Naevus: Symptoms, Types, Causes and Treatment

Naevi (singular: naevus), commonly known as moles or birthmarks, are a diverse group of benign skin lesions resulting from abnormal growths of various skin components. While most are harmless, their wide variety of appearances and potential for rare complications can cause confusion and concern. Understanding the symptoms, types, causes, and treatment options is essential for accurate diagnosis and effective management.

Symptoms of Naevus

Naevi can present with a wide array of symptoms depending on their type, location, and cellular origin. While most are asymptomatic, some may cause cosmetic concerns, discomfort, or rarely, medical complications. Recognizing their key features helps differentiate benign from potentially concerning lesions.

Symptom	Description	Frequency	Source(s)
Pigmentation	Brown, black, blue, or flesh-toned spots	Very common	1 2 3 4 5 9
Raised Lesion	Slightly elevated or nodular skin area	Common	3 4 8 9
Hair Growth	Presence of hairs in the lesion	Occasional	9 13
Discoloration	Speckled, bluish, or abnormal coloring	Variable by type	2 3 4 5
Location	Trunk, face, extremities, scalp, etc.	Site-specific	1 2 3 12 13
Texture Change	Rough, verrucous, or smooth surface	Type dependent	6 8 12
Systemic Signs	Jaw cysts, bone changes, other anomalies	Rare, syndromic	7 11

Table 1: Key Symptoms

Pigmentation and Appearance

Most naevi are recognized by their distinct coloration—ranging from light brown, dark brown, blue, to black. Some types, such as blue naevi or naevus fusco-caeruleus zygomaticus, display unique colors like blue or speckled gray that may raise suspicion for other skin conditions 2 3.

Physical Characteristics

Naevi can be flat (macular) or raised (papular or nodular). Certain types, such as plexiform spindle cell naevi, typically appear as slightly raised, pigmented lesions, often with a blue or dark tone 3. Hair growth within a naevus is especially common in congenital giant naevi, and may persist even after treatment 9 13.

Location and Distribution

The site of a naevus often provides diagnostic clues. For example, naevus sebaceous typically appears on the scalp or face, while naevus fusco-caeruleus zygomaticus involves the cheeks near the zygomatic bones 2 12. Some syndromic naevi, as in basal cell naevus syndrome, are associated with systemic signs beyond the skin 7 11.

Texture and Systemic Symptoms

Texture varies: some naevi are smooth; others, like sebaceous or epidermal naevi, may appear rough or warty 6 8 12. Most naevi are asymptomatic, but itching, tenderness, or complications can develop, particularly if they become inflamed, traumatized, or are associated with syndromes affecting multiple organ systems 7 11.

Types of Naevus

The diversity of naevi is remarkable, reflecting their varied cellular origins and clinical presentations. Some are present at birth (congenital), while others develop later (acquired). Classification often relies on histological features, clinical appearance, and associated syndromic findings.

Type	Key Features	Typical Age/Location	Source(s)
Congenital Melanocytic	Large, pigmented, present at birth	Trunk, scalp, limbs	9 10 13
Combined Naevus	Two+ naevus types in one lesion, can mimic melanoma	Trunk, head, limbs	1
Blue Naevus	Blue/black, raised, deep dermal pigmentation	Dorsum of hands, face	1 3 5
Spitz Naevus	Pink/red or pigmented, spindle/epithelioid cells	Children, face/extremities	4 5
Naevus Sebaceous	Yellow/orange, hairless plaque, risk of tumors	Scalp, face	6 12
Epidermal Naevus	Warty, linear, may follow Blaschko’s lines	Trunk, extremities	6 7
Becker’s Naevus	Hyperpigmented, hairy, adolescent onset	Shoulder, chest	8
Syndrome-associated	Multiple/systemic signs, genetic mutations	Variable	7 11

Table 2: Main Types of Naevus

Congenital Melanocytic Naevus

These large, often hairy naevi are present at birth and can cover significant skin areas. They carry a small but significant risk of melanoma transformation, especially when giant in size 9 10 13.

Combined Naevus

A combined naevus contains two or more types of melanocytic naevi within the same lesion. Their clinical and pathological similarity to melanoma frequently leads to misdiagnosis, emphasizing the need for specialized evaluation 1.

Blue Naevus and Plexiform Spindle Cell Naevus

Blue naevi are characterized by blue or black pigmentation due to the depth of melanin in the dermis. Plexiform spindle cell naevi, a variant, exhibit a unique architecture and often appear on the back or shoulders of young adults 3 5.

Spitz Naevus

Spitz naevi are typically pink, red, or brown lesions, often found in children. They display distinctive spindle or epithelioid cells histologically, and may be challenging to distinguish from melanoma without advanced imaging or biopsy 4 5.

Naevus Sebaceous, Epidermal, and Becker’s Naevus

Naevus sebaceous is a congenital hamartoma, usually arising on the scalp or face, and carries a low risk of secondary tumors 6 12. Epidermal naevi are linear, warty growths that often follow skin developmental patterns known as Blaschko’s lines 6 7. Becker’s naevus, more common in adolescent males, presents as a pigmented, hairy patch and is associated with increased androgen sensitivity 8.

Syndrome-Associated Naevi

Some naevi are features of genetic syndromes, such as basal cell naevus syndrome, phacomatosis pigmentokeratotica, or mosaic hedgehog spectrum disorders. These are often accompanied by systemic symptoms, including jaw cysts, bone changes, and developmental abnormalities 6 7 11.

Causes of Naevus

Understanding the causes of naevi sheds light on their diversity. While genetics plays a primary role, environmental factors and somatic mutations also contribute to their development and variation.

Cause	Mechanism/Description	Naevus Types Affected	Source(s)
Genetic Mutation	Inherited or postzygotic gene changes	Syndromic, congenital	6 7 11
Somatic Mutation	Acquired mutations after conception	Epidermal, mosaic	6 7
UV Exposure	Induces mutations in skin cells	Acquired melanocytic	5
Hormonal Factors	Androgen sensitivity or puberty triggers	Becker’s, sebaceous	8 12
Embryonic Development	Disruption in skin cell migration	Congenital, epidermal	6 8
Trauma	Injury to skin can alter existing naevi	Recurrent/traumatized	5

Table 3: Key Causes of Naevus

Genetic and Somatic Mutations

Many naevi arise due to genetic mutations. For example:

• Germline mutations in genes such as HRAS can cause syndromic presentations like Costello syndrome or phacomatosis pigmentokeratotica 6.
• Somatic (postzygotic) mutations in genes like SMO or PTCH1 are responsible for mosaic syndromes such as basal cell naevus syndrome and mosaic hedgehog spectrum disorders 7 11.

Environmental and Hormonal Influences

Acquired melanocytic naevi commonly develop due to UV exposure, which induces DNA mutations in skin cells 5. Hormonal changes during puberty can trigger the appearance or growth of certain naevi, such as Becker’s naevus and naevus sebaceous, likely due to androgen receptor sensitivity 8 12.

Embryonic and Developmental Factors

Some naevi, especially congenital and epidermal types, result from disruptions during embryonic development, leading to abnormal migration or proliferation of skin cells in specific patterns 6 8. This explains the linear or segmental distribution seen in some cases.

Trauma and Inflammation

Occasionally, trauma or inflammation can alter the appearance of existing naevi or contribute to the formation of so-called "recurrent" or "traumatized" naevi, complicating diagnosis 5.

Treatment of Naevus

Treatment approaches vary widely depending on the type, size, location, symptoms, and risk of complications. While many naevi require no intervention, others may need monitoring or removal for medical or cosmetic reasons.

Treatment Type	Indication/Approach	Pros/Cons	Source(s)
Observation	Benign, asymptomatic naevi	Non-invasive, safe	1 5 12
Surgical Excision	Suspicious, large, or symptomatic lesions	Definitive, scarring risk	9 10 12 13
Laser Therapy	Superficial pigmented or hair-bearing	Cosmetic, incomplete removal	10
Dermabrasion/Curettage	Partial removal, giant naevi	Less invasive, risk of recurrence	9 10
Medical Therapy	Syndrome-related, targeted drugs	For systemic management	11
Skin Grafting	Large area defects post-excision	Functional/cosmetic repair	13

Table 4: Main Treatment Options

Observation and Monitoring

Most benign naevi, especially those without atypical features, can be safely observed. Regular monitoring is essential for early detection of malignant transformation, particularly in congenital or atypical naevi 1 5 12.

Surgical and Minimally Invasive Approaches

• Surgical Excision: Indicated for giant congenital naevi, lesions with suspicious changes, or those causing symptoms. Complete removal provides tissue for diagnostic confirmation but may result in scarring 9 10 12 13.
• Laser Therapy, Dermabrasion, Curettage: These approaches target superficial pigmentation or hair, offering cosmetic improvement. However, they may not eliminate all naevus cells, so a small risk of recurrence or malignancy remains 9 10.
• Skin Grafting: Used for large defects after naevus removal, especially with giant congenital naevi. Artificial dermis and tissue expanders can help reconstruct functionally and cosmetically acceptable skin 13.

Medical and Targeted Therapies

For syndrome-associated naevi, such as basal cell naevus syndrome, systemic medical therapies (e.g., hedgehog pathway inhibitors) may be needed to manage multiple tumors or systemic manifestations 11.

Controversies and Guidelines

There is ongoing debate about the timing and necessity of excision for certain naevi, such as naevus sebaceous. Some clinicians recommend early removal to prevent malignancy, while others advocate for observation, especially given the low risk of cancer in childhood 12. Evidence-based guidelines are still evolving to standardize care.

Conclusion

Naevi are a complex and varied group of skin lesions, ranging from innocuous spots to markers of systemic disease. Understanding their symptoms, types, causes, and treatment options is crucial for ensuring proper care and peace of mind.

Key Points:

• Naevi present with a spectrum of symptoms, most commonly pigmentation and raised lesions, but can also involve hair growth, texture changes, and rarely, systemic signs [1–13].
• Types include congenital, combined, blue, Spitz, sebaceous, epidermal, Becker’s, and syndrome-associated naevi, each with characteristic features and risks [1–13].
• Causes span genetic and somatic mutations, environmental triggers, hormonal influences, and developmental disruptions [5–8,11].
• Treatment varies from observation to surgery, with emerging therapies for syndromic cases. Management decisions should be personalized and evidence-based [9–13].

Early recognition, accurate diagnosis, and individualized care remain the cornerstones of effective naevus management.