Congenital Nevus

Clinical Definition

Figure X-1: Congenital nevus with black spot | Photo courtesy of SCIENCEPhotoLIBRARY Opens in new window

Congenital nevi are simply defined as lesions present at birth. However, there are morphologically indistinguishable lesions that clearly arise after birth, usually in early childhood, known as “tardive” congenital pattern nevi. Clinically these lesions (congenital and tardive) have been divided into three major groups, namely:

1. small, which are nevertheless usually larger than most common acquired nevi,
2. intermediate, and
3. giant, which constitute a dramatic, cosmetically tragic, and, fortunately, rare phenomenon in which a child is born with a pigmented and often hairy lesion covering large areas of the body, also know for this reason as ‘garment nevus.’

Clinical Features

The simplest distinction among congenital nevi is according to their dimension. Small congenital nevi are defined as less than 1.5 centimeter in their greatest dimension.

Intermediate congenital nevi are generally defined as lesions that are larger than 1.5 centimeter yet amenable to resection with primary closure, ranging up to about 20 centimeter or so.

Giant lesions are larger than 20 centimeters (when in adolescents or in adults, in the newborn giant congenital nevi are said to occupy 5% or more of the skin surface). The size divisions noted above are arbitrary.

From the surgical point of view small congenital nevi can be entirely excised without a skin graft, which is needed for intermediate lesions, while giant congenital nevi can be reduced but not completely excised.

The evolution towards melanoma seems proportionate to the size of the lesion. Giant congenital nevi (Barnhill) have an approximately 6% lifetime risk of developing melanoma (a much more significant risk is suspected by some authors – Lorentzen, Marghoob).

Intermediate and small congenital nevi have a lesser risk; the exact degree of which is unknown, but it seems reasonable that the probability for such congenital nevi to evolve towards melanoma is roughly proportionate to their size.

The congenital nevus’ clinical stereotyped appearance is as a dark brown or maroon lesion with long terminal hair (a peculiar, although not specific, aspect of congenital nevi); the lesion is gently papillated or verrucous at its surface and is occasionally keratotic.

Frequently, intermediate or large lesions have small numerous “satellite” nevi all around them. In a few cases “satellites” are indeed scattered all over the bodies (Morishima). In large studies melanomas did not arise in such satellite lesions. Congenital nevi are stable lesions and do not grow more than the rest of the body.

From the pathologist’s point of view a few peculiar clinical entities should be known.

1. Congenital-nevus-like acquired nevi (“early onset” nevi, “tardive” congenital nevi, acquired nevi with congenital features)

As stated above, nevi which appear in early life share many similarities with congenital nevi (Rivers).

Clinically, they are brown to black in color, hypertrychotic and have larger dimensions than those of common acquired nevi (more than 1-1.5 centimeter in diameter).

This group of nevi is important; Kopf has suggested that such nevi are frequent in patients who develop melanoma (this is also our experience from a histological point of view).

2. Eccrine centered nevus

Clinically, these lesion are characterized by a punctated appearance (Morishima) which corresponds to clustering of melanin synthesizing melanocytes around the acrotrichia and the acrosyringia. This variant is most common on acral skin.

3. Congenital nevus of the scalp with “cutis-verticis-gyrata-like” features

This entity is a congenital or early onset nevus of the scalp with a distinct mamillary or nodular appearance which gives the neoplasm a disfiguring cerebriform configuration (Orkin, Jeanfils).

The lesion is localized usually in the parieto-occipital area, but keeps gradually enlarging over the years especially during puberty, eventually covering almost the entire scalp. An almost complete loss of hair is the rule. No involvement of subjacent neural structures has been reported.

4. Giant lesions covering a vast part of the body

These lesions can cover up to half of the body and have peculiar clinical findings. In these lesions alterations like ulcerations, nodules and plaques, which simulate an evolution towards melanoma, are frequently present in infancy.

5. Giant congenital nevus with neurofibromatosis-like features

Large congenital nevi with widespread neural differentiation can closely simulate neurofibromatosis (Jerdan, Lycka) both clinically and histologically. In fact, the skin of such patients has a pachydermatous aspect with large redundant folds overlapping each other.

Histologically, schwannian metaplasia with Verocay body formation is striking; the melanocytic phenotype and he overall picture are those of a neural neoplasm.

In the literature, there are recorded cases of congenial nevi diagnosed at first as neurofibromatosis; the correct diagnosis of a congenital nevus was made possible only later in childhood, when the lesion became pigmented.

Today, congenital nevi and von Recklinghausen neurofibromatosis Opens in new window are considered unrelated from a biological point of view and such nevi only simulate a neural neoplasm.

In spite of this clear-cut distinction, combined cases of giant congenital nevi and von Recklinghausen (type 1) neurofibromatosis have been reported.

6. Congenital nevus with meningeal melanosis (neurocutaneous melanosis)

These nevi are located on the scalp or over the spine, and infiltrate the mininges where melanoma can eventually arise (Gooneratine). In these types of nevus neurological disturbances, as well as intracranial hypertension, may occur.

Many of the symptomatic patients die before three years have elapsed from the beginning of the symptomatology because of a melanoma or as a consequence of compression of the neural structures. Asymptomatic cases with proven leptomeningeal involvement are, however, on the record (Frieden).

Other neural anomalies occasionally associated with other forms of congenital nevi are reported (spina bifida, syringomyelina, arachoid cyst, interspinal lipoma, etc).

7. Congenital nevi with large deformity of the underlying body structures

There are many cases of deformities of somatic structures on record, mostly osteo-articular, in the part of body covered by a giant congenital nevus; limbs are the favorite site with hypertrophy or atrophy of the underlying muscle or bone (Reyes-Mugica, Ohtsuka). Rarely deformities involve eyes or ears.

8. Regressing congenital nevus and halo congenital nevus

As a rule, congenital nevi are life-long stigmata; but some of them have been reported to fade away (Berger) with reduction of their dimension and loss of pigmentation (Kikuchi).

In large “regressed” congenital nevi, with reduction of the lesional size and depigmentation, the nevus tissue is persistent, although achromatic, and sometimes has extensive neural differentiation.

The halo phenomenon can occur in congenital nevi. A halo can develop either around or inside the nevus (Albert, Ridley).

Brownstein demonstrated that a halo can develop around a congenital nevus with no regression or depigmentation of the nevus itself; the white halo was a result of the depigmentation of the previously normal skin surrounding the nevus.

9. Congenital nevi and complex syndromes

A cohort of syndromes in which large or multiple congenital nevi can be present is reported. An extensive review on this matter has been presented by Marghoob. The syndromes that occur more than occasionally are:

• Carney complex
• epidermal nevus syndrome and linear nevus sebaceous syndrome
• premature aging
• short stature syndrome and allied diseases (mental retardation, hypospadia, lack of subcutaneous fat, etc)
• spina bifida

Other rare syndromes (like electroencephalogram syndrome, Goeminne syndrome, Turner syndrome) are less clearly related with congenital nevi.

As said above, the dimensions of the lesion do not increase beyond proportionate body growth in the course of life. However, nodules and plaques can develop inside a congenital nevus (especially in the largest forms) and constitute a source of clinical alarm and histological discomfort.

Histoloical Features

Recent studies have demonstrated important genetic distinctions between acquired and congenital nevi. Most acquired nevi contain mutations of the BRAF oncogene. These mutations are rare in true congenital nevi, which tend to have a mutated NRAS oncogene.

Tardive congenital pattern nevi (most of which are also relatively small) appear to resemble acquired nevi in tending to have BRAF oncogene mutations. Thus, they appear to represent a subset of acquired nevi.

Histologically, we can classify congenital nevi like we do acquired ones, namely into junctional, compound and intradermal types. The congenital junctional lesions are supposed to be vanishingly rare, but in reality small congenital nevi excised during the first year of life are frequently junctional (Rhodes, Nickoloff).

Therefore, it seems that the “maturation” of some congenital nevi takes place subsequently, when melanocytes descend into the dermis (according to the “abtropfung” theory).

As stated above, congenital nevi are more frequently compound or intradermal and histologically they look like their acquired counterpart. However, congenital lesions have some peculiar details (Walsh) which allow us to suspect or diagnose the congenital nature of the lesion using the following parameters:

• clinical history. Of course, photographic documentation is definite proof of the congenital nature of a nevus; the patient’s own recollection is far from being reliable especially for small lesions;
• large dimension of the lesion. It has been stated that a lesion larger than 1.5 centimeters is almost surely congenital or a congenital nevus-like acquired nevus (Rivers);
• depth of the lesion. As a rule, a congenital nevus is deep enough to reach portion of the dermis (directly or through perivascular, periadnexal or perineural ramification). Generally speaking, the depth of infiltration correlates with the size of the nevus (Barnhill). In half of large lesions, a congenital nevus reaches the subcutis and the melanocytes scattered among the adipocytes are probably diagnostic of the congenital nature of a nevus;
• general architectural pattern of the lesion. Melanocytes in a congenital lesion frequently have a band-like pattern occupying the entire span of the dermis;

• splaying (Indian filing) phenomenon. The cells in the deeper part of a congenital nevus are frequently arranged in an infiltrative pattern and are aligned in long rows among undisturbed collagen fibers;
• perivascular, perineural and periadnexal pattern. Melanocytes in a congenital nevus have a peculiar tendency to encircle vessels, nerves and adnexa (follicular and eccrine structures) which can “follow” them very far from the main mass of the nevus; this gives the nevus a patchy pattern. A closer view often shows a thin grenz-zone between the epithelial structures and the melanocytes.
  
  
  The so called eccrine centered congenital nevus has nests or single melanocytes around the external ends of the eccrine coil). Cells can also aggregate around the intradermal portion of the ducts, where they retain active melanin synthesis. Also follicular infundibula can have pigmented melanocytes aligned along the junction;
• adnexal colonization. Melanocytes in congenital nevi are occasionally found inside sebaceous glands, in the follicular sheath, inside erectors pilorum muscles and in the epithelium of eccrine glands. Nests can also bulge into lymphatic vessels. Melanocytes have also been reported in the placental villi of newborns with giant congenital nevi (Carroll, Antaya);

• presence of an increased number of terminal hairs. These large follicles can also be present in acquired nevi, but when numerous they usually indicate a congenital lesion;
• widespread neural differentiation. The presence of extensive neural differentiation, which can become extreme on some lesions of the scalp, is frequent in congenital nevi which reach the deep dermis. A neurofibroma-like appearance is also possible.

Although the above mentioned clues often are present together in a congenital nevus they can also be present singly in acquired ones (Katz). About half of the acquired nevi that appear in the first few years of life have a histological feature reminiscent of a congenital nevus (Clammensen).

To make things even more complicated nevi of unquestionable congenital nature occasionally do not have any histological finding indicating their congenital origin (Everett). For these reasons, a diagnosis of congenital nevus should be made carefully when formulated on the histological ground alone.