What is Angiomatoid Fibrous Histiocytoma (AFH)?

Angiomatoid Fibrous Histiocytoma (AFH)

Angiomatoid fibrous histiocytoma is a rare soft tissue tumor of intermediate malignant potential that predominantly affects children and young adults, characterized by specific histopathological features and genetic alterations.

Clinical Features

• Demographics and Presentation:

  • Most commonly affects children, adolescents, and young adults (age range 4-50 years, median ~15 years) 1, 2
  • Slight male predominance (ratio approximately 1.5:1) 2
  • Typically presents as a solitary nodule or mass 1
  • Often appears spontaneously without preceding trauma 1

• Anatomical Distribution:

  • Predominantly affects extremities (especially lower extremities) 1, 2
  • Can also occur in trunk, buttock, and inguinal regions 1, 2
  • Rare cases reported in unusual locations including lungs (endobronchial) 3
  • May develop in subcutaneous tissues (most common) or deeper soft tissues 2

Pathological Characteristics

• Gross Appearance:

  • Well-circumscribed nodular lesions 1
  • Often surrounded by a fibrous pseudocapsule 1, 4

• Microscopic Features:

  • Hemorrhagic non-endothelial-lined pseudocystic spaces 1
  • Sheets of spindle and ovoid cells 1
  • Dense surrounding lymphoplasmacytic infiltrate (lymphoid cuff) 1, 5

• Immunohistochemistry:

  • Typically positive for:
    • Desmin
    • CD68
    • CD99
    • Smooth-muscle actin 1
  • Some cases may show focal positivity for pancytokeratin and epithelial membrane antigen 3

• Molecular Genetics:

  • Characteristic gene fusions:
    • EWSR1-ATF1 1, 3
    • EWSR1-CREB1 2, 3
    • t(2;22)(q33;q12.2) has been reported 5
  • FISH testing can confirm EWSR1 gene rearrangements 5, 3

Diagnostic Challenges

• Frequently Misdiagnosed:
  • Often clinically confused with hematoma, hemangioma, or other soft tissue tumors 1, 4
  • MRI findings are typically nonspecific 2
  • Needle biopsies may be inconclusive 2
  • Definitive diagnosis usually requires complete excision and histopathological examination 1, 2

Treatment and Prognosis

• Treatment Approach:

  • Complete surgical excision with wide margins is the treatment of choice 1, 2
  • Treatment decisions should be made in multidisciplinary meetings involving teams specialized in soft tissue tumors 1

• Prognosis:

  • Generally favorable with complete excision 1
  • Intermediate biological potential (not benign but rarely aggressive) 4, 3
  • Recurrence rate approximately 29% in some series 2
  • Metastasis is rare but possible 2, 4
  • Cases with both EWSR1 and CREB1 gene rearrangements may have more aggressive behavior 2

Follow-up Recommendations

• Long-term follow-up is mandatory due to potential for late recurrence or metastasis 1
• Careful monitoring particularly important for cases with genetic markers associated with more aggressive behavior 2

Diagnostic Pitfalls

• Initial misdiagnosis is common due to rarity and nonspecific clinical presentation 1, 2
• Consider ultrasound-guided core needle biopsy as first diagnostic step rather than immediate excision 1
• AFH should be included in the differential diagnosis of soft tissue masses in children and young adults, even when clinical presentation suggests a benign process 4