Pilonidal sinus

Pilonidal sinuses result from the skin and subcutaneous tissue infections, typically occurring at or near the upper part of the natal cleft of the buttocks. As such is it often also termed an intergluteal pilonidal sinus. While it can also occur at other sites (see location section), this article is focused on intergluteal pilonidal sinuses.

Epidemiology

While it can potentially occur at any age, it is much less common in children and older individuals (e.g. those older than 45). The peak age of presentation is patients in their twenties. There is an increased male predilection.

Pathology

It is characterized by natal cleft suppuration and is thought to initially result from a hair follicle infection. This can then lead to the subsequent formation of a subcutaneous abscess from a persistent folliculitis. Hair can then enter the abscess cavity and provoke a foreign body tissue reaction.

Location

While it classically occurs in the intergluteal region, it can rarely occur at other sites which include

  • between digits: interdigital pilonidal sinus
  • umbilical region: umbilical pilonidal sinus 

Radiographic features

Ultrasound

May show sinus anatomy to a reasonable degree in superficial cases.

MRI

Allows visualization of tract anatomy also useful in assessment associated inflammation.

Fluoroscopy

Contrast is injected into the cutaneous opening to delineate the extent of sinus and its morphology. It may also identify if there are any fistulous tracts rather than merely a sinus.

History and etymology

It is thought to have been initially described by Herbert Mayo in 1833.

Differential diagnosis

An intergluteal pilonidal sinus can be clinically difficult to differentiate from a fistula-in-ano.