[Purpose] This study examines using ultrasonography and unenhanced computed tomography (CT) to determine the location of the internal maxillary artery (IMA) before orthognathic surgery.
[Patients and Methods] From January 2008 to February 2011, 15 patients (30 sides as bilateral) with jaw deformities agreed to participate in this study after informed consent was obtained. IMAs were visualized through the acoustic window formed by the zygomatic arch and mandibular notch using power Doppler ultrasonography. Ultrasonographic findings were classified into 2 patterns as follows: 1) clear pattern, indicating continuous or string-like structure; 2) unclear pattern, indicating discontinuous dot-like structure or no apparent blood flow. Each unenhanced CT image of the IMA location was categorized referring to the ultrasonographic image as predictable or unpredictable.
In addition, each predictable image was subclassified as lateral (located external to the lateral pterygoid muscle) or medial (other than the former).
[Results] The ultrasonography had 24 (80.0%) IMAs classified as clear and 6 (20.0%) as unclear. For the 24 clear patterns, the mean distance from the mandibular notch to the IMA was 2.77 mm (1.0-6.0 mm). The IMA location was detectable in all patients using unenhanced CT plus ultrasonographic imaging. Of the 26 (86.7%) IMAs located lateral to the lateral pterygoid muscle, the ultrasonographic artery findings were classified as clear for 24 and unclear for 2. Of the 4 (13.3%) IMAs located medial to the lateral pterygoid muscle, the ultrasonography findings were classified as unclear.
[Discussion] Paying attention to unclear-pattern images classified as lateral was necessary because they may indicate that the IMA is located in proximity to the ramus medially, and to clear-pattern images classified as lateral that approach the mandibular notch. We assume that the risk for hemorrhage during orthognathic surgery will increase if the IMA route is located in the surgery area.
[Conclusion] A combination of ultrasonography and unenhanced CT for determining the IMA route may provide safer orthognathic surgery.