Sinus tracts are an abnormal connection between a fluid collection with a mucous mucosal surface and/or skin ^1,2. It can result from acute or chronic processes and occasionally extend into the joints and bones ¹.

Terminology

The term sinus tract is non-specific; however, when used in soft tissue or bony infections, it generally delineates the extent of infection ¹. If the abnormal connection is between two epithelial surfaces such as between hollow organs, skin or vessels, the term fistula is used.

Aetiology

Sinus tracts can develop ²:

• spontaneously

• secondary to iatrogenic injury (e.g. surgical incision)

• post-traumatic

• underlying collection or necrotic material (e.g. necrotising pancreatitis)

• secondary to infective bone foci (e.g. osteomyelitis)

• secondary to infected membranous sacs (e.g. chronic empyema)

• secondary to an underlying foreign body (e.g. shrapnel)

Complications

Squamous cell carcinoma may rarely develop within the chronic sinus tracts in cases of chronic osteomyelitis ^3,4.

Radiographic features

Fluoroscopy

Direct visualisation of the sinus tract, its ramifications, and extent can be done using radio-opaque contrast material under fluoroscopic guidance.

MRI

Active tracts are typically ¹:

• T1: hypointense

• T2/T2FS: hyperintense

• T1 C+: tram-track pattern of peripheral enhancement

Chronic fibrosed sinus tracts typically demonstrate T1 and T2 hypointense signals without contrast enhancement ¹.

Radiological report

The radiological report should contain a description of the following:

• presence, location, size, and ramifications of the sinus tract

• associated findings

  • presence, location, and size of the underlying abnormal collection

  • extension into the joint or bone