| The lesion is
characterized by amelanotic ring upto several milimeters in width
around a melanocytic naevus.
Image Link(DermAtlas):click
(Clinical D/D: Meyerson's Naevus
-eczematous halo around the naevus).
Histologically, a dense
lymphocytic infiltrate is present in the dermis which may obscure the
melanocytic component.
click
on the image
Nevus cells are present in nests
or singly within the lymphocytic infiltrate. The number of nevus cells
depend on the stage at which the biopsy was taken.
Some cells show cytological
atypia. (D/D: In melanoma such a dense diffuse lymphocytic infiltrate is
usually not present.)
Some macrophages and factor XIIa-positive
dendrocytes may be present in the infiltrate.
In some cases, the melanocytes
may be epithelioid in type and may display some cytological atypia. The
lymphocytes are mostly CD8- positive lymphocytes. These cells express
CD69 and tumour necrosis factor -alpha.
Depigmented halo shows an
absence of melanin pigment and melanocytes in the basal layer.
(Both humoral and cell mediated
immunity are involved in the rejection of nevus cells and formation of
halo naevus.)
Image Links1(Dr
Weem)
;
Image2
Halo nevus or halo phenomenon? A
study of 142 cases.J
Cutan Pathol.
1995;22(4):342-8.
|