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

Gross appearance:

1) These are usually more than 4mm in diameter.
2) Dysplastic naevi  usually present as a macule with or without papular component. 
3) The border is usually irregular and fuzzy in appearance. (D/D- in melanoma, a well defined border is present.)  CLICK HERE
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 hyperplasia
2. 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. (D/D:  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 naevus.

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 5mm (often more than 8mm)
2.  Prominent host lymphocytic response in the papillary dermis
3.  Prominent cytological and architectural atypia.
4.  Pagetoid spread of atypical melanocytes is present.

           IMAGE1 ; IMAGE2 ; IMAGE3 ; IMAGE4     

                    DermAtlas- Related link

Abstracts:

Precursors to melanoma and their mimics: nevi of special sites.Mod Pathol. 2006 Feb;19 Suppl 2:S4-20.

Histologic similarities between lentigo maligna and dysplastic nevus: importance of clinicopathologic distinction.J Cutan Pathol. 2005 Jul;32(6):405-12.

Cutaneous melanocytic lesions: selected problem areas.Am J Clin Pathol. 2005 Dec;124 Suppl:S52-83.

Evaluation of surgical margins in melanocytic lesions: a survey among 152 dermatopathologists.J Cutan Pathol. 2005 Apr;32(4):293-9.

Variability in nomenclature used for nevi with architectural disorder and cytologic atypia (microscopically dysplastic nevi) by dermatologists and dermatopathologists.J Cutan Pathol. 2004 Sep;31(8):523-30.

Grading of atypia in nevi: correlation with melanoma risk.Mod Pathol. 2003 Aug;16(8):764-71.

Cyclin D1 expression in dysplastic nevi: an immunohistochemical study.Arch Pathol Lab Med. 2001 Feb;125(2):208-10.

Critical analysis of histologic criteria for grading atypical (dysplastic) melanocytic nevi.Am J Clin Pathol. 2001 Feb;115(2):194-204.

Atypical histologic features in melanocytic nevi. Am J Dermatopathol. 2000 Oct;22(5):391-6.

Malignant melanoma, dysplastic melanocytic nevi, and Spitz tumors. Histologic classification and characteristics.Clin Plast Surg. 2000 Jul;27(3):331-60

Dysplastic changes in different types of melanocytic nevi. A unifying concept.J Cutan Pathol. 1999 Feb;26(2):84-90.

Correlating architectural disorder and cytologic atypia in Clark (dysplastic) melanocytic nevi.Hum Pathol. 1999 May;30(5):500-5.

Correlation of histologic architectural and cytoplasmic features with nuclear atypia in atypical (dysplastic) nevomelanocytic nevi.Hum Pathol. 1990 Jan;21(1):51-8.

Histopathologic characteristics of dysplastic nevi. Limited association of conventional histologic criteria with melanoma risk group.J Am Acad Dermatol. 1990 May;22(5 Pt 1):727-33.

Dysplastic melanocytic nevi: a reproducible histologic definition emphasizing cellular morphology.Mod Pathol. 1989 Jul;2(4):306-19.