Pilonidal Sinus

What is a pilonidal sinus?

• Pilonidal means a 'nest of hairs'.
• A sinus tract is a small abnormal channel (like a narrow tunnel) in the body. A sinus tract typically goes between a focus of infection in deeper tissues to the skin surface. So the tract may discharge pus from time to time onto the skin.

A pilonidal sinus is sinus tract which commonly contains hairs. It occurs under the skin between the buttocks (the natal cleft) a short distance above the 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. There are various theories. For example, one theory is that the problem may develop from a minor congenital or hereditary abnormality in the skin of the natal cleft. This may explain why the condition tends to run in some families. Part of the abnormality in this part of the skin may be that the hairs grow into the skin rather than outwards.

Another theory is that you develop skin dimples (skin pits) in the skin between the buttocks. These may develop from damaged hair follicles (the small structures under the skin that make the hairs) due to local pressure or friction. 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 the skin and cause 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.

(A similar condition occurs between the fingers of hairdressers caused by customers' hair entering moist, damaged skin.)

Who gets pilonidal sinus?

Most cases occur in young adults or teenagers. It is rare in children and in people over the age of 40. It is much more common in men (as they are more hairy than women). In one study of students, the condition was found in 1 in 100 male students, and 1 in 1000 female students.

Certain factors increase the risk of developing the condition and include:

• Sedentary occupation (sitting a lot).
• Obesity.
• A previous persistent irritation or injury to the affected area.
• A family history of the condition.

This condition used to be called 'jeep seat' as it was common in army jeep drivers. More than 80,000 US soldiers were treated for 'jeep seat' during the second world war. This was probably a result of many hours driving and 'bouncing' on a hard seat which caused irritation, minor injury and pressure around the natal cleft.

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'

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

Chronic (persistent) symptoms
You 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 and not become severe. However, the infection never clears completely. So, typically the symptoms of pain and discharge can persist long-term, or flare up from time to time, until the sinus is treated.

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 acute symptoms
Symptoms can become very painful and an emergency operation to incise (puncture) and drain the abscess is often needed.

If you have chronic (persistent) symptoms
In most 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 the sinus but also cutting out a wide margin of skin which surrounds the sinus. The wound is not stitched but just left to heal by normal healing processes (healing by 'secondary intention'). So, the wound can take several weeks to heal, and requires regular dressing until it heals. The advantage of this method is that all inflamed tissue is removed and the chance of recurrence is low.
• Excision and primary closure. This means taking out the section of skin which contains the sinus. This is done by cutting the skin either side of the sinus (to form an ellipse shape around the sinus), taking out the sinus, and stitching together the two sides of the ellipse. The advantage for this is, if successful, the wound heals quite quickly. However, the risk of a recurrence, or of developing an infection of the wound after the operation, is higher than the above procedure.
• In some cases where the sinus recurs or is extensive, a plastic surgery technique may be advised to remove the sinus and refashion the nearby skin.

There are variations on the above procedures which may be suggested by your surgeon, depending on your circumstances, the size and extent of the sinus, and whether it is a first or recurrent problem.

After any operation

Your surgeon will usually advise the wound be kept clean and any hair growing near to the wound should be shaved or removed by other means. Some surgeons recommend that even when the wound is healed, you 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 or a recurrence of the problem.

© EMIS and PIP 2006   Updated: October 2006

The authors and editors of this article are employed to create accurate and up to date content reflecting reliable research evidence, guidance and best clinical practice. They are free from any commercial conflicts of interest.

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