BOOST training – endoanal US image review

Julia R. Fielding, M.D.April 21, 2010

Objectives

• 1. Review appearance of normal sphincter complex on US exams compared with line drawings

• 2. Show examples of sphincter tears at multiple levels

• 3. Show errors in technique• 4. Tips of the trade – make your life easier

Image analysis

• Is this exam too bright (overexposed) or too dark (underexposed)? Is your gain setting appropriate (brightness)?

• Is this exam interpretable?• Ask yourself these questions WHILE you are

doing the exam – Is your machine working correctly? Is the patient as comfortable as possible?

Image analysis

• Location – HAC1, HAC2, MAC and LAC• Tear IAS – discontinuity in dark ring• Tear EAS – discontinuity in bright ring• If tear, how large – clock-face and radial

degrees

HAC – High anal canal 11. This is the superior

most image of the exam.

2. Probe should be perpendicular to sphincter – puborectalis muscle is symmetric in appearance and makes a “V”

3. This “sets the clock” for the entirety of the exam.

Normal HAC

Key points: Look for puborectalis “V” and find anterior midline – 12:00

Problem HAC – too cephalad, cannot assess IAS well

Key points: Look for puborectalis “V” and find anterior midline – 12:00

Problem HAC1

Posterior angulation – compresses sphincter closest to spine and allows for mucosal overlap anterior to probe. False positive tear 12:00-1:00.

HAC2 – high anal canal 21. We will review this

level but it will not be included on the TEST

2. Located just caudal to HAC1

3. Check that probe has not changed position

4. Note that IAS makes a ring and EAS is incomplete

5. No “V” present

Normal HAC2

Key finding: EAS is incomplete

Tear HAC2

IAS tear 11:00-12:00 or 30 degrees, EAS intact

MAC – middle anal canal1. Check your position –

probe without ANGULATION or ROTATION.

2. Rotation resets the clock and causes errors in recording LOCATION of tear.

3. Angulation compresses one portion of the sphincter complex more than another leading to FALSE POSITIVE tear assessment

Normal MAC

Key finding: 2 concentric rings – hypoechoic (IAS) and hyperechoic (EAS)

Tear MAC

Tear EAS, 12:00-1:00 or 30 degrees, IAS intactKey point: make sure that you are caudal to HAC2!

Tear MAC

IAS defect: 9:00-4:00 or 210 degrees, EAS thin but intact

Pitfall: Scar IAS

Key point: No discontinuity IAS

LAC- Lower anal canal

1. This is the most caudal of the images

2. The IAS – black concentric ring, has disappeared

3. All that remains is the EAS, the hyperechoic ring

Normal LAC

Key finding: No dark ring, no IAS component

Problem LAC

Image too bright, overexposed, also portions of IAS are still visible, so image is a bit too cephalad. This exam would be considered “overexposed” If no better image available, then uninterpretable.