19.2 Dermoscopy of Non-Melanocytic Cutaneous Neoplasms

19.2 Dermoscopy of Non-Melanocytic Cutaneous Neoplasms

Overview and Diagnostic Strategy

In the Step 1 phase of the two-step dermoscopic framework, lesions lacking melanocytic features (pigment network, aggregated globules, branched streaks, homogeneous blue coloration, or parallel volar patterns) must be systematically evaluated for diagnostic signatures of non-melanocytic cutaneous neoplasms. A comprehensive mastery of non-melanocytic criteria is vital not only to avoid unnecessary surgical excisions of benign tumours such as seborrhoeic keratoses, hemangiomas, and dermatofibromas, but also to guarantee prompt identification of basal cell carcinomas and invasive keratinocyte malignancies.

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Seborrhoeic Keratosis

Seborrhoeic keratoses (SKs) represent the most frequent benign epithelial neoplasms in aging adults. Because pigmented variants may resemble malignant melanoma clinically, their characteristic dermoscopic criteria are essential for avoiding unnecessary excisions and missed melanomas.

                    SEBORRHOEIC KERATOSIS DERMOSCOPIC HALLMARKS
                    
             Milia-Like Cysts              Comedo-Like Openings (Crypts)
        (Bright white/yellow spheres)      (Crater-like brown-black plugs)
                   ○     ○                             ▼
                 ○         ○                         [ ▓ ]
             ─────────────────             ─────────────────────────
             Fissures & Ridges             Hairpin Vessels with Halo
            (Cerebriform gyri)            (Looped capillary in pale halo)
                  ╭──╮  ╭──╮                              ╭╮
                  │  │  │  │                             ( ╷ )
                  ┴──┴──┴──┴                              ╵╵

Hallmark Dermoscopic Criteria

1. Milia-Like Cysts (Horn Pseudocysts):
   • Dermoscopic Morphology: Small (0.1–1.0 mm), sharply circumscribed, round, starry, bright milky-white or pale yellowish spheres.
   • Optical Behavior: Readily visible under non-polarized contact dermoscopy (NPD) due to the sharp refractive index gradient between the dense intraepidermal keratin ball and surrounding epidermis. Under cross-polarized dermoscopy, they lose their distinct white glow and appear as faint, blurred yellowish dots.
   • Histopathology: Intraepidermal horn pseudocysts filled with concentric, laminated keratin.
2. Comedo-Like Openings (Crypts):
   • Dermoscopic Morphology: Sharply demarcated, round, oval, or irregularly shaped brown, dark brown, or black crater-like depressions, pits, or plugs.
   • Histopathology: Deep invaginations of the epidermis filled with cornified keratinous debris and oxidized melanin.
3. Fissures and Ridges ("Cerebriform" / Brain-Like Pattern):
   • Dermoscopic Morphology: Winding, curved, irregular linear crevices (fissures / sulci) separating flat-topped, elevated epidermal crests (ridges / gyri), creating an appearance reminiscent of cerebral cortex convolutions.
   • Histopathology: Marked papillomatous and hyperkeratotic acanthosis of the epidermis.
4. Hairpin Vessels Surrounded by a White Halo:
   • Dermoscopic Morphology: Looped, U-shaped capillary vessels with uniform caliber, each encased within a distinct, pale, whitish round halo.
   • Histopathology: Elongated, hairpin-like capillary loops ascending within the dermal papillae, encased by thickened, pale, acanthotic epidermal collarettes.
5. Moth-Eaten Borders:
   • Dermoscopic Morphology: Sharply demarcated, concave, curved, scalloped margins that resemble a fabric or wool garment nibbled by moths.
   • Histopathology: Abrupt transition between hyperkeratotic, acanthotic epidermal ridges and adjacent normal atrophic epidermis; typical of flat reticulated SKs and solar lentigines.
6. Fingerprint-Like Structures:
   • Delicate, light brown, parallel curved lines mimicking epidermal dermatoglyphics, characteristic of early flat seborrhoeic keratoses or solar lentigines.

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Basal Cell Carcinoma (BCC)

Basal cell carcinoma (BCC) is the most common cutaneous malignancy in Caucasian populations. The dermoscopic diagnosis of BCC is governed by a strict, validated rule: the lesion must NOT demonstrate a melanocytic pigment network (negative criterion) and must display at least one of the six classical positive criteria.

                      BASAL CELL CARCINOMA: DIAGNOSTIC CRITERIA
                                         │
                                         ▼
                  ABSENCE OF MELANOCYTIC PIGMENT NETWORK
                                         │
                  PLUS AT LEAST ONE OF SIX POSITIVE HALLMARKS:
    ┌──────────────────┬─────────────────┼──────────────────┬──────────────────┐
    ▼                  ▼                 ▼                  ▼                  ▼
Arborising       Blue-Grey         Blue-Grey          Spoke-Wheel        Maple Leaf-Like
Vessels          Ovoid Nests       Globules           Areas              Areas
(Sharp in-focus  (Large confluent  (Round discrete    (Radial projections(Bulbous brown
tree branches)   dermal masses)    micro-nests)       from central hub)  edge lobes)

The Six Classical Positive Criteria

1. Arborising (Tree-Like) Telangiectasias:
   • Morphology: Thick, bright red, prominent trunk vessels that divide sequentially into finer, sharply focused, tapering branchlets (dichotomous branching). Crucially, these vessels are in sharp optical focus, reflecting their immediate subepidermal, superficial location above basaloid tumour islands.
   • Significance: Pathognomonic for nodular BCC (positive predictive value >90%).
2. Large Blue-Grey Ovoid Nests:
   • Morphology: Large, well-defined, confluent, round-to-oval pigmented masses of blue-gray or dark slate-gray coloration, lacking connection to a network.
   • Histopathology: Large aggregates of basaloid tumour cells located in the mid-to-deep dermis, heavily laden with melanin; blue coloration results from the Tyndall scattering phenomenon.
3. Multiple Blue-Grey Globules:
   • Morphology: Clustered, distinct, round, tiny dark blue-gray or slate-gray dots and globules smaller than ovoid nests.
   • Histopathology: Small, discrete, round basaloid tumor nests in the papillary dermis.
4. Spoke-Wheel Areas:
   • Morphology: Well-circumscribed, radial, dark brown-to-blue projection lines radiating outward from a darker central hub or axis, resembling the spokes of a bicycle wheel.
   • Significance: Characteristic of superficial basal cell carcinoma and pigmented BCC.
5. Leaf-Like Areas (Maple Leaf-Like Structures):
   • Morphology: Brown, dark brown, or blue-gray bulbous, finger-like projections arranged in lobulated leaf-like arrays along the periphery of the lesion. They never connect to a pigment network.
   • Histopathology: Multifocal basaloid lobules budding horizontally from the basal layer of the epidermis into the papillary dermis; diagnostic hallmark of superficial BCC.
6. Ulceration and Multiple Small Erosions:
   • Morphology: One or more sharply punched-out craters, deep depressions, or superficial erosions covered with serosanguinous crusts, devoid of normal epidermis.

Shiny White Lines / Crystalline Structures (Chrysalis Structures)

• Morphology: Short, bright, orthogonal or intersecting shiny white linear streaks and rosettes.
• Optical Requirement: Visible strictly under cross-polarized dermoscopy. They disappear completely under non-polarized contact dermoscopy.
• Histopathology: Corresponds to stromal fibrosis, collagen bundle alteration, and compact connective tissue deposition surrounding basaloid tumour aggregates.

Dermoscopic Profiles of BCC Subtypes

• Superficial BCC: Leaf-like areas, spoke-wheel structures, multiple small erosions, shiny white blotches and strands, accompanied by fine, short, non-arborising telangiectasias.
• Nodular BCC: Prominent, thick, sharply focused arborising vessels, large blue-grey ovoid nests, deep ulceration, and shiny white lines.
• Infiltrative / Morphoeic BCC: Attenuated, sparse, fine branching vessels with few branches, porcelain-white structureless fibrotic areas, and prominent crystalline shiny white lines.

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Actinic Keratosis, Bowen Disease & Invasive Cutaneous Squamous Cell Carcinoma

Keratinocyte neoplasms reflect a biological progression from intraepidermal dysplasia to invasive malignancy, accompanied by systematic changes in vascular and follicular architecture.

                      KERATINOCYTE NEOPLASM SPECTRUM
                      
   Actinic Keratosis          Bowen Disease (In Situ)       Invasive cSCC
   (Strawberry Pattern)       (Glomerular Vessels)          (Polymorphous Vessels)
        ○   ○   ○                 §    §    §                 ╷  ( )  §
      ▒▒▒▒▒▒▒▒▒▒▒▒▒             ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒           ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒
    Red pseudonetwork +       Clustered coiled loops +    Central keratin mass +
    targetoid pale haloes     scaly yellowish surface     white halos & circles

1. Actinic Keratosis (AK)

• The Strawberry Pattern:
  • Morphology: A background of erythematous pseudonetwork (dilated interfollicular capillary networks) interspersed with prominent, yellowish-white targetoid hair follicle openings encased in a pale whitish perilesional halo.
  • Polarized Sign: Rosettes (four tiny, bright white dots clustered in a 4-leaf clover formation around follicular ostia), reflecting optical refraction at hyperkeratotic adnexal infundibula.

2. Bowen Disease (Squamous Cell Carcinoma In Situ)

• Glomerular (Coiled) Vessels:
  • Morphology: Tightly coiled, convoluted, looped capillary clusters arranged in discrete, irregular groups resembling renal glomeruli.
  • Surface Alteration: Overlaid by a scaly, yellowish-white, hyperkeratotic or crusted surface.
  • Linear / Clustered Alignment: Glomerular vessels are frequently arrayed in distinct linear tracks, loops, or clusters, distinguishing Bowen disease from inflammatory dermatoses such as plaque psoriasis (which displays uniformly distributed, non-clustered dotted vessels).

3. Invasive Cutaneous Squamous Cell Carcinoma (cSCC)

• Central Keratin Mass / Ulceration: Large, amorphous, yellowish-white or brownish crater of dense hyperkeratosis or necrotic ulceration.
• White Circles: Unpigmented, circular white outlines surrounding dilated hair follicles or keratin plugs.
• Polymorphous Vascular Pattern: Coexistence of multiple vessel morphologies: looped/hairpin vessels (each encased in a prominent white halo), linear-irregular vessels, and dotted vessels, distributed radially around the central keratin mass.

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Vascular Tumours: Hemangioma and Angiokeratoma

Vascular lesions are identified dermoscopically by the total absence of melanocytic networks and the presence of distinctive vascular pooling spaces:

• Red-Blue Lacunes (Lagoons): Multiple, round, oval, or polyhedral, sharply demarcated compartments filled with dark red, violaceous, or deep blue coloration.
• Whitish Fibrous Septa: Fine, pale, connective tissue strands separating individual vascular lacunes.
• Histopathology: Markedly dilated, thin-walled, erythrocyte-engorged ectatic vascular channels in the papillary and reticular dermis.
• Diagnostic Pitfall: Thrombosis within a hemangioma or angiokeratoma causes lacunes to turn dark purple, grayish-blue, or pitch-black, mimicking a nodular melanoma. Careful examination of the lesion periphery reveals patent, non-thrombosed red lacunes, establishing the benign vascular diagnosis.

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Dermatofibroma (Cutaneous Fibrous Histiocytoma)

Dermatofibroma (DF) is a benign mesenchymal proliferation of fibroblasts and histiocytes within the dermis.

• Classic Dermoscopic Hallmark:
  • Central White Patch: A central, structureless, ivory-white, scar-like patch, corresponding to dense, sclerotic collagen hypocellularity in the upper dermis.
  • Peripheral Pigment Network: A delicate, faint, fine, regular, light-brown pigment network at the outer margin, corresponding to epidermal basal layer hyperpigmentation over elongated, flattened rete ridges (epidermal induction).
• Physical Maneuver Correlation: The Fitzpatrick Pinch Sign (Dimple Sign)—lateral compression between thumb and index finger causes the nodule to dimple or invaginate downward into the subcutis due to fibrous dermal tethering.

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Comprehensive Non-Melanocytic Comparison Matrix