Case 1: A neonate with vesicular scalp lesions

A baby was born via vaginal delivery at 41 weeks' gestation to a 25-year-old primigravid with no known history of genital herpes simplex virus (HSV). Both parents reported previous oral HSV but no active lesions. Maternal history revealed a childhood varicella zoster virus (VZV) infection. Antenatal VZV titres were consistent with immunity. Integrated prenatal screen testing was declined. Membranes ruptured 8 h before delivery, with one documented maternal fever of 38.5°C. No genital HSV lesions were observed at delivery. At birth, eight well-demarcated vesicles were noted over the right parieto-occipital region, each approximately 0.5 cm to 1 cm in diameter. Some were ruptured. Focal alopecia was noted at the site. The surrounding hair was darker and thicker than hair on the rest of the scalp. The baby was afebrile and clinically stable. A full septic workup was performed and antiviral medication initiated until an HSV infection was excluded. Lumbar puncture revealed a cerebrospinal fluid white blood cell count of 0×106/L, a red blood cell count of 29×106/L, and normal protein and glucose levels. Blood and cerebral spinal fluid were negative for HSV polymerase chain reaction (PCR) and culture. Vesicular scrapings for HSV PCR were negative. Conjunctival, nasal, oral and rectal swabs were negative for HSV. In consultation with dermatology, the diagnosis was established. Multiple vesicular lesions over the right parieto-occipital region of the scalp. Lesions are surrounded by dark, thick hair consistent with the ‘hair collar sign’ Aplasia cutis congenita is a condition in which focal areas of epidermis and dermis are absent (1). Underlying structures, including bone and subcutaneous tissues, may also be absent. Atrophic, membranous and bullous varieties have been described. The latter, bullous aplasia cutis congenita, is a very rare subtype in which overlying vesicles or bullae are present. Fewer than 20 cases of the bullous variety of aplasia cutis have been reported. Of the reported cases, the majority had a single, large bullous overlying the scalp, which is in contrast to our patient, who had multiple smaller vesicles. These lesions may mimic HSV infection, neonatal VZV infection and epidermolysis bullosa (1). The absence of other lesions in a systemically well and afebrile neonate is reassuring; however, it does not exclude the other diagnoses. In particular, neonates with cutaneous HSV may be systemically well at the time of presentation but progress to more severe disease if the diagnosis is delayed or missed. A key clinical finding that distinguishes bullous aplasia cutis congenita from other diagnoses is the presence of a ‘hair collar sign’: an area of dark, thicker hair that surrounds the lesions. Focal alopecia can also be noted at the site. Some lesions may already be ruptured at the time of birth. Over time, the bullous lesions evolve into scarred, atrophic areas of skin (2). Aplasia cutis congenita, including the bullous form, may be suspected antenatally when maternal serum and amniotic fluid alpha-fetoprotein levels are elevated, amniotic fluid acetylcholinesterase is positive and ultrasound is otherwise normal (3). After birth, the diagnosis is made clinically. A biopsy is not necessary if the diagnosis is evident on physical examination. Bullous aplasia cutis congenita appears similar histologically to encephaloceles and meningoceles; therefore, it is suspected to be a form of neural tube defect. Consequently, magnetic resonance imaging is often recommended to determine the involvement of deeper tissues (2). Scalp ultrasound can also be useful to assess the integrity of underlying bone. Although usually isolated, cases of bullous aplasia cutis congenita have occurred in patients with other malformations including cleft palate, hydrocephalus, optic nerve atrophy and port wine stains (1). This highlights the importance of a detailed physical examination to rule out associated anomalies. Particularly if underlying tissues and bone are absent, there may be an increased risk for infection extending intracranially through the defect. However, there are generally no significant complications long term. Occasionally, extensive lesions require intervention, such as skin grafting; however, in the neonatal period, these lesions are typically managed conservatively (1). Various forms of aplasia cutis congenita exist, including atrophic, membranous and bullous varieties. Bullous aplasia cutis congenita should be considered on the differential for neonates with vesiculobullous eruptions, particularly if the lesions are present on the scalp immediately at birth. The presence of a hair collar sign aids the clinician in distinguishing bullous aplasia cutis congenita from other etiologies of neonatal vesiculobullous lesions.

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