Actinic keratosis (AK), squamous cell carcinoma in situ (SCCis/Bowen disease), and invasive squamous cell carcinoma (SCC) exist along a spectrum of keratinocytic atypia and share many dermoscopic features.
Across this spectrum, important findings include a central mass of keratin, abnormal vascular structures, white circles, rosettes, and pigmented structures.
There are 3 main vessel types seen in SCCs: dotted, glomerular and hairpin.
Small red dots
May be present in clusters or diffusely
Commonly seen in SCC and SCC in situ
The difference between SCC and SCCIS is usually clinically (when you palpate SCC, it will have more substance to it)
Dotted vessels are not specific for SCC and may also be seen in:
Porokeratosis
Clear cell acanthoma
Prurigo nodularis
Dermatofibroma
Spitz nevi
Pink/hypomelanotic melanoma
Psoriasis
Lichen simplex chronicus
Impetigo
Tightly coiled vessels resembling renal glomeruli
May occur individually or in clusters
Linear parallel vessels form a single loop (U-shaped)
May occasionally have a white halo surrounding them
Usually seen at the periphery (especially when there’s a central keratin plug)
Multi-looped tortuous vessels
Less common but can be seen
Differential for looped vessels: KA/SCC, SK, melanoma, BCC
There is a lot of clinical overlap between SCC’s and irritated SK’s and may be hard to tease out. Typically, in a SCC, you will see dotted vessels, branched linear vessels, white circles, peripherally arranged vessels and central scale. Diffusely arranged hairpin vessels can also be seen in an irritated SK but the presence of milia-like cysts and comedo-like openings will be more helpful in the diagnosis of an irritated SK.8
White Circles
White circles are an important dermoscopic clue for SCC and keratoacanthoma.
Bright white circles surrounding follicular openings
Highly specific for SCC and keratoacanthoma
May contain a central yellow-orange keratin plug
White circle
Acanthosis and hypergranulosis of the infundibular epithelium
Yellow-orange keratin plug
Dilated follicular infundibulum filled with keratin
Clinical Pearl:
The combination of a bright white circle surrounding a yellow-orange keratin plug is a particularly useful clue to a keratinizing squamous proliferation.
Four bright white dots arranged in a square or four-leaf-clover configuration
Seen with polarized dermoscopy
Thought to result from the interaction of polarized light with keratin-filled adnexal openings
May be numerous and diffusely distributed
Rosettes may be seen in:
Actinic keratosis
Squamous cell carcinoma
Chronically sun-damaged skin
Other keratinizing lesions
Clinical Pearl:
Rosettes support the presence of keratinization and actinic damage, but are not specific for SCC.
White to yellow and flaky
Correlates histologically to hyperkeratosis and parakeratosis
Vs crust which is yellow/orange, dried serum or blood
Diffusely distributed brown circles
May be particularly prominent in pigmented SCC in situ (pigmented Bowen disease)
May demonstrate a radial arrangement
Can occur alongside brown circles in pigmented Bowen disease
Clinical Pearl:
Pigmented Bowen disease can mimic a melanocytic lesion. Recognition of brown circles/dots together with characteristic vascular and keratinizing structures (scale/crust) can help suggest a keratinocytic origin.
Dermoscopic findings may evolve as a keratinocytic lesion progresses from actinic keratosis → SCC in situ → invasive SCC.
Look for:
Rosettes
Keratin-associated structures
Background features of chronic sun damage
Look for:
Dotted vessels
Glomerular vessels
Brown circles
Radially arranged brown dots
Keratinization
Rosettes
Pigmented lesions may demonstrate prominent brown circles and brown dots.
Look for:
White circles
Yellow-orange keratin plugs
Prominent keratinization
Hairpin vessels
Twisted loop vessels
Other polymorphous vascular structures
When evaluating a lesion along the AK–SCC spectrum, look for a combination of:
Keratin
Dotted vessels
Glomerular vessels
Hairpin vessels
Twisted loop vessels
White circles
Yellow-orange keratin plugs
Rosettes
Brown circles and radially arranged brown dots, particularly in pigmented Bowen disease
The combination of keratinization + abnormal vascular structures is an important clue to a squamous proliferation.