Birth moles or congenital melanocytic nevi

Today I am going to talk to you about birthmarks or congenital melanocytic nevus (CMN). It is a subject that can be a bit “unpleasant”, because there are many aspects about it that are still unknown or controversial, which complicates its handling.

Melanocytic nevi present at birth are called melanocytic nevi, although they can sometimes appear somewhat later, up to two years of age. They are common and affect approximately 1% of newborns.

They are characterized by being deeper in the skin (this can be seen when examining the nevus under a microscope after its removal). They are visible at birth, most often as a flat “spot”, and grow in proportion to the child. They may have hairs, and sometimes show a rough or cobblestone surface.


They can appear anywhere on the body and measure from a few millimeters to several centimeters. In an attempt to facilitate their practical classification they have been divided (arbitrarily) into small (less than 1.5 cm in diameter), medium or intermediate (between 1.5 and 19 cm) and large (more than 20 cm). Most congenital melanocytic nevi are small.

The reason why we dedicate a few words to NMC is twofold: on the one hand, the risk of malignization, and on the other hand, the aesthetic impact on the patient, both of which make us consider treatment and this is a challenge.

Although theoretically any CMN can become malignant (melanoma), the risk is low in the case of small or medium-sized CMNs (perhaps similar to that of acquired melanocytic nevus, although this is also controversial and there are studies that claim it is somewhat higher). This risk is higher in case of large nevi. There are several studies that have attempted to quantify the probability of malignization in large CMN but the results are variable, although we could establish this risk (understanding that we must consider the data with caution!!!) between 0 and 10%.

A point to note is that in case of malignization of a congenital nevus, most of the time it occurs on the nevus, but cases of melanoma outside the nevus have been described, especially in the nervous system. This occurs because some patients with congenital nevi (especially large ones) may have nevus cells in the central nervous system (this is called neurocutaneous melanosis), which may malign. But it does not mean that all congenital nevi have nerve involvement, nor that it is malignant if present.

The treatment of congenital nevi should be individualized. In addition to the size and risk of malignancy, the location and aesthetic repercussions must be considered.
Surgical removal is the safest method to remove all cells, but this is usually not necessary as these are benign lesions. In principle, the indication for surgery in large or giant CMN would be established in the first years of life. It should not be forgotten that sometimes several operations are necessary, that complications may be associated with them and that the esthetic result may be disappointing.

There are other forms of treatment such as curettage, peeling, dermabrasion or laser that only eliminate the most superficial component and achieve good aesthetic results. But these are controversial techniques because their long-term safety and influence on the development of melanoma is unknown.

As you can see, there are many unanswered questions. I wanted to give you a few hints on the subject, and to let you know that there is still no consensus on the best way to handle it. This should always be done on an individual basis, and whatever the therapeutic approach, the dermatologist should be consulted if there is any change in the mole.

Dr. Beatriz Fleta