In order to let you know more about nevus in one article, I am going to make a summary of common concerns, and hope it will be useful for you. At the same time, I am also going to talk to you about some of the current common treatments for nevus in the form of a rambling article and a detailed introduction to the common application of skin expansion for nevus treatment, which I hope will be useful to you.
I. General knowledge about nevus
Congenital melanocytic nevi are made up of clusters of melanocytes that usually appear at birth, but occasionally we see children who are born without a nevus and only develop a nevus several years after birth.
Some nevus lesions are very small and benign, but some nevi are very large or located in exposed areas such as the head and neck. The presence of nevi seriously affects the patient’s aesthetics and causes heavy psychological pressure on the patient; at the same time, both for the patient and his family, and for the surgeon, the fear of malignant nevus also brings heavy psychological pressure.
Second, one of the classifications of nevus
There are many ways to classify nevi, such as congenital melanocytic nevus and acquired melanocytic nevus according to the time of appearance of nevus; according to the different levels of skin where the melanin nest of nevus is located, there are three types of nevus: junctional nevus, intradermal nevus and mixed nevus. Since there is an obvious correlation between the location of nevi in the skin tissue and the rate of malignant transformation, the classification according to the distribution level is now preferred, and the characteristics of the 3 different types of nevi are
1. Junctional nevi
The nevus is named because it is located at the junction of the epidermis and the dermis. The lesion is located deep in the epidermis or at the junction of connective tissue adjacent to the dermis and epidermis or epithelium of the appendages. Junctional nevi appear mostly in infancy or childhood and appear as well-defined, brown to black patches or mildly elevated dermal papules, with nevi mostly within 0.6-0.8 cm in diameter and round or oval lesions with smooth edges and no hair. Junctional nevi can occur in any part of the skin and mucous membrane, while nevi occurring on the palms of the hands, toes and vulva are almost all junctional nevi.
Junctional nevi generally do not become malignant before puberty, and the percentage of junctional nevi in human skin nevi will gradually decrease with age; after puberty, most junctional nevi will become intradermal nevi, which generally do not become malignant; because the junctional activity of junctional nevi in the palms of hands, soles of feet and external genitalia can be maintained until adulthood, junctional nevi in these areas have the potential to become malignant.
2. Intradermal nevus
Because the lesions are distributed in the dermis, they are named intradermal nevi.
This is a common type of nevus in adults, which appears as a small hemispherical elevated dermal surface, light brown or skin-colored swelling, generally less than 1 cm in diameter, with a smooth surface and sometimes one or several hairs visible in the center; it is common in middle-aged and elderly people; no clinical reports of malignant transformation of intradermal nevus have been seen.
3.Mixed nevus
Because it has the characteristics of both junctional nevus and intradermal nevus, it is named as mixed nevus. Mixed nevus is a transitional manifestation of the evolution of junctional nevus to intradermal nevus, and it is more common in middle-aged and young people. The clinical manifestation is a brown to black papule or macule with clear boundaries, on which there is often hair growth, and the surrounding pigment gradually becomes lighter. Sometimes, the nevus cells can extend to the lower dermis and even to the subcutaneous fatty tissue.
In short, the 3 different types of melanocytic nevi can be different manifestations of the same disease process.
Three, the second classification of nevus
Congenital melanocytic nevi are one of the risk factors for the eventual formation of cutaneous melanoma and extracutaneous melanoma, and the risk is higher for larger nevi; therefore, some scholars also classify adult nevi according to the maximum diameter of nevi, and classify nevi into the following 4 categories.
1.Small nevi: nevi with a maximum diameter of no more than 1.5cm.
2.Medium nevi: nevi with a diameter of 1.5-19.9cm are medium-sized nevi.
3.Large nevi: nevi with a diameter greater than 20cm are considered large nevi.
4.giant nevi: nevi with diameter greater than 50cm or larger; usually, giant nevi are often accompanied by a large number of satellite nevi.
Incidence of nevus
According to relevant studies, the incidence of congenital nevus in newborns is 1%, which means that one out of 100 newborns will have a pigmented nevus; the incidence of large congenital melanin nevus is 1:20,000, while the incidence of giant nevus (diameter greater than 50cm) is lower and rarer.
V. Etiology and mechanism of nevus formation
At present, the etiology and pathogenesis of congenital melanocytic nevus are not clear; congenital melanocytic nevus is formed in utero at 5-24 weeks of gestation. Regarding the differentiation of melanocytes, a theory exists that early in embryonic development, with the formation of the neural tube, adult melanocytes migrate from the neural crest along the soft cerebrum to the embryonic dermis, and from the embryonic dermis, melanocytes migrate to the epidermis, where they form dendritic melanocytes within the epidermis. The abnormal migration, proliferation and differentiation of melanocytes within the skin and soft meninges may be associated with congenital melanocytic nevi as well as neurocutaneous melanosis.
Sixth, the problem of melanocytic nevus malignant transformation
Most of the patients who come to the hospital with “nevus” are worried about malignant change. In fact, the probability of cancer in acquired melanocytic nevus is very small, and it is only the junctional nevus or the junctional component of the mixed nevus that will become malignant, while intra-dermal nevus basically does not become cancerous.
Except for huge melanocytic nevi which are more prone to malignant transformation, other cases of malignant transformation are mostly dysplastic melanocytic nevi; domestic malignant melanoma is rare, and if malignant melanoma occurs, its occurrence sites are more common in the palms of hands, soles of feet, nail beds, external genitalia, etc. Most of the nevi in these sites are junctional nevi, therefore, if the nevi in these sites, within a short period of time Therefore, if the nevi in these areas suddenly become larger, have uneven pigmentation, have irregular edges, have “satellite nevi” around them, or even break down and bleed, we should not take it lightly and go to the hospital for pathological examination in time.
7. Most patients with nevi come to the hospital for medical reasons
Every normal adult has 15-20 moles on average, so it can be said that this is a very common “disease”, but not everyone wants to remove the moles on their body; most of them can actually be left untreated.
According to my observation, most of the people who come to the hospital for mole treatment are in 3 kinds of cases.
1. The moles are an eyesore: especially if the moles grow on the exposed parts of the face, if the area is large, the color is dark and there is hair, it will seriously affect the beauty.
2.Worry that moles will become malignant: surgical moles may evolve into malignant melanoma, and once it happens, the consequences will be serious; however, the chance of moles becoming malignant is very small, so we advise you not to do unnecessary panic; however, for moles on the palms of hands, soles of feet, external genitalia and other parts of the body, although the location is hidden and does not affect the beauty, for safety reasons, preventive excision can be considered.
3. Influenced by some specific traditional concepts and legends: There are some strange and weird sayings about moles, for example, the mole growing on the lower lip is called “eating mole”, the mole growing in the middle of the neck is called “bitterness mole”, and the mole growing in the lower eyelid and its vicinity is called “tear”. The moles that grow in and around the lower eyelids are called “tear moles”, and so on and so forth. In fact, these are just legends without scientific basis.
Diagnosis and clinical manifestations of melanocytic nevi
Usually, small or medium-sized congenital melanocytic nevi appear as round or oval homogeneous pigmented lesions with light to dark brown color, clear borders, papillary surface, and hairy (so sometimes they are also called nevus nigricans), and some parents often say their children have “animal skin nevus” when they bring them to the hospital. “In fact, this is a very irregular name); however, larger melanocytic nevi have asymmetrical and irregular edges, multiple colors, folds, and nodules on the surface, and large melanocytic nevi are often accompanied by many small satellite nevi.
As children grow and develop, especially after puberty, congenital melanocytic nevi may change in color, either becoming lighter or darker, more uneven or more uniform in texture; congenital melanocytic nevi may degenerate on their own; some patients may develop white spots, and proliferative nodules may appear from birth or after birth They may appear gradually. Congenital melanocytic nevi often have no clinical symptoms; however, in patients with larger nevi, itching, dry skin, fragile skin, erosions or ulcers, and decreased sweating ability of the affected skin may occur.
Because of the increased risk of melanoma in congenital nevi, scholars have made many efforts to try to differentiate congenital nevi from acquired nevi from a histological point of view, and the histological characteristics of congenital nevi are.
1. The nevus cells involve deep skin attachments and neurovascular structures (including hair follicles, sebaceous glands, erector spinae and blood vessel walls).
2. The nevus cells extend into the deep dermis and subcutaneous fat layer.
3. The presence of nevus cell infiltration between collagen bundles.
4, The presence of a subcutaneous zone deprived of nevus cells.
In contrast, acquired nevus nigricans usually consists of nevus cells confined to the papillary and reticular layers of the dermis, and does not involve the skin adnexa.
MRI of the nervous system is a very useful test for patients with a high suspicion of neurocutaneous nevus.
IX. Surgical treatment of melanocytic nevi
Large nevi, especially giant nevi, are very difficult to treat surgically; although the conclusion that congenital pigmented nevi are at risk of malignancy has reached a good level of confirmation, surgical treatment of large or giant nevi is still an extremely controversial issue. For large or giant nevi, there is no evidence in the literature confirming a corresponding decrease in the incidence of melanoma as the nevus is excised, and the secondary damage due to surgery is significant, while even after excision of the melanotic nevus from the skin, these patients remain at risk for increased occurrence of extracutaneous melanoma. However, because the presence of large melanocytic nevi can cause heavy psychological stress to the patient, most of the affected children or the parents of the affected children choose to treat them by surgical means. Therefore, we can say that the treatment of large nevi remains an extremely challenging task for plastic surgeons. Unfortunately, there are few specialized treatment centers within major hospitals for patients with congenital nevi, and nevus patient pairs are randomly distributed in various treatment centers.
For small nevi, since the possibility of transforming into malignant melanoma before puberty is almost zero, there is no need to rush treatment for such patients, and it is entirely possible to choose to wait and treat them when the child reaches a certain age and can tolerate surgery under local anesthesia; from another point of view, if the nevus is located in a location where surgery cannot be performed under local anesthesia or cannot be repaired On the other hand, if the nevus is located in a location that cannot be operated on under local anesthesia or cannot be repaired or reconstructed, and the early removal of the nevus can achieve better surgical results, then there is no need to wait and the surgery can be performed under general anesthesia; in addition, if the nevus is located in an exposed part of the face and the treatment is postponed, such as when the child is in elementary school, the presence of the nevus will become a source of ridicule for the child’s peers and will seriously affect the child’s psychological development. At this time, we should not consider the problem of anesthesia, but should choose early surgical treatment.
Common treatment methods for congenital melanocytic nevus
For large nevi or giant nevi, scholars have proposed many treatment methods to remove and reconstruct them.
1.Split excision of nevus
The method of excision of nevus in stages can limit the area of lesion, however, it is difficult to remove the lesion completely.
2.Nevus excision and free skin implant
Although this method has the advantage of simple surgery, the results are hardly satisfactory from both functional and aesthetic points of view after the surgery.
3.Dermal grinding, scraping, chemical peeling and laser
The reason is that these methods only remove the superficial part of the lesion, while usually, congenital pigmented nevus cells can be found in the subcutaneous fat or even in deeper structures. Although the above method of “excision” of nevus can reduce the total number of nevus cells and lighten the color of the lesioned area, the so-called “infiltration” of deeper nevus cells often occurs later, which may also manifest as abnormal skin color and increased hair; in addition, the scar formation caused by excision of nevus in layers also affects the follow-up to determine whether the nevus is malignant. The long-term effect of laser treatment on the participating nevus cells needs to be further studied.
4.Dermal expansion
It is one of the most commonly used methods to treat nevus in clinical practice.
5.Nevus excision with local flap transfer repair
6.Nevus excision, microsurgical free flap trauma covering surgery.