The normal location of the parietal hair whorl is several centimeters anterior to the posterior fontanelle, the majority (56 percent) being located slightly to the left of the midline. Thirty percent of hair whorls in normal individuals are right sided, and 14 percent have a midline location. Five percent of individuals have bilateral hair whorls posteriorly. Ninety-four percent of hair whorls are clockwise and 5 percent are counter-clockwise.
From the posterior hair whorl, the hair sweeps anteriorly toward the forehead. The growth of the forebrain and the upper face influences the bilateral frontal hairstreams, which emerge from the ocular puncta and arch outward in a lateral direction. Usually the anterior and posterior hair-streams meet on the forehead. If they meet above the forehead, an anterior upsweep of hair will result (cowlick). A mild to moderate anterior upsweep is found in 5 percent of normal individuals.
Frontal upsweeps to the anterior hairline, as well as unruly hair patterns, have been linked to abnormalities of frontal lobe development.
A widow's peak along the frontal scalp line is probably the result of the bilateral periorbital fields of hair growth suppression intersecting lower than usual on the forehead. This can occur when the periorbital fields of hair growth suppression are smaller than usual, or when they are widely spaced. Wide spacing also explains the association between ocular hypertelorism and widow's peak. The only common anomaly of the posterior hairline is low placement with a squared distribution, which may be seen in Turner syndrome, in Noonan syndrome, and with abnormalities of cervical spine fusion or segmentation.
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