Pilonidal sinus

What is pilonidal sinus?

A pilonidal sinus is a small tunnel in the skin at the top of the buttock cleft, near the tailbone, that often contains hairs. It usually first appears as an abscess. After the abscess settles, many people are left with a sinus that can flare up repeatedly. It is a benign condition and is not linked to cancer.

Pilonidal disease is a long-term inflammatory condition of the skin in the buttock crease, near the tailbone. Hairs, either growing locally or shed from elsewhere, are pushed into the skin and set up irritation and infection. Nearly everyone first notices it as an abscess. Once that settles, many are left with a sinus, a cavity under the skin connected to the surface by one or more small pits.

What causes a pilonidal sinus?

A pilonidal sinus forms when hairs, either growing locally or shed from elsewhere, are pushed into the skin of the buttock cleft by pressure or friction. It is more common in men, in people with thick, stiff body hair, in those who are overweight or sit for long periods, and between puberty and age 40.

• Loose or growing hairs pushed into the skin of the buttock cleft
• Pressure or friction in the area, including long periods of sitting
• Thick, stiff body hair
• Being male
• Being overweight
• Most often occurring between puberty and age 40

What are the symptoms?

A pilonidal sinus may only show as a small pit at the top of the buttock crease. When infected, it causes pain and swelling that can make sitting difficult, redness, and discharge of clear, cloudy or bloody fluid or pus. A severe infection can cause fever, and repeated flare-ups cause ongoing discharge.

• A small pit or dimple at the top of the buttock crease
• Pain and swelling at the top of the cleft, which can make sitting difficult
• Discharge of clear, cloudy or bloody fluid, or pus that may smell
• Redness and tenderness when infected
• Fever or feeling unwell with a severe infection

When should I see a surgeon about a pilonidal sinus?

See a doctor promptly if a lump at the top of the buttocks becomes painful, swollen, bleeding or leaking pus, as these signs of infection often develop over a few days. Seek urgent care for spreading redness or fever. Repeated flare-ups or a wound that is not healing also need review by a surgeon.

The warning signs below need prompt attention.

• A painful, swollen lump at the top of the buttocks that develops over a few days
• Spreading redness, fever or feeling generally unwell
• A wound that is not healing after surgery
• Repeated flare-ups with ongoing discharge

How is it diagnosed?

A pilonidal sinus is diagnosed by examining the buttock crease, where the pits and any swelling are usually visible. Your doctor asks about previous abscesses, discharge and treatment. Further tests are needed only if the diagnosis is uncertain or another condition is suspected.

• Examination of the buttock crease, which usually confirms the diagnosis
• Questions about previous abscesses, discharge and earlier treatment
• Further tests only when the diagnosis is uncertain or another condition is suspected

How is a pilonidal sinus treated?

A sinus that is not infected needs no treatment beyond hygiene and hair removal. An abscess is drained through a small cut. A sinus that keeps flaring is removed, either leaving the wound open to heal or stitching it closed, or treated by endoscopic ablation. Large or recurrent disease may need a flap repair.

• No treatment for a sinus that is not infected, with good hygiene and hair control
• Removal of hair in the area by shaving, hair removal cream or laser
• Draining an abscess through a small cut, with antibiotics if the skin infection is spreading
• Excision with the wound left open to heal from the base, which usually means a longer healing period
• Excision with the wound stitched closed, which heals faster but has a higher risk of wound infection
• Endoscopic ablation, cleaning and sealing the sinus through a camera without a cut
• Flap or plastic surgery for large or recurrent disease

What are the risks and complications?

The main risks after pilonidal sinus treatment are the sinus coming back and wound problems. Leaving the wound open lowers recurrence but takes longer to heal. Closing it heals faster but carries a higher chance of infection, and the wound may need to be reopened.

• The sinus coming back after treatment
• Wound infection, particularly after a closed wound
• Slow healing of open wounds, which need regular dressing changes
• Discomfort and time away from sitting, cycling or sport while healing