This transcript presents the pathological review of Case 5: a nodule found on the palmar surface of a 10-year-old boy's hand. The diagnosis is confirmed as Calcifying Aponeurotic Fibroma (CAF), a rare, benign lesion predominantly affecting young individuals. Microscopically, CAF exhibits a characteristic biphasic pattern, featuring islands of calcified or chondroid (cartilage-like) material surrounded by palisading round cells, intermingled with areas of fibroblastic spindle cells arranged in fascicles. Although benign, CAF carries a risk of local recurrence, particularly due to its location near tendons. The video also notes the recent description of an FN1-EGF gene fusion associated with this tumor, which may be useful in diagnostically challenging cases.
0:13 Case Presentation: The discussion centers on a well-circumscribed, heterogeneous nodule on the palmar surface of a 10-year-old boy's hand.
0:26 Microscopic Findings: Key features include calcification (darker, poorly delineated areas), palisading (fence-like arrangement) of round cells around the calcified islands, multi-nucleated giant cells, and areas demonstrating chondroid (cartilage-like) differentiation.
1:08 Diagnosis Confirmation: The combination of findings and patient history leads to the confirmed diagnosis of Calcifying Aponeurotic Fibroma (CAF).
1:34 Demographics: CAF is a rare lesion typically seen in young individuals, generally ranging from 5 to 15 years old, though it can occasionally appear in young adults.
1:51 Classic Biphasic Pattern: CAF is characterized by its biphasic architecture:
Chondroid/myxohyaloid islands with variable calcification, often surrounded by palisading, round cells (likened to spokes on a bicycle wheel).
Transition areas composed of fascicles of thin, spindle-like fibroblastic cells.
3:00 Variations and Diagnostic Challenges: Longer-standing or lesions in older patients may show excessive calcification and cartilage metaplasia, which can obscure classic features and lead to misdiagnosis (e.g., mistaken for synovial chondromatosis).
3:36 Associated Features: Osteoclastic giant cells are commonly present, which is typical when calcification or bone formation occurs.
4:05 Clinical Behavior: CAF is benign but has a tendency for local recurrence, often attributed to its close proximity and attachment to tendons and tendon sheaths in the hands and feet.
4:34 Molecular Pathology: A gene fusion, FN1 fused with EGF, has been described in CAF. While usually not required for diagnosis, this fusion test can be considered for difficult or atypical cases.