Sebaceous Naevus

Synonyms: Naevus sebaceous, naevus sebaceous of Jadassohn, Jadassohn's disease II, verrucous epidermal naevi (closely related and probably a variant manifestation of the same entity).¹

This is a well demarcated hamartomatous lesion composed mainly of sebaceous glands. They are very closely related to verrucous epidermal naevi, and many authors consider them to be variant manifestations of the same pathological entity.² The most commonly affected area is the scalp, where there is an area of hair loss circumscribing a tan or yellow-orange plaque which is often described as waxy or velvety in texture. They may also develop a warty appearance. Other areas that may be affected less frequently include around the ears, on the face, the neck, trunk or rarely in the oral mucosa.

They are usually quiescent lesions but they have a tendency to develop benign tumours within them, and there is a small but appreciable risk of malignant transformation. The lifetime risk of malignant transformation is quoted at 5–22%,³ but more recent prospective analyses suggest this figure may be lower.² Malignant transformation of the lesion is rare before adolescence/adulthood. The most frequent benign tumour to arise in sebaceous naevi is trichoblastoma. The most frequent malignant tumours are basal cell carcinoma and squamous cell carcinoma. A wide variety of benign and malignant tumours may arise from them and there are reports of several different tumour types arising within one lesion in individual patients.⁴

Estimated prevalence in newborns in the US is 0.3%.²

• Usually a single hairless patch (round or linear) is noted on the scalp at birth, or shortly thereafter.
• The classical velvety-tan or yellow-orange appearance may be noted.
• The lesion may appear more prominent in newborns due to the effects of maternal sex hormones.
• In adolescents the lesion tends to take on its nodular verrucoid appearance due to the influence of sex hormones.
• In later life there may be overgrowth of components of the lesion indicating possible benign or malignant tumours developing within the lesion.

The appearance of sebaceous naevi is fairly characteristic, but the following lesions may have a similar appearance or affect similar areas of the body.

• Aplasia cutis congenita
• Nevus syringocystadenomatosus papilliferus
• Juvenile xanthogranulomata
• Solitary mastocytoma
• Other causes of alopecia.

Biopsy may be considered for diagnostic purposes or to investigate the nature of tumours that arise within them.

Sebaceous naevi may be associated, in a minority of cases, with an epidermal naevus syndrome (Jadassohn naevus phakomatosis), of which there are several variants.⁵ There are extensive sebaceous naevi associated with disorders affecting the central nervous system, bones and the eye. Problems that arise include:

• Epilepsy
• Mental retardation
• Neurological deficits
• Vitamin-D-resistant rickets
• Spina bifida
• Hyperplastic bone growth
• Ptosis
• Nystagmus
• Optic nerve defects
• Occulomotor dysfunction.

• Some advocate the use of phototherapy with topical aminolaevulinic acid to allow ablation of the lesion in selected cases.²
• Others advocate watchful waiting with biopsy of any suspicious lesions that arise in adolescence or adulthood.
• Due to the difficulty of quantifying the risk of malignant transformation, some advocate full-thickness skin excision before adolescence.
• Some cases will not be suitable for excision due to their size and location.
• Seek the advice of a dermatologist and/or plastic surgeon to help decide on the need for, and timing of excision.
• Any lesion that changes its appearance significantly, ulcerates, becomes painful, bleeds or shows other signs of potential malignancy should be biopsied and considered for referral to a dermatologist.

• Poor cosmetic appearance
• Development of benign or malignant tumour within the lesion
• Complications associated with removal of the lesion.

• Good on the whole
• There is a significant incidence of benign tumours
• The lifetime rate of malignant transformation is uncertain but is as high as 22% in some series.