The nevus simplex, or salmon patch, is the most common, benign vascular malformation seen in infants of all races and ethnicities (Kanada et al., 2012). Studies estimate its prevalence to be anywhere between 20% and 80% of newborns (Juern et al., 2010).
Nevus simplex usually affects sites corresponding to areas of neuroectodermal fusion during embryogenesis. The lumbosacral, occipital, glabellar, and scalp regions affected by nevus simplex are also known sites for neural tube defects or dysraphism (Juern et al., 2010). When nevus simplex involves the face, the overlying skin is derived from an embryologic structure known as the frontonasal prominence (Spock et al., 2015). Thus, nevus simplex is thought to be a persistence in fetal circulation secondary to defective neural regulation of the capillaries supplying the skin of affected regions (Shirley et al., 2013).
CLINICAL FEATURES AND NATURAL COURSE
Nevus simplex typically presents as a flat, dull, pink macule or patch that is blanchable on physical examination. It occurs in approximately 30%–40% of white infants but is less prevalent in infants with skin of color (Techasatian et al., 2019). The areas most affected include the posterior neck and occiput; however, there may also be involvement of the scalp, forehead, eyelids, glabella, or face, including the nose and nasolabial regions (see Figure 1 for example images; Juern et al., 2010). More extensive involvement can include multiple sites and is known as nevus simplex complex (Juern et al., 2010). When located on the posterior neck, the lesion is commonly referred to as a stork bite. When located on the forehead or glabella, the lesion is commonly referred to as an angel kiss. When located in the lumbosacral region, the lesion is referred to as a butterfly-shaped mark. Sacral lesions may be associated with occult spinal dysraphism (OSD) in children with another local defect, such as a dimple, sinus, excess hair, or skin aphasia (Choi et al., 2020). However, an isolated sacral lesion does not necessarily predict an increased risk of OSD on its own, and in unclear cases, prompt referral to a pediatric dermatologist or experienced pediatric practitioner should be considered.
Nevus simplex is typically an isolated lesion without any associated findings. Lesions on the posterior neck or occiput, however, may develop an associated overlying dermatitis, a condition known as Meyerson phenomenon. Meyerson phenomenon, also known as halo dermatitis, is characterized by the presence of a halo or eczematous patch over a preexisting skin lesion, including a nevus simplex (Loh & Kenny, 2010).
Nevus simplex is a clinical diagnosis. The differential diagnosis may include a port wine stain (PWS) or nevus flammeus. Unlike a nevus simplex, a PWS tends to be unilateral and persists beyond the first or second year of life (Elias et al., 2021). Physical examination findings that may help differentiate a PWS from a nevus simplex include a lesion that progressively darkens or has vascular blebs on its surface (Choi et al., 2020). PWSs have an early, temporary lightening shortly after birth, which reflects fetal hemoglobin reaching its physiologic nadir. This should not be confused with the lightening seen in nevus simplex as it occurs earlier. If these findings are challenging to appreciate, a referral to a dermatologist is recommended to differentiate between the two as a PWS can be either an isolated lesion or associated with various syndromes.
Because 95% of facial lesions fade within the first 2 years of life (Juern et al., 2010), treatments are usually unnecessary for nevus simplex. Lesions on the posterior neck or scalp may persist indefinitely. These lesions are usually covered by hair and also require no treatment. Exceptions include lesions with an associated overlying dermatitis, which may respond to topical corticosteroid treatment or pulsed dye laser if the lesion is in cosmetically sensitive areas without hair.
If sacral lesions are present with additional local findings, magnetic resonance imaging (MRI) of the spine may be considered to work up the possibility of OSD. MRI is the preferred imaging modality as multiple abnormalities are often present in patients with OSD.
Nevus simplex is a benign vascular malformation most commonly seen in infants. Although nevus simplex generally fades over time and thus requires no treatment, a referral to a pediatric dermatologist should be considered when there is an atypical clinical phenotype or additional local anomalies.
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