What is the Frieden Classification for Aplasia Cutis?

When your doctor mentions the Frieden classification, they are referring to a standardized medical system used to categorize aplasia cutis congenita (ACC) based on where the missing skin is located and whether there are any other physical differences present. For parents, hearing this term can be confusing, but categorizing the lesion into one of nine groups simply helps the medical team predict how the skin will heal, check for hidden health risks, and coordinate the right specialists for your child’s specific needs ^[1][2].

Why Doctors Use the Frieden Classification

Aplasia cutis congenita is not always just a surface-level skin condition; sometimes, it serves as a clue about how a baby developed in the womb. Created in 1986, the Frieden classification system acts as a clinical roadmap. By identifying exactly which group a baby belongs to, doctors know whether they need to look deeper—such as ordering an ultrasound to check the skull beneath the skin—or if they can safely focus on simple wound care ^[2][3].

This system ensures that if there are associated internal or genetic conditions, they are caught early so that your child gets the safest, most comprehensive care possible.

The 9 Frieden Classification Groups

The system organizes ACC into nine distinct groups. Your doctor will carefully examine your baby from head to toe to determine which group applies.

• Group 1: Scalp ACC without major anomalies. This is by far the most common form ^[4]. It typically involves a single, small patch of missing skin at the very top of the head (the vertex). In this group, the issue is isolated to the skin, though doctors will sometimes check to ensure the skull bone immediately underneath has fully closed, as delayed bone healing can sometimes happen even in isolated cases ^[5][6]. In most babies in Group 1, the spot heals well with gentle wound care (such as applying protective ointment and keeping it clean), leaving only a small, bald scar ^[7][3].
• Group 2: Scalp ACC with limb abnormalities. Sometimes called Adams-Oliver syndrome, babies in this group have missing scalp skin along with differences in their hands or feet, such as shortened or missing fingers and toes ^[5][8]. Genetic testing is often recommended for this group.
• Group 3: Scalp ACC with birthmarks. The missing skin occurs alongside other distinct skin changes, such as epidermal nevi (raised, colored birthmarks) or sebaceous nevi ^[9][10].
• Group 4: ACC over deeper developmental issues. Unlike Group 1, where any bone delay is localized, this is a critical group to identify because the skin defect sits directly over a deeper embryologic malformation, such as a spinal defect (neural tube defect) or brain tissue protruding through a significant gap in the skull. Identifying Group 4 ensures specialists are brought in to address the deeper, hidden malformation safely ^[1][11].
• Group 5: ACC associated with fetus papyraceus. This occurs in twin or multiple pregnancies where one baby did not survive early in the pregnancy (a “vanishing twin”). This event can leave the surviving baby with extensive, symmetrical, star-shaped patches of missing skin on their body or limbs ^[12][13].
• Group 6: ACC with skin blistering. Often historically called Bart syndrome, this group is linked to Epidermolysis Bullosa (EB), a genetic condition where the skin is highly fragile and blisters easily ^[5]. Genetic testing may be utilized to identify the specific type.
• Group 7: ACC on the limbs without blistering. The missing skin is found on the arms or legs, but the surrounding skin is not fragile and does not blister ^[14].
• Group 8: ACC caused by pregnancy exposures. This group is linked to very specific and rare exposures to certain medications (like anti-thyroid drugs such as methimazole) or severe infections (like varicella or herpes viruses) while the baby was in the womb ^[15]. It is important to know that these exposures are uncommon, and normal common illnesses during pregnancy do not cause this.
• Group 9: ACC linked to genetic syndromes. The missing skin is part of a broader genetic condition, such as Trisomy 13 or Wolf-Hirschhorn syndrome ^[1][16].

What This Means for Your Care

Learning that a diagnosis falls into a specific medical “group” can sound intimidating, but it is actually a vital tool that protects the patient. For most babies in Group 1, treatment is highly individualized but often involves simple wound care at home. If the diagnosis falls into another group, the classification simply tells the care team exactly which experts—like a pediatric neurologist, geneticist, or orthopedic surgeon—should be involved to provide the best possible support.