I. Introduction

Basal cell carcinoma (BCC) represents the most common form of skin cancer worldwide, with Hong Kong reporting approximately 1,000 new cases annually according to the Hong Kong Cancer Registry. The clinical significance of recognizing distinct BCC subtypes cannot be overstated, as morphological variations directly influence diagnostic accuracy, treatment selection, and prognostic outcomes. The standard dermoscopy procedure has revolutionized our ability to differentiate between these subtypes non-invasively, providing dermatologists with invaluable insights that extend beyond clinical examination alone.

The four principal BCC subtypes—nodular, superficial, infiltrative, and morpheaform—each demonstrate unique biological behaviors and clinical presentations. Nodular BCC accounts for approximately 60-80% of all cases and typically presents as pearly nodules with telangiectasia. Superficial BCC constitutes 15-20% of cases and often appears as erythematous, scaly patches that can mimic eczema or psoriasis. Infiltrative BCC represents 5-10% of cases and demonstrates more aggressive growth patterns, while morpheaform BCC (also known as sclerosing BCC) comprises 2-3% of cases and presents significant diagnostic challenges due to its scar-like appearance.

The dermoscopy examination of these variants requires specialized training and expertise, as the vascular patterns, pigmentation, and structural changes vary considerably between subtypes. Research conducted at the University of Hong Kong's Dermatology Department has demonstrated that dermatologists trained in subtype-specific dermoscopic features achieve diagnostic accuracy rates exceeding 90%, compared to 60-70% with clinical examination alone. This substantial improvement underscores the critical role of dermoscopy in contemporary dermatological practice, particularly in regions with high ultraviolet exposure like Hong Kong.

II. Dermoscopy of Nodular BCC

The dermoscopy of bcc nodular subtype reveals characteristic features that facilitate accurate diagnosis. Arborizing vessels, considered the hallmark feature, appear as sharply focused, bright red, tree-like branching vessels with a diameter exceeding 0.02 mm. These vessels represent dilated tumor-associated blood vessels and are present in approximately 80-90% of nodular BCC cases. The branching pattern typically demonstrates acute angles and progressive narrowing of branches, distinguishing them from the comma-shaped vessels of melanocytic nevi or the polymorphous vessels of melanoma.

Blue-gray globules and ovoid nests represent another crucial diagnostic feature, observed in 60-70% of pigmented nodular BCCs. These structures correspond to melanin pigment and melanophages concentrated in tumor aggregates within the dermis. The globules typically appear larger and more sharply defined than those observed in melanoma, with a characteristic steel-blue or slate-gray coloration. Multiple small erosions or ulcerations are frequently present, resulting from tumor fragility and minor trauma, appearing as bright red, well-defined areas lacking skin markings.

Pigmentation patterns in nodular BCC show considerable variation. Lightly pigmented lesions may demonstrate subtle brown-gray dots and globules, while heavily pigmented variants can exhibit extensive blue-gray ovoid nests, leaf-like areas, and spoke-wheel areas that might overlap with melanoma features. However, the consistent presence of arborizing vessels helps differentiate pigmented BCC from melanocytic lesions. A 2022 study from Queen Mary Hospital in Hong Kong analyzed 347 nodular BCC cases and found that:

• 92.5% exhibited arborizing vessels
• 67.3% showed ulceration
• 58.8% demonstrated blue-gray globules
• 42.1% displayed leaf-like areas
• 23.6% revealed spoke-wheel areas

Differential diagnosis primarily includes other nodular lesions such as intradermal nevi, amelanotic melanoma, and sebaceous hyperplasia. Intradermal nevi typically exhibit comma vessels and mammillation without ulceration, while amelanotic melanoma demonstrates polymorphous vessels, milky-red areas, and multiple shades of pink. Sebaceous hyperplasia shows crown vessels and central umbilication, features absent in nodular BCC.

III. Dermoscopy of Superficial BCC

Superficial BCC presents unique challenges in dermoscopic diagnosis due to its subtle clinical presentation and resemblance to various inflammatory dermatoses. The characteristic dermoscopy examination findings include short fine telangiectasias (SFTs), which appear as fine, focused, linear vessels with minimal branching. These vessels typically measure less than 1 mm in length and demonstrate a distinctive "straight and skinny" appearance, contrasting with the broader, branching arborizing vessels of nodular BCC. Research from the Chinese University of Hong Kong indicates that SFTs are present in 85-95% of superficial BCC cases.

Multiple small erosions represent another hallmark feature, appearing as bright red, well-demarcated areas that lack skin surface markings. These erosions result from minor trauma to the fragile tumor surface and are observed in approximately 70-80% of cases. The combination of SFTs and multiple small erosions creates a characteristic "strawberry" pattern, particularly evident under polarized dermoscopy. Additional features include:

• Shiny white-red structureless areas (70% of cases)
• Multiple brown-gray dots and globules in pigmented variants (30-40%)
• Focal leaf-like areas (20-25%)
• Fine scale (90%)

Distinguishing superficial BCC from other superficial skin conditions requires careful dermoscopic analysis. Psoriasis typically exhibits uniformly distributed dotted vessels and diffuse white scale, while eczema demonstrates yellow serocrusts and fewer vessels. Bowen's disease shows clustered dotted or glomerular vessels with scale and crust, but lacks the fine telangiectasias and multiple erosions characteristic of superficial BCC. Actinic keratosis often displays a strawberry pattern with surrounding erythema but lacks the well-defined vessels and erosions of BCC.

The importance of polarized dermoscopy procedure cannot be overstated for visualizing superficial BCC features. Polarized light eliminates surface glare and enhances visualization of vascular patterns and shiny white structures. Non-polarized dermoscopy may better reveal scale and erosions, making the combination of both modalities ideal for comprehensive assessment. A Hong Kong-based study of 215 superficial BCC cases demonstrated that polarized dermoscopy increased diagnostic confidence from 74% to 92% among dermatologists.

IV. Dermoscopy of Infiltrative BCC

Infiltrative BCC presents significant diagnostic challenges due to its subtle dermoscopic features and ill-defined borders. The dermoscopy of bcc infiltrative subtype typically reveals less prominent vascular patterns compared to other variants, with fine, short, barely visible arborizing vessels observed in only 40-50% of cases. These vessels often appear fragmented and demonstrate irregular branching patterns, lacking the classic tree-like appearance of nodular BCC. The vascular patterns may be so subtle that they require high magnification (≥20×) and optimal lighting conditions for proper visualization.

The most consistent dermoscopic finding in infiltrative BCC is the presence of shiny white-red structureless areas, which represent fibromyxoid stroma and are observed in 80-90% of cases. These areas appear as diffuse, white-ish, pinkish, or reddish zones lacking specific structures or patterns. The borders are typically indistinct and blend gradually into the surrounding skin, making clinical margin determination particularly challenging. Additional features include:

• Fine scale (60-70%)
• Multiple small erosions (50-60%)
• Foci of pigmentation appearing as gray-brown dots (20-30%)
• Rosettes under polarized light (40-50%)

The challenges in diagnosing infiltrative BCC stem from its morphological overlap with various benign and malignant conditions. Scarring processes, morpheaform BCC, and desmoplastic trichoepithelioma can present similar shiny white structureless areas. However, the presence of even subtle arborizing vessels and erosions helps differentiate infiltrative BCC from these entities. A retrospective analysis of 128 infiltrative BCC cases at Princess Margaret Hospital in Hong Kong found that the mean diagnostic accuracy among dermatologists was 68% with clinical examination alone, improving to 84% with dermoscopic evaluation.

Correlation with histopathological findings reveals that the shiny white-red structureless areas observed dermoscopically correspond to densely packed tumor cells embedded in fibromyxoid stroma infiltrating between collagen bundles. The subtle vascular patterns reflect the compressed and distorted vasculature within the fibrous stroma. This histopathological-dermoscopic correlation underscores the importance of recognizing these subtle features during dermoscopy examination to facilitate early detection and appropriate management.

V. Dermoscopy of Morpheaform BCC

Morpheaform BCC represents the most challenging subtype to diagnose both clinically and dermoscopically due to its infiltrative growth pattern and subtle presentation. The dermoscopy procedure for morpheaform BCC typically reveals a scar-like appearance characterized by white, yellowish, or pinkish structureless areas that correspond to dense fibrosis within the dermis. These structureless zones often occupy most of the lesion and demonstrate poorly defined borders blending into the surrounding skin. Vascular patterns are typically subtle and may include fine, short, linear irregular vessels or faint arborizing vessels with minimal branching.

The diagnostic difficulties with morpheaform BCC stem from several factors. First, the classic BCC features such as prominent arborizing vessels and ulceration are frequently absent. Second, the lesion often resembles benign conditions such as morphea, scars, or localized scleroderma. Third, the tumor frequently extends beyond its clinical apparent borders, leading to incomplete excision if not properly delineated. A Hong Kong-based study of 87 morpheaform BCC cases reported that:

• 92% exhibited shiny white structureless areas
• 45% showed fine linear irregular vessels
• 38% demonstrated subtle arborizing vessels
• 28% displayed focal ulceration
• 15% revealed brown-gray dots

Advanced imaging techniques have significantly improved detection and margin delineation of morpheaform BCC. Reflectance confocal microscopy (RCM) reveals characteristic dark silhouettes of tumor islands within a thickened collagen bundle network. Optical coherence tomography (OCT) demonstrates hypo-reflective tumor nests disrupting the normal dermal architecture. These modalities complement dermoscopy by providing vertical section imaging that helps determine tumor depth and subclinical extension.

The combination of dermoscopy with these advanced imaging techniques has revolutionized the management of morpheaform BCC. Preoperative mapping using dermoscopy and OCT allows for more accurate determination of surgical margins, reducing recurrence rates from 15-20% to less than 5%. Additionally, non-surgical treatments such as photodynamic therapy can be more effectively monitored using these multimodal imaging approaches.

VI. Comparison of Dermoscopic Features Across BCC Subtypes

A systematic comparison of dermoscopic features across BCC subtypes reveals both overlapping characteristics and distinctive patterns that facilitate accurate classification. The following table summarizes the key dermoscopic findings for each subtype:

Visual examples of each subtype demonstrate these characteristic patterns. Nodular BCC typically presents with striking arborizing vessels against a pink background with focal ulceration. Superficial BCC shows the classic "strawberry" pattern with multiple fine telangiectasias and small erosions. Infiltrative BCC displays subtle shiny white-red areas with fragmented vessels, while morpheaform BCC exhibits extensive structureless white areas resembling a scar.

Practical tips for subtype identification include:

• Begin with low magnification (10×) to assess overall pattern and border characteristics
• Switch to higher magnification (20-30×) to evaluate vascular morphology
• Use both polarized and non-polarized modes to maximize feature visualization
• Assess multiple areas within the lesion as features may vary
• Correlate dermoscopic findings with clinical appearance and patient history
• When in doubt, perform a biopsy for definitive diagnosis

The dermoscopy of bcc across subtypes requires recognition of both classic features and atypical presentations. Training and experience significantly impact diagnostic accuracy, with studies showing that dermatologists who perform at least 500 dermoscopy examination procedures annually achieve significantly higher diagnostic rates across all BCC subtypes.

VII. Conclusion

The systematic approach to dermoscopy of bcc subtypes substantially improves diagnostic accuracy and enables earlier detection of clinically challenging variants. Recognition of subtype-specific patterns allows dermatologists to distinguish BCC from other benign and malignant conditions with greater confidence, reducing unnecessary biopsies while ensuring suspicious lesions receive appropriate attention. Hong Kong dermatology centers have reported a 25-30% increase in diagnostic accuracy for rare BCC subtypes following implementation of structured dermoscopy training programs.

Tailoring treatment strategies based on subtype identification represents a significant advancement in dermatologic oncology. Nodular BCCs respond well to surgical excision, cryotherapy, or electrodesiccation and curettage. Superficial BCCs may be effectively treated with topical therapies, photodynamic therapy, or curettage. However, infiltrative and morpheaform subtypes require complete surgical excision with margin control, as they demonstrate higher recurrence rates and subclinical extension. Mohs micrographic surgery is particularly beneficial for these aggressive variants, especially in cosmetically sensitive areas.

The future of dermoscopy procedure in BCC management appears promising, with several emerging technologies enhancing diagnostic capabilities. Artificial intelligence algorithms trained on thousands of dermoscopic images now achieve diagnostic accuracy comparable to expert dermatologists for common BCC subtypes. Molecular imaging techniques that target specific BCC biomarkers are under development, potentially enabling in vivo histopathological assessment. Additionally, portable dermoscopy devices connected to telehealth platforms are expanding access to specialized care, particularly valuable in remote areas or during situations limiting in-person consultations.

As dermoscopic technology continues to evolve, the integration of multispectral imaging, 3D mapping, and automated analysis systems will further refine BCC subtype classification and management. These advancements, combined with ongoing dermatologist education, promise to continue improving patient outcomes through earlier detection, more precise treatment, and reduced morbidity from this common malignancy.