What Is a Pilonidal Sinus, What Causes Them and What Are The Symptoms of Pilonidal Sinus?

What is a pilonidal sinus?

Pilonidal means a ‘nest of hairs’. A narrow tunnel (a small abnormal channel) in the body is what we call a sinus tract. It 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 sinus tract which commonly contains hairs is called a pilonidal sinus. It occurs under the skin between the buttocks (the natal cleft) a short distance above the back passage (anus). It goes in a vertical direction between the buttocks. Nevertheless, there are some rare cases when a pilonidal sinus occurs in other sites of the body.

What causes a pilonidal sinus?

There are various theories about what can cause a pilonidal sinus and the exact cause is not clear. For example, one theory is that the problem may develop from a minor abnormality, which you were born with, in the skin between the buttocks. This explains 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.

The development of skin dimples (skin pits) in the skin between the buttocks is another theory. They may develop as a result of local pressure or friction causing damage to the small structures below the skin which are responsible for making hairs (the hair follicles). Growing hair in the natal cleft may get pushed into the skin pits because of local pressure.

No matter what the cause is, once hair fragments become ‘stuck’ in the skin they irritate it and cause inflammation. Inflamed skin quickly becomes infected and so a recurring or persistent infection tends to develop in the affected area. This kind of infection causes the sinus to develop which often contains broken pieces of hair.

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

Who gets pilonidal sinus?

It is estimated that 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

This condition used to be called ‘jeep seat’, as it was common in army jeep drivers. 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?

It 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’.

1. Rapid-onset (acute) symptoms

Over a number of days you may develop increasing pain and swelling 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.

2.Persistent (chronic) symptoms

There are some cases (around 4 in 10 people) where people have a recurrence of their pilonidal sinus. Sometimes you may develop some pain which is less intense than the acute symptoms. Usually the sinus discharges some pus. This tends to release the pressure and so the pain tends to ease off and not become severe. 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.

What is the treatment for pilonidal sinus?

1. 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.

2. If you have rapid-onset (acute) symptoms

If you have an infection then you may be given some medicines called antibiotics. Painkillers (such as paracetamol and/or ibuprofen) may be very helpful to improve the pain. Maybe you will need 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.

3. If you have persistent (chronic) symptoms

In most cases, an operation will be advised. There are various operations to cure this problem. Your surgeon should 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 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.
• 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 your circumstances, the size and extent of the sinus, and whether it is a first or recurrent problem. Your surgeon should discuss with you in detail the most suitable type of operation.

New techniques are being researched to try to improve the recovery after having an operation.

After any operation

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. 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 of the problem coming back (recurring).