http://www.histopathology-india.MelanocyticTumours.htm

Ancient Naevus  
Halo naevus
Balloon cell naevus  
Combined Naevus
Recurrent melanocytic naevus
                   
2. Spindle and epithelioid cell naevi

Spitz naevus
Pigmented spindle cell naevus

3. Blue naevi

Common blue naevus 
Cellular blue naevus

4. Dermal melanocytoses

Naevus of Ota
Naevus of Ito  
Mongolian spot  

5. Congenital melanocytic naevi

6. Dysplastic melanocytic naevi

Variation according to the site:

Vulvar or genital naevi :  In premenopausal woman show atypical histological features characterized by enlarged junctional nests and variable shape , size and position of nests. Pagetoid spread of melanocytes often present. In pregnant woman nevi may display increase in basal melanocytes and increased mitotic activity.
Flexural naevi :  Display nested pattern with variation in size and arrangement of nests.
Conjunctival  naevi : Atypical features are noted.   
Palm and soles : There may be diagnostic difficulty due to presence of skin markings (dermatoglyphics). Acral lentiginous nevus present on plantar skin  may  display  features similar to dysplastic naevus. However, these lesions do not show any  evidence cytological atypia or lamellar fibroplasia .
Nail matrix naevi: These are mostly junctional in type . In the compound lesions  the naevus cells show little maturation with depth. The pagetoid spread of cells is confined to suprabasal  layer.

                            JUNCTIONAL NAEVUS  

Junctional naevi are characterized by evenly spaced theques and/or lentiginous hyperplasia together with variable keratinocytic hyperpigmentation. 

Image Link

In junctional naevus the theques are of similar size, gradually becoming smaller at the periphery.

Continuous runs of melanocytes are also noted (lentiginous spread).

There is evidence of circumscription characterised by presence of junctional theques at the periphery. In malignant melanoma individual cells demarcate the periphery.

                            COMPOUND NAEVUS

Compound naevi are characterized by junctional melanocytic theques as well as melanocytes in the dermis. These are symmetrical lesions and  display homogeneous growth pattern. Shrinkage and separation artifacts may be present. There is evidence of maturation with depth.   
(Type A-  round or epithelioid melanocytes in the papillary dermis;   Type-B- lymphocyte like in the mid -dermis;  TypeC- neuroid of fusiform  in the deepest portion).  

                            INTRADERMAL NAEVUS

Nevus cells are confined to the dermis. No epidermal junctional theques are present. The cells demonstrate maturation with depth.  The naevus  cells are arranged in nests or in cords and in the deeper part may display neuroid differentiation.

Image1 ;  Image2  ; Image3  

                     


Degenerative (secondary) changes in naevi:

1. Amyloid
2. Bone
3. Neurofibroma like appearance
4. Adipose tisue (liponeuronevi)
5. Epidermal spongiosis -producing eczematous halo- Meyerson's nevus
6. Myxoid change
7.  Increased  elastic fibre in the dermis
8. Separation and shrinkage artifact (pseudovascular or lymphatic space formation)
9. Folliculitis
10.  Tricholemmal , dermoid or epidermal cyst formation
11. Psammoma body formation
12. Paramyxovirus like inclusion
13. Focal epidermal necrosis
14. Incidental molluscum contagiosum or associated  trichoepithelioma , basal cell carcinoma  or syringoma .

Prognostic parameters of melanoma

Lentigo maligna melanoma

Superficial spreading melanoma

Nodular melanoma

Acral lentiginous melanoma

Desmoplastic /Spindle cell /
Neurotropic melanoma

Naevoid melanoma

Balloon cell melanoma