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At a glance

A usually inherited disorder that manifests at birth typically as a single (occasionally multiple), circumscribed or more extensive skin lesion that may extend to underlying tissues and usually heals with a hypertrophic scar. The majority of ACC patients have no other congenital anomalies (non-syndromic ACC), but neurologic and cardiac comorbidities have occasionally been described.

Synonyms

Congenital Scalp Defect; Congenital Defects of Skull and Scalp.

Incidence

ACC affects approximately 1-3 in 10,000 newborns. Females are approximately 1.4 times more often affected than males. No racial predilection has been reported.

Genetic inheritance

Most cases seem to be sporadic, but autosomal dominant and autosomal recessive inheritance have also been reported. Recent research identified a mutation in the ribosomal GTP-ase BMS1 (the ribosome biogenesis factor) that has been mapped to chromosome 10q11.21 and results in a decreased cell proliferation rate and can lead to autosomal dominant, non-syndromic ACC.

Pathophysiology

The pathomechanisms that lead to the skin defects are not well understood, but it has been speculated that a skin cell proliferation defect in areas where a steady expansion of brain structures requires rapid proliferation of the overlying skin may be involved in ACC. Another pathogenetic factor that has been discussed is amniotic bands resulting from early rupture of the amniotic membranes. Environmental factors (such as toxins and teratogens [eg, maternal cocaine abuse, misoprostol, methimazole exposure during pregnancy, intrauterine infections] and early embryonic vascular abnormalities with compromised blood flow to a circumscribed area of the skin) have also been considered.

Diagnosis

Based on the clinical findings. While the skin lesions can occur anywhere on the body, more than 80% of all solitary lesions are found on the scalp in close proximity to the vertex of the skull. There is an extremely rare and universally fatal variant of ACC where basically the entire body surface is affected by the disease.

Clinical aspects

Noninflammatory and well-demarcated lesions have different shapes, with diameters ranging from 0.5 to 10 cm with dilated scalp veins radiating from the periphery of scalp defect. The defect is often located in the area of the vertex of the skull. In a few cases, almost complete absence of skin and skull bone (partial acrania) have been reported and are associated with high mortality secondary to infection, hemorrhage, and/or thrombosis. The aspect of the lesion is quite variable because it depends upon the stage of intrauterine development at the time of the insult. Defects caused in early gestation may have healed before birth and appear as an atrophic, transparent membrane or a fibrotic scar. However, defects that develop later in gestation may present as ulcerations of variable depth. Although most defects are limited to the epidermis, occasionally the ulcerations are deeper and involve ...

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