Male, pigmented nodule, skin of buttockShow diagnosis & comments
Cellular blue naevus
CELLULAR BLUE NAEVUS (ALLEN)
- Most common in gluteal region, but also occurs on dorsa of hands and feet, and other body sites
- Presents as a skin nodule or tumour, sometimes well over 1 cm in size
- Superficial parts show the picture of common blue naevus (Jadassohn-Tièche), with slender elongated cells, variably pigmented, infiltrating between de preexistent collagen and often forming some finely fibrillar collagen as well.
- Towards deeper parts, there is a transition to a densly cellular multinodular tumour, nodules bulging into the subcutis.
- This cellular part shows compact sheets of oval to elongated cells, sometines devoid of pigment, and often areas with a 'biphasic architecture', with nests of pale plump cells surrounded by dendritic pigmented naevus cells lying in a collagenous matrix
- Larger and longstanding lesions often show degenerative changes: myxoid change (sometimes leading to cystic change), hyaline thickening of vessel walls, diffuse paucicellular sclerosis, fibrin deposition, hemorrhage.
- Focal balloon cell change is not uncommon
- Mitosis are commonly found but not numerous (< 2 per 2 mm square) and with few exceptions, coagulation necrosis is absent
- Rare examples are exophytic rare the bulging down into the subcutis, or are amelanotic