A Painful Lump Above the Tailbone: What It Is and What to Do

The usual story is that there has been a small pit or dimple above the buttocks for years, occasionally discharging a little and otherwise ignored. Then over two or three days it becomes swollen, red and increasingly painful, until sitting, driving and lying on the back are all impossible.

This is a pilonidal abscess — an acute infection of a pre-existing pilonidal sinus — and it needs drainage.

Recognising it

• A tender, firm, swollen lump in the midline cleft above the buttocks, usually four to eight centimetres above the anus
• Redness and warmth of the overlying skin
• Constant throbbing pain that builds over days
• Pain markedly worse on sitting, driving or lying flat
• Fever and feeling generally unwell
• Often one or more small pits visible in the midline nearby
• Sometimes a hair visible protruding from a pit

Why antibiotics alone will not fix it

An abscess is a walled-off collection of pus. Antibiotics circulate in the bloodstream and reach the surrounding tissue, but they do not penetrate the collection itself in effective concentration.

What frequently happens is that antibiotics reduce the fever and the surrounding redness, giving the impression that things are improving, while the collection continues to enlarge underneath. Meanwhile the pain does not resolve, and the infection has more time to track through tissue planes.

Antibiotics have a genuine role — in diabetics, in immunosuppressed patients, and where there is extensive surrounding cellulitis or systemic illness. But they support drainage rather than replace it.

What drainage involves

Incision and drainage is a short procedure. It can be done under local anaesthesia for a superficial collection, though a short general or spinal anaesthetic is often better — local anaesthetic works poorly in acutely inflamed tissue and may not allow a thorough enough assessment of the cavity.

An incision is made over the most fluctuant point, deliberately placed slightly off the midline where possible, since midline wounds in this area heal poorly. The cavity is opened widely enough that it will not seal over prematurely, all internal partitions are broken down, and any hair inside is removed.

The cavity is irrigated and usually left open with a light dressing. Relief from the pain is typically immediate and dramatic.

Why the definitive surgery is not done at the same time

It is tempting to think that since the area is already open, the whole sinus should be dealt with in one go. In practice this usually gives worse results.

Acutely infected tissue is swollen, friable and inflamed. The true extent of the sinus and its branches cannot be assessed reliably, tissue does not hold sutures well, and flap procedures performed in an infected field have high failure rates.

The better sequence is to drain thoroughly, allow six to eight weeks for the inflammation to settle completely, and then perform definitive treatment on a quiet field — whether that is laser closure, endoscopic treatment, pit picking or a flap procedure.

Patients occasionally interpret this as being sent away half-treated. It is the opposite: it is what makes the definitive procedure work.

Recovery after drainage

• Pain relief is usually immediate
• The wound is left open and heals from the base upward over two to four weeks
• Daily cleaning and dressing as instructed; the frequency reduces as it heals
• Avoid sitting directly on the area; use a cushion
• Keep the area meticulously clean and dry
• Most patients return to desk work within three to seven days
• Clip or remove hair from the area as advised once the acute phase has settled
• A review at six to eight weeks to plan definitive treatment

What to do right now if this is you

• Do not apply hot compresses hoping it will burst — this can allow infection to spread deeper
• Do not attempt to squeeze or drain it yourself
• Do not start a course of antibiotics and wait a week
• Take paracetamol for pain and see a surgeon the same day or the next
• If you have fever with rapidly spreading redness, or you are diabetic and the pain is severe and worsening quickly, treat it as urgent

And afterwards

An abscess is the acute event. The sinus that caused it is still there, and roughly speaking, if you have had one abscess, you are likely to have another unless the sinus is treated.

The interval between drainage and definitive surgery is a good time to start hair reduction in the area, since this is what will ultimately prevent the whole cycle from repeating. Beginning it before rather than after the definitive procedure gives a head start on the part of treatment that matters most in the long run.