Bullous aplasia cutis congenita: case report and review of the literature.

Aplasia cutis congenita is a rare condition characterized by the absence of skin and sometimes other underlying structures such as bone or dura. It can be a part of various syndromes and can be associated with multiple genetic diseases, malformation patterns, or a combination of all. It is even considered as a form frustre of a neural tube defect in several literatures. Bullous aplasia cutis congenita is a clinical subtype of the condition, with extremely few cases reported in the literature. It presents as a cystic or bullous lesion at birth, which eventually transforms into an atrophic, flat scar covered by a thin epithelium. Some cases present with a dark collar hair sign around the lesion, which can be even more indicative of an underlying neural tube defect. Management remains controversial and depends on the characteristics of the lesion, but conservative treatment is usually chosen.

Introduction

Aplasia cutis is a condition in which localized or generalized areas of skin are absent at birth. It is associated with many genetic diseases or syndromes[12]. Bullous aplasia cutis congenita is a subtype rarely seen in its initial form; in most cases, it is found as a flat scar once the bullae have already reabsorbed. In some cases, there is underlying neural tube defects. There are only 17 cases reported in the literature including the one discussed in this paper.

Case Report

A 2-day-old male infant presented to our Dermatology service with a 2-cm tense blister filled with serous liquid located on the vertex of the head [Figure 1]. An ultrasound reported no bony defects underlying the lesion. The patient had no other physical abnormalities. The diagnosis of bullous aplasia cutis congenita was made, and we recommended conservative management. Till now the child has no developmental alterations.

Figure 1

Bullous lesion on the vertex of the neonate

Discussion

Aplasia cutis congenita is a rare condition characterized by the absence of skin and in some cases underlying structures such as bone or dura (20%–30% of patients).[12] The estimated incidence is 3 in 10,000 births. It can present as a localized congenital defect with familial incidence (usually on the scalp) or be widespread with less familial incidence.[3] It has been associated with dysgenic hydrocephaly, extensive unilateral linear epidermal nevus, hemangiomas, and multiple defects.[1]

Bullous or membranous aplasia cutis congenita is a clinical subtype of this condition, with extremely few cases reported in the literature (17),[1] either because of underreporting or to it being so rare. The lesions are cystic or bullous at birth and eventually transform into an atrophic, flat scar covered by a thin epithelium, which is how doctors most commonly find aplasia cutis. Many present with a collarette of dark, coarse hair around the defect on the vertex (collar sign).[45]

The etiology of aplasia cutis is unknown. It probably is not attributable to a single cause but to a combination of genetic factors, teratogens,[6] compromised vasculature to the skin, and trauma.[3] The increased incidence of lesions on the vertex is considered to be the result of a point of maximum tensile forces during rapid brain growth, inducing disruption of the overlying skin at 10–18 weeks of gestation.[2] Some authors have proposed that membranous aplasia cutis congenita is an incomplete type of neural tube defect and may be derived from a similar embryological defect. This is supported by several facts. First, the collar sign that is a relatively specific marker for cranial neural tube closure defects.[1] Second, the thin epithelial covering resembles that of encephaloceles and meningoceles both clinically and histologically. Finally, membranous posterior cranial closure sites in neural tube defects resemble the findings in membranous aplasia cutis.[17]

The diagnosis is primarily clinical and a biopsy is not needed nor suggested routinely,[2] but characteristically there is an absence of epidermis and dermis and decreased subcutaneous tissue as deep as muscle and fascia. Healed lesions often demonstrate flattened epidermis, proliferation of fibroblasts, newly formed capillaries, and complete absence of adnexal structures.[2]

The diagnosis can be suspected in utero with elevated amniotic fluid alpha-fetal protein levels, positive acetylcholinesterase, and normal ultrasound findings.[8] In all patients with aplasia cutis congenita, a complete obstetric and family history should be obtained, as well as a medical examination guided by the pattern of the lesions. Genetic counseling of the family regarding the risk of recurrence is recommended.[2]

Management remains controversial, because the location, size, and depth of the defect must be considered. Good results are obtained with conservative treatment in a defect up to 4×7 cm in size (silver sulfadiazine or antibiotic ointments). Larger defects that extend into the dura need early surgery.[910]

In summary, bullous aplasia cutis congenita is an extremely rare or much under-reported type of aplasia cutis. It is hypothesized to be a form fruste of a neural tube defect. Some cases present with a dark hair collar sign or an altered hair pattern surrounding the lesion, which can be even more indicative of an underlying neural tube defect. Recognizing the condition is important in order to rule out associated defects.