Jadassohn's sebaceous nevus
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Jadassohn's sebaceous nevus (Latin: naevus sebaceus Jadassohn) is a congenital malformation of the skin belonging to the group of epidermal nevi. It is a hamartoma, that is, a focal developmental disorder involving structures normally present in the skin but with abnormal architecture and proportions. The lesion is usually present from birth or early childhood and is most often located on the hair-bearing skin of the scalp and face. During puberty, under the influence of androgens, it thickens and the sebaceous component becomes more pronounced. Although in most cases it is benign, secondary adnexal tumors of the skin may develop within it — mostly benign, less often malignant.
Pathogenesis and molecular basis
Jadassohn sebaceous nevus is a classic example of genetic mosaicism. This means that the mutation arises after fertilization (a somatic mutation), and therefore is not present in all the cells of the organism, but only in a specific population of them. In many cases activating mutations have been demonstrated in genes of the RAS (HRAS, KRAS) family, which encode proteins involved in the regulation of cell proliferation, differentiation and survival via the MAPK/ERK signaling pathway.
The consequences of these disturbances are:
- abnormal differentiation of keratinocytes,
- hyperplasia of sebaceous glands,
- abnormal structure of hair follicles,
- excessive proliferation of skin adnexal structures.
The sebaceous nevus is classified among the so-called epidermal nevus syndromes. When neurological, skeletal or ophthalmic lesions coexist, the diagnosis is sebaceous nevus syndrome (Schimmelpenning syndrome), which results from a more extensive mosaicism involving tissues of ectodermal and mesodermal origin.
Jadassohn's nevus - clinical presentation and stages of development
The lesion undergoes three characteristic developmental stages:
1. Infantile and childhood phase
In the neonatal and early childhood period the lesion appears as:
- a flat or slightly elevated plaque,
- yellowish, salmon, or light brown in color,
- a smooth, matte surface,
- absence of hair within the lesion.
It is most often located in:
- the hair-bearing skin of the scalp (60–70% of cases),
- the forehead and temporal area,
- less commonly the neck.
2. Maturation phase
During puberty, under the influence of androgens, the following occurs:
- thickening of the lesion,
- development of a papillomatous or folded surface,
- an increase in the number and activity of sebaceous glands,
- enhancement of the adnexal component.
The lesion becomes more clearly demarcated and elevated.
3. Adult phase
In adulthood there is the possibility of development of secondary tumors originating from cutaneous adnexa. In the past the risk of malignant transformation was overestimated. Currently it is accepted that:
- 10–20% of lesions develop secondary tumors,
- the majority of which are benign,
- the risk of developing basal cell carcinoma is relatively low (estimated below 1–3%).
Jadassohn nevus - dermoscopy and differential diagnosis
Dermatoscopic examination is a key element in the assessment of the lesion. Typical features include:
- yellowish, structureless areas corresponding to proliferation of sebaceous glands,
- absence of follicular openings,
- irregular, papillomatous architecture,
- absence of the classic pigment network.
The differential diagnosis should include:
- verrucous epidermal nevus,
- seborrheic dermatitis (in early stages),
- seborrheic keratosis,
- congenital melanocytic nevus,
- neoplastic adnexal lesions of the skin.
The final diagnosis in uncertain cases is determined by histopathological examination.
Jadassohn's nevus and tumors
Secondary tumors usually occur in the third decade of life and later. The most common are:
Benign tumors:
- trichoblastoma,
- syringocystadenoma papilliferum,
- sweat gland adenoma.
Malignant tumors (rare):
- basal cell carcinoma,
- occasionally other skin adnexal carcinomas.
Alarm symptoms are:
- rapid growth of the lesion,
- ulceration,
- bleeding,
- change in color,
- pain or infiltration of the underlying tissue.
Any such situation requires urgent diagnostic evaluation and usually surgical treatment.
Sebaceous nevus and Schimmelpenning syndrome
If the nevus coexists with developmental disorders, nevus sebaceus syndrome is diagnosed. Possible symptoms include:
- epilepsy,
- psychomotor developmental delay,
- structural brain defects,
- bone abnormalities (asymmetries, scoliosis),
- eye abnormalities.
In such cases, multidisciplinary diagnostics including neurological examinations and imaging studies (MRI) are necessary.
Jadassohn's sebaceous nevus - treatment
The management strategy depends on the patient's age, the lesion's location, and the presence of features suggesting malignant transformation.
1. Observation
In children without concerning features, conservative management may include:
- regular dermatoscopic examination,
- photographic documentation,
- dermatologic follow-up every 6–12 months.
The risk of malignancy in childhood is very low, therefore routine excision of all lesions at this age is not currently standard.
2. Surgical treatment
Surgical excision of the lesion with a margin of healthy tissue is the method of choice in cases of:
- suspected malignant transformation,
- rapid growth,
- clinical symptoms (ulceration, bleeding),
- aesthetic or psychological indications.
The procedure is performed:
- under local anesthesia (small lesions),
- under general anesthesia (extensive lesions, especially in children).
All excised material must undergo histopathological examination.
3. Alternative methods
Ablative laser therapy (e.g., CO₂) and dermabrasion may improve the cosmetic result, however:
- they do not remove the lesion through the full thickness of the skin,
- they do not eliminate the potential risk of malignancy,
- they do not allow full histopathological assessment.
For this reason, they are not considered radical methods and should not replace surgical excision when there are medical indications.
Jadassohn nevus - clinical management and follow-up
Each congenital skin lesion should be:
- assessed dermatoscopically,
- photographically documented,
- monitored systematically.
The physician's experience in differentiating benign from potentially malignant lesions is of key importance. In clinical practice, the decision to excise should be individualized and based on an analysis of oncologic risk as well as functional and aesthetic aspects.
