Endoanal ultrasound

Your anal sphincter is actually two separate muscles working together — the internal sphincter, which squeezes automatically without you thinking about it, and the external sphincter, which you control consciously when you squeeze. Endoanal ultrasound uses a small, smooth probe (slightly narrower than a finger) inserted into the anal canal to take 360-degree images of both of these muscles and the space between them.

It shows whether there is a tear, a scar, or a gap in the sphincter in considerable detail — more informative than an external examination alone. For complex anal fistulas, it is also a reliable way to map the tunnel and its relationship to the muscle before deciding on treatment.

How this compares to MRI: for some complex or deep fistulas, an MRI of the pelvis is used instead of (or alongside) endoanal ultrasound. The two tests are complementary rather than competing, and whichever is most useful for your situation will be chosen or arranged.

• You have faecal incontinence (leakage) and a precise look at where the sphincter is damaged and how large the gap is, is needed
• You have a complex anal fistula and the scan is needed to understand how the tunnel relates to the sphincter muscles before deciding on treatment
• You have Crohn's perianal disease — endoanal ultrasound is often combined with an EUA to assess and treat fistula tracks in this group
• You had a significant tear during childbirth (an obstetric sphincter injury) and the scan is needed to check whether the muscle has healed
• You are being planned for sphincteroplasty (sphincter repair) — the scan maps exactly where the gap is so the repair is as accurate as possible
• You are having an EUA for an undiagnosed perianal lump, swelling, or pain and a closer look at the muscle layer is needed

• Very detailed real-time images of both sphincter muscles — no radiation at all
• Finds tears, scars, and gaps in the sphincter that would be completely missed on an external examination
• Provides a precise map of your anatomy before any repair, helping make subsequent surgery safer and more targeted
• For complex fistulas, helps clarify the anatomy and guide the safe placement of a seton
• Because it is done at the same sitting as your EUA or endoscopy, you only need to be sedated once and there is no separate visit, scan appointment, or recovery day

Endoanal ultrasound adds essentially no risk of its own to the procedure you are already having — the scan itself is quick, well tolerated, and uses no radiation. The sedation, fasting, and small bleeding/perforation risks that apply on the day are those of the underlying procedure (the EUA, colonoscopy, or flexible sigmoidoscopy) — see those pages for the full discussion.

The only scan-specific point worth knowing is that in rare cases where the anal canal is very narrow (for example, from severe scarring or a tight stricture), the probe cannot be comfortably inserted, and an alternative such as MRI will be used instead.

Preparation is exactly the same as for the underlying procedure you are booked for — there is nothing extra you need to do for the scan itself. Please follow the instructions on the relevant procedure page:

• Examination under anaesthetic (EUA) — usually a small enema beforehand and standard fasting
• Colonoscopy — full bowel preparation and fasting
• Flexible sigmoidoscopy — enema and fasting

If you are unsure which procedure you have been booked for, please call our rooms — the booking will confirm exactly what is planned.

The arrival, sedation, and recovery elements of the day are exactly as described on the underlying procedure's page. The scan-specific part takes only a few minutes within the larger procedure:

• Once you are positioned and sedated for the EUA or endoscopy, the small ultrasound probe is gently inserted into the anal canal.
• The probe is rotated to capture 360-degree images of the sphincter and surrounding tissues — this typically takes 5–10 minutes.
• The images are reviewed on screen and saved. Where a fistula is being treated, the imaging guides the safe placement of any seton or definitive procedure in the same sitting.

There is nothing to recover from for the scan itself. Your recovery follows the requirements of the underlying procedure — see the relevant procedure page for what to expect afterwards. The imaging findings, what was treated on the day, and what comes next will be discussed with you at your follow-up appointment.

Questions or concerns after your scan: Please call our rooms on (03) 9816 3951 and leave a message — this will be sent directly as a text to Mr Nguyen. Alternatively, you may text the office mobile on 0499 090 126. We aim to respond promptly during business hours.

Emergencies: For any life-threatening emergency, call 000 immediately or go to your nearest emergency department. Do not wait for a call back from our rooms. For the Austin Hospital Emergency Department: (03) 9496 5000.