# Melanocytic Nevi (모반) --- ## 1. Definition  - **Benign proliferations of melanocytes (멜라닌세포 증식성 병변)** that form nests or theques in the epidermis, dermis, or both. - Usually appear in childhood or adolescence, stabilize in adulthood, and may regress in older age. - **Clinical importance**: Though most are benign, a subset can transform into **malignant melanoma (흑색종)**. --- ## 2. Classification ### A. By Location of Melanocytes 1. **Junctional Nevus (접합부 모반)** - Melanocytes at epidermal–dermal junction. - **Appearance**: Flat, uniformly pigmented brown macules, usually <1 cm. - **Histology**: Nests of nevus cells at dermoepidermal junction. - **Laser relevance**: Nd:YAG or Q-switched pigment lasers may lighten pigment, but recurrence common. 2. **Compound Nevus (복합 모반)** - Melanocytes in both junction and dermis. - **Appearance**: Slightly raised, pigmented papules. - **Histology**: Nests in junction + dermis. - **Laser relevance**: Requires CO₂ laser for ablation due to dermal component. 3. **Intradermal Nevus (진피내 모반)** - Melanocytes entirely within dermis. - **Appearance**: Dome-shaped, often skin-colored or lightly pigmented, can be papillomatous. - **Histology**: Maturation with depth; deeper cells smaller, less pigmented. - **Laser relevance**: CO₂ laser preferred, as pigment-targeting lasers are ineffective. 4. **Blue Nevus (청색 모반)** - Dermal melanocytes deep in reticular dermis. - **Appearance**: Blue-gray macule or papule (Tyndall effect). - **Laser relevance**: Limited response to lasers due to deep pigment. --- ### B. By Onset - **Congenital Nevi (선천성 모반)**: Present at birth or early infancy. Larger lesions (especially giant congenital nevi) carry a higher melanoma risk. - **Acquired Nevi (후천성 모반)**: Appear in childhood/adolescence; risk of transformation lower. --- ## 3. Histopathology - **Junctional nevus**: nests at dermoepidermal junction. - **Compound nevus**: junction + dermis. - **Intradermal nevus**: only dermis, with maturation (cells become smaller, less pigmented, spindle-shaped with depth). - **Cytology**: Nevus cells have uniform nuclei, small nucleoli, and lack mitotic activity. _(Contrast: Melanoma shows atypia, mitoses, pagetoid spread, lack of maturation.)_ --- ## 4. Pathophysiology - **Genetic drivers**: - **BRAF mutations** (especially BRAF V600E) common in acquired nevi. - **NRAS mutations** more frequent in congenital nevi. - These mutations cause melanocyte proliferation, but additional genetic/epigenetic hits are required for malignant transformation. - **Hormonal influence**: Nevi may darken during puberty or pregnancy. - **UV exposure**: May induce new nevi or darken existing ones. --- ## 5. Clinical Features - Size: usually <6 mm (bigger lesions = higher suspicion). - Symmetry, regular borders, uniform color → benign. - Common on face, trunk, extremities. - May involute with age (especially intradermal nevi). --- ## 6. Risk of Malignancy - **Acquired small nevi**: very low risk. - **Dysplastic (atypical) nevi (이형성 모반)**: architectural disorder, cytologic atypia → moderate melanoma risk. - **Congenital giant nevi (>20 cm)**: lifetime melanoma risk up to 5–10%. --- ## 7. Management - **Observation**: Most nevi need no treatment. - **Excisional biopsy**: Gold standard if suspicious features present (ABCDE rule). - **Laser treatment**: - Cosmetic only, not diagnostic. - Must rule out atypia/melanoma first (biopsy if uncertain). - **Nd:YAG (532/1064 nm)** for junctional/epidermal pigment. - **CO₂ laser** for raised dermal nevi. --- ## 8. Clinical Pearls 1. **Never laser a nevus without diagnostic certainty.** Histology is lost after ablation. 2. **Maturation with depth** = hallmark of benignity. Lack of maturation = melanoma. 3. **“Ugly duckling sign”**: One nevus that looks different from the others warrants biopsy. 4. **Patient counseling**: Educate about self-monitoring, especially for dysplastic nevi or family history of melanoma.