Melanoma Subtypes: Nodular, Amelanotic, Spitzoid

01Nodular melanoma represents 10-15% of all melanomas but a disproportionate fraction of melanoma deaths. The tumor is biologically distinct: rapid vertical growth from the outset, minimal radial-growth phase, and minimal junctional component. Hypothesized origin from dermal melanocytes (versus dermoepidermal junction for SSM) explains why most SSM dermoscopic criteria (atypical network, irregular dots, streaks, regression) are absent. Diagnosis depends on three rules: blue-black coloration, atypical vascular pattern, and milky-red coloration.

02The blue-black rule (Argenziano 2011) flags pigmented nodular melanoma. Simultaneous presence of blue and black color within a single nodular lesion, in the absence of clear comedo-like openings (seborrheic keratosis), milia-like cysts, or vascular lacunas (hemangioma), is highly suggestive of pigmented nodular melanoma. The blue-black rule is simple, has high specificity, and works without requiring full pattern analysis on a tumor that lacks classical pattern features.

03Atypical vascular pattern in nodular melanoma includes linear-irregular vessels (vessels with multiple kinks, sometimes called arborizing-irregular), corkscrew vessels (looped vessels twisted around an axis), and the simultaneous presence of more than two morphological vessel types. Vessels are best evaluated under polarized light with light contact (heavy compression empties vessels and gives false-negative results). Polymorphic vessels in a solitary nodular lesion warrant excision regardless of pigment status.

04Milky-red coloration appears as structureless pink-red zones within a nodular lesion. It corresponds to a dense vascular network in the upper dermis with overlying epidermal acanthosis. Milky-red areas commonly coexist with atypical vessels and signal vertical-growth phase tumors. In purely amelanotic nodular melanoma, milky-red plus polymorphic vessels plus white shiny structures may be the only diagnostic clues.

05Amelanotic and hypomelanotic melanoma lacks pigment-based criteria. The tumor accounts for roughly 10% of melanomas and a disproportionate share of missed diagnoses because pigment is the visual signal most clinicians use. Diagnosis depends on vessel morphology: polymorphic vessels (more than one type in a lesion), milky-red structureless areas, white shiny structures (chrysalis under polarization), and residual subtle pink-red coloration. A pink papule or nodule with polymorphic vessels in any adult should be excised even without pigment.

06The Menzies study of amelanotic and hypomelanotic melanoma (Arch Dermatol 2008) identified pink color, residual scattered brown globules, milky-red areas, and polymorphic vessels as the most discriminatory features versus benign vascular tumors. The classic teaching is that pink lesions in adults need a closer look than brown ones; the dermoscopic threshold for amelanotic melanoma is intentionally lower because the consequences of missing it are higher.

07Spitzoid melanoma versus Spitz nevus is one of the hardest dermoscopic discriminations. Symmetric starburst pattern, peripheral pigmented streaks, and homogeneous coloration favor Spitz/Reed nevus in children and young adults. Asymmetric starburst, irregular streaks, multicomponent pattern, and atypical vessels favor melanoma. Patient age is the strongest single discriminator: spitzoid lesions in patients over 12 years carry significant melanoma risk and most experts recommend excision of any spitzoid pattern in adults regardless of dermoscopic appearance.

08Argenziano's pitfalls study showed that melanoma can rarely exhibit a starburst pattern, making symmetric starburst in adults a non-trivial differential. The International Dermoscopy Society 2017 guideline recommends excision of any flat pigmented spitzoid lesion in patients aged 12 years or older, while management of palpable spitzoid lesions in younger children can be observation. The threshold reflects the rarity of true spitzoid melanoma in young children versus its real occurrence in adults.

09Animal-print pattern (irregular reticular pattern with thick, broken, network lines and asymmetric dark hyperpigmented zones) describes a melanoma variant where atypical broadened network with abrupt color and density transitions creates a leopard-skin appearance. The pattern overlaps with multicomponent SSM and dysplastic-pattern melanomas. It is most often described in slow-growing melanomas on the trunk and is occasionally mistaken for atypical Clark nevi. Asymmetric overall configuration plus the abrupt transitions typical of animal-print pattern signal melanoma.