Dysraphism refers to neural tube closure abnormalities and midline closure abnormalities of the skin, paravertebral muscles, vertebrae and meninges. Cranial dysraphism (CD) and occult spinal dysraphism (OSD) may be discovered via evocative skin signs present at birth or appearing later in childhood or even in adulthood. This review describes the various types of skin signs associated with CD and OSD. All congenital midline skin lesions, particularly on the frontonasal area, the vertex or the occipitocervical and low back regions, should prompt suspicion of underlying dysraphism. The main evocative midline skin abnormalities are: (i) for underlying DCEO: a nodule, swelling, skin openings and hair collar sign or hair tuft; (ii) for underlying DSO, localized hypertrichosis, an atypical or complex lower back dimple, a dermoid fistula, infantile haemangioma, caudal appendage and lipoma. In the event of suspected DCEO or DSO, spinal or medullary MRI constitutes the reference examination.

We report two cases of aplasia cutis congenita associated with hair collar signs and hemangioma simplex in their parietal regions. A hair collar sign and a hemangioma are known to suggest the possibility of underlying neural tube defects. However, no obvious bone defects or heterotopic neural tissue were observed in the imaging and histopathological examinations. Nevertheless, some pathological observations similar in both cases suggested abnormalities in the process of ectodermal fusion. A flat epidermis and a lack of appendages were recognized. Both cases also exhibited the presence of melanocytes in a portion of the superficial dermal layer. An increase in the number of macrophages was observed in the dermal area with neither elastic fibers nor normal collagen fibers. The peripheral hair follicles grew horizontally.

We present a rare case of focal facial dermal dysplasia type 4 (FFDD4) in an otherwise healthy boy infant, presenting as bilateral preauricular scarlike defects surrounded by a hair collar, resembling membranous aplasia cutis congenita. The presence of a hair collar supports the hypothesis that FFDD is caused by abnormal closure at facial embryonic fusion lines, but unlike midline scalp defects is not associated with neurological compromise. Other types of FFDD occur at different sites and can be associated with cranial dysgraphism. Awareness of this rare condition by dermatologists is imperative to enable prompt recognition and minimize diagnostic delay.

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