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First step:
Diagnostic Algorithm for Differentiating
Melanocytic from Non-Melanocytic Lesions
[Modified according to Kreusch, Stolz, and Menzies]


  Criteria for melanocytic lesion

- Pigment network - pseudonetwork (See exception 1)
- Aggregated globules (not multiple blue-gray globules)
- Branched streaks
- Homogeneus blue pigmentation
(See exception 2)
- Parallel pattern (on palms/soles and mucosal areas)


  Criteria for seborrheic keratosis

- Multiple milia-like cysts
- Comedo-like openings
(irregular crypts)
- Light-brown fingerprint-like structures
- Fissures/ridges
(brain-like appearance)


  Criteria for basal cell carcinoma

- Absent pigment network AND one of:
- Arborizing vessels
- Leaf-like areas
- Large blue-gray ovoid nests
- Multiple blue-gray globules
- Spoke wheel areas
- Ulceration
(See exception 3)


  Criteria for vascular lesion

- Red-blue lacunas
- Red-bluish to red-black homogeneus areas


  None of the listed criteria


Exception 1:

Pigment network or pseudo-network is also present in solar lentigo and seborrheic keratosis. A delicate, annular pigment network is commonly seen also in dermatofibroma (clue for diagnosis of dermatofibroma: central white patch).
Exception 2:

Homogeneous blue pigmentation (dermoscopic hallmark of blue nevus) is also seen (uncommonly) in some hemangiomas and basal cell carcinomas and (commonly) in intradermal melanoma metastases.
Exception 3:

Ulceration is also seen less commonly in invasive melanoma.


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