A 60-year-old man consulted for this black-blue tumor on his back.

Patient did not know when this lesion appeared.

Dermoscopy revealed a homogenous blue pattern with whiter areas.

Two diagnosis were suspected:

- blue nevus

- melanoma

This lesion was excised and pathology revealed a blue nevus with fibrous involution

Blue lesion on a leg

A 58-year-old woman consulted for a pigmented lesion on her right leg present for many years.

NB: a scar is due to a former fracture.

Dermoscopy revealed an homogeneous blue pattern in favor of a benign blue nevus.

Symmetric blotch

Fig 1 Blotch

A blotch (fig 1)  is a dark-brown or black structure-less area where other dermoscopic features cannot be seen. Symmetric blotches are in favour of benign lesions. Assymetrically distributed blotches are in favour of melanomas.

In our case, the blotch was symmetrically disposed and a peripheral reticular network was visible. This kind of blotch is also called black lamella.

This lesion was corresponding to a benign melanocytic nevus.

It has to be distinguished from the blue structure-less pattern or blue homogeneous pattern of a blue nevus (fig 2).

Fig 2 Blue homogeneous pattern

Homogeneous blue pattern

A 65-year-old man presented 6 blue lesions located on his trunk. Dermoscopy revealed a blue structure-less pattern (homogeneous blue pattern).
This patient had been treated 10 years before for a leukaemia. These blue lesions with blue homogeneous patterns not well demarcated corresponded to radiotherapy tattoos.

Radiotherapy tattoo

Radiotherapy tattoo

The main other cause of blue homogeneous pattern is blue nevus.
Here are above two examples of blue nevi.

Blue nevus

Blue nevus

Blue nevus

A 43-year-old woman consulted for a dark bue lesion on her left buttock.

Dermoscopy revealed an homogeneous pattern made of bluish to white-blue structureless pigmentation, in favor of a blue nevus.

Blue nevus

A 24-year-old man presented a dark blue lesion on her right arm. Pathology revealed a blue nevus.
Dermoscopy revealed a blue pigmentation and an area of brown pigmentation and dots.
Blue nevi do not have systematically a blue homogeneous pattern and in some cases dermoscopy reveal islands of depigmentation or areas of brown pigmentation.

Blue nevus

Some blue nevi can present areas of depigmentation.

Polychromous blue nevus

A 37-year-old woman consulted for a pigmented lesion on her left leg. The lesion was excised and pathology revealed a blue nevus.
Blue nevi are typically described as tumors showing steel-blue pigmentation with an homogeneous or structureless pattern. In fact blue nevi are not always blue on dermoscopy and these nevi have sometimes areas of discoloration, some of them can be tan (brown blue nevi) or variegated (polychromous blue nevi)

Blue nevus

A 32-year-old woman consulted for this blue lesion on her nose.
Dermoscopy revealed an homogeneous blue pattern in favor of a blue nevus.

Blue nevus

A 34-year-old woman consulted for a dark blue lesion on her left ankle. The lesion was not enlarging for many years.

Dermoscopy revealed a blue homogenous pattern with hypopigmented area.

The lesion was removed and pathology confirmed the diagnosis of blue nevus.