Fat fingers

Typical presentation of a seborrheic keratosis with network like structures and fat fingers.

In this case there are no other signs of seborrheic keratosis (milia-like cysts, comedo-like openings, fingerprint-like structures, hairpin blood vessels)

Collision tumor

A 57-year-old man consulted for a bi-coloured lesion on his back.



Dermoscopy revealed a typical reticular pattern and some brown globules (red circle) in favor of a melanocytic nevus and a lighter brown pigmentation (green circle) without pigment network. Delicate fat fingers were present on this part in favor of a seborrheic keratosis.

The lesion was excised and pathology confirmed the diagnosis of collision tumor which associated a seborrheic keratosis and a melanocytic compound nevus.

A collision tumor is defined as a side-by-side occurence of two tumors (benign or malignant). For example: confluence of a seborrheic keratosis and a basal cell carcinoma, confluence of a melanoma and a BCC, confluence of an angioma and a Clark nevus.

Fat fingers

A 53-year-old woman consulted for this pigmented lesion on her back.
Dermoscopy revealed brown structures typical of fat fingers, in favor of a seborrheic keratosis.
Fat fingers are an important dermoscopic sign to know for diagnosing seborrheic keratosis in absence of other typical signs (milia-like kysts, comedo-like structures, fingerprint-like structures, sharp margins, hairpin blood vessels)

Kopf and al, "Fat fingers", a clue in the dermoscopic diagnosis of seborrheic keratoses J Am Acad Dermatol
2006;55:1089-91