First described in 1835, congenital melanocytic nevi (CMN) are benign proliferations of melanocytes that can be detected in utero but usually appear within the first few months of life.11,12 CMN occur in 1% to 6% of newborns,13 and they may occur at any location throughout the body.13,14
CMN are subdivided by their diameter: small (<1.5 cm), medium (1.5-20 cm), large (20-40 cm), and giant (>40 cm).15 Giant CMN can be further categorized by the number of satellite lesions. Small congenital nevi are the most common, whereas large and giant nevi carry the greatest risk for complications such as melanoma.15
The size and appearance of a nevus can change as a patient ages. At birth, CMN usually are sharply demarcated, flat, and a pale tan color.14 Small, dark brown macules can occur within the light-tan parent lesion during infancy. As the patient ages, CMN may become consistently darker and develop thick, coarse hair. Lesions also can become hypopigmented but rarely regress.
The texture of the lesion may become pebbly, verrucous, or cerebriform, and the extent of textural change can differ from patient to patient.13,14 Nodules or irregular borders can form, particularly in large- and giant-sized CMN, and these changes must be monitored by clinicians for neoplastic transformation.16
The dermoscopic patterns of CMN vary and are associated with the locations of nevi and age of the patient. Globular, reticular, and reticuloglobular patterns are seen as well as hypertrichosis.17 Patients <12 years of age are more likely to present without a predominant pattern or globules. Reticular patterns typically are seen in individuals aged >12 years.17 Reticular lesions are more likely to be present in the lower extremities than in the head, neck, and trunk. Globular lesions are more likely to be present in the head, neck, and trunk than in the extremities.17,18
On histologic examination, CMN share some features with acquired nevi; however, these conditions have unique histologic characteristics that allow for distinction between the two. In CMN, nevus cells extend into the lower two-thirds of the dermis and subcutaneous tissue.19 They tend to occur around nerves, vessel walls, hair follicles, and sebaceous glands. Nevus cells also are located between collagen bundles in cords of cells or in single-file lines.13,14,19 The depth and pattern of distribution of the nevus cells are established early in life and typically do not change as the patient ages.14
CMN is associated with increased risk for melanoma and, rarely, risk for neurocutaneous melanosis. The risk for neoplastic transformation in small- and medium-sized CMN is estimated to be <1% over a lifetime, but that estimate is controversial. On the other hand, the association between large- and giant-sized CMN and melanoma is well established, with the estimated lifetime risk of patients with these CMN developing melanoma being approximately 5%.13,14 Patients with multiple medium-sized lesions or several satellite nevi are at increased risk of developing melanoma. Melanoma typically occurs in the parent lesion rather than the satellite lesions.13
Individual considerations dictate the management of small- and medium-sized CMN. Functional or cosmetic concerns may warrant simple excision. Baseline photographs and longitudinal monitoring are necessary due to the risk for melanoma. In small- and medium-sized CMN, melanomas typically develop at the dermal-epidermal junction, so they can easily be recognized by clinicians.13,18 Parents and patients should be taught to examine the lesion and report changes in texture, color, or border. In addition, patients should be instructed to protect their skin from sun damage. Dermabrasion, laser therapy, and curettage may provide cosmetic benefit when surgery is not feasible.13,14
Prophylactic early surgical removal of large- and giant-sized CMN is recommended due to the risk for melanoma and emotional and behavioral issues. Due to deep penetration of nevus cells in large- and giant-sized CMN, melanoma can develop deep within the parent lesion, making them more difficult to detect clinically.13,18 Large CMN are associated with emotional and behavioral problems in up to 30% of patients due to the cosmetic appearance of the lesion, anxiety about melanoma risk, and pain from surgery.13 Complete surgical resection of CMN is challenging because of nevus cell penetration into underlying fat, fascia, and potentially muscle. Therefore, longitudinal observation is required after surgery.16
Patients with large- or giant-sized CMN, or multiple medium-sized CMN, should be screened for neurocutaneous melanocytosis. Gadolinium-enhanced magnetic resonance imaging of the central nervous system should be performed 4 to 6 months after birth. In addition, patients require longitudinal neurologic examinations.16
The differential diagnosis of CMN includes congenital dermal melanocytosis, plexiform neurofibroma, café au lait macule, acquired nevus, and mastocytoma. Plexiform neurofibromas usually present with other signs and symptoms that suggest neurofibromatosis-1 and have discrete nodules along the tracks of nerves.20 Café au lait macules typically are lighter in color than CMN. Mastocytomas can be differentiated from CMN by skin biopsy or the presence of a Darier sign.21 CMN and acquired nevi can be differentiated histologically, as described above. Congenital dermal melanocytosis lesions typically appear more green or blue and have less-definite borders.
After discussing various therapies, the patient’s parents decided to forgo surgery and continue with longitudinal observation with a dermatologist and pediatrician for neoplastic and neurologic changes.
Table. Congenital Dermal Melanocytosis vs Congenital Melanocytic Nevus
Niki Iranpour, BS, and Emily Burns, BA, are medical students at Baylor College of Medicine, and Christopher Rizk, MD, is a dermatologist at Elite Dermatology in Houston, Texas.
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