Pilonidal Sinus

Chronic inflammatory condition of the natal (intergluteal) cleft in which hair penetrates the skin and causes a foreign body reaction, forming a sinus or abscess. The cause is acquired. Loose hairs are driven into the midline pits by friction and suction in the cleft.

• It affects about 26 per 100,000 people per year, mostly males (3 to 4 times more than females) between 15 and 30 years of age, and is rare after age 40.
• Risk factors: male sex, hirsutism, deep natal cleft, obesity, sedentary work and prolonged sitting (driving, office work), poor hygiene, local trauma, family history, and sweating.
• Disease is typically in the sacrococcygeal midline, although it occurs in the umbilicus, the interdigital spaces of barbers and hairdressers, and the axilla.
• The condition has a high recurrence, 5 to 30% depending on the technique used. Squamous cell carcinoma rarely develops in longstanding disease (0.1% or less).

• Asymptomatic stage: one or more midline pits in the natal cleft, seen only on examination, sometimes with hair tufts.
• Acute abscess: severe pain, swelling, redness, tenderness and fluctuance over the sacrococcygeal area, a palpable lump, with or without fever and malaise. The abscess is often off the midline.
• Chronic sinus: intermittent or continuous discharge of pus or blood, with a foul smell, with midline pits and one or more lateral openings, and recurrent flares.
• Pain is made worse by sitting, and relieved by standing.
• Differential diagnosis: perianal abscess and fistula-in-ano (the track enters the anal canal), hidradenitis suppurativa of the buttocks, furuncle, infected epidermoid cyst, osteomyelitis of the sacrum or coccyx, Crohn disease, tuberculosis, actinomycosis, sacrococcygeal teratoma, anal fissure and coccydynia.
• Complications: recurrent abscess, cellulitis, chronic non-healing wound, secondary fistula, bacteraemia (uncommon), and malignant change (squamous cell carcinoma) in longstanding sinuses.

• Clinical. Examine the cleft, identify midline pits, the sinus tracks, and the lateral openings. Look for perianal disease and test the anal canal if a fistula is suspected.
• Swab pus in recurrent disease, or when the patient is immunosuppressed.
• Ultrasound or MRI for recurrent or complex disease, suspected deep extension or perianal communication, or when the diagnosis is uncertain.
• Check glucose in recurrent disease, and take a full blood count and inflammatory markers if there is fever.
• Biopsy any non-healing or chronic wound with raised, indurated edges, to exclude carcinoma.

• Asymptomatic pits require no surgery. Advise hair removal and hygiene.
• Acute abscess: incision and drainage, which is the definitive acute treatment.
  • Use local anaesthesia, lidocaine 1% with adrenaline up to 7 mg/kg (about 500 mg, 50 mL in an adult), or lidocaine 1% plain up to 4.5 mg/kg (about 300 mg, 30 mL).
  • Make a small longitudinal incision 1 to 2 cm lateral to the midline (to avoid midline wounds, which heal poorly), open all loculi, remove hair and debris by curettage, and irrigate with saline.
  • Leave the cavity open, with a light packing or wick for 24 to 48 hours, then daily irrigation and dressing until the cavity fills with granulation.
  • A pit excision at the time of drainage (pit picking) reduces recurrence.
  • Antibiotics are not needed for a drained abscess without cellulitis. Give them for spreading cellulitis, systemic signs, diabetes, or immunosuppression: co-amoxiclav 625 mg orally 8 hourly for 5 to 7 days, or cefalexin 500 mg 6 hourly with metronidazole 400 mg 8 hourly (clindamycin 300 to 450 mg 8 hourly in penicillin allergy). IV therapy (co-amoxiclav 1.2 g 8 hourly, or cefuroxime 1.5 g 8 hourly with metronidazole 500 mg 8 hourly) is used for sepsis.
  • Analgesia with paracetamol 1 g orally 6 hourly and ibuprofen 400 mg 8 hourly with food.
• Conservative management of chronic disease (mild cases, pits only, or recurrent minor flares):
  • Remove hair from the natal cleft and the surrounding 5 to 10 cm by shaving every 1 to 2 weeks, depilatory cream, or laser hair removal (4 to 6 sessions at 4 to 6 week intervals, which reduces recurrence by 50% or more).
  • Clean the cleft daily with soap and water, dry thoroughly, and avoid prolonged sitting.
  • Lose weight, and avoid friction.
• Minimally invasive procedures (day case, with local anaesthetic and fast recovery):
  • Pit picking: excision of midline pits with a small, 2 to 3 mm punch or elliptical incision, curettage of the sinus track through a lateral incision, and the wound left open. Recurrence 10 to 20%.
  • Endoscopic pilonidal sinus treatment: video assisted endoscopic ablation of the sinus track and removal of hair under direct vision, with a 1 cm incision. Healing 2 to 4 weeks, recurrence 5 to 10%.
  • Laser ablation of the track (limited evidence).
  • Phenol injection (80%) into the cavity after curettage, left for 1 to 3 minutes then suctioned. Recurrence about 10 to 30%, with a risk of chemical burn. Limited evidence.
• Surgical excision (for recurrent or extensive disease, or failed conservative care):
  • Off midline closure is preferred because it heals faster and recurs less (about 1 to 5%) than midline closure (10 to 30%), and open healing by secondary intention takes 6 to 12 weeks, with recurrence of about 10 to 20%.
  • Rhomboid rotation flap: excise the diseased area and close with a rotation flap, which flattens the cleft. Recurrence about 1 to 5%.
  • Asymmetric excision with lateral flap closure: excise off the midline and close with a lateral flap. Recurrence about 1 to 3%.
  • Cleft lift: lift of the natal cleft with shifting of the midline.
  • Marsupialisation (suturing of the edges of the opened sinus to the base) shortens the healing time.
  • Wide excision with open healing, or negative pressure wound therapy, is used for large wounds.
  • Perioperative antibiotic prophylaxis: cefazolin 2 g IV once, plus metronidazole 500 mg IV once, at induction.
• Postoperative care: keep the wound clean, shave or remove hair from the surrounding skin every 1 to 2 weeks for at least 6 months, and avoid prolonged sitting for 2 to 4 weeks. Drain and dressing care are important to flap success.
• Special groups:
  • Pregnancy: drain abscesses, and delay definitive surgery until after delivery. Use cefalexin for antibiotics, with clindamycin if allergic. Avoid metronidazole in the first trimester where possible.
  • Diabetes: control glucose carefully, give early antibiotics, and expect slower healing.
  • Adolescents: pit picking or endoscopic treatment is favoured to limit the scar and disruption of schooling.
  • Obesity: advise weight loss, and expect higher recurrence.
  • Immunosuppression and Crohn disease: investigate for perianal disease and treat the underlying condition.
• Recurrence: re-examine for missed tracks, new pits, and hair debris, and offer an off midline flap procedure. Refer to a colorectal or plastic surgeon for complex or repeated disease.
• Follow up: review at 1 to 2 weeks after drainage or surgery, then every 2 to 4 weeks until healed, and again at 6 and 12 months for recurrence.