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Chapter 63. Nevus Sebaceus

Definition

A hamartoma of epidermis, epithelial structures of adnexa, and presumably dermal elements, typified, when fully formed, by a papillated or verrucous yellowish plaque situated usually on the scalp. The condition may present itself as a solitary lesion or as multiple lesions that follow Blaschko’s lines and, when systematized, is almost always associated with other congenital abnormalities.

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Course

A lesion of nevus sebaceus usually is present at birth and typically on the scalp, where it appears as an alopecic, slightly yellowish macule. For years it remains flattish and grows at the same pace as the growth of the child who bears it. At puberty, however, the lesion tends to become mammillated and more yellow. As time goes on, the surface may become increasingly papillated and may even become verrucous.

Benign neoplasms develop commonly in fully-formed lesions of nevus sebaceus, chief among them trichoblastomas that are often markedly pigmented hemispherical papules. Much less often a malignant neoplasm arises in a nevus sebaceus, usually a trichoblastic (basal-cell) carcinoma. Trichoblastomas are at least 10 times more common than basal-cell carcinomas in lesions of nevus sebaceus. Once a lesion of nevus sebaceus has come into being, it persists for a lifetime.

Integration: Unifying Concept

Nevus sebaceus is the quintessential example of an organoid nevus, i.e., a hamartoma that, in the skin, consists of various elements indigenous to the organ. The components of nevus sebaceus are epidermal in the form of gentle mammillation, prominent papillation, or even digitations. They are sebaceous in the form of clusters of pyriform lobules of sebocytes, and follicles as primitive germs and a papilla situated just beneath surface epithelium (and absence of terminal follicles within the substance of the hamartoma itself). The apocrine component takes the form of numerous tubular structures that reside within the dermis and sometimes the subcutaneous fat.

A variety of cysts, cystic hamartomas, and benign and malignant neoplasms may develop within a nevus sebaceus. Even in a newborn, it is not uncommon for a benign neoplasm of apocrine character, namely, syringocystadenoma papilliferum, to be present in association with nevus sebaceus. An apocrine cyst, called apocrine hidrocystoma, is often present in a nevus sebaceus, as are cystic hamartomas like steatocystoma. The commonest neoplasm that occurs in nevus sebaceus is not basal-cell carcinoma, as has been asserted for almost three-quarters of a century, but trichoblastoma, the benign analogue of basal-cell carcinoma. Among the malignant neoplasms that sometimes appear in nevus sebaceus, in addition to basal-cell carcinoma, are sebaceous carcinoma and apocrine carcinoma.

Therapy

Simple surgical excision is preferable if the decision is made to remove the lesion. It is not necessary, however, to extirpate every nevus sebaceus, as was advocated in times past when trichoblastomas that often develop in them were thought to be basal-cell carcinomas. In fact, however, a malignant neoplasm may arise in the course of a nevus sebaceus, just as a melanoma may originate in conjunction with a melanocytic nevus. Not all nevi need to be excised, and so it is, too, for nevus sebaceus.

Distribution

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Fig. 63-1

A yellowish plaque.


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Fig. 63-2

Numerous linear yellow lesions, some of them exuberantly exophytic.


Configuration

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Fig. 63-3

A linear plaque with a surface that is partially cerebriform and partially gently mammillated.


Arrangement

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Fig. 63-4

Papules in linear array.


Individual Lesions

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Fig. 63-5

A slightly elevated, flat-surfaced, alopecic plaque.


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Fig. 63-6

A gently mammillated alopecic plaque.


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Fig. 63-7

A verrucous alopecic plaque.


Variations

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Fig. 63-8

A pigmented papule of trichoblastoma in a plaque of nevussebaceus.


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Fig. 63-9 A

A black nodule and a rust-colored nodule of trichoblastoma in a plaque of nevus sebaceus.


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Fig. 63-9 B

A black nodule and a rust-colored nodule of trichoblastoma in a plaque of nevus sebaceus.


New! Additional Images

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Fig. 63-10 A

Nevus sebaceus: A brown dome-shaped trichoblastoma is present in a pebbly yellowish plaque of nevus sebaceus.


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Fig. 63-10 B

Nevus sebaceus: A brown dome-shaped trichoblastoma is present in a pebbly yellowish plaque of nevus sebaceus.


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Fig. 63-11

Nevus sebaceous: A peculiar-shaped, yellow-tan, slightly elevated, gently papillated plaque of nevus sebaceus with a rust-colored papule of syringocystadenoma papilliferum within it.