Melanocytic Nevi: Congenital, Dysplastic & Acquired

• Melanocytic nevi are benign neoplasms of melanocytes and manifest as cutaneous pigmented lesions.
• Melanocytic cells form nevi and are called nevomelanocytes.
• Melanocytic hyperplasia is the term for increased melanocytes confined to the basal epidermal layer without nest formation.
• Melanocytic nevi are junctional (acquired) or congenital (from neural-crest melanocytic precursors).
• Dysplastic nevi display atypical architectural and cytologic features.
• Dysplastic nevi is the most frequently utilized term in nomenclature, and is used to modify other melanocytic neoplasias.
• Nevi described include congenital melanocytic nevi, nevus spilus, acquired melanocytic nevi, blue nevi, Spitz nevi, pigmented spindle cell nevi, dysplastic nevi, and nodal nevi.
• Benign melanocytic hyperplasias described include lentigo simplex and solar lentigo.

Congenital Melanocytic Nevi

• Pigmented neoplasms evident at birth, they can range in size.
• Large or giant lesions has significant melanoma risk.
• Cranial or midline nevi and those with satellite lesions increase risk of leptomeningeal involvement.
• Histology: extensive nevomelanocytic infiltration of dermis, accentuation along adnexa and nerves, single-filing between collagen bundles, often involving subcutaneous tissues. Incidence: in 1% to 3% of neonates across ethnicities.
• Most lesions are small to medium in size and present at birth.
• Tardive congenital nevi are congenital nevi (>1.5 cm) that appear between 1 month and 2 years of life.
• The most common locations are the trunk and extremities, but scalp and facial involvement are also seen.
• Uncommon giant CMNs attain 99 mm or more in diameter, seen in approximately 1 of every 20,000 newborns.
• Giant CMNs with a garment distribution affect 1 of every 500,000 newborns.
• Grouping is based on size of congenital onset nevi: small, medium, and large sizes.
• Size limits are arbitrary as lesion diameters lie on a continuum.
• Standardizing size is important because of increased melanoma risk associated with large and giant CMNs.
• System of measurement is based on expected nevus size in adult life because CMNs grow proportionally to the affected anatomic region.
• Projected adult sizes are used to classify CMNs, ranging from small (<1.5 cm) to giant (>60 cm).
• Classification includes rating the number of satellite nevi (S1: <20, S2: >20-50, S3: >50).
• CMNs present as flat brown patches or plaques with smooth or slightly uneven borders.
• Many CMNs show hypertrichosis.
• Most congenital nevi begin with even pigmentation, but some variability of pigmentation and irregularity of surface texture evenuates.
• Potential lesion appearances: pebbly, rugose, verrucous, or lobular.
• Dermoscopic features: variable and can include reticular, globular, homogeneous, and cobblestone pattern or a combination thereof.
• Dermoscopy in dysplastic nevi overlaps CMN features but history with regards to onset differentiates.
• Large CMN dermoscopy utility can be limited from significant variability in pigmentation and structure as melanomas may develop in the deep components. Clinical appearance: significant color variegation and irregularities in outline and surface contour.
• Colors include dark brown, black, or blue.
• These features often correlate with atypical histopathologic findings.
• Other findings: loss of pigmentation, halo depigmentation, and regression.
• Neurocutaneous melanosis (NCM): Congenital nevi are on the head, neck, or posterior midline condition with cutaneous nevi involving brain meninges and parenchymal cells.
• Symptomatic NCM presents with seizures and hydrocephalus during first few years when melanocytes diffuse along meninges.
• Neurologic deficits and vomiting come from increased intracranial pressure.
• Advanced stage presents as intracranial mass and may present symptoms later in life.
• Symptomatic NCM is poor as patients often die within 3 years of symptom onset.
• Greatest complication risk is melanoma development at approximately 1% to 2%.
• Melanoma risk is proportionate to the number of melanocytes comprising the nevus.
• Small- and medium-sized lesions have a low risk of developing melanoma, and larger- and giant-sized lesions have a greater risk.
• Satellite nevi is associated with increased melanoma risk.
• Melanoma arising from CMN is at the dermal-epidermal junction may have a tendency to arise in deeper dermal and subcutaneous components of the nevus.
• Aggressive tumors derive from greater Breslow thickness at presentation.
• Presentation may be sudden appearance of dermal or subcutaneous nodule.
• Lymph node metastasis precedes clinical detection of primary melanoma.
• Concern for melanoma: dark pigmentation, ulceration, bleeding, or onset of sensory symptoms.
• No ethnic predilection is shown for melanoma development in CMN.
• Cranial, midline, or CMN with multiple satellite lesions carry leptomeningeal involvement (NCM) risk.
• Symptomatic NCM prognosis suffers without malignant degeneration and central nervous system melanoma.
• Proliferative nodules: significant complication of congenital nevi that require excising.
• Presentation: lightly pigmented or flesh-colored nodule developing in preexisting congenital nevus.
• Histopathologic examination is required to discern proliferative nodules that behave in benign fashion from the findings of a clear-cut melanoma.
• Familial clustering of congenital nevi are rare.
• Patients with neurofibromatosis type 1 have an increased incidence of giant CMNs.
• Postzygotic somatic mutations of proteins involved in the mitogen-activated protein kinase (MAPK) pathway within the embryonic melanocyte cause CMN.
• Mutations primarily include NRAS, resulting in melanocytic cell accumulation along migration pathways during development.
• NRAS mutations are most prevalent in large- and giant-sized CMNs as small- and medium-sized lesions have reported to have activating mutations in BRAF.
• Some congenital nevi have both NRAS mutations or activating mutations in BRAF.
• The proportion of cases with NRAS or BRAF mutations varies due to the differing methodologies used in the studies.
• Mutational event timing insights come from clinical findings of congenital divided nevus of the eyelid, arising during palpebral buds development during the 7th week of gestation.
• The upper and lower eyelids fuse and separate during the 20th week of gestation and presumed that the nevus cells migrated sometime during or after eyelid fusion.
• Congenital nevus diagnosis is usually straightforward, the more challenging problem is whether areas necessitate biopsy.
• CMNs on head or axial midline warrant NCM question.
• Histopathologic features of suggests congenital nevi with involvement of entire skin and subcutaneous tissue.
• Nevomelanocytes in subcutaneous septae and with slightly larger cells at in the upper levels of the dermis and along the junctional zone.
• Some lesions are densely cellular and cells tend to surround neurovascular bundles, appendageal structures, and folliculosebaceous units.
• The junctional zone may be involved by cells that are sing and in small nests.
• The junctional cells are larger than those beneath them, and basilar hyperpigmentation is common.
• Many small congenital nevi do not involve then subcutaneous tissue and display melanocytes splayed as cords and strands within the deep or mid reticular dermis at the base of the lesion.
• Neurotization areas show where schwannian differentiation occurs.
• Instead of small round melanocytes, one sees small S-shaped spindle cells can be created due to the lobulation and redundancy of tissue corresponding clinically by neural differentiation.
• Histologic variations include combined epithelioid cell (Spitz) phenotype in 74% of children younger than 3 years.
• Architectural disorder (mostly mild or moderate), and pagetoid scatter present architectural disorder.
• Proliferative Nodules shows large round hypercellular aggregates of melanocytes often blending with background nevus cells and mitotic.
• Imaging studies detect NCM include magnetic resonance imaging of brain or spinal cord cord concordant with the anatomic location of the nevus with special tests.
• Dynamic evolution has been demonstrated by CMNs that distort the the skin can surface changing during growth spurts.
• Lightly pigmented may become darkly pigmented, and darkly pigmented may develop halo of depigmentation.
• Proliferative nodules may develop then stabilize however CMNs in fully grown stable and excellent prognosis unless complicated by NCM or melanoma.
• The risk of melanoma may occur.

Management

• CMN treatment depends on the melanoma risk, cosmetic and functional considerations of which risk is size related.
• The early first few life years are key for melanomas to arise.
• Debulking large nevi and excision of smaller or medium-sized ones is desired when feasible, especially in serial stages done for large nevi.
• It is prudent to delay treatment until later to reduce surgical and anesthetic risks.
• Management of patients with large and giant individualize from available graft sites or abandoning prophylactic lifelong surveillance.
• The treatment goals are to remove functional as much of the is potential as possible while cosmetics preserving and improving function appearance.
• Other indications is for symptomatology pruritus pain such as chronic ulcertation.
• Destructive does does dermabrasion not address destruction malignant address lasers potential such of surgical congenital as excisionUnlike CMN. Atypical-appearing CMNs can cause concern for immediate benign clinically excision gross or defects improvements are not always options for improvement or resulting considered in patients, with improvement, health and careful general.

Prevention and Counseling

• No preventive genetic approach factors to avoid appear the the development direct number relationship is of to CMNs acquired a screening relationship decrease.
• UV exposure should without with be patients minimize encouraged from

Explore melanocytic nevi, benign melanocyte neoplasms manifesting as pigmented skin lesions. Learn about congenital, dysplastic, and acquired nevi, including their characteristics and distinctions. Understand melanocytic hyperplasia and the various types of nevi.