Naevus sebaceus of Jadassohn
NSJ; sebaceous naevus; "organoid naevus" (older); Jadassohn naevus; (in extensive form, schimmelpenning syndrome / linear sebaceous naevus syndrome)
The naevus sebaceus of Jadassohn (NSJ) is a common congenital cutaneous hamartoma — present from birth or appearing in early infancy as a yellow-orange waxy hairless plaque on the scalp or face. It is caused by postzygotic somatic mosaic gain-of-function mutations of HRAS (~95%) or KRAS in epidermal keratinocytes — making NSJ a "RASopathy of the skin". The lesion progresses through three classical stages — a smooth alopecic infantile patch, a verrucous adolescent plaque (driven by androgen-mediated sebaceous proliferation at puberty), and an adult phase with the development of secondary cutaneous tumours within the lesion in 10–20%. The most common secondary tumours are benign — most often trichoblastoma and syringocystadenoma papilliferum — but malignant secondary tumours, particularly basal cell carcinoma and rarer adnexal carcinomas, also occur. Historically, prophylactic excision of all NSJ during adolescence was advocated; modern guidance is more conservative, with surveillance and excision of any lesion that develops a clinical change suggesting a secondary tumour.
Clinical features & three stages
- Stage 1 — infantile: smooth, alopecic, yellow-orange to skin-coloured, slightly raised plaque on the scalp (commonest), face, neck or trunk; present from birth or appearing in the first year.
- Stage 2 — adolescent: develops a verrucous, papillomatous, waxy surface texture during puberty driven by androgen-mediated sebaceous gland enlargement and verrucous epidermal hyperplasia.
- Stage 3 — adult: secondary tumours develop within the lesion in 10–20% of patients in adulthood (median age ~40).
- Distribution — scalp (~60%), face / neck (~30%), trunk; usually solitary and unilateral.
- Linear or whorled distribution along Blaschko lines in extensive cases — see Schimmelpenning syndrome.
- Schimmelpenning syndrome (linear sebaceous naevus syndrome) — extensive linear NSJ + neurological abnormalities (intellectual disability, seizures) + ocular abnormalities (lipodermoid, coloboma) + skeletal abnormalities. Caused by more extensive postzygotic HRAS / KRAS mosaicism.
Genetics
- Postzygotic somatic mosaic gain-of-function mutations of:
- HRAS — ~95%; most commonly p.G12V or p.G13R.
- KRAS — ~5%.
- Mutations confined to the affected lesion (not detectable in blood / unaffected skin).
- The same RAS pathway alterations underlie the related congenital hamartoma "epidermal naevus syndrome" and Schimmelpenning syndrome.
- Mosaic KRAS / HRAS mutations also drive secondary tumours within the lesion (BCCs and trichoblastomas in NSJ harbour the same RAS mutation as the surrounding NSJ).
Secondary tumours
- Lifetime risk ~10–20% of developing one or more secondary tumour within the NSJ.
- Benign (the majority):
- Trichoblastoma — the commonest secondary tumour; previously many such lesions were misdiagnosed as basal cell carcinoma.
- Syringocystadenoma papilliferum — papillary apocrine ductal lesion; second commonest.
- Sebaceoma, trichilemmoma, hidradenoma papilliferum, syringoma.
- Malignant:
- Basal cell carcinoma — the principal malignant concern; risk historically over-estimated because of the misdiagnosis of trichoblastoma as BCC; more recent series suggest BCC arises in ~1–2% of NSJ.
- Squamous cell carcinoma, sebaceous carcinoma, apocrine carcinoma, microcystic adnexal carcinoma — rare.
- Median age at secondary tumour development ~40; rare in childhood / adolescence.
- Warning signs:
- Sudden growth of a discrete nodule within the lesion.
- Ulceration.
- Bleeding.
- Crusting.
- Itching / pain disproportionate to baseline.
Management
- Conservative approach (current preferred):
- Surveillance with photographic documentation; biopsy / excision of any clinical change suggesting a secondary tumour.
- Particularly appropriate for small / non-cosmetically-disfiguring lesions in young patients given the low absolute lifetime malignancy risk.
- Prophylactic excision:
- Historically advocated during adolescence to remove the lesion before secondary tumour development.
- Modern indications — large or cosmetically disfiguring lesions, parental / patient preference, lesions on cosmetically prominent sites where late excision and reconstruction would be more disfiguring than early excision.
- Timing — typically deferred until the patient can give informed consent (~14+) and tissue expansion or other reconstructive techniques can be planned.
- Surgical technique:
- Full-thickness excision down to fascia.
- Reconstruction depends on size / location — primary closure for small lesions, tissue expansion or local flaps for larger scalp lesions, full-thickness skin grafts for facial lesions where flaps are not feasible.
- Refer to plastic surgery / paediatric plastic surgery.
- Suspected secondary tumour — full-thickness excision of the discrete nodule with margin including some surrounding NSJ; histological assessment by an experienced dermatopathologist (trichoblastoma is the major histological mimic of BCC).
- Schimmelpenning syndrome — multidisciplinary care (paediatric neurology, ophthalmology, orthopaedics, plastic surgery, clinical genetics).
References
- Cribier B et al. Tumors arising in nevus sebaceus — a study of 596 cases. J Am Acad Dermatol; 2000.
- Groesser L et al. Postzygotic HRAS and KRAS mutations cause nevus sebaceous and Schimmelpenning syndrome. Nat Genet; 2012.
Spot a correction?
If any clinical statement, citation or link on this page needs updating, please email admin@skinoncology.net with the page name, the proposed correction and the supporting source.