Nevus Sebaceus1 (Follicular appendage)

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 An 'ASIDE' to the Presentation on the Follicular Hamartoma
 by Richard J. Reed, M.D.

Fig. 1: The epidermal changes of nevus sebaceus may be slight or may be prominently verrucous as in this field. There is marked papillomatosis. The basal layer of the altered epidermis is often accentuated. The admixture of small and large keratinocytes, which distinguish a seborrheic keratosis, is not a feature of the epidermis of an organoid nevus. In young nevus sebaceus as encountered early in life, the epidermis may not show significant alterations.


Fig. 2: The designation, nevus sebaceus, places great emphasis on changes in sebaceous glands. In the case illustrated by Dr. Weems, the sebaceous lobules are few in number and small. In this case (the 'Aside'), the lobules are increased in number and vary in size. Some of the lobules show daughter or secondary lobules. The lobules are also characterized by a single row of germinative cells; they are mature.


Fig. 3: In this field, the pilosebaceous unit is distorted. The unit has a poorly developed follicular component. The unit is short and broad near the dermal-epidermal interface. The distortions qualify as features of a dysplasia and as a sign of immaturity. The follicular component of pilosebaceous units of a nevus sebaceus characteristically shows a defect in maturation with a primitive bulb and papillae in the mid-dermis. The hair follicles do not cycle in concert with the follicles of the scalp outside the domain of the nevus. If anagen phases are represented in any follicles cut in cross section beneath a nevus sebaceus, they generally will be found attached to the epidermis outside the domain of the nevus. The sebaceus glands of nevus sebaceus respond to hormonal and neural impulses; the pilar units do not. The pilar remain immature and cannot be afforded great significance in the evaluation of maturity or degree of dysplasia. The sebaceous gland lobule is cystic centrally. This is a common alteration of the sebaceus glands in nevus sebaceus but is not diagnostic. I attribute the description of the alteration to E. Wilson Jones.


Fig. 4: The characteristic alteration of a sebaceous gland lobule is seen as a small central cyst.


Fig. 5: The sebaceous changes of mature nevus sebaceus are shown at the top of the field. A mature pilar unit is not a feature. The sweat gland at the bottom of the field is of apocrine type. Apocrine sweat glands are common in the domain of nevus sebaceus. In some examples, both apocrine and eccrine glands are deficient in number in nevus sebaceus.

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