Presentation
Long-time anal discharge and discomfort.
Patient Data
There is a perianal fistula tract of about 6 cm long, an external opening seen at approximately the 10 o'clock position (detected at the time of examination on the patient), which is a superficial low-type intersphincteric fistula, with the internal opening being at a distance of about 16mm from the anal verge in the posterior wall of the anal canal (curved tract).
Tiny echogenic foci in the tract are referred to as gas vs. faecolith.
There is no evidence of abscess formation.
Case Discussion
Perianal fistulas are abnormal communications between the anal canal and the perirectal spaces, which may or may not be associated with a collection.
Percutaneous perianal ultrasound examination is informative, rapid, and low-cost. We utilised a linear probe with a frequency of 7.5 MHz and, at times, a convex probe with a frequency of 3.5 MHz. In this case, the images were taken with the probe positioned in a "12 o'clock to 6 o'clock" plane while the patient was examined in a knee-chest position.
Learning points:
In the report of a perianal ultrasound, ensure to include the following details:
fistula length
internal and external opening position
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fistula path, including branches
if multiple fistulae, document the number of internal openings
fistula type: high or low
document presence/absence of abscess/colelction
Acknowledgements: Dr. Syed Hadi Hassan, consultant radiologist, MD, FRCR at National Guard Hospital Al-Ahsa Saudi Arabia, who first placed the probe on perianal for fistula diagnosis prior 20 years ago ref.
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