Nevus

Key takeaways

Nevus belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nevus to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nevus from memory before moving on to harder problems.

Reference excerpt

Nevus or naevus (pl. nevi or naevi) is a nonspecific medical term for a visible, circumscribed, chronic lesion of the skin or mucosa. The term originates from naevus, which is Latin for "birthmark"; however, a nevus can be either congenital (present at birth) or acquired. Common terms (mole, birthmark, beauty mark, etc.) are used to describe nevi, but these terms do not distinguish specific types of nevi from one another.

Classification The term nevus is applied to a number of conditions caused by neoplasias and hyperplasias of melanocytes, as well as a number of pigmentation disorders, both hypermelanotic (containing increased melanin, the pigment responsible for skin color) and hypomelanotic (containing decreased melanin). Suspicious skin moles which are multi-colored or pink may be a finding in skin cancer.

Increased melanin

Usually acquired Melanocytic nevus Melanocytic nevi can be categorized based on the location of melanocytic cells Junctional: epidermis Intradermal: dermis Compound: epidermis and dermis Atypical (dysplastic) nevus: This type of nevus must be diagnosed based on histological features. Clinically, atypical nevi are characterized by variable pigmentation and irregular borders. Becker's nevus Blue nevus (rarely congenital): A classic blue nevus is usually smaller than 1 cm, flat, and blue-black in color. Hori's nevus Nevus spilus (speckled lentiginous nevus): This lesion includes dark speckles within a tan-brown background. Pigmented spindle cell nevus Spitz nevus Zosteriform lentiginous nevus

Usually congenital Congenital melanocytic nevus These nevi are often categorized based on size, however, the lesions usually grow in proportion to the body over time, so the category may change over an individual's life. This categorization is important because large congenital melanocytic nevi are associated with an increased risk of melanoma, a serious type of skin cancer. Small: <1.5 cm Medium: 1.5–19.9 cm Large: ≥ 20 cm Nevus of Ito Nevus of Ota

Decreased melanin

Acquired Nevus anemicus

Congenital Nevus depigmentosus

Additional types of nevi do not involve disorders of pigmentation or melanocytes. These additional nevi represent hamartomatous proliferations of the epithelium, connective tissue, and 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.

Verrucous epidermal nevus Nevus sebaceous Nevus comedonicus Eccrine nevus Apocrine nevus

Connective tissue nevi Connective tissue nevi represent abnormalities of collagen in the dermis, the deep layer of the skin.

Collagenoma Elastoma

Vascular nevi These nevi represent excess growth of blood vessels, including capillaries.

Nevus simplex (nevus flammeus nuchae), also known as a stork bite or salmon patch.

Intramucosal nevi An intramucosal nevus is a nevus within the 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. Intramucosal nevi account for 64% of all reported case of oral nevi.

Diagnosis

Nevi are typically diagnosed clinically with the naked eye or using dermatoscopy. More advanced imaging tests are available for distinguishing melanocytic nevi from melanoma, including computerized dermoscopy and image analysis. 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 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. In addition to histopathological examination, some lesions may also warrant additional tests to aid in diagnosis, including special stains, immunohistochemistry, and electron microscopy. Typically, the nevi that exist since childhood are harmless.

Differential diagnoses Hypermelanotic nevi must be differentiated from other types of pigmented skin lesions, including:

Lentigo simplex Solar lentigo Café au lait macule Ink-spot lentigo Mucosal melanotic macule Mongolian spot (dermal melanocytosis)

Management

The management of a nevus depends on the specific diagnosis, however, the options for treatment generally include the following modalities:

Observation

Destruction Chemical peels Cryotherapy Dermabrasion Electrodessication 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), ulceration, infection, and concern for potential malignancy.

Syndromes The term nevus is included in the names of multiple dermatologic syndromes:

Basal cell nevus syndrome Blue rubber bleb nevus syndrome Dysplastic nevus syndrome Epidermal nevus syndrome Linear nevus sebaceous syndrome

Illustrations

Worked examples

Example 1 — a first encounter with Nevus

Start with the simplest possible case. Write down what Nevus claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nevus before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nevus ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nevus

In research: Nevus appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nevus in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nevus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Dermatologic terminology, Disturbances of human pigmentation, so understanding it makes those chapters shorter.
In everyday life: Look for Nevus outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Nevus in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nevus means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nevus out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nevus in simple terms?

Nevus or naevus (pl. nevi or naevi) is a nonspecific medical term for a visible, circumscribed, chronic lesion of the skin or mucosa. The term originates from naevus, which is Latin for "birthmark"; however, a nevus can be either congenital (present at birth) or acquired.

Why does Nevus matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nevus?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nevus.