A newborn girl is noted to have a midline lumbar depression at birth. She is twin A born by uncomplicated vaginal delivery at 38 weeks and 5 days of gestation to a 31-year-old gravida 2, now para 3 mother after dichorionic/diamniotic twin pregnancy via in vitro fertilization. The pregnancy was otherwise complicated by diet-controlled gestational diabetes and maternal history of herpes simplex virus without lesions or prodromal symptoms at the time of delivery. Maternal medications during pregnancy included prenatal vitamins and valacyclovir prophylaxis. The infant transitions well and requires only routine care at the time of delivery.Her initial physical examination reveals a circumferential 1 × 0.5-cm punched-out, skin-covered lesion overlying the midline spine at the level of L4-L5 vertebrae with surrounding dermal melanocytosis extending from the midline to the left flank (Fig 1). The examination findings are otherwise normal, with appropriate tone for age, symmetrical movement of all extremities, and intact neonatal reflexes. Spinal ultrasonography is performed on the second day after birth because of the cutaneous findings and is notable for a low-lying spinal cord with conus termination at the level of L3-L4 with a thickened appearance of the filum terminale. Head ultrasonography is also performed, and findings are normal.The differential diagnosis of a punched-out skin lesion overlying the lumbar region includes, but is not limited to, a lumbosacral dimple, vascular malformation, skin atrophy, cutis aplasia, dermal sinus, and ulcerative or necrotizing skin infection. A sacral dimple is a depression in the skin of the lower back, typically occurring just above the crease between the buttocks. Lumbosacral dimples are common in newborn infants and are usually normal anatomic variants when solitary and located entirely in the gluteal cleft. However, the presence of multiple dimples, dimples with a diameter greater than 5 mm or located greater than 2.5 cm above the anus, or those associated with other cutaneous abnormalities warrant further evaluation for underlying occult spinal dysraphism (OSD). (1) Vascular malformations, including port-wine stains and hemangiomas, vary from simple macules to complex structures involving multiple layers of skin and subcutaneous tissue. They can be composed of arteries, veins, capillaries, and/or lymphatic vessels and may be markers of OSD when overlying the spine. Skin atrophy is characterized by thinning of the epidermis, dermis, and underlying subcutaneous tissue. Cutis aplasia, or aplasia cutis congenita (ACC), is the congenital absence of skin, which can appear ulcerated or scarred at birth. (2) Primarily a clinical diagnosis, cutis aplasia overlying the lumbosacral spine has also been associated with OSD. (2)A dermal sinus is a midline epithelium-lined tract from the skin to the cranial or spinal cavity caused by incomplete neural tube closure. Dermal sinuses predispose the infant to serious infections, including bacterial meningitis and intraspinal abscesses. (1)(3) Necrotizing soft tissue infections are characterized by the destruction of the skin and underlying soft tissues and can involve the epidermis, dermis, subcutaneous tissue, fascia, and muscle. In neonates, necrotizing infections most typically occur in the abdominal or perineal area as omphalitis, balanitis after circumcision, or surgical site infection after hernia repair. (4)Term infants with midline cutaneous lesions overlying the spine, including elevated lesions (eg, tissue appendages, masses, hair patches), cutis aplasia, hemangiomas, or atypical sacral dimples, require neuroimaging with spinal ultrasonography and/or magnetic resonance imaging (MRI) to ensure early detection of underlying spinal dysraphism. (5) Due to concern for underlying OSD, our patient underwent a nonsedated MRI of the head and lumbar spine. Although notable for suboptimal quality due to low image resolution and significant motion artifact, the MRI demonstrated a low-lying conus medullaris without clear visualization of the filum terminale. The diagnosis of cutis aplasia with an underlying tethered spinal cord is made based on physical examination and neuroimaging.First reported in the mid-18th century, cutis aplasia, also known as ACC, is a dermal examination finding that can be seen in isolation (incidence 1:3,000) or in conjunction with various trisomies or syndromes. (6)(7) Patients with ACC are classified into 1 of 9 groups based on the location and configuration of the skin defect, presence of associated abnormalities, and mode of inheritance. This classification system has recently been updated to include specific molecular-genetic diagnoses associated with some lesions. (2)(8) Patients with ACC have a 20% mortality rate, although this is likely secondary to associated underlying syndromes rather than the cutaneous lesion itself. (9)(10) Sex distribution is equivalent and familial cases have been reported, although no singular underlying cause has been identified. (11) Most lesions are small (<3 cm in diameter) but have been reported up to 7.5 cm. (12)(13) The lesion is typically a well-circumscribed area with absence or thinning of the epidermis and underlying dermal atrophy on histologic examination. (12) Most cases of cutis aplasia occur on the scalp (∼80%–85%) and extremities; alternative locations include the anterior chest wall and trunk. (2) A ring of dark, coarse hair may surround the cutaneous lesion, known as “hair collar sign.” (14)Cutis aplasia of the scalp may be associated with aplasia of the skull itself as well as a sagittal or dural sinus hemorrhage. (12) Although isolated cutis aplasia in the lumbosacral region is a well-recognized neurocutaneous marker for OSD, our literature review revealed only 1 case report and 1 textbook photograph of this rare, but important, physical examination finding. (15)(16)ACC has also been noted in surviving infants of multiple-gestation pregnancies complicated by fetus papyraceus, a phenomenon of fetal mummification after intrauterine death. In these cases, the questionable area can appear in a stellate, rather than a circumferential, shape and usually appears on the trunk. (17) Interestingly, fetus papyraceus has been increasingly seen in the era of assisted reproductive technology and a higher incidence of multiple-gestation pregnancies, leading to a proposed increased risk of cutis aplasia in this specific population. However, up to 95% of the reported fetus papyraceus cases are seen in monochorionic twin pregnancies with a first-trimester fetal demise, and our case was the product of a dichorionic/diamniotic twin pregnancy. In addition, the lesion in our patient was the traditional circumferential shape versus the alternative stellate pattern commonly seen in fetus papyraceus. (17) The fetus papyraceus lesion can have a similar appearance as skin atrophy, although the history of the twin gestation will be foretelling.The treatment of cutis aplasia is focused primarily on management of the cutaneous defect. Small lesions (<3 cm) may not require surgical intervention because the skin typically heals via secondary intention. This is generally the case with parchment paper–like lesions, which have the appearance of thinning tissue with a crinkled or scarlike external layer. Wound care of granulomatous-appearing lesions includes local infection precautions to allow epithelialization of the lesion, which may take weeks to months. Commercial wound care products may decrease healing time. More extensive lesions (≥4 cm) may require the involvement of dermatology and plastic surgery for tissue expansion and skin grafts or flaps depending on the breadth of the area involved and surgeon evaluation/preference. (18) Lesions over bony prominences at risk for prolonged pressure in primarily supine-positioned infants carry a substantial risk of infectious and hemorrhagic complications, and these lesions may require early surgical intervention. (7)(19)Cutaneous markers concerning for OSD, including cutis aplasia, should prompt medical care teams to perform neuroimaging studies. If a tethered cord is identified on MRI, management varies based on the child’s age at diagnosis. For patients presenting with neurologic symptoms such as pain or loss of bladder or bowel control, timely repair is indicated to preserve neurologic function. The decision to perform the untethering is controversial in asymptomatic patients and requires a risk/benefit analysis because the procedure does not consistently result in improved neurologic outcomes and carries a risk of subsequent retethering. (20) All children with a tethered cord warrant ongoing evaluation by both their primary care provider and subspecialty teams through adolescence to monitor for neurologic dysfunction and orthopedic abnormalities.Due to clinical suspicion, the infant was transferred to a pediatric subspecialty center to undergo MRI at 3 months of age. The repeated MRI confirmed a low-lying conus medullaris terminating at the mid-L3 vertebral body with a rightward deviation of the most inferior aspect (Fig 2). After diagnostic evaluation by pediatric neurosurgery, the infant underwent an uncomplicated tethered cord release and excision of the overlying cutis aplasia at 6 months of age. After surgery she remained at the tertiary care center for 2 weeks to facilitate immediate postoperative management and recovery. After discharge she continues monthly home-based early intervention monitoring with physical therapy for gross motor development follow-up. She is progressing well, with no current neurodevelopmental impairments. Owing to the risk of retethering, follow-up with the neurosurgeon may be required if she demonstrates any new signs of neurologic deterioration, including gait abnormality, muscle atrophy, bowel or bladder dysfunction, lumbosacral pain, foot deformities, or scoliosis.