Case Number : Case 744 - 23 Apr Posted By: Guest

Melanocytic lesion with architectural (lamellar fibroplasia, bridging) and minimal / mild cytological atypia. No pagetoid spread and I cannot identify mitoses. Would call this a mildly dysplastic naevus.

I can't see random cytologic atypia of any significant degree. I would call this lesion lentiginous junctional melanocytic nevus.

Mild dysplastic naevus

Nevus

Nested and lentiginous atypical melanocytic proliferation. Nests vary in size and shape, and some tend to be irregularly located at the side of rete ridges. Some nests are horizontally oriented with focal bridging (Picture #2, left). Host response takes form of lymphocytic infiltrate and lamellar fibroplasia. Cytologic atypia is mild, that melanocytic nuclei are as large as keratinocytes nuclei.
There’s no intradermal component.
I think it's a low-grade junctional dysplastic nevi.

Lentiginous junctional dysplastic nevus, mild. Slight architectural disorder with nests at tips or rete and creeping up the sides, peri-rete lamellar fibrosis, minimal cytologic atypia, and a mild host immune response - all features of a mildly dysplastic nevus.

[font=georgia,serif][size=3]Ah, nothing so factious as interpretation of the humble benign nevus. Don't think there will be any wrong answers on this one!

I favor a mildly dysplastic junctional nevus, likely arising in preexisting nevus.
The differential dx would be a 'nevus of special site' (flexural area) given popliteal location. The inflammation is the main differentiator for me to push it to dysplastic (likely arising in pre-existing special-site junctional nevus, given the far lateral nests that appear uninvolved).

[b]Benign nevus of special site features:[/b]
- Nests are slightly irregular in size and placement, but predominantly at tips of rete pegs.
- No significant rete bridging (there seem to be keratinocytes involved at all junctures, therefore I think these are tangential 'pseudobridging').
- Overall bilateral symmetry. Tapering edges, and widely scattered edge nests. Lentiginous component is centrally restricted.[/size][/font]
[b]Dysplastic features:[/b]
[font=georgia,serif][size=3]- Slight periretal fibrosis
- Targeted lichenoid inflammation.
- Melanocytes withlow-grade atypia (at best): roughly the same size as basal keratinocytes in nuclear size, even chromatin, lack of hyperchromatism, pink cytoplasm with coarse/giant melanosomes, focally prominent nucleoli, lack of proliferative activity.[/size][/font]

This lesion occurs on a flexural site and that makes differential diagnosis tricky. However in my opinion, this melanocytic lesion meets the criteria for dysplastic nevus, as there is architectural atypia, dermal response and one can always find slight cytological atypia when needed. It is completely removed, and that is ok. I would hesitate in case margin was involved, but would probably advice narrow reexcision. This is a low grade lesion, but not as low I could sleep well.

junctional dysplastic nevus vs site specific

I see nested and few lentiginous melanocytic proliferation with some atypia. The nests are located at the side and tip of rete ridges. I did not see bridging. I think it is a special site benign melanocytic nevus.

I will call it mildly dysplastic junctional nevus.

Junctional melanocytic nevus from special-site type (flexural site)[list]
[*]architectural atypia
[*]no cytological dyplasia
[*]discohesiveness
[/list]

atypical junctional nevus

Again, it is great to see so many comments. I think that this is a difficult lesion to interpret and the differential diagnosis certainly lies between a flexural-type nevus and a dysplastic nevus. When I photographed the case I particularly included figure 4 to show at high power that the lesion was very much a nested lesion with the nests residing at the tips of the rete ridges. There is very little in the way of a lentiginous element. The architectural disorder of a dysplastic nevus is therefore absent. I do not think that there is any real cytological atypia although its presence would not really distinguish between the two entities. The stromal changes are common to both. My diagnosis therefore rests with the growth pattern and stromal changes and I regard this lesion as a nevus of special sites (flexural type). I must comment that such nevi may be seen just about anywhere and therefore the term should one day become redundant. I would not be concerned if people called this a junctional nevus! Jim Davie sumarized the situation quite nicely with his first sentence. I think that it is important not to call this lesion a dysplastic nevus because of the implications for the patient (unless of course you don't believe in the concept of dysplastic nevus!!!).

PS I will be back on Mondays and Tuesdays in a couple of weeks.

[quote name='Jim Davie MD' timestamp='1366724177']
[font=georgia, serif][size=3]Ah, nothing so factious as interpretation of the humble benign nevus. Don't think there will be any wrong answers on this one! [/size][/font]
[/quote]
Just perfect, Dr. Davie!