Musculoskeletal and Skin Pathology for Medical II Students

Lab 2c Intradermal Nevus (01000-87500)

The term "nevus" by itself implies faulty development. We usually think of moles as "nevi" and they in fact do represent one form of nevus, in which a modified form of melanocyte proliferates to form a kind of benign tumor. But one can also have "nevi" of other structures in the skin, including epidermis (epidermal nevi), sebaceous glands and other structures (nevus sebaceus), collagen or elastic fibers (connective tissue nevus), or fatty tissue (nevus lipomatosus). If you understand this concept, you probably know more about the subject than most practicing physicians! Nevus cells of melanocytic origin migrate to the skin from the neural crest during embryonic life. They typically aggregate along the dermal-epidermal junction, forming junctional nevi, and later "drop off" into the dermis, forming compound nevi and ultimately (when no more nevus cells remain at the junction), intradermal nevi. If left alone and the individual lives long enough, nevi are thought to eventually disappear. They are removed by various surgical means, both for cosmetic reasons and because they can mimic malignant melanoma. Nevi are not obligate precursors of malignant melanoma, but melanoma can develop in a pre-existing nevus, particularly in a congenital or "dysplastic" nevus. When this occurs, the atypical melanocytes most often originate from the dermal-epidermal junction zone.

Slides D10 & D11 | Slides D12 & D13

Slide D12 High power of the heavily pigmented cells underneath the epidermis and the mass of non-pigmented nevus cells in streaks and clusters.
Slide D13 High power of the pigmented cells as well as the clusters of nevus cells. Neval cells are distinct from Schwann cells.

Digital Legends for Labs/Cases
Lab 1
1a | 1b | 1c | 1d | 1e | 1f | 1g
Gross & Radiographs
a | b | c | d | e | f | g | h 
Lab 2
2a | 2b | 2c | 2d | 2e | 2f

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Medical II

Updated August 28, 2007