What is the pathophysiology of 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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Answer

After the onset of puberty, sex hormones affect the pilosebaceous glands, and subsequently, the hair follicle becomes distended with keratin. In pilonidal disease, a folliculitis develops, which produces edema and follicle occlusion. The infected follicle extends and ruptures into the subcutaneous tissue, forming a pilonidal abscess. This results in a sinus tract that leads to a deep, subcutaneous cavity.

In 90% of cases, the direction of the sinus tract is cephalad, which coincides with the directional growth of the hair follicle. This usually places the tracking follicle approximately 5-8 cm from the anus. In the rarer instance that the sinus is located caudally, it is usually found 4-5 cm from the anus. The caudal location of the sinus can be easily mistaken for a fistula-in-ano and should be considered before treatment. [3]

The laterally communicating sinus overlying the sacrum is created as the pilonidal abscess spontaneously drains to the skin surface. The original sinus tract from the natal (intergluteal) cleft becomes an epithelialized tube. The laterally draining tract becomes a granulating sinus tract opening.

Loose hairs are drilled, propelled, and sucked into the pilonidal sinus by friction and the movement of the buttocks whenever a patient stands or sits. This bending and sitting action tightens the skin of the gluteal cleft and lifts it from the fascia. The negative pressure drives hair deeper into the sinus and appears to be exaggerated with a deep gluteal cleft. [4]

Hair enters tip first, and the barbs on the hair prevent it from being expelled, causing the hair to become entrapped. Physical examination occasionally may reveal a tuft of hair emerging from the midline opening in the natal cleft. This trapped hair stimulates a foreign body reaction and infection. Rarely, foreign bodies other than human hair can cause this disease process. Rare case reports exist in which the hair did not come from the patient but instead came from a bird's feather, the type used to stuff feather bedding.


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