Nevus Disorders
Introduction And Definition
- Represents developmental disorder characterized by circumscribed hyperplasia of epidermal or dermal structures.
- Broadly subdivided into melanocytic, dermal, epidermal, adnexal, and vascular categories.
Melanocytic Nevi Classification
| Nevus Type | Histological Location | Clinical Presentation And Course |
|---|---|---|
| Junctional Nevus | Nests localized strictly at dermoepidermal junction. | Flat, discrete, brown macules developing in early childhood. |
| Compound Nevus | Nests located at dermoepidermal junction and within dermis. | Elevated, dome-shaped smooth papules developing in childhood. |
| Intradermal Nevus | Nests restricted completely to dermis. | Distinctly elevated, verrucous or pedunculated lesions. Seen exclusively in adults. |
Congenital Versus Acquired Melanocytic Nevi
Acquired Melanocytic Nevi
- Emerge after birth, increasing gradually throughout childhood.
- Number reaches plateau during third decade, decreasing subsequently.
- Sun exposure strongly determines final nevus count.
Congenital Melanocytic Nevi
- Present universally at birth.
- Classified by size: small (<1.5 cm), medium (1.5-20 cm), large (20-40 cm), giant (>40 cm).
- Giant congenital nevi favor posterior trunk.
- Giant variants carry significant risk for leptomeningeal melanocytosis.
- Malignant melanoma develops in 1-2 percent of giant nevi.
- Giant variants frequently harbor Nras pathogenic variants.
Atypical Melanocytic Nevi
- Characterize dysplastic nevus syndrome.
- Present as large, irregularly bordered macules with variegated color.
- Carry significantly elevated lifetime risk for malignant melanoma.
Dermal Melanocytosis Syndromes
- Result from entrapment of migrating melanocytes within dermis.
| Clinical Entity | Diagnostic Morphology | Anatomical Distribution | Clinical Course |
|---|---|---|---|
| Mongolian Spot | Slate-gray or blue macules. | Lumbosacral region, buttocks, posterior thighs. | Fades spontaneously by early childhood. |
| Nevus Of Ota | Speckled, partially confluent blue-black patches. | Trigeminal nerve distribution (first and second divisions). | Persists lifelong. May involve sclera and conjunctiva. |
| Nevus Of Ito | Diffuse, mottled blue-gray hyperpigmentation. | Supraclavicular, scapular, and deltoid regions. | Persists lifelong. Treated with laser therapy. |
| Blue Nevus | Solitary, smooth, dome-shaped blue-gray papule. | Dorsal aspects of hands and feet. | Benign acquired lesion. Color reflects optical depth effect. |
Epidermal And Adnexal Nevi
- Hamartomatous lesions demonstrating hyperplasia of epidermis or adnexal structures.
| Nevus Variant | Pathophysiology | Clinical Characteristics |
|---|---|---|
| Epidermal Nevus | Epidermal hyperplasia. | Linear, verrucous, hyperpigmented plaques arranged along Blaschko lines. |
| Nevus Sebaceus | Excessive sebaceous gland proliferation. Driven by HRAS and KRAS mutations. | Yellow-orange, hairless plaque on scalp or face. Develops rubbery nodules during puberty. |
| Nevus Comedonicus | Malformed, dilated pilosebaceous follicles. | Linear plaques containing horny keratinous plugs simulating comedones. |
| Becker Nevus | Increased basal melanocytes and epidermal hyperplasia. | Unilateral hyperpigmented patch developing localized hypertrichosis on upper torso. |
Distinct Clinical Nevus Variants
Spitz Nevus
- Spindle and epithelioid cell nevus.
- Presents as pink to red, smooth, firm, hairless papule.
- Frequently mimics malignant melanoma histopathologically.
Halo Nevus
- Features peripheral zone of depigmentation surrounding central melanocytic nevus.
- Driven by autoimmune destruction of melanocytes.
- Associated frequently with vitiligo.
Nevus Anemicus
- Localized pale macules present at birth.
- Stroking evokes absolutely no erythematous flare, indicating localized adrenergic vasoconstriction.
Nevus Depigmentosus
- Achromic, hypopigmented patches with irregular borders.
- Represents focal defect in melanosome transfer to keratinocytes.
Nevus Spilus
- Speckled lentiginous nevus.
- Features flat brown patch containing darker raised melanocytic elements.
Diagnostic Evaluation And Management Protocol
- Uncomplicated acquired nevi require mere clinical observation.
- Atypical melanocytic nevi mandate regular monitoring utilizing photographic mapping.
- Excision indicated for suspicious morphological changes including rapid growth, color variation, bleeding, or ulceration.
- Giant congenital melanocytic nevi require serial neurological evaluation and potential surgical excision to mitigate melanoma risk.
- Epidermal nevi require full-thickness surgical excision to prevent recurrence.