Functional analysis of vocal folds by transcutaneous laryngeal ultrasonography in patients undergoing thyroidectomy

Transcutaneous laryngeal ultrasound (TCLUS) can assess Vocal folds (VF) by subjectively identifying mobility or objectively by calculating vocal fold displacement velocity (VFDV). Optimal diagnostic approach (subjective assessment, VFDV estimation or a combination of both) is unresolved; hence, we conducted this prospective study in patients undergoing thyroidectomy.

Two anaesthetists performed TCLUS pre- and post-operatively for functional assessment of 200 VFs on 100 patients. Their findings were compared with pre-operative flexible laryngoscope (FL) performed by surgeons and with post-operative C-Mac video laryngoscope (C-Mac VL) by another independent anaesthetist. Correlation between FL and TCLUS findings and inter-rater agreement between TCLUS findings of both anaesthetists was analysed. Decision curve analysis (DCA) was performed to compare clinical benefit of hoarseness, subjective VF movement, VFDV, and combined assessment for detecting disabled VFs.

We found good correlation between VF mobility on TCLUS and FL (Spearman's r = 0.93, P < 0.0001) as well as C-Mac VL (Spearman's r = 0.83, P < 0.0001) with excellent inter-rater agreement between both anaesthetists. DCA showed combined assessment to have marginally higher clinical benefit than other diagnostic approaches at intermediate threshold probabilities while its benefit was similar to subjective evaluation at higher threshold probabilities.

Provided achievement of optimal acoustic window, TCLUS can reliably assess disabled VFs with FL reserved for their confirmation or doubtful cases. Subjective assessment of VF mobility should suffice in most cases with additional VFDV estimation reserved pre-operatively for situations with higher risk of VFs disability, and post-operatively when subjective VF assessment findings are discordant from pre-operative status.