Aplasia Cutis Congenita: Scalp Vertex Cutis Aplasia, Temporal Triangular Alopecia

KEY POINTS

Aplasia cutis congenita (ACC) is a congenital absence of skin, most commonly affecting the scalp and characterized by raw areas that mature into atrophic scars devoid of hair.
ACC can occur in isolation or associated with other abnormalities and malformations, such as spinal dysraphism, encephaloceles, epidermal nevus, or nevus sebaceous syndrome.
The cause of ACC is heterogeneous and can include vascular disruption, infection, trauma, teratogens, and a range of genetic factors.
Treatment of ACC depends on the size and depth of the lesion and may involve wound care, excision, and reconstruction.
Early closure of extensive scalp defects is important to prevent complications such as hemorrhage or meningitis.

GENESIS

Aplasia cutis congenita (ACC) is a congenital, localized absence of skin that most commonly affects the scalp. The frequency is 1 per 3000 live births and can occur in isolation or as part of a heterogeneous group of syndromes. Frieden’s classification system divides ACC into nine subtypes ( Table 39.1 and Figs. 39.1–39.8 ). ACC begins as multiple or solitary, sharply marginated raw areas with absence of skin (resembling ulceration); these areas mature into atrophic scars devoid of hair, usually in the scalp vertex area or midline superior occipital region. Although most defects are small and superficial, approximately 20% involve absence of the skull, exposing the brain and sagittal sinus and increasing the risk for hemorrhage or infection. When associated dura is absent, there is usually no bony regeneration. The cause of these ACC lesions is heterogeneous and includes incomplete closure of the neural tube, vascular disruption of watershed areas of necrosis (from placental insufficiency), intrauterine infection, amniotic adhesions, trauma, teratogens, and genetic factors. Because vascular disruption and placental infarcts are seen in antiphospholipid antibody syndrome, some cases of extensive ACC may be related to this maternal disease state or other genetic causes of thrombophilia during pregnancy.

Table 39.1

Freiden’s Classification of Aplasia Cutis Congenita

From Frieden IJ. Aplasia cutis congenita: a clinical review and proposal for classification. J Am Acad Dermatol . 1986;14:646–660.

Group	Definition	Inheritance
1	Isolated scalp involvement; may be associated with single defects	AD ( BMS1 )/sporadic
2	Scalp ACC with limb-reduction defects (Adams-Oliver syndrome); may be associated with encephalocele	AD ( ARHGAP31 , DLL4 , NOTCH1 , RBPJ )/AR ( DOCK6 , EOGT )
3	Scalp ACC with epidermal nevus	Sporadic
4	ACC overlying occult spinal dysraphism, spina bifida, or meningoencephalocele	Sporadic
5	ACC with placental infarcts	Sporadic
6	ACC with epidermolysis bullosa	AD/AR or sporadic
7	ACC localized to extremities without blistering; usually affecting pretibial areas and dorsum of hands and feet	AD or AR
8	ACC caused by teratogens (e.g., varicella, herpes, methimazole)	Sporadic
9	ACC associated with malformation syndromes (e.g., trisomy 13, deletion 4p-, deletion Xp22.1, ectodermal dysplasia, Johanson-Blizzard syndrome, Adams-Oliver syndrome, amniotic band disruption complex)	Variable