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Pilonidal sinus

Introduction

A pilonidal sinus is a small hole or "tunnel" in the skin. It usually develops at the top of the cleft of the buttocks, where the buttocks separate.

Most people associate the word sinus with the nose, but sinuses can occur anywhere in the body. Sinus is simply a medical term for channel or cavity.

A pilonidal sinus can become infected by bacteria, causing pain and swelling. A pus-filled abscess can then develop within the sinus. This will require an operation to open the sinus up and drain away any pus, bacteria or other waste materials. A pilonidal sinus will not cause any symptoms until it becomes infected. See Pilonidal sinus - symptoms for more information.

The exact cause of a pilonidal sinus is unclear, although it is thought to be caused by loose hair piercing the skin. See pilonidal sinus - causes for more information.

Outlook

If a pilonidal sinus becomes infected, it should be treated immediately to prevent the infection spreading. It is important to stop the infection spreading into the blood (called sepsis) as this can be serious.

You may initially be treated with antibiotics, but you will also need to have the pus drained out of the abscess. This is called incision and drainage.

If the sinus keeps becoming infected, surgical removal of the sinus is usually recommended. Several techniques can be used to do this, including:

  • leaving the wound open to heal and packing it daily with a dressing
  • closing the wound with a flap of skin and stitches

See Pilonidal sinus - treatment for more information about the treatment options.

How common is pilonidal sinus?

Pilonidal sinuses are rare, affecting 26 in 100,000 people each year.

Pilonidal sinuses affect twice as many men as women. The average age for a pilonidal sinus to occur is 21 years of age in men and 19 years of age in women.

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Symptoms

Most pilonidal sinuses occur just below the tail bone, in the area of skin between the buttocks. However, some cases of pilonidal sinus have been recorded in the belly button or hands, such as between the fingers.

A pilonidal sinus will not cause any symptoms until it becomes infected, although you may notice its presence as a small pit or depression in the surface of your skin. Sometimes, there may be more than one pit.

Once the sinus becomes infected, the pit will start to swell and you may experience symptoms, including:

  • pain
  • redness of the skin
  • pus draining from the sinus (the pus usually smells unpleasant)
  • blood draining from the sinus 
  • a high temperature of 38C (100.4F) or above

Pain

The pain caused by a pilonidal sinus can be severe and, without treatment, it may get worse. Therefore, see your GP as soon as possible.

The pain can make it difficult to sit or lie down comfortably, which may affect your sleep. The pain may also interfere with your ability to work and may increasingly affect your daily activities.

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Causes

The exact cause of pilonidal sinuses is unclear. It is generally thought that they are caused by loose hairs that get pushed into the skin. There are several theories as to how this could happen.

Hair follicles

Hair follicles are the small holes that an individual hair grows out of. It is thought that pressure and friction on a hair follicle could somehow damage it, causing a pilonidal sinus.

There are two suggestions for how a hair or a hair follicle causes a sinus:

  • A hair follicle may become blocked, causing the follicle to become enlarged and then burst.
  • A broken hair may be inserted into the skin, leading to an infection.

The cleft between the buttocks is an ideal place for bacteria to spread because it is often moist and warm. The pressure that is applied to this area - such as from sitting - can also push more hairs or debris into the pit that forms. 

There have been reports of hairdressers developing pilonidal sinuses on their hands. This may be caused by hair from their clients becoming trapped in moist, damaged skin between a hairdresser’s fingers.

Infection of the pilonidal sinus

If a broken hair is pushed into the skin, this irritates the skin and causes it to become red and swollen. Bacteria can quickly infect this skin.

The immune system (the body’s natural defence against infection and illness) will send white blood cells to fight the infection. A collection of dead white blood cells and bacteria will then build up, resulting in pockets of pus, known as anabscess.

Risk factors

Factors that are known to increase your risk of pilonidal sinuses include:

  • obesity - having a body mass index (BMI) of 30 or above
  • having an above-average amount of body hair
  • having a deep cleft between your buttocks 
  • having a family history of the condition - over one-third of people have a family member with the condition 
  • having a job that involves a lot of driving or sitting down for long periods

Jeep seat

During World War Two, thousands of army jeep drivers developed pilonidal sinuses. The condition became so widespread that it was nicknamed jeep seat or jeep disease.

The fact that so many men doing the same sort of job developed pilonidal sinuses suggests that environmental factors must play an important role in the development of the condition. Examples of such factors include:

  • wearing restrictive clothing, such as army uniforms
  • repetitive motion, such as bouncing around on the seat of a jeep

 

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Diagnosis

See your GP as soon as possible if you think you have a pilonidal sinus. Without treatment, the pain and infection may get worse.

Your GP should be able to diagnose a pilonidal sinus after carrying out a visual examination of the affected area of skin. Further testing is not usually required.

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Treatment

Incision and drainage

If you develop an infection inside a pilonidal sinus, you will need an operation to open the sinus up and drain away any pus, bacteria or other waste materials. This type of operation is known as incision and drainage.

You may be prescribed antibiotics to keep the infection under control while you wait to see a surgeon. However, antibiotics will not cure the pilonidal sinus.

Incision and drainage will usually be carried out at your local hospital. The procedure is most commonly performed under general anaesthetic, where you are asleep throughout the operation. As the incision and drainage procedure is relatively minor, you should be able to return home after you have recovered from the effects of the anaesthetic. This will usually be the same day as the operation.

After the operation, a dressing will be applied to the affected area to allow your skin to heal. You will need to arrange for your dressing to be changed daily by the practice nurse at your local GP surgery.

Treating recurring infection

If you have recurring infections in a pilonidal sinus, surgery may be recommended to remove the sinus and prevent further infections. The classic sign of a recurring infection is pain followed by swelling and then discharge.

The two main types of operation to remove a pilonidal sinus are:

  • wide excision 
  • excision and primary closure

Wide excision

During wide excision, the surgeon will cut out the section of skin that contains the sinus. The wound is left open and packed with a dressing.

The advantage of having a wide excision is that, after the procedure, the chances of the infection returning are low. The disadvantage is that the wound will take a long time to heal and your dressings will need to be changed daily for two or three months.

Excision and primary closure

In an excision and primary closure, the surgeon will cut out the section of affected skin before closing and sealing the wound with stitches. The advantage of this technique is that the wound will heal quite quickly. The disadvantage is that the chances of the infection returning are higher than with a wide excision.

The surgeon may remove the sinus from:

  • the centre, between the buttocks (midline closure)
  • away from the centre of the buttocks (off-midline surgical closure)

The off-midline surgical closure technique is considered to be better than the midline closure technique. This is because there is a better flow of air to the wound and it is easier to keep clean, so it tends to heal better.

Some studies have found that midline surgical wounds take around five days longer to heal, and there is a higher chance of the infection returning than with off-midline surgical wounds.

Possible off-midline surgical methods include:

  • the cleft lip procedure, also known as Bascom’s procedure
  • the rhomboid flap, also known as the Limberg flap
  • the Karydakis flap 
  • Z-plasty

These are different methods of using a flap of your own skin and tissue to fill and close the wound that is left after removing your pilonidal sinus. Your surgeon can explain the technique that they will be using in more detail.

Having surgery

Before deciding which type of operation to have, discuss the advantages and disadvantages of each technique with your surgeon.

Surgery may be carried out under:

  • general anaesthetic - where you are asleep throughout surgery
  • local anaesthetic - where the area is numbed 
  • spinal anaesthesia - where the spinal nerves are numbed

During surgery, some surgeons insert a small drain, which is usually removed the following day.

You may feel some discomfort after your operation. The healthcare professionals looking after you should be able to provide pain relief. You may also be given painkillers to take at home after you have left hospital. You will usually be discharged on the day of your operation or, in some cases, the following day.

After your operation, you will probably need to take some time off work, although this will depend on how you are feeling and the type of work you do. Avoid strenuous work for up to two weeks.

You can start to exercise and do sporting activities as soon as you feel able to. However, if you have stitches, you may need to avoid activities that could disrupt the stitches for two to four weeks.

Wound care

Whatever type of surgical procedure you decide to have, it is very important that you keep the site of the wound clean after the operation. Your surgeon can give you advice about how to do this. This may include some of the following points:

  • Have a shower or bath at least once a day if your wound is being left open and packed with a dressing. 
  • If your wound is closed with stitches, avoid having a bath. You may be advised to keep the wound completely dry for the first few days. Ask your surgeon for advice. 
  • When washing the wound, do not use soap because this will irritate your skin. Use plain water and a soft cloth instead. 
  • Do not use talcum powder. 
  • Use wet wipes to clean the area when you are away from home. 
  • Carefully dry the area after washing using a soft towel, but do not rub the skin. Using a hair dryer is an effective alternative method of drying the area. 
  • Always remove a damp or wet dressing and replace it with a dry, clean one. 
  • Wear loose-fitting cotton underwear and avoid synthetic underwear, such as nylon. 
  • Eat foods that are high in fibre, such as vegetables, fruit and bran flakes, because they will help to soften your stools and reduce any straining when you go to the toilet. 
  • You will probably be advised to shave any hair growing near the site of the wound. It may be recommended that you shave this area even after the wound has healed to prevent the pilonidal sinus from returning.
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