Congenital melanocytic nevus
Encyclopedia
The congenital melanocytic nevus is a type of melanocytic nevus
(or mole) found in infant
s at birth
. This type of birthmark
occurs in about 1% of infants in the United States
; it is located in the area of the head
and neck
15% of the time.
The congenital melanocytic nevus (plural, nevi) presents as a circumscribed, light brown to black patch or plaque, potentially very heterogeneous in consistency, covering any size surface area and any part of the body. The appearance of the congenital melanocytic nevus is similar to those of nevi acquired after birth. However, congenital ones are usually larger in diameter
and may have excess terminal hair
, a condition called hypertrichosis
. If over 40 cm projected adult diameter with hypertrichosis, it is sometimes called giant hairy nevus; more usually these largest forms are known as large or giant congenital melanocytic nevus. The estimated prevalence for the largest forms is 0.002% of births .
Microscopically, congenital melanocytic nevi appear similar to acquired nevi with two notable exceptions. For the congenital nevus, the neval cells are found deeper into the dermis
. Also, the deeper nevus cells can be found along with neurovascular bundle
s, with both surrounding hair follicle
s, sebaceous gland
s, and subcutaneous fat
. Such annexes and the hypodermis can also be hypoplasic or, conversely, present aspects of hamartoma
.
Many are surgically removed for aesthetics and relief of psychosocial burden, but larger ones are also excised for prevention of cancer, although the benefit is impossible to assess for any individual patient. Proliferative nodules are usually biopsied and are regularly but not systematically found to be benign . Estimates of transformation into melanoma vary from 2-42% in the literature, but are most commonly considered to be at the low end of that spectrum due to early observer bias.
Benign congenital nevi can have histological characteristics resembling melanomas, often breaking most if not all of the ABCD rules. Dermatoscopic findings of the smaller forms of benign congenital nevi can aid in their differentiation from other pigmented neoplasms.
Melanocytic nevus
A melanocytic nevus is a type of lesion that contains nevus cells .Some sources equate the term mole with "melanocytic nevus". Other sources reserve the term "mole" for other purposes....
(or mole) found in infant
Infant
A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...
s at birth
Birth
Birth is the act or process of bearing or bringing forth offspring. The offspring is brought forth from the mother. The time of human birth is defined as the time at which the fetus comes out of the mother's womb into the world...
. This type of birthmark
Birthmark
A birthmark is a benign irregularity on the skin which is present at birth or appears shortly after birth, usually in the first month. They can occur anywhere on the skin. Birthmarks are caused by overgrowth of blood vessels, melanocytes, smooth muscle, fat, fibroblasts, or...
occurs in about 1% of infants in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
; it is located in the area of the head
Head
In anatomy, the head of an animal is the rostral part that usually comprises the brain, eyes, ears, nose and mouth . Some very simple animals may not have a head, but many bilaterally symmetric forms do....
and neck
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
15% of the time.
The congenital melanocytic nevus (plural, nevi) presents as a circumscribed, light brown to black patch or plaque, potentially very heterogeneous in consistency, covering any size surface area and any part of the body. The appearance of the congenital melanocytic nevus is similar to those of nevi acquired after birth. However, congenital ones are usually larger in diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
and may have excess terminal hair
Hair
Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....
, a condition called hypertrichosis
Hypertrichosis
Hypertrichosis is an abnormal amount of hair growth on the body; extensive cases of hypertrichosis have informally been called werewolf syndrome. There are two distinct types of hypertrichosis: generalized hypertrichosis, which occurs over the entire body, and localized hypertrichosis, which is...
. If over 40 cm projected adult diameter with hypertrichosis, it is sometimes called giant hairy nevus; more usually these largest forms are known as large or giant congenital melanocytic nevus. The estimated prevalence for the largest forms is 0.002% of births .
Microscopically, congenital melanocytic nevi appear similar to acquired nevi with two notable exceptions. For the congenital nevus, the neval cells are found deeper into the dermis
Dermis
The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
. Also, the deeper nevus cells can be found along with neurovascular bundle
Neurovascular bundle
A Neurovascular bundle is a term applied to the body nerves, arteries, veins and lymphatics that tend to travel together in the body...
s, with both surrounding hair follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
s, sebaceous gland
Sebaceous gland
The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...
s, and subcutaneous fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
. Such annexes and the hypodermis can also be hypoplasic or, conversely, present aspects of hamartoma
Hamartoma
A hamartoma is a benign, focal malformation that resembles a neoplasm in the tissue of its origin. This is not a malignant tumor, and it grows at the same rate as the surrounding tissues. It is composed of tissue elements normally found at that site, but which are growing in a disorganized mass...
.
Many are surgically removed for aesthetics and relief of psychosocial burden, but larger ones are also excised for prevention of cancer, although the benefit is impossible to assess for any individual patient. Proliferative nodules are usually biopsied and are regularly but not systematically found to be benign . Estimates of transformation into melanoma vary from 2-42% in the literature, but are most commonly considered to be at the low end of that spectrum due to early observer bias.
Types
Congenital melanocytic nevi may be divided into the following types:- Large or giant congenital melanocytic nevus (Bathing trunk nevus, Giant pigmented nevus)
- Medium-sized congenital nevus
- Small-sized congenital nevus
Clinical Findings
The lesions are often flat at birth, brown to black in color . They often grow proportionally to the body size as the child matures. As they mature, they often develop thickness, and becomes elevated, although these features can also be present from birth. Prominent terminal hairs often form, especially after puberty. With maturity, the nevus can have variation in color, and the surface might be textured with proliferative growths.Benign congenital nevi can have histological characteristics resembling melanomas, often breaking most if not all of the ABCD rules. Dermatoscopic findings of the smaller forms of benign congenital nevi can aid in their differentiation from other pigmented neoplasms.
Malignancy Potential
Large and especially giant congenital nevi are at higher risk for malignancy degeneration into melanoma. Because of the premalignant potential, it is an acceptable clinical practice to remove congenital nevi electively in all patients and relieve the nevocytic overload.Treatment
Surgical excision is the standard of care. Some individuals advocate the use of hair removal laser for the treatment of congenital nevi. While this is likely safe and effective for small congenital nevus, laser removal for larger lesions might pose a liability for the laser surgeon if malignancy developed from a deep (dermal) component of the nevus that is not reached by the laser. Repigmentation after laser treatment of congenital nevi or superficial curettage supports this concern.External links
- Congenital Nevus photo library at Dermnet
- Nevus Outreach, Inc. -- http://www.nevus.org