A pilonidal sinus is a chronic inflammatory condition characterised by a sinus tract or cavity in the sacrococcygeal region, the cleft between the buttocks containing hair, debris and granulation tissue. The term derives from the Latin pilus (hair) and nidus (nest), reflecting the pathological finding of a nest of loose hairs within the sinus. The condition is thought to arise from penetration of loose shed hair into the skin of the natal cleft, driven by friction and the suction effect created by movement of the buttocks provoking a foreign body reaction, secondary infection and sinus tract formation. It predominantly affects young adult males, particularly those who are hirsute, overweight, or engage in prolonged sitting and is rare after the age of 40 when hair follicle activity diminishes. A pilonidal abscess represents the acute phase of the disease, while a chronic pilonidal sinus with persistent discharge represents the established, recurrent form.
Symptoms
In its acute form, pilonidal disease presents as a tense, exquisitely tender, fluctuant swelling in the natal cleft, a pilonidal abscess associated with severe localised pain, erythema, swelling and systemic features of infection including fever and malaise. In the chronic form, patients report intermittent or persistent purulent or blood-stained discharge from one or more pit openings in the natal cleft, associated with low-grade discomfort, recurrent swelling and difficulty with prolonged sitting. On examination, characteristic midline pit openings are visible in the natal cleft, with lateral sinus openings indicating more complex or recurrent disease. The condition significantly impacts quality of life and occupational activity due to its tendency for recurrence.
Diagnosis
The diagnosis is entirely clinical, based on the characteristic location, the presence of midline pits and the history of recurrent discharge or acute abscess formation in the natal cleft. No imaging is routinely required for straightforward disease. MRI or ultrasound may be employed in complex or recurrent cases to map the extent of sinus tracts, identify secondary extensions, and guide surgical planning particularly when previous surgery has distorted the normal anatomy.
Treatment
Acute pilonidal abscess is managed by incision and drainage under local or general anaesthesia as a day-case procedure the abscess cavity is opened, drained and the wound left open to heal by secondary intention. This provides rapid relief but does not treat the underlying sinus and definitive surgery is subsequently required to prevent recurrence. For chronic pilonidal sinus, definitive surgical excision is the standard of care. Wide local excision with open wound healing (healing by secondary intention) achieves thorough removal of all sinus tracts but requires prolonged wound care of several weeks. Flap reconstruction techniques particularly the Limberg rhomboid flap or Karydakis flap procedure are now the preferred surgical approaches, excising the sinus and reconstructing the natal cleft with a transposition flap that flattens the cleft, eliminating the hair-trapping environment and significantly reducing recurrence rates to below 5%. Minimally invasive techniques such as pit picking and Video-Assisted Ablation of Pilonidal Sinus (VAAPS) offer promising results with faster recovery in carefully selected patients with limited disease. Post-operative meticulous hair removal from the natal cleft whether by shaving or laser epilation is essential to minimise the risk of recurrence regardless of the surgical technique employed.