Pili trianguli et canaliculi is a defect of inner root sheath keratinization: ultrastructural observations of anomalous tonofilament organization in a case.

A 4-year-old Caucasian girl with pili trianguli et canaliculi had distinctive findings. These included unique ultrastructural alterations consisting of tonofilament-desmosomal detachment and tonofilament clumping within inner root sheath cells. We believe that the hair anomaly in this condition may be due to a compromised cytoskeleton with subsequent configurational changes of the inner root sheath. Despite these configurational changes keratinization of the inner root sheath occurs. As inner root sheath keratinization typically precedes keratinization of the hair shaft, the abnormally configured inner root sheath determines the surface characteristics of the hair shaft in pili trianguli et canaliculi.