Pilonidal Cyst

(Pilonidal Sinus; Pilonidal Abscess)


A pilonidal cyst is a fluid-filled developmental defect at the base of the spine.The terms cyst, sinus, and abscess refer to different stages of the disease process.
  • Cyst—not infected
  • Abscess—pocket of pus
  • Sinus—opening between a cyst or other internal structure and the outside
While the cyst is not serious, it can become infected and may need to be treated if problems develop. When a pilonidal cyst gets infected, it forms an abscess, eventually draining pus through a sinus.
Pilonidal Cysts
Pilonidal cyst
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A pilonidal cyst may be congenital or acquired. If congenital, it probably began as a defect that existed when you were born. Sometime later, the defect allowed an infection to develop. If acquired, it may be the enlargement of a simple hair follicle infection or the result of a hair penetrating the skin and causing an infection.

Risk Factors

The following factors increase your chance of developing a pilonidal cyst:
  • Personal or family history of similar problems such as acne boils, carbuncles, folliculitis, and sebaceous cysts
  • Large amounts of hair in the region
  • Tailbone injury
  • Horseback riding, cycling
  • Prolonged sitting
  • Obesity


A pilonidal cyst may cause:
  • Painful swelling over your sacrum, which is the area just above your tailbone
  • A foul smell or pus draining from that area


You will be asked about your symptoms and medical history. A physical exam will be done. You may be referred to a surgeon for treatment. There are no diagnostic tests required.

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