The congenital melanocytic nevus is a type of
melanocytic nevus
A melanocytic nevus (also known as nevocytic nevus, nevus-cell nevus and commonly as a mole) is a type of melanocytic tumor that contains nevus cells. Some sources equate the term mole with "melanocytic nevus", but there are also sources that equat ...
(or mole) found in
infant
An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used to ...
s at
birth
Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the f ...
. This type of
birthmark
A birthmark is a congenital, 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, melanocy ...
occurs in an estimated 1% of infants worldwide; it is located in the area of the
head
A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...
and
neck
The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
15% of the time.
Signs and symptoms
![Congenital nevus from CDC](https://upload.wikimedia.org/wikipedia/commons/f/f2/Congenital_nevus_from_CDC.jpg)
The congenital melanocytic nevus appears 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.
As compared with a
melanocytic nevus
A melanocytic nevus (also known as nevocytic nevus, nevus-cell nevus and commonly as a mole) is a type of melanocytic tumor that contains nevus cells. Some sources equate the term mole with "melanocytic nevus", but there are also sources that equat ...
, congenital melanocytic nevi are usually larger in
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
and may have excess terminal hair, a condition called
hypertrichosis
Hypertrichosis is an abnormal amount of hair growth over the body. The two distinct types of hypertrichosis are generalized hypertrichosis, which occurs over the entire body, and localized hypertrichosis, which is restricted to a certain area. H ...
. If over 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.
Melanocytic nevi often grow proportionally to the body size as the child matures. As they mature, they often develop thickness, and become 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.
Neurocutaneous melanosis
Neurocutaneous melanosis is a congenital disorder characterized by the presence of congenital melanocytic nevi on the skin and melanocytic tumors in the leptomeninges of the central nervous system. These lesions may occur in the amygdala, cerebe ...
is associated with the presence of either giant congenital melanocytic nevi or non-giant nevi of the skin. It is estimated that neurocutaneous melanosis is present in 2% to 45% of patients with giant congenital melanocytic nevi. Neurocutaneous melanosis is characterized by the presence of congenital melanocytic nevi on the skin and melanocytic tumors in the
leptomeninges
In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...
of the central nervous system.
Cause
Large congenital nevi are caused by a mutation in the body's cells that occurs early in embryonic development, usually within the first twelve weeks of pregnancy. Mutations are sometimes found in genes that code for
NRAS and
KRAS
''KRAS'' (Kirsten rat sarcoma virus) is a gene that provides instructions for making a protein called K-Ras, a part of the RAS/MAPK pathway. The protein relays signals from outside the cell to the cell's nucleus. These signals instruct the cell ...
proteins. There is no known method of prevention.
Diagnosis
![Pie chart of incidence and malignancy of pigmented skin lesions](https://upload.wikimedia.org/wikipedia/commons/d/d3/Pie_chart_of_incidence_and_malignancy_of_pigmented_skin_lesions.png)
Benign congenital nevi can have histological characteristics resembling
melanomas
Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, intestines, or eye (u ...
, often breaking most if not all of the
ABCDE rules.
Dermatoscopic findings of the smaller forms of benign congenital nevi can aid in their differentiation from other pigmented neoplasms.
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
The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...
. Also, the deeper nevus cells can be found along with
neurovascular bundle A neurovascular bundle is a structure that binds nerves and veins (and in some cases arteries and lymphatics) with connective tissue so that they travel in tandem through the body.
Structure
There are two types of neurovascular bundles: superficia ...
s, with both surrounding
hair follicle
The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between h ...
s,
sebaceous gland
A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...
s, and
subcutaneous fat
The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the layer are fibroblasts, adipose cells, and mac ...
. Such annexes and the
Subcutaneous tissue
The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the layer are fibroblasts, adipose cells, and macr ...
can also be hypoplasic or, conversely, present aspects of
hamartoma
A hamartoma is a mostly benign, local malformation of cells that resembles a neoplasm of local tissue but is usually due to an overgrowth of multiple aberrant cells, with a basis in a systemic genetic condition, rather than a growth descended fr ...
.
Classification
![Giant congenital melanocytic nevus](https://upload.wikimedia.org/wikipedia/commons/5/57/Giant_congenital_melanocytic_nevus.jpg)
Congenital melanocytic nevi may be divided into the following types:
* ''Small-sized congenital melanocytic nevus'' is defined as having a diameter less than .
* ''Medium-sized congenital melanocytic nevus'' is defined as having a diameter more than but less than .
* ''Giant congenital melanocytic nevus'' (also known as "bathing trunk nevus," "garment nevus," "giant hairy nevus", and "nevus pigmentosus et pilosus") is defined by one or more large, darkly pigmented and sometimes hairy patches.
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.
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.
Prognosis
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.
See also
*
Albinism
Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino.
Varied use and interpretation of the term ...
*
List of cutaneous conditions
Many skin conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against t ...
*
Vitiligo
Vitiligo is a disorder that causes the skin to lose its color. Specific causes are unknown but studies suggest a link to immune system changes.
Signs and symptoms
The only sign of vitiligo is the presence of pale patchy areas of depigmen ...
Notes
* Kahn, Michael A. ''Basic Oral and Maxillofacial Pathology'', Volume 1. 2001.
References
External links
{{Skin tumors, nevi and melanomas
Melanocytic nevi and neoplasms
fr:Naevus