8. Defination
• Junctional naevus are benign localized neoplastic proliferations of
naevus cells (a type of melanocyte).
• Like all melanocytic naevi, these lesions are defined by the presence
of nests of melanocytes.
9. Clinical Features
• These are localized, generally symmetrical and uniformly pigmented
lesions, typically <5 mm in diameter.
• They have been assumed to evolve from initial junctional
proliferations to compound and then dermal naevi with
accompanying development of a papular component, loss of the
junctional component, and loss of pigment;
10. Gross
Here is a Gross image of
a Dome Shaped,Symmetrical, U
niformly pigmented, non
ulcerated lesion with
Mammillated surface pattern.
11. Histopathology
• The naevoid melanocyte is larger than the native melanocyte population
from which it has evolved, generally has less prominent dendrites, and
often contains pigment (in particular when junctional or in the
superficial dermis).
• In a dermal naevus, there is no junctional component and there is often
loss of pigment. Cells in the dermis may evolve from large epithelioid
type A naevus cells (often arranged in nests in the upper dermis) to
small lymphocyte-like type B cells to spindled type C cells.
12. • These cells often have signs of Schwannian differentiation, such as
wavy fibre bundles, serpentine nuclei, structures mimicking sensory
nerve end organs, and a lesser tendency to nesting.
• Although usually called maturation, the underlying mechanism of this
phenotypic change is unclear.
13.
14. Intradermal nevus: nests of melanocytes around pilosebaceous unit
(H&E, scanning magnification).
16. Differential Diagnosis
• The most important differential diagnosis is with melanoma.
• The major criteria that distinguish melanoma from common acquired
naevi include size, symmetry, circumscription, ulceration,
cellularity,pagetoid scatter, continuous basal (lentiginous)
proliferation, cytological atypia, mitotic activity, failure of dermal cell
maturation, and lymphovascular and perineural invasion.
