[acantha, Greek =thorn, sharp spiny structure]

= rare benign neoplasm characterized by localized proliferation of squamous epithelium and central keratinized crater

Cause: exposure to sunlight, coal tar, other chemical carcinogens, trauma, immunocompromised state, vaccination, arterial puncture, burns

Path: keratin fills a central tumor crater; surrounding overhanging edges of normal epidermis

Histo: marked acanthosis (= diffuse thickening of stratum spinosum) + hyperkeratosis; proliferation of large squamous cells with glassy cytoplasm

Maybe associated with: eczema, psoriasis, atopic dermatitis, xeroderma pigmentosum

Peak age: 5^th decade; M >F

• painful
• crescent-shaped soft-tissue mass
• osteolytic defect of underlying bone ← pressure erosion
• NO periosteal reaction / bone sclerosis

MR:

• intermediate SI on T1WI + mixed SI on T2WI
• thin peripheral rim enhancement

Prognosis: spontaneous involution within 12 months leaving a small pitted scar

Cx: malignant transformation to squamous cell carcinoma