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Pilonidal Sinus

What is a pilonidal sinus?

A pilonidal sinus is an infected tract under the skin between the buttocks. Treatment commonly involves an operation. After the operation you should keep the area free of growing hair by regular shaving or other means of hair removal.

Pilonidal means a 'nest of hairs'.

A sinus tract is a narrow tunnel (a small abnormal channel) in the body. A sinus tract typically goes between a focus of infection in deeper tissues to the skin surface. This means that the tract may discharge pus from time to time on to the skin.

A pilonidal sinus is a sinus tract which commonly contains hairs. 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.

What causes a pilonidal sinus?

The exact cause is not clear although it seems likely that a blockage occurs in one of the hair follicles. Hair fragments can then become 'stuck' in the skin causing irritation and inflammation. Inflamed skin quickly becomes infected and so 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.

What are the symptoms of pilonidal sinus?

A pilonidal sinus may not cause any symptoms at first. You may not be aware that you have 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
You 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 40% present with pain which is less intense than those with acute symptoms. Usually the sinus discharges some pus. This releases the pressure and so the pain tends to ease off and not become severe. However, the infection rarely 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.

Who gets pilonidal sinus?

This condition affects around 26 in 100,000 people each year in the UK. It is rare in children and in people over the age of 40. It is four times more common in men (as they are hairier than women). 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

What is the treatment for pilonidal sinus?

If you have no symptoms
If you have no symptoms then you will normally be advised to clear the affected area of hairs (by shaving, etc) and to keep the area clean with good personal hygiene.

If you have rapid-onset (acute) symptoms
If you have an infection then you may be given painkillers and antibiotics by your GP, although it is likely that you need to have an emergency operation to puncture (incise) and drain the ball of pus (abscess). This is usually done in hospital.

If you have persistent (chronic) symptoms
In many cases, an operation will be advised. There are various operations which are done to cure this problem. Your 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 (excising) the sinus. The wound is not closed but just 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. The disadvantage is the length of time to healing and the dressing changes required.

Cleft-lift Procedure. This means taking out the section of skin which contains the sinus. This is done by cutting out a sail-shaped flap of skin, which takes out the sinus, and stitching the skin edges together such that the wound lies to one side of the midline. 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 can be higher than the above procedure but is minimized by moving the line of stitches away from the midline.

A plastic surgery technique. In a few 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, and your surgeon will be able to discuss with you in detail the most suitable type of operation

After any operation

The procedure will usually be performed as a day case. You may be discharged with a small drain which the District Nurse will remove for you at home on the day following your surgery. The stitches will usually be dissolvable and small sticky tapes dressings (steristrips) may also be used to secure the wound. Your surgeon will usually advise that the wound should be kept clean and any hair growing near it be shaved or removed by other means.

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