Module 17: Intradermal Nevus
Source: Dermoscopy Educational Course Author of source chapter: Rainer Hofmann-Wellenhof
1. Learning Objectives
After completing this module, the learner should be able to:
- Define intradermal nevus (IDN) and explain its histopathological basis as a dermal melanocytic neoplasm.
- Distinguish the three clinical-dermoscopic variants of IDN: eclipse nevus, Miescher nevus, and Unna nevus.
- Identify the stereotypic dermoscopic features of each IDN variant, including comma vessels, cobblestone pattern, and homogeneous structureless areas.
- Recognize the anatomical predilection sites for each IDN variant (scalp for eclipse, face for Miescher, trunk for Unna).
- Differentiate intradermal nevi from their clinical mimics, including nodular melanoma, basal cell carcinoma, neurofibroma, and skin tag.
- Apply the "wobble sign" as a clinical clue supporting the diagnosis of an intradermal nevus.
- Identify features of irritated or traumatized Unna nevi and explain why they may mimic malignancy.
- Determine when an IDN requires excision versus clinical or digital dermoscopic monitoring.
2. Prerequisites
- Module 01: Introduction and Principles of Dermoscopy -- understanding of polarized vs. nonpolarized dermoscopy and image acquisition.
- Module 02: Histopathologic Correlations of Dermoscopic Structures -- knowledge of dermoscopic-pathologic correlation for colors, vessels, and structural patterns.
- Module 16: Acquired Melanocytic Nevi -- familiarity with the general dermoscopic patterns of melanocytic nevi (reticular, globular, homogeneous), nevus subtypes, and the natural evolution of acquired nevi.
3. Key Concepts
3.1 Definition
Intradermal nevi (IDN) are benign melanocytic neoplasms composed of nests of nevomelanocytes located predominantly in the dermis. All IDN share a single unifying clinical criterion: they are elevated, forming a papule or nodule.
3.2 Classification: Three Variants
IDN can be classified into three variants based on clinical morphology, dermoscopic morphology, and anatomical location:
| Variant | Eponym Origin | Morphology | Preferred Location |
|---|---|---|---|
| Eclipse nevus | Named for its eclipse-like appearance | Compound nevus with dermal center and junctional rim | Scalp (especially children) |
| Miescher nevus | Alfred Guido Miescher (Zurich, 1935) | Dome-shaped, endophytic, wedge-shaped nests extending to deep reticular dermis | Face (91% of cases) |
| Unna nevus | Paul Gerson Unna (1896, "soft nevus") | Papillomatous/exophytic, fibroepithelial polyp-like; nests do NOT reach the reticular dermis | Trunk |
3.3 Histopathological Distinction
- Miescher nevi: Nevus cells often extend to the deep reticular dermis in a wedge-shaped pattern. The growth is endophytic.
- Unna nevi: Nevus cell nests do not reach the reticular dermis. The growth is exophytic (papillomatous/polypoid).
- This deep vs. superficial dermal distribution is the key histological difference between the two classic IDN types.
3.4 Embryogenetic Hypothesis for Miescher Localization
The preferential facial localization of Miescher nevi may be linked to the embryogenetic origin of the dermis:
- The dermis of the frontal, temporal, maxillary, and mandibular regions derives from the neural crest.
- The dermis of the parietal/occipital regions originates from the paraxial mesoderm (somites and somitomeres).
- In studies dividing the head/neck into two regions, 89% of nevi in the neural crest-derived region (face + temporal + frontal + high neck) were Miescher type, versus only 2% in the mesodermal region (parietal + occipital + low neck).
4. Core Content
4.1 Eclipse Nevus
Clinical Features
The eclipse nevus is a compound nevus with a central portion resembling an intradermal nevus surrounded by a junctional component. Clinically, this creates a characteristic pattern:
- Central portion: Tan, elevated papule (dermal component)
- Peripheral rim: Darker brown pigmented ring (junctional component)
- In some cases the brown peripheral rim can be disrupted or have a stellate appearance.
- Preferred anatomic location: scalp, especially in children.
- Evidence suggests that eclipse nevi may transform into pure intradermal nevi over time.
Dermoscopic Characteristics
Dermoscopy reveals two distinct components:
- Central elevated part:
- Light brown to skin colored
- Papillomatous surface forming a cobblestone pattern
- Short, curved vessels (comma vessels)
- Pigmented periphery:
- Brown shades with reticular or homogeneous pattern
- On rare occasions, disrupted pigmentation or streaks creating a stellate appearance
Management
- The typical eclipse nevus is benign and does not need to be excised.
- Irregular-appearing eclipse nevi can be monitored via digital dermoscopy.
Check Your Understanding
What is an eclipse nevus, and where is it most commonly found?
An eclipse nevus is a compound nevus with a central elevated tan papule (dermal component) surrounded by a darker brown pigmented rim (junctional component), resembling a solar eclipse. It is most commonly found on the scalp, especially in children, and may transform into a pure intradermal nevus over time.
4.2 Miescher Nevus
Clinical Features
- Dome-shaped papule with a smooth surface
- Located predominantly on the face (91% of Miescher nevi are facial; 94% of facial IDN are Miescher type)
- Color: brown to nearly skin colored
- Diameter: typically 4-6 mm
- Terminal hairs frequently emanate from Miescher nevi
- Usually remain stable over a lifetime
- Rare secondary changes: fibrous papule transformation; secondary ossification (osteo-nevus of Nanta)
Dermoscopic Characteristics
The dermoscopic appearance of Miescher nevi is relatively nonspecific:
- Pattern: Homogeneous pattern is most common
- Color distribution: Center can be slightly darker than the periphery
- Vessels: Frequently visible; include:
- Linear curved vessels (comma vessels)
- Serpentine vessels
- Arborizing vessels
- Golden brown halo: May assist in differentiating Miescher nevus from basal cell carcinoma
Differential Diagnosis
- Basal cell carcinoma (arborizing vessels, blue-gray structures)
- Fibrous papules
- Adnexal tumors
Melanoma Risk
There are no reports in the literature of melanoma arising in a Miescher nevus.
Key Takeaways
- Intradermal nevi typically show a cobblestone pattern of closely packed, large, angulated globules corresponding to large nests of melanocytes in the dermis.
- Comma vessels (short, slightly curved vessels) are the characteristic vascular pattern of intradermal nevi and correlate with vessels in the dermal papillae.
- The structureless light-brown homogeneous pattern is the second most common presentation of intradermal nevi, often seen in nonpigmented variants.
Clinical Scenario
A 55-year-old woman presents with a 5 mm dome-shaped, skin-colored papule on her right cheek that has been stable for over 20 years. Dermoscopy shows a homogeneous light brown pattern with comma vessels and a subtle golden-brown halo around the lesion.
What is the diagnosis, and what feature helps distinguish it from BCC?
Miescher Nevus (Intradermal Nevus)
A dome-shaped facial papule stable over decades with a homogeneous pattern and comma vessels is classic for a Miescher nevus. The golden-brown halo is a helpful differentiating clue from nodular BCC, which lacks this warm-toned halo and instead shows bright red arborizing vessels, blue-gray ovoid nests, and ulceration. There are no reports of melanoma arising in Miescher nevi.
4.3 Unna Nevus (Papillomatous Nevus)
Clinical Features
- Synonymous with "papillomatous nevus"
- Sessile to pedunculated papules with a papillomatous surface
- Location: predominantly on the trunk
- Median diameter: 5.0 mm
- Colors: light brown, dark brown, or skin colored
- Pigment distribution: usually uniform; sometimes central pigmentation with skin-colored periphery
- Prevalence: almost one-third of Caucasians have at least one Unna nevus (based on a screening population of 700 persons)
Dermoscopic Characteristics
Colors:
- Light brown or dark brown most common
- White and red regions can also be seen
- Color distribution patterns: uniform pigmentation, multifocal hypo/hyperpigmentation, or central hyperpigmentation
Patterns:
- Homogeneous pattern
- Globular pattern
- Cobblestone pattern (characteristic)
Vessels:
- Comma vessels (curved vessels) -- stereotypic for Unna nevi
- Dotted vessels (occasionally)
- Atypical vessels (occasionally)
- Vessels can be more prominent in irritated Unna nevi
Surface features:
- Papillomatous surface with deep invaginations filled with keratin
- Keratin-filled sulci can resemble comedo-like openings associated with seborrheic keratosis
The Wobble Sign:
- Described by Braun et al.
- Technique: Place the dermatoscope on the lesion and apply horizontal pressure in a back-and-forth motion
- IDN will wobble (due to their dermal component)
- Lesions without a dermal component will slide and not wobble
- Useful clinical clue supporting the diagnosis of IDN
Irritated/Traumatized Unna Nevus
- Irritated Unna nevi display more prominent vessels
- Irregular vessels and a red background may be evident
- These features can mimic melanoma or other malignancies
- Clinical context (history of trauma, shaving, clothing friction) is essential
Melanoma Risk
There are only a few reports in the literature of melanoma arising in association with a papillomatous nevus.
Differential Diagnosis
- Skin tags
- Fibromas
- Neurofibromas
- Adnexal tumors
Check Your Understanding
What dermoscopic pattern is characteristic of the Unna (papillomatous) nevus?
The Unna nevus characteristically shows a cobblestone pattern with closely aggregated large globules, comedo-like openings, and fissures resembling a cerebriform (brain-like) surface. It is an exophytic, soft, pedunculated lesion that can dermoscopically mimic seborrheic keratosis due to the shared papillomatous architecture.
4.4 Dermoscopic Patterns of IDN (Comprehensive Summary)
The following dermoscopic features may be seen across IDN variants:
Cobblestone pattern: Angulated globule-like structures resembling cobblestones; characteristic of Unna nevi and the central portion of eclipse nevi.
Comma vessels (curved vessels): Short, curved, comma-shaped vessels; the most stereotypic vascular pattern for IDN. Present in all three variants.
Homogeneous/structureless light brown areas: The most common overall pattern; particularly characteristic of Miescher nevi.
Globular pattern: Aggregated brown globules; seen in Unna nevi.
Papillomatous surface with keratin-filled sulci: Deep surface invaginations filled with keratin that may mimic comedo-like openings of seborrheic keratosis; characteristic of Unna nevi.
Golden brown halo: Subtle warm-toned halo around the lesion; described as a differentiating clue for Miescher nevi (vs. BCC).
Serpentine and arborizing vessels: Can be seen in Miescher nevi; may create confusion with BCC.
Dotted or atypical vessels: Occasionally seen in Unna nevi, more prominent in irritated lesions.
Central hyperpigmentation with lighter periphery: A pattern of pigment distribution more frequent in older patients with Unna nevi.
Peripheral reticular or homogeneous pattern: Seen in the junctional rim of eclipse nevi.
Key Takeaways
- Adipose globules (yellow-white lobular structures) can appear in intradermal nevi, corresponding to fat entrapment within the dermal nevus, and should not be confused with pathology.
- Papillomatous intradermal nevi (Unna nevi) show exophytic projections with fissures and a cerebriform surface that can mimic seborrheic keratosis.
- Milia-like cysts in intradermal nevi represent intraepidermal keratinous cysts and are a shared feature with SK, making differentiation challenging in some cases.
Clinical Scenario
A 48-year-old man presents with a soft, pedunculated, 6 mm papule on his upper back. He reports it was nicked during shaving 2 weeks ago. Dermoscopy shows a cobblestone pattern with prominent irregular vessels and a reddish background. The wobble sign is positive.
What is the most likely diagnosis, and why might this lesion mimic melanoma?
Irritated Unna Nevus (Papillomatous Intradermal Nevus)
The cobblestone pattern with a positive wobble sign strongly supports an intradermal nevus (Unna type). The prominent irregular vessels and reddish background are caused by recent trauma/irritation, not malignancy. Irritated Unna nevi can mimic melanoma due to their atypical vascular features. Clinical context (history of trauma, trunk location, pedunculated morphology) and the absence of melanoma-specific criteria (atypical network, blue-whitish veil, regression) help distinguish them. Short-term follow-up after trauma resolution is appropriate.
4.5 IDN Mimicking Other Lesions
IDN Mimicking Basal Cell Carcinoma
- Miescher nevi may show arborizing vessels and a dome-shaped morphology that overlaps with nodular BCC.
- The golden brown halo of a Miescher nevus is a helpful differentiating feature (BCC lacks this warm-toned halo).
- BCC-specific features to look for (absent in IDN): blue-gray ovoid nests, leaf-like areas, spoke-wheel structures, ulceration.
IDN Mimicking Melanoma
- Irritated or traumatized Unna nevi can display irregular vessels and a red background, mimicking melanoma.
- Rare eclipse nevi with disrupted peripheral pigmentation or stellate streaks may raise concern.
- Rare Unna nevi with polymorphous vessels or atypical pigmentation patterns may cause diagnostic uncertainty.
- The wobble sign, clinical context, and lack of melanoma-specific criteria (atypical network, blue-whitish veil, regression structures) help distinguish IDN from melanoma.
IDN Mimicking Seborrheic Keratosis
- The keratin-filled sulci of Unna nevi can closely resemble the comedo-like openings characteristic of seborrheic keratosis.
- Additional SK features (milia-like cysts, sharp demarcation, "stuck-on" appearance) help differentiate.
4.6 Management Considerations
| Scenario | Recommended Action |
|---|---|
| Typical eclipse nevus | No excision needed; observation |
| Irregular eclipse nevus | Digital dermoscopic monitoring |
| Typical Miescher nevus | Observation; no excision required |
| Typical Unna nevus | Observation; no excision required |
| IDN with atypical features (irregular vessels, asymmetry) | Excision or close digital follow-up |
| Irritated/traumatized Unna nevus | Clinical correlation; consider short-term follow-up after trauma resolution |
| Diagnostic uncertainty vs. melanoma or BCC | Excision for histopathological examination |
Key Takeaways
- Intradermal nevi must be differentiated from amelanotic melanoma, BCC, and neurofibroma; the presence of comma vessels and cobblestone pattern strongly favors intradermal nevus.
- Excision is warranted for any intradermal nevus showing blue-white veil, polymorphous vessels, shiny white lines, or progressive asymmetric growth.
- In elderly patients, a new or changing dome-shaped nodule should not be assumed to be an intradermal nevus without careful dermoscopic evaluation for BCC or melanoma features.
5. IDN Pattern Reference Table
| Dermoscopic Feature | Eclipse Nevus | Miescher Nevus | Unna Nevus |
|---|---|---|---|
| Cobblestone pattern | + (center) | - | ++ |
| Homogeneous pattern | + (periphery) | ++ | + |
| Globular pattern | - | - | + |
| Reticular pattern | + (periphery) | - | - |
| Comma vessels | + | ++ | ++ |
| Serpentine vessels | - | + | - |
| Arborizing vessels | - | + | - |
| Dotted vessels | - | - | +/- |
| Golden brown halo | - | + | - |
| Papillomatous surface | + (center) | - | ++ |
| Keratin-filled sulci | - | - | + |
| Central hyperpigmentation | - | +/- | + (older patients) |
| Terminal hairs | - | + | - |
| Stellate peripheral rim | +/- | - | - |
Key: ++ = characteristic/frequent; + = present; +/- = occasionally; - = absent/rare
6. IDN vs. Nodular Melanoma Differential Table
| Feature | Intradermal Nevus | Nodular Melanoma |
|---|---|---|
| Growth history | Stable over years | Rapid growth (weeks to months) |
| Symmetry | Symmetric | Often asymmetric |
| Color | Light brown, tan, skin-colored (uniform) | Blue-black, multicolored, or amelanotic |
| Vessels | Comma/curved vessels (monomorphous) | Polymorphous vessels (dotted, linear-irregular, milky-red) |
| Surface | Smooth (Miescher) or papillomatous (Unna) | Ulceration common |
| Blue-whitish veil | Absent | May be present |
| Regression structures | Absent | May be present (white scar-like, peppering) |
| Wobble sign | Positive (wobbles) | Not described as characteristic |
| Dermoscopic pattern | Homogeneous, cobblestone, globular | Structureless blue-black, atypical pattern |
| Golden brown halo | Present (Miescher) | Absent |
| Comedo-like openings | May be present (Unna) | Absent |
| Comma vessels | Stereotypic | Absent |
| Terminal hairs | May be present (Miescher) | Absent |
| Patient age | Any age; stable | Typically older adults; de novo |
7. Clinical Pearls
The comma vessel is your friend. Comma-shaped (curved) vessels are the single most characteristic vascular pattern of IDN. Their presence in an elevated lesion strongly supports a benign intradermal nevus.
Face = Miescher, Trunk = Unna. When encountering a dome-shaped papule on the face, think Miescher nevus first. When seeing a papillomatous papule on the trunk, think Unna nevus.
The golden brown halo differentiates Miescher from BCC. A warm golden-brown halo surrounding a dome-shaped facial lesion favors Miescher nevus over basal cell carcinoma, which lacks this feature.
Use the wobble sign. Press the dermatoscope horizontally against the lesion in a back-and-forth motion. IDN will wobble due to their dermal component; flat lesions without a dermal component will slide.
Keratin sulci are not comedo-like openings. The keratin-filled invaginations of Unna nevi can mimic the comedo-like openings of seborrheic keratosis. Look for additional SK features (milia-like cysts, fissures and ridges, sharp demarcation) before diagnosing SK.
Traumatized does not mean malignant. Irritated Unna nevi can develop irregular vessels and red backgrounds that mimic melanoma. Always ask about trauma history (shaving, clothing friction, scratching) before deciding on excision.
Eclipse nevi on children's scalps are benign. Eclipse nevi, especially on the scalp in children, are benign and do not require biopsy. They may evolve into pure intradermal nevi over time.
Miescher nevi have essentially zero melanoma risk. There are no reported cases of melanoma arising in a Miescher nevus, making it one of the safest nevus subtypes.
One-third of Caucasians have an Unna nevus. They are exceedingly common, and familiarity with their dermoscopic patterns prevents unnecessary excisions.
Polymorphous vessels break the IDN pattern. If the vascular pattern is not monomorphous comma vessels but instead shows polymorphous or linear-irregular vessels, reconsider the diagnosis and evaluate for melanoma or BCC.
Clinical Vignettes
Clinical Scenario A 40-year-old woman presents with a 5 mm dome-shaped, smooth, skin-colored papule on the tip of the nose. She reports it has been present for over 10 years without change. Dermoscopy reveals a homogeneous pattern with different shades of light brown blending into the background skin color. Comma-shaped (curved) vessels are scattered across the surface. A subtle golden-brown halo surrounds the lesion base. No blue-gray structures, ulceration, or arborizing vessels are visible.
What is the most likely diagnosis?
Diagnosis: Miescher nevus (facial intradermal nevus).
This is a classic Miescher nevus presentation. The facial location with dome-shaped morphology is characteristic (Clinical Pearl 2: Face = Miescher). The comma-shaped vessels are the signature vascular pattern of intradermal nevi (Clinical Pearl 1). The golden-brown halo surrounding the lesion differentiates this from BCC, which lacks this warm-toned peripheral hue (Clinical Pearl 3). The long history of stability (>10 years) and Miescher nevi having essentially zero melanoma risk (Clinical Pearl 8) are additional reassuring factors. No biopsy is needed.
Clinical Scenario A 55-year-old man presents with a 9 mm soft, papillomatous, pedunculated papule on the upper back. He is concerned about possible skin cancer. Dermoscopy reveals a papillomatous surface with keratin-filled invaginations and sulci. Comma-shaped vessels are visible between the papillae. The overall color is tan with focal light brown areas. No milia-like cysts, fissures and ridges, or sharp demarcation is seen.
What is the most likely diagnosis?
Diagnosis: Unna nevus (truncal intradermal nevus).
The trunk location with papillomatous morphology is classic for Unna nevus (Clinical Pearl 2: Trunk = Unna). The keratin-filled sulci can mimic comedo-like openings of seborrheic keratosis, but the absence of additional SK features (milia-like cysts, fissures and ridges, sharp demarcation) helps distinguish them (Clinical Pearl 5). The monomorphous comma vessels confirm the intradermal nevus diagnosis. Approximately one-third of Caucasians have an Unna nevus (Clinical Pearl 9), making this an exceedingly common lesion. Familiarity with the pattern prevents unnecessary excisions.
Clinical Scenario A 62-year-old woman presents with a 7 mm elevated, slightly pink papule on the right shoulder. She reports recent trauma from a bra strap. Dermoscopy reveals an irregular pattern with a reddish background, prominent linear and dotted vessels, and focal areas of hemorrhagic crusting. No comma vessels, pigment network, or blue-gray structures are visible. The wobble sign is positive (the lesion wobbles with lateral pressure).
What is the most likely diagnosis?
Diagnosis: Traumatized (irritated) Unna nevus -- clinical context is critical.
This case illustrates Clinical Pearl 6: irritated Unna nevi can develop irregular vessels and red backgrounds that mimic melanoma. The history of mechanical trauma from clothing friction explains the atypical dermoscopic features. The positive wobble sign (Clinical Pearl 4) confirms a dermal component consistent with intradermal nevus. However, the absence of monomorphous comma vessels and the presence of irregular/polymorphous vessels (Clinical Pearl 10) means the diagnosis cannot be made with certainty by dermoscopy alone. The prudent approach is to ask about trauma history, allow 2-4 weeks for inflammation to resolve, and re-examine. If the atypical features persist after the traumatic stimulus is removed, biopsy is warranted to exclude amelanotic melanoma or other malignancy.
9. Cross-References
| Topic | Reference |
|---|---|
| Introduction to IDN and classification | Chapter 7c, p. 157 |
| Eclipse nevus (clinical and dermoscopy) | Chapter 7c, pp. 157-158; |
| Miescher nevus (clinical features) | Chapter 7c, pp. 157-158; |
| Miescher nevus (dermoscopy, golden brown halo) | Chapter 7c, pp. 157-160; |
| Unna nevus (clinical features) | Chapter 7c, pp. 158-159; |
| Unna nevus (cobblestone pattern) | Chapter 7c, p. 159; |
| Unna nevus (smooth surface variants) | |
| Unna nevus (central hyperpigmentation) | |
| Unna nevus (vessel patterns) | Chapter 7c, pp. 159-162; |
| Traumatized Unna nevus | |
| Keratin plugs and comma vessels | |
| Wobble sign | Chapter 7c, p. 162; |
| Summary and stereotypic IDN | Chapter 7c, p. 163; |
| Anatomical distribution of Miescher nevi | Sanchez Yus et al. — Ref. 7, Chapter 7c |
| Embryogenetic hypothesis | Fernandez-Flores et al. — Ref. 8, Chapter 7c |
10. Related Modules
| Module | Relationship |
|---|---|
| Module 01: Introduction and Principles of Dermoscopy | Prerequisite -- equipment use, polarized vs. nonpolarized dermoscopy |
| Module 02: Histopathologic Correlations | Prerequisite -- understanding dermoscopic-pathologic correlations for vessels, colors, and patterns |
| Module 16: Acquired Melanocytic Nevi | Prerequisite -- general nevus patterns (reticular, globular, homogeneous), nevus evolution, atypical nevi |
| Module 15: Congenital Melanocytic Nevi | Related -- shares cobblestone pattern and perifollicular hypopigmentation features |
| Module 18: Blue Nevi and Variants | Follow-up -- combined nevi (blue nevus + IDN), structureless blue pattern differential |
| Module 09: Basal Cell Carcinoma | Cross-reference -- differential diagnosis for Miescher nevus (arborizing vessels, dome-shaped lesion on face) |
| Module 12: Solar Lentigines, SK, and LPLK | Cross-reference -- comedo-like openings differential (Unna nevus keratin sulci vs. SK) |
| Module 22: Nodular Melanoma | Cross-reference -- critical differential diagnosis for elevated IDN (polymorphous vessels, blue-black color, ulceration) |
| Module 13: Vascular Lesions | Cross-reference -- vascular pattern analysis and vessel morphology classification |
Module 17 v1.0 -- Dermoscopy Educational Course Supplement Part of the Dermoscopy Educational Course.