Postoperative control of functional muscle flaps for facial palsy reconstruction: Ultrasound guided tissue monitoring using contrast enhanced ultrasound (CEUS) and ultrasound elastography.

BACKGROUND AND OBJECTIVES: Facial paralysis causes excruciating impairments including facial asymmetry, limited eye closure, oral incontinence and social dysfunction. Modern plastic surgical reconstructions render favorable results with well-perfused dynamic muscle flaps. Post-operative tissue monitoring is a critical determinant for success. Contrast-enhanced Ultrasound (CEUS) and elastography have proven superior properties to evaluate tissue perfusion in various organs. We evaluated their role for functional muscle flaps positioned at the sub-skin level in facial palsy patients.

METHODS: From 2016-2017 five patients received muscle flap reconstructions. Flaps included four free transplants and one pedicled transfer. Postoperatively tissue vitality and blood flow were assessed with CEUS. One experienced examiner using linear probes (6-9, 6-15 MHz) and bolus injections of Sulphur-hexafluoride microbubbles evaluated tissue perfusion. Using the time intensity curve- (TIC)-analysis measurements were recorded for TTP (time to peak) and AUC (Area under curve). Tissue elasticity was assessed with ultrasound elastography.

RESULTS: All flaps were successful and showed no major complications. TTP-values in flap tissue showed slightly decreased values of 35.12±33.99 s and 25.04±10.86 s compared to surrounding tissue with 19.88±6.94 s. AUC-analysis however revealed higher values of 292.25±169.52 RU and 274.51±115.88 RU than surrounding tissue with 150.90±40.21 RU. Elastography demonstrated predominantly elastic flap tissue whereas surrounding tissue confirmed a slightly harder tissue quality. CEUS in combination with elastography verified tissue vitality and blood flow in a safe and reproducible manner.

CONCLUSIONS: Post-operative perfusion monitoring in muscle flaps positioned at a sub-skin level may be performed superiorly by CEUS and elastography in a quick, reproducible and minimally-invasive fashion.