Early hair follicles with sloping downgrowth
Hair being produced
Surface hair patterning evident
Normal and Abnormal Hair Patterns encephalocoele or microcephaly, would be expected to produce aberrations in scalp hair patterning, and these are indeed found. Eighty-five percent of patients with primary microcephaly have altered scalp hair patterning, indicating an early onset of the problem in brain development. Aberrant scalp patterning is also found frequently in association with established syndromes including Down syndrome. Thus, aberrant scalp hair patterning may be used as an indicator of altered size and/or shape of the brain before 12 weeks gestation.
On the forehead, two normal patterns of hair growth can be distinguished: the forehead stream (growing from the area of inner canthus upwards), and the parietal stream (growing from the parietal whorl to the supraorbital area). As the two steams meet, they give rise to the shape of the eyebrows. Eyebrow shape also reflects the underlying supraorbital ridge shape present in early fetal life. At 18 weeks of gestation, hair grows over the entire scalp and face. Later the hair growth in the eyebrow area and over the scalp will predominate, while hair growth over the remainder of the face suppressed.
Early anomalies in development of the eye and face can secondarily affect hair patterning over the eyebrow and frontal area, presumably related to altered growth tension of the skin during the period of hair follicle formation. Gross anomalies in development of the ear can also secondarily affect hair patterning, especially in the sideburn area.
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