What is the anatomy of the pilonidal sinus relative to pilonidal disease?

Updated: Jun 11, 2018
  • Author: M Chance Spalding, DO, PhD; Chief Editor: John Geibel, MD, MSc, DSc, AGAF  more...
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A pilonidal sinus can occur in many different areas of the body, but most are found in the sacrococcygeal area, in the natal cleft, approximately 5 cm from the anus. The characteristic pilonidal sinus is a midline opening in the sacrococcygeal area in the natal cleft. Not uncommonly, the patient may have a series of openings in the midline or may have secondary lateral openings superior to the midline pit.

The sinus tract itself is smooth and lined with squamous epithelium. Eventually, the sinus tract leads to a subcutaneous cavity lined with granulation tissue and filled with nests of hair. The sinus tract openings are actually an extension of the deep cavity. This is why an abscess formation may present either in the midline or lateral to the midline.

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