# Nevus
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{{Short description|Mole or birthmark; visible, circumscribed, chronic skin lesion}}
{{Distinguish|Naevius (disambiguation){{!}}Naevius|Nevis|Nevius}}
{{Redirect|Polychromia|the red blood cell disorder|Polychromasia}}
{{Wiktionary|nevus|nevi}}
{{Infobox medical condition (new)
| name = Nevus
| synonyms = {{hlist|nevi|mole}}
| image = Nevus NCI.jpg
| caption = A benign nevus
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'''Nevus''' or '''naevus''' ({{plural abbr|'''nevi''' or '''naevi'''}}) is a nonspecific [medical term](/source/medical_terminology) for a visible, circumscribed, [chronic](/source/chronic_(medicine)) [lesion](/source/lesion) of the [skin](/source/skin) or [mucosa](/source/mucosa).[{{cite journal |last=Happle|first=Rudolf |year=1995 |title=What is a nevus? A proposed definition of a common medical term |journal=[Dermatology](/source/Dermatology_(journal)) |volume=191 |issue=1 |pages=1–5 |pmid=8589475 |doi=10.1159/000246468}}] The term originates from {{wikt-lang|la|naevus}}, which is [Latin](/source/Latin) for "[birthmark](/source/birthmark)"; however, a nevus can be either congenital (present at birth) or acquired. Common terms (''mole'', ''birthmark'', ''[beauty mark](/source/beauty_mark)'', etc.) are used to describe nevi, but these terms do not distinguish specific types of nevi from one another.
{{TOC limit|3}}
==Classification==
The term ''nevus'' is applied to a number of conditions caused by [neoplasias](/source/Neoplasm) and [hyperplasia](/source/hyperplasia)s of [melanocyte](/source/melanocyte)s,[{{Cite book|title=Fitzpatrick's Dermatology in General Medicine|publisher=The McGraw-Hill Companies, Inc.|year=2012|isbn=978-0-07-166904-7|chapter=Chapter 122. Benign Neoplasias and Hyperplasias of Melanocytes}}] as well as a number of pigmentation disorders, both hypermelanotic (containing increased [melanin](/source/melanin), the pigment responsible for skin color) and hypomelanotic (containing decreased melanin).[{{Cite book|title=Fitzpatrick's Dermatology in General Medicine|publisher=The McGraw Hill Companies, Inc.|year=2012|isbn=978-0-07-166904-7|chapter=Chapter 75. Hypomelanoses and Hypermelanoses}}] Suspicious skin moles which are multi-colored or pink may be a finding in [skin cancer](/source/skin_cancer).[{{cite book|url=https://books.google.com/books?id=ekr4Bt683c8C&pg=PT113|title=Baran and Dawber's Diseases of the Nails and their Management|last1=Baran|first1=Robert|last2=Berker|first2=David A. R. de|last3=Holzberg|first3=Mark|last4=Thomas|first4=Luc|date=2012|publisher=John Wiley & Sons|isbn=9781118286708|page=PT113|language=en}}]
===Increased melanin===
==== Usually acquired ====
* [Melanocytic nevus](/source/Melanocytic_nevus)
** Melanocytic nevi can be categorized based on the location of melanocytic cells[{{Cite book|title=Melanocytic Lesions - Springer|year=2014|isbn=978-1-4939-0890-5|chapter=Dysplastic (Atypical) Nevi|doi=10.1007/978-1-4939-0891-2 |editor-last1=Hoang |editor-last2=Mihm |editor-first1=Mai P. |editor-first2=Martin C. }}]
* [Becker's nevus](/source/Becker's_nevus)
* [Blue nevus](/source/Blue_nevus) (rarely congenital): A classic blue nevus is usually smaller than 1 cm, flat, and blue-black in color.[{{Cite book|title=Fitzpatrick's Dermatology in General Medicine|publisher=The McGraw-Hill Companies |year=2012|isbn=978-0-07-166904-7|chapter=Chapter 118. Benign Epithelial Tumors, Hamartomas, and Hyperplasias}}] connective tissue,[{{Cite book|title=Fitzpatrick's Dermatology in General Medicine|publisher=The McGraw-Hill Companies |year=2012|isbn=978-0-07-166904-7|chapter=Chapter 66. Dermal Hypertrophies and Benign Fibroblastic/Myofibroblastic Tumors}}] and vascular malformations.[{{Cite book|title=Fitzpatrick's Dermatology in General Medicine|publisher=The McGraw Hill Companies |year=2012|isbn=978-0-07-166904-7|chapter=Chapter 172. Vascular Malformations}}]
===Epidermal nevi===
These nevi represent excess growth of specific cells types found in the skin, including those that make up oil and sweat glands.[{{Cite book|title=Fitzpatrick's Dermatology in General Medicine|publisher=The McGraw-Hill Companies, Inc.|year=2012|isbn=978-0-07-166904-7|chapter=Chapter 107. Neonatal, Pediatric, and Adolescent Dermatology}}]
* '''Nevus simplex''' ([nevus flammeus nuchae](/source/nevus_flammeus_nuchae)), also known as a ''stork bite'' or ''salmon patch''.
File:NaevusSebaceus res.jpg|Nevus sebaceous
File:Nevus flammeus nuchae ("stork bite" "Storchenbiss").JPG|Nevus flammeus nuchae
===Intramucosal nevi===
An ''intramucosal nevus'' is a nevus within the [mucosa](/source/mucosa) as found in for example the mouth and genital areas. In the mouth, they are found most frequently on the hard palate. They are typically light brown and dome-shaped.[{{cite web|title=Oral Nevi|url=https://emedicine.medscape.com/article/1079272-overview|website=MedScape|access-date=23 January 2018}}] Intramucosal nevi account for 64% of all reported case of oral nevi.[{{cite journal|last1=Buchner|first1=A.|last2=Merrell|first2=P. W.|last3=Carpenter|first3=W. M.|title=Relative frequency of solitary melanocytic lesions of the oral mucosa|journal=Journal of Oral Pathology and Medicine|volume=33|issue=9|year=2004|pages=550–557|issn=0904-2512|doi=10.1111/j.1600-0714.2004.00238.x|pmid=15357676}}]
== Diagnosis ==
[[File:Pie chart of incidence and malignancy of pigmented skin lesions.png|thumb|Various [differential diagnoses](/source/differential_diagnosis) of pigmented skin lesions, by relative [rates](/source/Incidence_(epidemiology)) for biopsied lesions, and malignancy potential, including "nevus" at left and top.]]
Nevi are typically diagnosed clinically with the naked eye or using [dermatoscopy](/source/dermatoscopy). More advanced imaging tests are available for distinguishing melanocytic nevi from melanoma, including computerized dermoscopy and image analysis.[{{Cite journal|last1=Rigel|first1=Darrell S.|last2=Russak|first2=Julie|last3=Friedman|first3=Robert|date=2016-10-01|title=The evolution of melanoma diagnosis: 25 years beyond the ABCDs|journal=CA: A Cancer Journal for Clinicians|volume=60|issue=5|pages=301–316|doi=10.3322/caac.20074|issn=1542-4863|pmid=20671054|doi-access=free}}] The management of nevi depends on the type of nevus and the degree of diagnostic uncertainty. Some nevi are known to be benign, and may simply be monitored over time. Others may warrant more thorough examination and [biopsy](/source/biopsy) for histopathological examination (looking at a sample of skin under a microscope to detect unique cellular features). For example, a clinician may want to determine whether a pigmented nevus is a type of melanocytic nevus, dysplastic nevus, or melanoma as some of these skin lesions pose a risk for malignancy. The ABCDE criteria (asymmetry, border irregularity, color variegation, diameter > 6 mm, and evolution) are often used to distinguish nevi from melanomas in adults, while modified criteria (amelanosis, bleeding or bumps, uniform color, small diameter or de novo, and evolution) can be used when evaluating suspicious lesions in children.[{{Cite journal|last1=Scope|first1=Alon|last2=Marchetti|first2=Michael A.|last3=Marghoob|first3=Ashfaq A.|last4=Dusza|first4=Stephen W.|last5=Geller|first5=Alan C.|last6=Satagopan|first6=Jaya M.|last7=Weinstock|first7=Martin A.|last8=Berwick|first8=Marianne|last9=Halpern|first9=Allan C.|title=The study of nevi in children: Principles learned and implications for melanoma diagnosis|journal=Journal of the American Academy of Dermatology|volume=75|issue=4|pages=813–823|doi=10.1016/j.jaad.2016.03.027|pmc=5030195|pmid=27320410|year=2016}}] In addition to histopathological examination, some lesions may also warrant additional tests to aid in diagnosis, including special stains, [immunohistochemistry](/source/immunohistochemistry), and electron microscopy.[{{Cite book|title=Melanocytic Lesions - Springer|year=2014|isbn=978-1-4939-0890-5|chapter=Ancillary Techniques in Diagnosing Melanocytic Lesions|doi=10.1007/978-1-4939-0891-2 |editor-last1=Hoang |editor-last2=Mihm |editor-first1=Mai P. |editor-first2=Martin C. }}] Typically, the nevi that exist since childhood are harmless.
Image:Dermatoscope.jpg|A modern polarized dermatoscope
Image:Dermatoscope1.JPG|A dermatoscope
=== Differential diagnoses ===
Hypermelanotic nevi must be differentiated from other types of pigmented skin lesions, including:[{{Cite book|title=Melanocytic Lesions - Springer|year=2014|isbn=978-1-4939-0890-5|chapter=Dermal melanocytosis|doi=10.1007/978-1-4939-0891-2 |editor-last1=Hoang |editor-last2=Mihm |editor-first1=Mai P. |editor-first2=Martin C. }}][{{Cite book|title=Melanocytic Lesions - Springer|year=2014|isbn=978-1-4939-0890-5|chapter=Lentigo, Other Melanosis, and the Acquired Nevus|doi=10.1007/978-1-4939-0891-2 |editor-last1=Hoang |editor-last2=Mihm |editor-first1=Mai P. |editor-first2=Martin C. }}]
* [Lentigo simplex](/source/Lentigo_simplex)
* [Solar lentigo](/source/Solar_lentigo)
* [Café au lait macule](/source/Caf%C3%A9_au_lait_macule)
* [Ink-spot lentigo](/source/Ink_spot_lentigo)
* Mucosal melanotic macule
* [Mongolian spot](/source/Mongolian_spot) (dermal melanocytosis)
File:CALSpot.jpg|Cafe au lait
File:Mongolianspotphoto.jpg|Mongolian spot
== Management ==
thumb|Cryotherapy
The management of a nevus depends on the specific diagnosis, however, the options for treatment generally include the following modalities:
=== Observation ===
=== Destruction ===
* [Chemical peel](/source/Chemical_peel)s
* [Cryotherapy](/source/Cryotherapy)
* [Dermabrasion](/source/Dermabrasion)
* [Electrodessication](/source/Electrodesiccation_and_curettage)
* [Laser ablation](/source/Laser_ablation)
=== Surgery ===
The decision to observe or treat a nevus may depend on a number of factors, including cosmetic concerns, irritative symptoms (e.g., [pruritus](/source/pruritus)), ulceration, infection, and concern for potential malignancy.