Cutis aplasia, formally called aplasia cutis congenita (ACC), is a condition where a baby is born with one or more areas of missing skin. The affected spot looks like a raw, open wound or sometimes a healed scar, and it most commonly appears on the scalp near the crown of the head. It is rare, and while the appearance can be alarming, most cases heal well with basic wound care and no surgery.
What It Looks Like at Birth
The missing skin can range from a small, coin-sized patch to a larger area spanning several centimeters. Some lesions are shallow, affecting only the outermost layers of skin, while deeper ones can extend through the full thickness of skin and, in rare cases, down to the bone or the membranes covering the brain. At birth, the area may appear as an open, glistening wound, a thin membrane, or occasionally as a flat, hairless scar if it partially healed in the womb.
The scalp is the most common site, but aplasia cutis can also appear on the trunk, arms, legs, hands, and feet. Some babies have a single lesion, while others have multiple patches, which may be round, oval, star-shaped, or linear. Hair does not grow in the affected area, and once healed, the spot typically remains as a smooth, hairless scar.
What Causes It
There is no single cause. The condition likely results from a disruption in skin development during pregnancy, and several factors have been identified. Genetic mutations play a role in some cases, particularly when cutis aplasia runs in families or appears as part of a broader syndrome. Disrupted blood flow to the developing skin, incomplete closure of the neural tube, and intrauterine infections can also contribute.
Certain medications taken during pregnancy have been linked to the condition. Methimazole, a drug used to treat overactive thyroid, has received the most attention, though the evidence stops short of proving a direct causal relationship. Infections with varicella (chickenpox) or herpes simplex during pregnancy are recognized triggers as well. In twin pregnancies, the death of one twin early in gestation (known as fetus papyraceus) or placental infarcts can cause multiple skin defects in the surviving twin.
The Nine Types
Dermatologists classify aplasia cutis congenita into nine groups, a system proposed by Frieden in 1986 that is still used today. The groups are organized by where the missing skin is located and whether other abnormalities are present.
- Group 1: Scalp lesion without other major anomalies. This is the most common type by far.
- Group 2: Scalp lesion with limb abnormalities such as shortened fingers, fused digits, or clubfoot.
- Group 3: Scalp lesion alongside certain birthmarks (epidermal or organoid nevi), sometimes with eye abnormalities or seizures.
- Group 4: Skin defect sitting over a deeper structural malformation, such as a spinal defect or abdominal wall abnormality.
- Group 5: Multiple skin defects in a symmetric pattern, linked to a lost twin or placental infarcts. Lesions often appear star-shaped or linear across the scalp, chest, and limbs.
- Group 6: Skin absence on the extremities associated with epidermolysis bullosa, a genetic blistering condition.
- Group 7: Skin absence on the shins, hands, or feet without blistering and without other anomalies.
- Group 8: Skin defects caused by specific teratogens, including methimazole or intrauterine infections.
- Group 9: Skin defects as part of a broader genetic syndrome, such as trisomy 13, Adams-Oliver syndrome, or Johanson-Blizzard syndrome.
Group 1, the isolated scalp defect, accounts for the majority of cases. Most parents dealing with cutis aplasia will be in this category, where the prognosis is generally excellent.
Associated Genetic Syndromes
When cutis aplasia appears alongside other birth defects, doctors will evaluate for underlying syndromes. Adams-Oliver syndrome combines scalp skin defects with limb abnormalities, particularly shortened or missing fingers and toes. Trisomy 13, a serious chromosomal condition, includes scalp defects among its features. About 15% of babies with Wolf-Hirschhorn syndrome, caused by a deletion on chromosome 4, also have a scalp skin defect.
An isolated patch of missing skin on the scalp with no other abnormalities is far less likely to signal a genetic syndrome. But when multiple defects are present, genetic testing and karyotyping are typically recommended to guide care.
How It Is Detected
Most cases are diagnosed at birth when the skin defect is immediately visible. In some cases, prenatal ultrasound can pick up signs before delivery. Standard two-dimensional ultrasound can detect structural abnormalities in the limbs, and three-dimensional ultrasound offers more detailed views of skin coverage and the surface anatomy of fingers and toes. On ultrasound, normal fetal skin appears as a bright (hyperechoic) line, and when aplasia cutis is present, that bright line is absent in the affected area. If a defect is suspected prenatally, fetal genetic testing is generally recommended.
Potential Complications
Small, superficial lesions carry minimal risk. Larger or deeper defects, especially on the scalp, come with more serious concerns. The major risks are hemorrhage, infection (including meningitis if the brain’s protective membranes are exposed), and blood clots in the large vein that runs along the top of the skull, called the sagittal sinus. These complications are uncommon but can be life-threatening when they occur, which is why deeper scalp defects are monitored closely in the newborn period.
Treatment and Healing
The good news is that most cases of cutis aplasia heal on their own with conservative wound care, even when the defect is large. Treatment focuses on keeping the wound clean, moist, and protected from infection. Typical wound care involves gentle rinsing with saline, applying a topical agent such as silver sulfadiazine cream or antibiotic ointment, and covering the area with a sterile dressing. In one published case, even lesions as large as 14 by 12 centimeters healed successfully without surgery using this approach.
Healing timelines vary with the size and depth of the defect. Small lesions may close within weeks, while larger ones can take several months. As the wound heals, a hairless scar forms. Once the area is stable, a cream to soften scar tissue may be used to improve the cosmetic result.
Surgery is not the first-line treatment. It is generally reserved for correcting cosmetic concerns after the wound has healed, such as tissue expansion to stretch nearby hair-bearing skin over the scarred area. In the rare situation where underlying bone is missing and vital structures like the brain or its blood vessels are exposed, more urgent surgical coverage may be needed. But for the vast majority of babies with cutis aplasia, conservative care is simple, effective, and sufficient.