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Precision and accuracy of CT-based measurements of masticatory muscles in patients with hemifacial microsomia

¹ Department of Orthodontics, Academic Centre for Dentistry, Amsterdam, The Netherlands; ² Department of Orthodontics, Craniofacial Centre of the Erasmus Medical Centre Rotterdam, The Netherlands; ³ Department of Plastic and Reconstructive Surgery, Craniofacial Centre of the Erasmus Medical Centre Rotterdam, The Netherlands; ⁴ Department of Radiology, University Hospital Utrecht, The Netherlands

*Correspondence to: Dr CE Huisinga-Fischer, Craniofacial Centre of the Erasmus Medical Centre Rotterdam, Department of Orthodontics, Dr Molewaterplein 60, 3015 GJ Rotterdam, The Netherlands; Email: chuisinga{at}xs4all.nl

Received 8 November 2002; revised 1 July 2003; accepted 8 January 2004

Objective: The objective of this study was to quantitatively assess masticatory muscle volumes in patients with hemifacial microsomia. Until recently, this congenital malformation was only studied in terms of restoring bony and skin morphologies. Study of the masticatory muscles, however, adds a new dimension.

Materials and methods: Contiguous 1.5 mm CT scans were made using a Philips Tomoscan 350 in six patients with hemifacial microsomia and in one patient without asymmetry. These CT scans were processed by a Cemax 1500X 3D workstation. The volume of the masseter, temporal, and medial and lateral pterygoid muscles was measured from CT scans using three-dimensional (3D) segmentation followed by 3D imaging. The precision and accuracy of measurements of masticatory muscle volumes were investigated. The precision of 3D imaging was assessed by carrying out repeated measurements by two observers. The accuracy of the volume determination technique was assessed by scanning a piece of porcine muscle tissue with a known volume.

Results: Intraobserver repeatability was near perfect, with the lowest being 0.96 (for the medial pterygoid muscle). All interobserver correlations were high (>0.99). The accuracy of the method of measurement demonstrated differences ranging from 2.3% to 4.4%.

Conclusion: Craniofacial soft tissue measurements obtained from CT scans in patients with hemifacial microsomia were accurate and reproducible but time consuming.

Keywords: hemifacial microsomia; muscles of mastication; computed tomography; three-dimensional imaging; precision and accuracy