CONGENITAL MELANOCYTIC NAEVUS
A congenital melanocytic naevus (usually abbreviated to CMN) is one of a wide variety of different types of birthmarks that may occur in newborn babies:
congenital indicates that the abnormality is present at birth
melanocytic is the adjective derived from the word melanocyte
a melanocyte is a type of cell, which is present in normal shin and in certain other organs ? its function is to produce melanin ? a brown pigment.
naevus is the technical (Greek) word used to describe any type of birthmark that occurs in the skin.
Birthmarks can be regarded as manufacturing errors, the visible effects of aberrations that have occurred during a child's development before birth. The causes of such errors are not known for certain, but may include some types of infection during pregnancy, exposure to radiation and some specific drugs during pregnancy, and, perhaps, certain chemicals including some that may be present in food. However, none of these have in fact been implicated in the case of CMNs.
A CMN is composed of an abnormally large collection of melanocytes, and is regarded as a type of benign tumour. Why such a collection develops is still unknown.
Melanocytes originate in the region of the developing spine, and migrate along nerves that emerge from the spinal cord and connects it with the skin. As they arrive in the skin melanocytes normally spread out and become evenly and thinly distributed among the other skin cells. Their function in the skin is to produce melanin pigment, which protects the skin from damage by ultraviolet rays. The amount of pigment they produce depends on the skin colour and the degree of exposure to sunlight. It seems likely that a CMN reflects a failure of the normal process of migration of melanocytes into the skin. Instead of flowing out smoothly and evenly into the skin, many cells gather at the same spot. This might happen because their progress is somehow impeded, or because they are positively attracted to this site and collect there as a result.
Symptoms and Characteristics
A CMN is primarily an abnormally large collection of melanocytes in the skin. CMNs show a number of characteristics which vary considerably, and which may change somewhat in any one CMN over a period of time. These include:
? Size: CMNs vary greatly in size, from a few millimetres to many centimetres across. The very largest may cover most of a limb or much of the trunk.
? Site: Most common site is the head and neck. After the head and neck, the commonest site is the trunk, where most CMNs occur in the mid-line of the back. Very large CMNs may cover parts of the body in such a way as to resemble items of clothing.
? Pigmentation: The colour of a CMN depends to a great extent on the background skin colour of the child. CMNs therefore tend to be a lighter brown in blond-haired children, dark in Asians and in Orientals, and black in Afro-Caribbean's. Over the years, there may be frequent changes. Darker areas or lumps may appear, but these changes rarely need cause medical anxiety.
? Texture: CMNs tend to be different from that of normal skin, being softer, more wrinkled and looser. The skin tends to be more fragile than normal tearing quite easily if traumatised.
? Hairiness: CMNs are usually hairier than normal areas of skin, but this is also very variable.
? Lumpiness: Smaller CMNs are generally more or less flat, flush with the surrounding normal skin. However, when a CMN is more extensive, it is more frequent for there to be raised or lumpy areas.
There are different types of treatment, depending on the size of the CMN. The treatments available are:
? Excision (full-thickness removal)
? Rotation flaps
? Tissue expansion
? Partial thickness removal
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