NEVUS SEBACEUS OF JADASSOHN WITH THE DEVELOPMENT OF A
BASAL CELL CARCINOMA VERSUS A BASAL CELL CARCINOMA SIMULANT
Many texts quote the older literature indicating a significant incidence of basal cell carcinoma arising in nevus sebaceus of Jadassohn (NSJ). Some of the more recent literature would indicate that the incidence is very low. One of the reasons for this disparity revolves around the varying interpretation of the nests of basaloid cells that sometimes arise in the background of NSJ. On the one hand, such nests have been interpreted as basal cell carcinoma. On the other hand, such nests have been interpreted as representing follicular induction with the formation of  primitive follicular or trichoblastic structures. A similar problem occasionally is seen over dermatofibromas. Current thinking favors the benign interpretation.

See OTHER for more discussion of nevus sebaceus of Jadassohn.

These pictures are from a scalp lesion from a 55 year old male. He had developed a verrucoid lesion in the area during puberty.
 
 
Scan power view. There are no large, anagen phase hair follicles in most of the field, and there are no fibrous tracks of the type that follow a telogen phase follicle. This is characteristic of nevus sebaceus of Jadassohn. The variety and degree of proliferation of follicular components varies from lesion to lesion.
Composite low power view of above. 
High power view of above. The hyperplastic mature keratinocytes could be interpreted as infundibular keratinocytes. The basaloid cells form interconnecting ribbons, and there is stromal participation with the formation a hair bulb papilla near the center of the picture. I  interpret this type of proliferation as benign.
Scan power view from another area. The hyperplastic, verrucoid surface can be interpreted as infundibular hyperplasia of malformed follicle/s. There is a focus composed of strands of primitive epithelium that interconnect with a follicle and also a larger, more solid nest of basaloid cells. 
Medium power view of above. The more solid nest of basaloid cells is associated with abundant specialized stroma. Such a solid nest is more likely to be interpreted as carcinoma though there is no evidence of aggressive behavior in this example.
High power view of above. Peripheral palisading of elongate nuclei and retraction are illustrated.

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