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Causes and Diagnosis of ACC

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Aplasia cutis congenita (ACC) is a rare birth defect where a baby is born missing a patch of skin, usually on the scalp. It typically happens by chance due to blood flow interruptions, genetics, or rare pregnancy exposures. Doctors diagnose ACC by examining the skin for missing hair follicles.

Key Takeaways

  • • Aplasia cutis congenita (ACC) is a condition where a baby is born with a localized absence of skin, most often happening by chance.
  • • Potential causes include interrupted blood flow during fetal development, genetic mutations, and rarely, certain medications or infections during pregnancy.
  • • ACC can be associated with a 'vanishing twin' (fetus papyraceus) due to changes in blood flow in the womb.
  • • Doctors distinguish ACC from birth trauma and other conditions by looking for the complete absence of skin appendages like hair follicles and sweat glands.
  • • The presence of a 'hair collar sign' helps doctors determine if the condition goes deeper than the surface skin.

When a baby is born with a skin defect, parents often search for a reason. It is a complex medical condition with several possible biological triggers. In the vast majority of cases, ACC is completely out of your control and happens entirely by chance [1][2].

Why Does It Happen?

The exact cause of ACC is often unknown, but researchers have identified several biological mechanisms that can lead to the absence of skin at birth:

  • Vascular Disruption: This is one of the most common theories. It suggests that a brief interruption in blood flow to the skin occurred while the baby was developing in the womb [3][4]. This is particularly common in twin pregnancies where one twin stops developing (a condition called fetus papyraceus), which can cause blood flow changes in the surviving baby [5][6].
  • Genetic Factors: Some cases are linked to specific genetic mutations that affect how skin and blood vessels form [7][8]. While many cases are sporadic (happening for the first time in a family), some can be part of inherited syndromes like Adams-Oliver syndrome [9].
  • External Triggers: Rarely, exposure to certain substances or infections during the first trimester can interfere with skin development. These include teratogens such as methimazole (used to treat an overactive thyroid) [10][11] or intrauterine infections like varicella-zoster (chickenpox) [12][13]. It is important to remember that these are exceedingly rare causes.

How Doctors Confirm the Diagnosis

Because ACC can look like other conditions, doctors use a process called differential diagnosis to rule out other possibilities. They are looking to distinguish ACC from:

  • Birth Trauma: Scalp injuries from forceps or vacuum extractors can look similar. However, birth trauma is usually associated with a difficult delivery and typically heals differently than ACC, which is a developmental absence of skin rather than a mechanical injury [14][11].
  • Nevus Sebaceous: This is a common birthmark that often appears on the scalp. Unlike the open or scarred appearance of ACC, a nevus sebaceous is typically a yellowish-orange, slightly raised, pebbly patch [15][16].
  • Epidermolysis Bullosa (EB): This is a group of genetic disorders that cause the skin to be very fragile and blister easily. When ACC occurs alongside EB (often with nail abnormalities), it is known as Bart Syndrome [17][18].

Diagnostic Tools

To be certain, specialists may use two main tools:

  1. Dermoscopy: A doctor uses a specialized magnifying lens (dermoscope) to look at the lesion. In ACC, they typically see a shiny, “atrophic” (thinned) patch where hair follicle openings are completely absent [15][19]. They also look for the hair collar sign—a ring of longer, darker hair around the defect—which can sometimes indicate that the defect goes deeper than the skin [20][21].
  2. Histopathology: If a tiny sample of skin is taken (a biopsy), a pathologist looks for the absence of skin appendages, such as hair follicles and sweat glands, and a characteristic thinning of the deeper layers of the skin [22][16]. In ACC, these structures never formed in that specific area.

To learn more about the different groups and how ACC is categorized, visit Types and Classifications of ACC.

Frequently Asked Questions

What causes Aplasia Cutis Congenita (ACC)?
The exact cause of ACC is often unknown, but it typically happens entirely by chance. It may result from a brief interruption of blood flow in the womb, genetic factors, or rarely, exposure to certain medications or infections during pregnancy.
Can a vanishing twin cause my baby's ACC?
Yes, vascular disruption associated with a vanishing twin (known as fetus papyraceus) is one of the common theories for why ACC occurs. Changes in blood flow to the surviving baby can prevent the skin from developing properly in a specific area.
How do doctors tell the difference between ACC and birth trauma?
While scalp injuries from forceps or vacuum extractors can look similar, birth trauma usually follows a difficult delivery and heals differently. ACC is a developmental absence of skin and hair follicles rather than a mechanical injury.
What is the 'hair collar sign' on a baby's scalp?
The hair collar sign is a ring of longer, darker hair surrounding the skin defect. Doctors look for this sign during an examination because it can sometimes indicate that the defect extends deeper than the surface of the skin.
Does taking thyroid medication during pregnancy cause ACC?
Very rarely, taking certain thyroid medications like methimazole during the first trimester can interfere with fetal skin development. If you took this medication, be sure to inform your baby's doctor so they have a complete medical history.

Questions for Your Doctor

  • • Based on the clinical findings, can you explain why you’ve ruled out birth trauma or other conditions like sebaceous nevus?
  • • Does my baby have a 'hair collar sign' around the lesion, and does that change our next steps?
  • • Do we need to perform dermoscopy or a biopsy to confirm the diagnosis, or is the clinical appearance sufficient?
  • • Are there any signs of Bart Syndrome, such as nail changes or blistering elsewhere on the body?

Questions for You

  • • Did I take any medications for my thyroid, like methimazole or carbimazole, early in my pregnancy?
  • • Did I experience any infections, specifically chickenpox (varicella), while I was pregnant?
  • • Was there any mention of a 'vanishing twin' or fetus papyraceus during my prenatal ultrasounds?

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References

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    Oxford medical case reports 2022; (2022(1)):omab141 doi:10.1093/omcr/omab141.

    PMID: 35083055
  2. 2

    Aplasia cutis congenita: a report of two cases from National Hospital Abuja, Nigeria and review of the literature.

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    The Pan African medical journal 2020; (36()):291 doi:10.11604/pamj.2020.36.291.24523.

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    Aplasia Cutis Congenita with Ischemic Cortical Change and Normal Array Cytogenetic Analysis with a Fetus Papyraceus Twin.

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    Trichorhinophalangeal syndrome type II associated with aplasia cutis congenita in a neonate.

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  10. 10

    [Aplasia cutis congenita and antithyroid drugs during pregnancy: Case series and literature review].

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    PMID: 27033749
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    A Case Series of Aplasia Cutis Congenita and Its Management.

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    Aplasia Cutis Congenita in a Newborn Child Associated with Two Fetus Papyraceous.

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    PMID: 26724883
  13. 13

    Aplasia Cutis Congenita as a Sole Manifestation of Congenital Varicella Syndrome.

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    Case reports in pediatrics 2020; (2020()):6147250 doi:10.1155/2020/6147250.

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  14. 14

    Topical sucralfate cream treatment for aplasia cutis congenita with dystrophic epidermolysis bullosa: a case study.

    Yaşar Ş, Yaşar B, Cebeci F, et al.

    Journal of wound care 2018; (27(11)):768-771 doi:10.12968/jowc.2018.27.11.768.

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  15. 15

    Dermoscopic Findings of Scalp Aplasia Cutis Congenita.

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  16. 16

    A Case of Membranous Aplasia Cutis Congenita and Dermoscopic Features.

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  17. 17

    Bart Syndrome: A Case with Extensive Skin Lesions and Multiple Congenital Anomalies in a Preterm Neonate.

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    Bart syndrome with musculoskeletal deformity: a rare case report.

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  19. 19

    Dermoscopic characteristics of membranous aplasia cutis congenita: Report of 56 cases.

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    PMID: 35988062
  20. 20

    Low risk of clinically important central nervous system dysraphism in a cohort study of 69 patients with isolated aplasia cutis congenita of the head.

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  21. 21

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  22. 22

    Aplasia cutis congenita of the scalp: Histopathologic features and clinicopathologic correlation in a case series.

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This page explains the causes and diagnostic process for Aplasia Cutis Congenita (ACC) for educational purposes. Always consult your pediatrician or pediatric dermatologist for an accurate diagnosis and evaluation of your baby's skin.

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