A pilonidal sinus is an infected tract under the skin between the buttocks. Treatment commonly involves an operation. After the operation one should keep the area free of growing hair by regular shaving or other means of hair removal.
  • Pilonidal means a 'nest of hair'.
  • A pilonidal sinus is a sinus tract which commonly contains hair. It occurs under the skin between the buttocks (the natal cleft) a short distance above the back passage (anus). The sinus track goes in a vertical direction between the buttocks. Rarely, a pilonidal sinus occurs in other sites of the body.

Causes of pilonidal sinus :

The exact cause is not clear. There are various theories. One theory is that the problem may develop from a minor abnormality, which you were born with, in the skin between the buttocks. This may explain why the condition tends to run in some families. Part of the abnormality in this may be that the hairs grow into the skin rather than outwards.
Another theory is the development of skin dimples as a result of local pressure or friction causing damage to the hair follicles. Because of local pressure, growing hair in the natal cleft may get pushed into the skin pits.
Whatever the cause, once hair fragments become 'stuck' in the skin they irritate it and cause inflammation followed by infection and a recurring or persistent infection tends to develop in the affected area. The infection causes the sinus to develop which often contains broken pieces of hair.

Risk factors for pilonidal sinus :

Certain factors increase the risk of developing the condition and include:
  • A job involving a lot of sitting (a sedentary occupation)
  • Being overweight (obesity)
  • A previous persistent irritation or injury to the affected area
  • Having a hairy, deep natal cleft
  • A family history of the condition

Symptoms of pilonidal sinus :

A pilonidal sinus may not cause any symptoms at first. Person may not be aware that he/she has one. Some people notice a painless lump at first in the affected area when washing. However, in most cases, symptoms develop at some stage and can be 'acute' or 'chronic'.

Rapid-onset (acute) symptoms
One may develop increasing pain and swelling over a number of days as a ball of pus with surrounding skin infection (an infected abscess) develops in and around the sinus. This can become very painful and tender.

Persistent (chronic) symptoms
Around 4 in 10 people have a recurrence of their pilonidal sinus. One may develop some pain which is less intense than the acute symptoms. Usually the sinus discharges some pus. This releases the pressure and so the pain tends to ease off. However, the infection never clears completely. This can mean that the symptoms of pain and discharge can last long-term, or flare up from time to time, until the sinus is treated by an operation.

Treatment for pilonidal sinus :

If there are no symptoms
If there are no symptoms then person is advised to clear the affected area of hairs (by shaving, etc) and to keep the area clean with good personal hygiene.

If there are rapid-onset (acute) symptoms
If there is an infection then one may be given some antibiotics and painkillers to improve the pain. It may be that one needs to have an emergency operation to puncture (incise) and drain the ball of pus with surrounding skin infection (abscess). This is usually done in hospital.

If there are persistent (chronic) symptoms
In most cases, an operation will be advised. There are various operations which are done to cure this problem. The surgeon will be able to give the details and the pros and cons of each operation. The options include the following:

  • Wide excision and healing by secondary intention. This operation involves cutting out (excision of) the sinus but also cutting out a wide margin of skin which surrounds the sinus. The wound is left open to heal by natural healing processes (healing by 'secondary intention'). This usually requires several weeks of regular dressing changes until it heals fully. The advantage of this method is that all inflamed tissue is removed and the chance of the condition coming back (recurrence) is low.
  • Excision and primary closure. This means taking out the section of skin which contains the sinus. This is done by cutting out an oval-shaped (ellipse) flap of skin either side of the sinus, which takes out the sinus, and stitching together the two sides of the ellipse. The advantage for this is, if successful, the wound heals quite quickly. The risk of a recurrence or of developing a wound infection after the operation is higher than the above procedure. This risk may be reduced by using a wound technique in which the line of stitches was moved away from between the buttocks.
  • A plastic surgery technique. In some cases, where the sinus recurs or is extensive, plastic surgery may be advised to remove the sinus and refashion the nearby skin.

There are variations on the above procedures, depending on the circumstances, the size and extent of the sinus, and whether it is a first or recurrent problem. The surgeon will be able to discuss in detail the most suitable type of operation.

After any of the above operation :

The wound should be kept clean and any hair growing near it be shaved or removed by other means. Some surgeons recommend that, even when the wound is healed, one should keep the area free of hair growing by shaving every few weeks, or by other methods to remove the hair. This reduces the chance of the problem coming back (recurring).