Pilonidal disease

• Pilonidal disease is a common, acquired, usually benign inflammatory disease that arises where a hair penetrates and irritates the skin of the natal cleft rather than from a congenital cyst.
• It occurs mainly in young adults, especially men, and is fostered by a deep natal cleft, hirsutism, obesity, family history and sitting pressure.
• Most patients have either an acute abscess (painful, fluctuant swelling) or a chronic draining sinus (pits with purulent, bloody or mucoid discharge); many others are completely symptom-free.
• The diagnosis is clinical. Imaging is reserved for uncertainty, and the differential ranges from hidradenitis to Crohn disease, fistula in ano, sacral infection and, rarely, skin cancer.
• Treatment is surgical at its core: incision and drainage for an abscess, then a definitive procedure matched to disease extent, from hair removal and pit excision to flap reconstruction for recurrent or complex disease.

By the end of this page you should be able to:

1. Explain why pilonidal disease is now viewed as an acquired disease of hair follicles rather than a congenital cyst.
2. Take a history and examine a patient, distinguishing the three common presentations (asymptomatic, acute abscess, chronic sinus).
3. Work through a safe differential diagnosis and decide when imaging or biopsy is justified.
4. Plan acute and chronic management, including antibiotics, incision and drainage, minimally invasive options and flap procedures.
5. Counsel about recurrence and about the small risk of malignant change in long-standing disease.
6. Adapt management when theatres, imaging and specialist reconstruction are not available.

The name comes from the Latin "hair nest", but a pilonidal cavity is not a true cyst. It lacks a proper epithelial lining and contains hair, debris and granulation tissue. Current consensus, including the 2019 guideline from the American Society of Colon and Rectal Surgeons (ASCRS), is that it is an acquired condition intimately related to hair in the gluteal cleft: loose hairs trapped in the natal cleft traumatise and penetrate the skin and create a foreign-body reaction that leads to midline pits and sometimes secondary infection. ^[1]

There are three useful clinical pictures:

• Asymptomatic disease. Midline pits or sinuses are found incidentally, or a patient has a painless pit with no history of swelling or drainage. Asymptomatic disease should not be treated. ^[2]
• Acute abscess. Infection of a chronic sinus produces a tender, often fluctuant swelling, with pain on sitting and sometimes fever.
• Chronic pilonidal disease. A persistent cyst and sinus with drainage through midline and sometimes lateral pits, often with intermittent acute flares.

Pilonidal disease is common among otherwise healthy young adults. One estimate is 26 per 100,000 people per year, with men affected about 2.2 times as often as women. ^[3] In the United States alone, roughly 70,000 patients are affected each year. ^[1] Global figures vary widely: sacrococcygeal disease has been estimated at around 0.1% of the population in some settings and as high as 6.6% in others. ^[4]

The condition usually declares itself after puberty, in the second and third decades of life; women are also affected, but peak presentation in men is in the twenties and thirties. ^[4] It is rare in children, and in immunosuppressed patients malignant degeneration, though still rare, may be slightly more common. ^[1]

Pilonidal disease was once believed to be congenital, arising from vestiges of the embryonic tissues. That idea has been abandoned. It is now considered an acquired disease of hair follicles. ^[3]

Bascom's summary of Karydakis's three-factor model remains a useful way to picture the process. ^[3][4]

1. Hair or a foreign body. Hair shed from the back, buttocks, gluteal folds or occiput accumulates in the natal cleft. Hairs caught in the disease show a hook-like shape under the microscope and seem able to move in only one direction, so once they lodge they are driven forward. ^[3]
2. A force. Sitting, walking and body movement draw the hair tips against the skin and push them into widened follicle openings, where they penetrate and coil inside granulation tissue.
3. Vulnerable skin. A deep and narrow natal cleft, maceration and friction allow these hairs to pierce the skin and set up a foreign-body reaction. The trapped hair acts like a needle, and the surrounding tissue responds with granulation tissue and sinus formation.

The resulting cavity has no complete epithelial lining, which is why it is not a true cyst. A secondary abscess may form, and the body then creates true sinus tracts that drain back to the skin surface as chronic openings. An anaerobic, hair-laden environment and skin bacteria can superimpose infection. The disease is therefore a problem of anatomy and physics as much as of microbes: the cleft is a hair trap. ^[3][4]

Patients may present in three ways.

• "I found a small hole at the top of my bottom, with a bad smell from time to time, but no pain." This is asymptomatic disease. Pits are visible, but there has been no abscess and nothing to drain.
• "I have a painful lump there that came on over the last few days, and I cannot sit on my backside." This is an acute abscess. Pain rises quickly, sitting and driving become impossible, the overlying skin may be red and warm, and there may be fever or a tender groin node.
• "It keeps oozing dark fluid, sometimes blood, sometimes pus, and the soreness never really goes." This is chronic pilonidal disease. Patients describe a repeated wet patch on clothing, recurrent swelling and subjective pain from the pits, often with acute flare-ups followed by partial resolution.

A useful reminder is that patients often ignore chronic disease for months or years because it does not stop them working; acute abscess is the event that brings them to care.

The examination is done in the prone or lateral position with the gluteal folds gently parted. Look for:

• Midline pits in the gluteal cleft, sometimes with surrounding erythema or a slight dimple;
• secondary lateral openings or sinus orifices, most of which course upward but some course downward;
• induration and tenderness if there is active infection;
• a fluctuant mass when an abscess is present;
• cellulitis of the surrounding skin;
• any hard fixed or ulcerating mass, which should trigger biopsy.

Always perform a thorough anorectal examination to exclude concurrent fistulous disease, Crohn disease and other anorectal pathology. ^[1] In chronic disease the main finding is a chain of pits in the midline with sometimes small amounts of drainage.

Rarely, a hard indurated mass or an ulcer that does not heal despite care should raise concern for malignant change, particularly after many years of chronic disease in an immunosuppressed patient. ^[1][5]

The diagnosis is usually clinical from the history and characteristic midline pits. Where uncertainty remains, imaging can separate the conditions. Another practical point is to remember that perianal conditions can coexist: finding a pit does not exclude a fistula, and finding a fistula does not exclude pilonidal disease.

Pilonidal disease is a clinical diagnosis, and no further tests are needed in an obvious case. ^[3] A few tools are useful when the diagnosis is not clear or when management planning depends on them.

• Ultrasound, and in some contexts transperineal ultrasound, can clarify the extent of sinuses and exclude perianal sepsis. It is cheaper and quicker than MRI. ^[3]

• MRI is more expensive and time consuming, but useful when there is concern for inflammatory bowel disease, fistula in ano, pelvic sepsis or neoplastic change. ^[3]

• Methylene blue injection into the sinuses during surgery can demonstrate the extent of the tract, although its usefulness depends on how the surgeon uses the stain. ^[3]

• Laboratory tests are nonspecific; white cell count, CRP and ESR may be raised during infection, but they do not diagnose the condition.

• Histopathology. All excised specimens should be sent for histological assessment, because malignant change, although rare, is reported in chronically diseased tissue. ^[3][5]

The management of an acute abscess is the same physiological principle as for any abscess: get the pus out. Insert the incision off the midline, over the point of maximal fluctuance, without trying to remove the midline pits at that visit. ^[1][4] Off-midline drainage is believed to drain the cavity while minimising pressure and tension on the wound postoperatively. ^[4]

When simple incision and drainage is performed for a first episode of acute abscess, one guideline cites healing in about 60% of patients; the rest require a later procedure. ^[1] Recurrence is estimated at 15% to 40% after simple incision and drainage alone, probably because the hair and tracts remain. ^[1] Nonetheless, draining the abscess first appears protective in the long term, compared with immediate definitive excision. ^[1]

Removal of the midline pits at the time of drainage has not been shown to decrease recurrence or improve healing compared with drainage alone, so it should be left to a planned definitive procedure. ^[4]

Curettage and laying open. Unroofing and curettage of the cavity with removal of debris emerged as a single-stage option. In a randomised trial, curettage achieved complete healing at 10 weeks in 96% compared with 79% without it, and a recurrence rate of 10% compared with 54% at up to 65 months. ^[1] A meta-analysis put the recurrence rate of the lay-open and curettage method at about 4.5%. ^[2]

There is no single best operation for everyone. The three broad categories are excision with primary closure (including off-midline flap methods), excision with healing by secondary intention and excision with marsupialisation. The choice depends on disease extent, patient preference, surgeon experience and local resources. ^[1]

Off-midline closure, rather than midline closure, is the principle with the clearest support. Closing in the midline after excision is associated with frequent wound dehiscence and a higher recurrence rate, and several guidelines advise against it. ^[1][2] A 2010 Cochrane review reached the same conclusion, so when closure is chosen, closing off the midline should be standard. ^[1]

Hair removal and hygiene. Because hair is central to the pathogenesis, hair removal is rational as a primary measure in active disease without an abscess and as an adjunct after surgery. Shaving (or laser epilation) should be repeated every 1 to 2 weeks until healing occurs, together with hygiene education. ^[1] Surgeon-delivered shaving during treatment and patient-delivered shaving after healing have both been associated with better outcomes, whereas patient shaving in the early postoperative period has been associated with higher recurrence. ^[1]

Laser hair removal has been used both as an adjunct to surgery and as a primary treatment. Reported recurrence after laser depilation ranges from 0 to 28%, with comparative studies generally showing lower recurrence when it is used. ^[3] The German guideline does not formally recommend postoperative laser depilation but allows it to be considered individually in young patients with prior recurrence and a positive family history. ^[2] Laser requires multiple sessions and may be unavailable or unaffordable; shaving remains the cheap and effective mainstay.

Laser epilation may require local anaesthetic and repeated treatments, so expectations should be set accordingly. Overall, evidence remains heterogeneous; ^[3] guidelines in different regions recommend different approaches, which should be explained to patients rather than presented as a single global rule. ^[2]

Phenol. In patients with acute or chronic pilonidal disease without an abscess, phenol application is an effective nonoperative technique that can produce rapid and durable healing. ^[1] Crystallised phenol is injected or applied after hair removal and curettage; minor complications occur, and disease resolves in 67% to 100% of patients, with elimination of recurrence in at least 80% in guideline figures. ^[1] Multiple applications are common, and phenol is banned in Germany on toxicity grounds. ^[2]

Fibrin glue. Fibrin glue has been used to fill dead space and sinus tracts after excision, in place of surgical closure, and after curettage of pits. Success is reported in observational series but remains uncertain; a Cochrane review concluded the evidence for benefit was unclear. ^[1]

Pit picking and similar procedures. These are targeted excisions of midline pits with cleansing or drainage of subsidiary tracts. They require minimal pain and short time away from work, but recurrence is expected in 8% to 26% between 1 and 10 years after surgery, and long-term data are still lacking. ^[2] They are most suitable in previously untreated patients with limited disease. ^[2]

Sinusectomy (limited excision). The midline pit and its entire tract are closely excised, usually under local anaesthesia. Reported recurrence is 1.6% to 7% over 20 to 43 months, but the method is best applied when there are fewer than three pits and the database is small. ^[2]

EPSiT (endoscopic pilonidal sinus treatment). A fistuloscope allows cleaning of tracts under vision with removal of hair and debris. Meta-analyses report a failure rate of about 8% (recurrence 4% and persistent disease 4%), an average of 3 days away from work and healing over about a month. ^[2] In a randomised trial, the 1-year recurrence rate was 3% with EPSiT and similar with cleft lift, but time out of work was longer after cleft lift. ^[2] Many national guidelines reserve formal recommendation for this technique until larger multicentre data become available. ^[2]

Laser treatment of the tract (PiLaT, SiLaC). Laser energy obliterates the tract after minimal excision of pits. Some series report about 90% healing, but there are no prospective randomised comparisons with other minimally invasive techniques, and many guidelines give this no formal recommendation. ^[2]

For recurrent or complex chronic disease, where pits are numerous, the cleft is deep and hirsute, or earlier procedures have failed, flap procedures are used to excise the diseased tissue and reconstruct the region off the midline. They are technically more demanding and require experience. ^[1]

• Limberg flap (rhomboid flap). Excision of all affected skin and sinuses with rotation of a fasciocutaneous flap that lateralises the scar and flattens the cleft. Disease recurrence is reported at 0 to 6% in ASCRS citations, although wound dehiscence can be sizeable in some trials and seroma is common. ^[1] In studies of the modified Limberg flap, an incision that does not cross the natal cleft performed better than the original form. ^[2]
• Karydakis flap. An ovoid excision of the pathological tissue with a fasciocutaneous flap sutured off the midline onto the sacral fascia. In a long reported experience of more than 6500 cases, recurrence was under 2% and complications 8%. ^[3] Guideline figures are 0 to 6% recurrence at 10 years, with 8% to 23% wound dehiscence, 2 to 3 weeks off work and a hospital stay of 0 to 3 days. ^[2]
• Bascom cleft lift. This modification of the Karydakis principle uses a flap that both lateralises the wound and reduces the depth of the natal cleft. It is often offered as day-case surgery, has a reported cure rate of 95.6% in a refractory series of 69 patients, and only 3 recurrences in a 74-patient series at 12 to 51 months follow-up. ^[4]
• Other flaps (V-Y, Z-plasty and others) have been reported but are rarely used. ^[2]

Comparison of two meta-analyses: a large pooled analysis reported a 10-year recurrence rate of 20% after open healing, 2% after Karydakis flap, and 11% after Limberg flap; ^[2] different definitions of recurrence explain much of the spread.

| EPSiT (endoscopic treatment) | Failure 8% (4% recurrence, 4% persistent disease) and 3% at 1 year in one trial | German guideline ^[2] | | Excision and open healing | 20% at 10 years in Stauffer meta-analysis; older reports 2% to 35% depending on population and definition | German guideline ^[2] | | Midline closure | 8.7% after primary midline closure versus 5.3% after healing by secondary intention (Cochrane); German meta-analysis 4% to 45% versus 0% to 4% | ASCRS guideline ^{[1] [2]} | | Karydakis flap | 0 to 6% at 10 years; under 2% in a very large single-institution series | German guideline and StatPearls ^[2][3] | | Cleft lift / Bascom | 0 to 5% at 10 years; 95.6% cured in a 69-patient refractory series | German guideline and Practical Management ^[2][4] | | Limberg flap | 0 to 6% in ASCRS-cited series; 3% or less in some surgical series | ASCRS guideline and Practical Management ^[1][4] | | Phenol application without abscess | Recurrence about 13% to 19% in small trials; reported elimination of recurrence in at least 80% overall | ASCRS guideline ^[1] | | Laser as recurrence prophylaxis | Reported after laser hair removal: 0% to 28%; a systematic review shows lower recurrence with epilation | StatPearls ^[3] |

The use of antibiotics is controversial and should not be a routine adjunct to surgery. ^[1] The 2019 ASCRS guideline gives a weak recommendation based on moderate evidence for individualised consideration of prophylactic intravenous and topical antibiotics in pilonidal surgery. ^[1]

There is evidence both for and against routine prophylaxis. Single-dose cefoxitin before primary excision showed no benefit, whereas another large retrospective series found reduced surgical site infection in those receiving a single prophylactic dose. Perioperative administration including metronidazole appeared beneficial in at least one small randomised trial, and no consistent difference was found between 1 and 4 days of therapy. ^[1]

The practical, patient-safe interpretation supported by the guidelines is that antibiotics are for complicated cases, not for the disease itself: treat severe cellulitis, underlying immunosuppression or systemic illness with appropriate antibiotics, and otherwise rely on timely drainage and definitive surgery. ^[1] Empirical surgery without source control in an abscess remains the real error.

The thread running through every technique is that excision of hair, debris and granulation tissue is only part of the cure. Regular local hair removal and hygiene after healing are essential and should be reinforced at review. Patients should know that recurrences may appear years later and that a pit that stops draining can flare again under friction or hygiene changes. ^[1][3]

• Recurrent abscess is the commonest complication of simple drainage, driven by retained hair and tracts. ^[1]
• Chronic midline wound or failure to heal can follow excision and open healing with secondary intention, and it is the main concern after wide excision left to granulate. ^[2]
• Wound dehiscence, haematoma and seroma are more likely after flap procedures and midline closure. ^[1]
• Infection and surgical site infection occur variably; rates are broadly similar between closed and open healing. ^[1]
• Time lost includes prolonged secondary healing and time away from work, which is why minimally invasive techniques have become popular. ^[2]
• Disease-related complications include cellulitis and, rarely, osteomyelitis or malignant change. ^[3]

For most patients the prognosis is good: pilonidal disease is benign, and adequate treatment and behavioural modification control it in the majority. ^[3] Recurrence, however, is common and can occur months or years after the first operation, which is why settings that report very early "cure" should be treated cautiously. ^[2][3]

There is one consistent lesson across guideline families: avoid midline closure after excision, because the rate of wound problems and recurrence is higher there than with healing by secondary intention or off-midline closure. ^[1][2] Even so, no single method satisfies every desirable feature of being simple, painless, fast healing and low recurrence, and treatment must be matched to the presentation and resources. ^[2]

One additional nuance relevant to patients is that a family history may predict a higher recurrence rate after surgery. ^[1] The German and Italian guideline families lean against open healing, whereas the ASCRS guideline leaves healing strategy more to surgeon and patient preference. Patients should hear this honestly; the evidence base has room for legitimate disagreement. ^[2]

Pilonidal disease is almost always benign, but long-standing recurrent disease may be rarely complicated by malignant transformation. Pilonidal sinus may affect up to about 5% of the general population, and malignant transformation occurs in roughly 0.1% of patients, reported only in recurrent disease. ^[5] The most common tumour type is squamous cell carcinoma. ^[5]

Pathogenesis is thought to parallel that of other chronically inflamed skin, with repeated cycles of injury and repair, free oxygen radical damage and impaired DNA repair. ^[5] Risk becomes clinically relevant when there is a long history of recurrent pilonidal disease, an increasing mass, central ulceration or routine surveillance after many years. ^[1][5]

When such a change is suspected, biopsy is mandatory. ^[1][5] Malignant transformation of pilonidal disease is associated with nodal metastasis in about 14% of patients at diagnosis, bone invasion in around 8%, a local recurrence rate of 40% to 50%, and 5-year survival of roughly 55% to 61%. ^[5] It occurs more often in immunosuppressed patients. ^[1]

The consequence for routine care is that all excised specimens should go to histopathology and any mass should not be presumed to be benign from history alone. ^[3][5]

Children. Pilonidal disease is uncommon in children and, when seen in childhood, is more commonly a complex problem. The more common skin abscess in a child is different from pilonidal disease, and the principles of drainage remain the same. ^[3] The 2019 guidelines cited evidence from children treated with EPSiT but the volume of paediatric data is small, so treatment should stay individualised.

Pregnancy. No guideline-specific evidence is available in the sources used here. On general principles, an abscess can be drained under local anaesthetic, deferring definitive surgery; any drug or anaesthetic choice in pregnancy should be agreed locally.

Immunosuppressed patients. Malignant change is slightly more common in these patients, so a low threshold for biopsy and histopathology is wise. ^[1]

The diagnostic starting point, which costs nothing, is a disease-specific history and a careful anorectal and gluteal examination. ^[1] In many places this alone suffices. Practical points include:

• Drain an abscess with a scalpel under local anaesthetic, making the incision off the midline. Packing may be omitted when safe local practice allows; I&D is what matters, not the dressing. ^[1][4]
• Keep curettage, methylene blue and unroofing for settings and teams in which they are routine; they can raise cure rates where expertise exists but are not a precondition for treating an abscess. ^[1]
• Defer definitive excision until the acute infection has settled. ^[1]
• Where theatre, imaging and reconstructive expertise are limited, excision combined with open healing by secondary intention remains a workable treatment and is used worldwide; it costs more time and wound care, and is not the worst failure. ^[2]
• Where closure is planned, midline closure is the avoidable error; reserving closure for clinicians comfortable with off-midline techniques reduces wound breakdown. ^[1][2]
• Shaving and hygiene are cheap and physiologically rational, and they are the interventions a patient can do after discharge. ^[1]
• Antibiotics should be reserved for severe cellulitis, systemic illness or immunosuppression; they do not replace drainage and surgery. ^[1]
• Send excised tissue for histology wherever pathology is available; biopsy lesions that are hard, expanding or ulcerating. ^[3][5]

• Pilonidal disease is an acquired foreign-body reaction to hair in the natal cleft, not a congenital cyst, although older theories blamed congenital causes.
• It affects young adults, especially men (roughly 2.2 times as often as women), with an estimated incidence of 26 per 100,000 people per year.
• The risk factors include a deep and narrow natal cleft, hirsutism, obesity, prolonged sitting, an athletic lifestyle, family history and local trauma.
• Presentations are asymptomatic pits, acute abscess and chronic draining sinus with purulent, bloody or mucoid discharge.
• Always perform a full anorectal examination and consider Crohn disease, hidradenitis suppurativa, perianal abscess and fistula, sacral infection, tuberculosis, syphilis and, rarely, skin cancer in the differential.
• The diagnosis is clinical; ultrasound and MRI are reserved for difficult cases, and pathology prevents missing malignant change.
• For abscess, drain it with an incision placed off the midline. Incision and drainage heals only about 60% of first episodes; the remainder need later definitive treatment.
• Antibiotics are an adjunct for severe cellulitis, systemic illness or immunosuppression; they do not cure pilonidal disease.
• For limited chronic disease, hair removal and hygiene, phenol injection, pit picking, sinusectomy, EPSiT and laser all play a role with short convalescence but higher recurrence.
• For recurrent or complex chronic disease, off-midline flap procedures (Limberg, Karydakis and the Bascom cleft lift) give the lowest recurrence rates at the cost of greater experience and effort.
• A recurring theme across guidelines is to avoid midline closure after excision.
• Never promise rapid, complete and permanent cure from any single method; recurrence is common, and the choice of operation must be matched to the disease and the resources available.
• Rare complications include malignant transformation, usually squamous cell carcinoma, in roughly 0.1% of patients, mainly after long-standing recurrent disease. ^[5]

This topic has no verified MedGrasp topic links in its front matter. In the wider literature the closest neighbours are hidradenitis suppurativa, fistula in ano, Crohn disease, perianal abscess and anorectal infection. Their MedGrasp pages should be linked by plain name, not by generated links, until those topics are verified.