Random Dermatology MCQ - Aplasia Cutis Congenita

A newborn is noted to have a solitary, well-demarcated, oval-shaped defect over the vertex of the scalp. The lesion is 2 cm in diameter, has a clean, smooth base without inflammation, and is partially covered by a thin, translucent membrane. There is no underlying bony defect. The infant is otherwise healthy. What is the most likely diagnosis and the most common associated finding in this classic presentation?

A. Aplasia cutis congenita of the scalp, which is often an isolated finding but can be associated with limb anomalies in certain syndromes.
B. A traumatic forceps injury, which would show signs of acute inflammation or bruising.
C. Focal dermal hypoplasia (Goltz syndrome), which presents with linear, atrophic lesions and fat herniation.
D. Congenital candidiasis, which presents with erosions and pustules, not a clean membrane-covered defect.
E. Epidermolysis bullosa, which presents with blisters and erosions in response to minimal trauma.

Correct Answer: A. Aplasia cutis congenita of the scalp, which is often an isolated finding but can be associated with limb anomalies in certain syndromes.

Answer and Explanation

The correct answer is A. This question describes the classic "membranous" or "membranous" type of aplasia cutis congenita (ACC) affecting the vertex of the scalp in a newborn. The key features are the solitary, oval, non-inflammatory defect with a smooth base and characteristic "hair collar" sign (a ring of long, dark hair surrounding the lesion) that is sometimes present, though not explicitly mentioned here. The translucent membrane is a classic finding. This form (Type 1 ACC) is most often sporadic and isolated. However, it is crucial to know that ACC can be associated with other anomalies, most notably limb abnormalities (e.g., in Adams-Oliver syndrome).

Why the Other Options are Incorrect:

• B. Traumatic forceps injury: This would present with bruising, abrasion, or laceration in a pattern corresponding to the instrument, not as a clean, congenital, membrane-covered defect.

• C. Focal dermal hypoplasia (Goltz syndrome): This is an X-linked dominant disorder characterized by linear streaks of atrophic, hypoplastic skin that often herniate fat ("fat papillomas"), not a full-thickness scalp defect.

• D. Congenital candidiasis: This presents as a diffuse, scaly, erythematous rash or pustules/erosions, not a solitary, clean scalp defect.

• E. Epidermolysis bullosa: This presents with blisters and erosions at sites of friction or trauma, not as a single, well-defined, congenital defect.

Additional High-Yield Information for Exams:

• Classification (Frieden's Classification): Type I is the most common: Scalp ACC without multiple anomalies. The question highlights the importance of knowing other types:

  • Type II: Scalp ACC associated with limb reduction abnormalities (Adams-Oliver syndrome).

  • Type V: ACC associated with placental infarcts or thrombosis (e.g., in fetus papyraceus).

  • Type VI: ACC associated with epidermolysis bullosa.

  • Type VII: ACC localized to the extremities without blistering.

  • Type VIII: ACC caused by teratogens (e.g., methimazole, carbimazole).

  • Type IX: ACC associated with malformation syndromes (e.g., Trisomy 13, Johanson-Blizzard syndrome).

• Differential Diagnosis: Includes birth trauma, ectodermal dysplasias, and other congenital erosive/vesicular disorders. The clean, non-inflammatory appearance and specific location are key.

• Associated Conditions & Prognosis:

  • Adams-Oliver Syndrome: The most important syndromic association (Type II ACC). Features include ACC of the scalp and terminal transverse limb defects (e.g., shortened digits, syndactyly, absence of distal limbs). Cardiovascular anomalies (e.g., cutis marmorata telangiectatica congenita, heart defects) are also common.

  • Prognosis: For isolated scalp lesions, prognosis is excellent. Small lesions heal spontaneously by epithelialization over weeks to months, leaving a scar with alopecia. Large lesions or those with a bony defect may require surgical repair.

• Management & Rationale:

  • Rationale: The goals are to prevent infection, promote healing, rule out underlying bony defect or serious associated anomalies, and determine if the lesion is isolated or syndromic.

  • First-line for a small, isolated lesion: Conservative management with gentle cleansing and application of a bland ointment (e.g., petrolatum) to keep the area moist and prevent eschar formation, which can delay healing. The membrane often dries and falls off.

  • Essential Investigations:

    • Imaging: Skull ultrasound or X-ray to rule out an underlying bony defect (which increases risk of meningitis) and cranial ultrasound to evaluate for intracranial vascular anomalies (e.g., in Adams-Oliver).

    • Physical Examination: A careful, full-body examination is mandatory to look for limb abnormalities, other cutaneous lesions (e.g., cutis marmorata), and signs of other syndromes.

  • Surgical Intervention: Indicated for large lesions, those with significant bleeding, or those with a bony defect that fails to ossify.