Congenital Melanocytic Nevus

Nevi that are present at birth or develop within the first 2 years of life are considered congenital melanocytic nevi (CMN).
Small or medium CMN are common and occur in 1% to 3% of neonates.

As opposed to acquired nevi that present later in life, CMN show melanocytes extending deeper into the dermis and tend to surround hair follicles and nerves. Melanocytes are also found singly lined up in between collagen bundles.

CMN present as tan to light or dark brown/black, flat or raised macules or papules of varying size.
CMN are classified according to their predicted final adult size as small, medium, or large.
- Small CMN have a final size of <1.5 cm in largest diameter.
- Medium CMN have a final size of 1.5 to 19.9 cm in greatest diameter (Fig. 1.24).
- Large (or giant) CMN have a predicted adult size of 20 cm (equivalent to 9 cm on the head of an infant or 6 cm on the body of an infant) (Fig. 1.25).
Large CMN have an estimated incidence of 1 in 20,000 and are associated with an increased risk of melanoma and neurocutaneous melanosis.
Lesions enlarge in proportion to the child's growth.
Over time CMN can become darker or lighter in color, develop a mottled pigmentation, increase in thickness, and even spontaneously regress. Surface changes such as hypertrichosis, verrucous changes, and proliferative nodules can also occur (Fig. 1.26).

Speckled lentiginous nevus or nevus spilus (Fig. 1.27) is a subtype of CMN that initially presents as a variably sized (usually 1 to 4 cm) tan patch, resembling a café au lait spot, that over time develops superimposed darker pigmented macules and papules, representing nevi.
The risk of melanoma development within nevus spilus is thought to be proportional to the size of the lesion and suspicious changes within lesions should be evaluated histologically.

The risk for the development of melanoma in CMN is not exactly known and is the subject of much debate and investigation but is believed to correlate with the size of the CMN.
Currently the risk of melanoma in small and medium CMN is thought to be <1% over a lifetime and almost always occur after puberty.
For large CMN, the risk of melanoma is approximately 5% to 10% over a lifetime and commonly occurs in childhood.
Melanoma can present as a focal area of change within the nevus or as a proliferative nodule.
Patients with large CMN who also have numerous smaller (“satellite”) nevi (Fig. 1.28.) or those with multiple medium-sized nevi are at increased risk for the development of neurocutaneous melanosis, which is the proliferation of melanocytes within the leptomeninges.

Differential Diagnosis

Dermal Melanocytosis (aka Mongolian Spot)

Ill-defined irregular borders, fades over time.

Café au Lait Spots

Remain lightly pigmented and stable over time.

Management

A complete skin examination should be performed and the CMN should be measured and categorized as small, medium, or large.
Parents should be counseled about the risk for the future development of melanoma.
In general, prophylactic removal of small and medium CMN is not recommended if there are no concerning features and no obstacles to monitoring.
Small and medium CMN can be managed on a case-by-case basis taking into account whether there are worrisome clinical features, cosmetic or parental concerns, and the ease of monitoring lesion given its location.
Most of the time regular clinical monitoring is all that is needed.
Surgical excision can be performed especially for cosmetically disfiguring lesions to avoid the potential psychosocial impact of the lesion on the developing child.
Patients with large CMN, especially those on the posterior axis or those with smaller satellite nevi, and patients with multiple medium CMN should be screened for neurocutaneous melanosis with an MRI of the brain and spine ideally before 4 to 6 months of age.
For large CMN, early and complete surgical excision is often recommended and desired by parents. However, decision to perform surgical removal should be individualized taking into account the risks of the procedure versus the benefits of surgical removal.
Staged excision with tissue expansion can be performed by specialized surgeons and is often initiated between 6 and 9 months of age when the risk of anesthesia decreases.
While surgical excision will improve cosmetic appearance, it does not completely eliminate the risk for melanoma because it is usually impossible to remove every nevus cell due to their deep extension into the fat, fascia, and muscle.
In some large CMN, surgical removal is not feasible and other methods such as curettage, dermabrasion, or resurfacing lasers can have a cosmetic benefit.
Regardless of intervention, large CMN should be closely followed with periodic skin examinations, dermoscopic evaluation, photographic documentation, and palpation.

Helpful Hints

The risk of melanoma in small and medium CMN is estimated to be <1% over a lifetime.
Patients with large CMN and their families may benefit from organizations such as Nevus Outreach, Inc. (www.nevus.org), which offers annual family conferences, educational information, and a social support network.

Points to Remember

Parents should be counseled on how to recognize concerning features in nevi and bring to the attention of the physician any focal changes in color, border, or surface appearance of the nevus.
When examining large CMN it is important to palpate the lesions to detect for presence of firm nodules as melanoma can arise deep.
Risk of neurocutaneous melanosis is greater if more than 20 satellite nevi are present or if large CMN is >40 cm.

section name header

Basics ⬇

Pathogenesis ⬆ ⬇

Clinical Manifestations ⬆ ⬇

Clinical Variant ⬆ ⬇

Diagnosis ⬆