subcutaneous tissue adjacent to 5th metatarsal
• T1: Intermediate signal, iso-intense to muscle
• T2: Heterogeneous high signal with areas of low signal ("triple sign" or "bowl of grapes" appearance)
• Gadolinium: Heterogeneous enhancement
• Well-defined margins but no true capsule
• Abuts the 5th metatarsal periosteum but no cortical invasion
• Displaces but does not encase lateral plantar neurovascular bundle
• No skip lesions

CT Chest (Staging):

• No pulmonary metastases
• No mediastinal lymphadenopathy

Histopathology

Core Needle Biopsy Result:

• Biphasic synovial sarcoma
• Epithelial and spindle cell components present
• Immunohistochemistry: CK7+, EMA+, bcl-2+, TLE1+
• FISH positive for SYT-SSX translocation t(X;18)
• Grade: High grade (FNCLCC Grade 3)

Questions & Model Answers

Key Teaching Points

Common Examiner Follow-up Questions

1. "What is clear cell sarcoma and why is it important in the foot?"

   • Also called "melanoma of soft parts"
   • Involves tendons and aponeuroses
   • Predilection for foot and ankle
   • S100 positive, HMB45 positive (like melanoma)
   • Has EWSR1-ATF1 translocation
   • Highly aggressive, poor prognosis

2. "What are Mankin's principles of biopsy?"

   • Study showed 3x higher error rate at referring hospitals
   • Biopsy by treating surgeon
   • Longitudinal incision
   • Through muscle not between compartments
   • Track must be excisable
   • Avoid haematoma

3. "What is the FNCLCC grading system?"

   • French grading system for soft tissue sarcomas
   • Based on: Differentiation, Mitotic count, Necrosis
   • Grade 1 (low), Grade 2 (intermediate), Grade 3 (high)
   • Predicts metastatic risk

Related Topics

• Soft Tissue Sarcomas
• Biopsy Principles in Musculoskeletal Oncology
• Clear Cell Sarcoma
• Below Knee Amputation
• Staging of Musculoskeletal Tumours