Ultrasound-Guided Needle Electromyography of the External Anal Sphincter.

BACKGROUND: Anal sphincter needle electromyography (EMG) is a useful tool to evaluate various neurologic lesions. However, landmark-based needle placement has risks of missing the intended target including risk of bowel penetration. Ultrasound guidance has been widely used to enhance needle placement for various interventional procedures, but it has not been previously reported for use in anal sphincter EMG.

OBJECTIVE: To demonstrate the accuracy of ultrasound-guided needle insertion into the external anal sphincter (EAS).

DESIGN: Observational study.

SETTING: Tertiary care university hospital.

PARTICIPANTS: A single live male participant and six fresh cadavers.

METHODS: A preliminary study was conducted in a single live male participant to investigate the utility of ultrasonography imaging for the EAS and proper transducer location. After this preliminary study, 12 sides of the EAS in six fresh cadavers were assessed. A hooked fine wire was inserted into the EAS under ultrasound guidance.

MAIN OUTCOME MEASURES: Accuracy of needle placement was assessed after cadaver dissection.

RESULTS: The EAS was easily identified with ultrasound in preliminary and cadaver studies. The needle tips were located in the EAS in 11 of 12 cadavers.

CONCLUSIONS: Ultrasound-guided needle EMG of the EAS is convenient and accurate in cadavers and may be useful in clinical practice. Further studies comparing ultrasound-guided and landmark-guided needle EMG of the EAS in live patients will be needed.