A Nevus, or mole, is a common skin growth composed of special pigment-producing cells called nevomelanocytes. Nevomelanocytes are related to pigment producing cells normally found in the skin, called melanocytes. A congenital nevus is a mole present at birth.

Since nevi can exist on any part of the body, and grow in proportion to body growth, it is difficult to find one specific definition for the terms 'large nevus' or 'giant nevus'. There are at least four common ways a doctor may use to define a nevus as 'giant' or 'large'. None are universally accepted, and additional definitions do exist. Some doctors may even provide separate definitions for a 'giant' and 'large' nevus.

We have listed what we consider to be the most common definitions. Your doctor may use any or none of these in determining if you or your child has a Large Nevus.

Some doctors define a large nevus as one that would take more than one surgical excision to remove. Surgeons, or others involved with the removal of nevi, sometimes use this definition.

Another definition is that a nevus is large if it covers more than 2% of the patient's total body surface area, or is larger than the palm of the patient's hand.

Others define a nevus as large if it measures over eight inches in diameter. If using this definition and measuring a nevus on a newborn or child, the nevus is 'large' if it is expected to become over eight inches in diameter by the time the person is fully-grown. This definition provides a definite and exact number to large nevi.

Another definition for a large nevus is one that covers a major portion of a major anatomical site. This definition provides allowances for nevi of the head, legs or arms to be categorized as large even if they do not meet any of the previous definitions.

What does this mean?

Most Giant Nevi are brown in color, and have an increased tendency for hair growth. The texture of the skin can be smooth or leathery. Usually, a person does not sweat within a Giant Nevus, because sweat glands do not form properly. Many nevi have tumors just below the skin that give the nevus a lumpy or folded appearance.

Aside from the cosmetic issues, people with Giant Nevi have an increased risk of developing skin cancer. Also, these same nevus cells that appear on the skin can form in the central nervous system. This condition, known as neurocutaneous melanosis, has very limited treatment and no known cure. It causes neurological problems, such as hydrocephalus (water on the brain), developmental delays, and seizures. It is potentially fatal, often within the first few years of life, and can strike anyone with a nevus.