Conclusions: The gross and microscopic pathologic findings in our 354 patients overwhelmingly favor the theory of acquired origin in most patients with pilonidal sinus. The facts appear to show that the reason there has been so much debate over whether pilonidal disease is congenital or acquired in origin is because there are two different types of the disease.
A new classification of pilonidal disease based on etiology is proposed as a result of this study. In this classification the disease is divided into two groups: (1) congenital, and (2) acquired. These two types are further subdivided; the congenital into the neurogenic and ectodermal, and the acquired into the post-traumatic and postsurgical.
Neurogenic and ectodermal pilonidal sinuses are relatively uncommon, probably less than 10 per cent of the total, whereas the acquired variety of post-traumatic and postsurgical lesions constitute 90 per cent of the cases.
(C) The ASCRS 1962