This presentation details myofibroma, a mesenchymal tumor predominantly found in infants but also occurring in adults. Clinically, it presents in three forms: solitary (dermal or Sub-Q nodules, often head/neck), multifocal (multiple nodules, sometimes involving bone), and the rare, life-threatening generalized form in infants involving visceral organs. Despite the rarity of recurrence and the potential for spontaneous resolution, the generalized form carries high mortality. Histologically, the classic myofibroma is biphasic, characterized by pseudo chondroid or myoid nodules interspersed with hypercellular zones of bland spindle cells and prominent staghorn vasculature. While typically an H&E diagnosis (positive for Actin, negative for Desmin), a challenging subset exists exhibiting atypical, potentially malignant-mimicking features, including hypercellularity, high mitotic activity, necrosis, and infiltrating borders, yet these variants have been shown to maintain a uniformly benign biological behavior.
Myofibroma: Clinical Presentations and Histological Variations
0:00 Clinical Scope: Myofibroma is common in children and babies but also occurs in adults, including the elderly.
Single Solitary Form: Dermal or subcutaneous nodule, frequently in the head and neck.
Multifocal Form: Multiple nodules in the skin, sometimes with bone involvement (e.g., jaw).
Generalized Form (Rare): Multiple myofibromas involving internal organs in babies, associated with mortality due to the extent of visceral involvement, despite the tumor being benign.
1:10 Benign Behavior: Myofibromas are rarely recurrent after simple excision and can sometimes spontaneously resolve.
1:18 Classic Biphasic Morphology (Key Takeaway): The textbook appearance features two distinct zones:
Nodules: Bluish or pink, referred to as "pseudo chondroid" or "myoid nodules."
Cellular Zones: Hypercellular areas of non-descript oval to spindle cells that may show mitosis but lack pleomorphism.
Vessels: Characterized by dilated, branching, "staghorn" vessels (02:12).
2:40 Morphological Challenges: Some myofibromas appear vague or lack the crisp biphasic appearance, making morphological diagnosis more challenging.
3:54 Recurrence Risk: Although recurrence is rare, the speaker notes a case that persisted/recurred about a year later after an incomplete (shave) excision.
4:18 Immunohistochemistry: The tumors are generally positive for Actin (showing a wispy, tram-track pattern) and negative for Desmin, though diagnosis is often made solely on H&E slides.
4:35 Atypical Features (Crucial Detail): A subset of myofibromas can exhibit concerning atypical features, including hypercellularity, intersecting fascicles (herringbone pattern), necrosis, mitotic activity, and infiltrating borders (5:25).
5:19 Prognosis of Atypical Forms (Key Takeaway): Despite microscopically "scary" features that might suggest malignancy, studies show these atypical myofibromas uniformly behave in a benign manner.