Dysplastic nevi are usually compound nevi with peripheral lentiginous and junctional activity and random cytological atypia in the
epidermal component.
Dysplastic (atypical) nevus syndrome includes familial (originally known
as B-K mole syndrome) and sporadic occurrence of multiple dysplastic
nevi in an individual.
Gross appearance:
Tumour is characterized by ABCDE
[A: Asymmetry, B: Border Irregularity,
C: Colour Variation,
D: Diameter more than 4mm,
E: Elevation.]
1) These are usually more than 4mm in diameter.
2) Dysplastic nevi usually present as a macule with or without papular
component.
3) The border is usually
irregular and fuzzy in appearance. (Differential Diagnosis - In
melanoma, a well defined border is present.)
4) The lesion displays colour variegation. A mixture of tan, dark brown
and pink areas are noted.
[A:
Asymmetry , B: Border Irregularity, C: Colour Variation, D: Diameter more than 4mm , E: Elevation.]
Salient Histological
Features:
(Usually a low-power diagnosis)
1) Lentiginous hyperplasia2) Random cytological atypia
3) Stromal response.
4) Architectural atypia
Lentiginous and
nested hyperplasia noted in dysplastic naevus is characterized by proliferation of melanocytes singly and in groups along the basal layer.
'Junctional nest disarray' refers to uneven distribution and pattern of junctional component.
The rete ridges of the epidermis show hyperplasia
and fusion of adjacent retes.
The narrow elongated spindle shaped melanocytes run horizontally between the rete- ridges forming part of a
bridge.
Random cytological atypia is characterized by occasional cells with hyperchromatic nuclei and prominent nucleoli.
The atypia is usually
graded into low grade and severe.
There is no universally accepted
criteria for grading.
(Differential diagnosis : In melanoma the atypia is often 'non-random' in that all the nuclei are abnormal with enlarged irregular
nuclei).
The stromal response includes lamellar and concentric fibroplasia.
The stroma around the rete ridges appear more condensed and eosinophilic
than the collagenous stroma in the papillary dermis.
There may be some
fibrosis in the papillary dermis together with patchy superficial
chronic inflammatory infiltrate.
Host lymphocytic response around the
vessels in the papillary dermis is prerequisite for the diagnosis of
dysplastic nevus.
Architectural atypia (according to Ackerman et al.) includes 'shoulder
phenomenon' characterized by peripheral extension of the junctional
component, beyond the dermal component.
Reactive
mononuclear cells are often present ; melanophages are noted in the upper
dermis; there may be irregular distribution of pigment.
Radial growth phase
melanoma is the most important differential diagnosis:
1. The
diameter is more than 5 mm (often more than 8 mm)
2. Prominent host lymphocytic response in the papillary dermis
3. Prominent cytological and architectural atypia.
4. Pagetoid spread of atypical melanocytes is present.
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WHO
CRITERIA FOR DYSPLASIA :
Major Criteria :
-Basal (lentiginous and nesting) proliferation
of melanocytes.
-Melanocytic atypia, lentiginous/epithelioid
cell type.
Minor Criteria:
-Inflammation
-Increased vascularity with
endothelial hyperplasia
-Concentric eosinophilic fibrosis
/ lamellar fibroplasia
-Bridging of epidermal rete ridges
by atypical melanocytes
Surgical excision is the
only therapy that should be done for
dysplastic nevus.
Regular follow up is highly
recommended for all patients with
dysplastic nevus.
All patients with dysplastic
nevi should be educated about sun protection measures and self-examination
techniques.
Dermatopathology Quiz Case 134
Diagnosis: Mildly
Dysplastic Compound Melanocytic -Nevus (Atypical Nevus)
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