Abstract
The purpose of this study was to examine the efficacy of ultrasonography (US) and unenhanced magnetic resonance imaging (MRI) to determine the location of the internal maxillary artery (IMA) before orthognathic surgery. The study subjects were 19 patients (seven males and twelve females) with mandibular prognathism seen at the authors’ institution between March 2012 and April 2013. The distance from the skin to the IMA (S-IMA) and the distance from the mandibular notch to the IMA (MN-IMA) were measured. Using the US and coronal MRI images, S-IMA(cl) and MN-IMA(cl) in the closed position and S-IMA(op) and MN-IMA(op) in the open position were measured at a total of four points in each cross-section. There were significant correlations between the distances measured on coronal MRI and US for all groups ( P < 0.05). A total of 35 (92%) IMAs were classified as clear and three (8%) as unclear based on the US findings. Regarding the location of the IMA, 37 of the 38 sides studied (97%) were of the lateral type, while only one (3%) was of the medial type. The results of this study indicate that US can be used effectively to determine the location of the IMA.
Many surgical procedures are performed on the mandible each year worldwide. The intraoral vertical ramus osteotomy (IVRO) and sagittal split ramus osteotomy (SSRO) are the most commonly used surgical procedures to treat mandibular prognathism. Reported complications of orthognathic surgery include haemorrhage, nerve damage, infection, and bone necrosis. Despite taking all necessary precautions, potentially life-threatening uncommon acute and subacute vascular complications may occur. Haemorrhage is usually controlled with pressure packing, although the proximal end of the vessel must occasionally be clamped and cauterized and then clipped or tied. Haemorrhage associated with mandibular osteotomy, especially to the extent that it becomes life-threatening, is a rare occurrence, with a risk lower than that following maxillary orthognathic surgery. However, haemorrhage from some arteries may be serious.
When performing an IVRO, there is the risk of potential injury to the internal maxillary artery (IMA) leading to major haemorrhage. For example, this artery may be lacerated when the bone cut is made close to the sigmoid notch. The IMA is potentially the most important source of haemorrhage following IVRO. Kodama et al. reported that ultrasonography (US) plays a complementary role to non-enhanced computed tomography (CT) in delineating the IMA for preoperative evaluations of patients with jaw deformities. However, CT has the disadvantage of X-ray exposure.
The purpose of this study was to examine the efficacy of US and unenhanced magnetic resonance imaging (MRI) to determine the location of the IMA before orthognathic surgery.
Patients and methods
Subjects
The study subjects were 19 patients (seven males and twelve females) with mandibular prognathism treated at the authors’ institution between March 2012 and April 2013. The patients ranged in age from 15 to 48 years (mean 23.5 ± 10.2 years). Informed consent was obtained from all patients, and this study was approved by the institutional review board of the study institution. The details of each case, including gender, age, diagnosis, and operation planned, are presented in Table 1 .
| Patient number | Gender | Age, years | Diagnosis | Operation planned |
|---|---|---|---|---|
| 1 | F | 24 | Post-traumatic mandibular deformity (L) | Bi-IVRO |
| 2 | F | 17 | Mandibular protrusion | Bi-IVRO |
| 3 | F | 27 | Mandibular protrusion | Bi-IVRO |
| 4 | F | 40 | Mandibular protrusion | Bi-IVRO |
| 5 | F | 30 | Mandibular protrusion | Bi-IVRO |
| 6 | M | 21 | Mandibular protrusion | Bi-IVRO |
| 7 | F | 48 | Mandibular protrusion | Bi-IVRO |
| 8 | F | 18 | Mandibular protrusion | Bi-IVRO |
| 9 | M | 18 | Bi-Maxil protrusion (L) | LFI + Bi-IVRO |
| 10 | M | 19 | Mandibular protrusion | Bi-IVRO |
| 11 | F | 19 | Mandibular protrusion | Bi-IVRO |
| 12 | M | 17 | Deep overbite (R) | Bi-IVRO |
| 13 | M | 46 | Mandibular asymmetry (L) | Bi-IVRO |
| 14 | F | 15 | Goldenhar syndrome | LFI + IVRO |
| 15 | F | 19 | Maxillary protrusion | AM + Bi-IVRO |
| 16 | M | 15 | Mandibular asymmetry (R) | Bi-IVRO |
| 17 | M | 21 | Mandibular protrusion | Bi-IVRO |
| 18 | F | 17 | Mandibular asymmetry (L) | Bi-IVRO |
| 19 | F | 16 | Mandibular protrusion | Bi-IVRO |
Methods
All patients were evaluated using US and unenhanced MRI.
For the US assessment, a 13 to 5-MHz linear array transducer (HI VISION Avius; Hitachi Medical Co., Chiba, Japan) was applied. Based on the method of Hayashi et al., the IMA was visualized through the acoustic window formed by the zygomatic arch and the mandibular notch using power Doppler US. With regard to the position of the probe, the horizontal plane was visualized by a parallel scan to Camper’s plane and the vertical plane was visualized by an orthogonal to Camper’s plane ( Fig. 1 ). The US findings in the horizontal plane were classified into the two following patterns: (1) a clear pattern, indicating a continuous or string-like structure, and (2) an unclear pattern, indicating a discontinuous dot-like structure or no apparent blood flow. For the clear patterns, the distance from the skin to the IMA (S-IMA) and the distance from the mandibular notch to the IMA (MN-IMA) were measured ( Fig. 2 ). The examination consisted of two lateral sections in the closed position and two lateral sections in the open position for each acoustic window. A mouth gag was used to stabilize an open mouth position during the exposure; the distance between the central incisors when using the mouth gag was 30 mm.
The MRI machine used was a high-intensity 1.5-T device (Signa Excite; General Electric, Chalfont St. Giles, UK) with a 3-inch dual surface coil. The imaging parameters for the first spin echo images included a repetition time of 2000 ms, echo time of 9.1 ms, field of view of 180 mm, acquisition matrix of 256 × 256, and slice thickness of 2.5 mm with a gap of 0.3 mm. The S-IMA and MN-IMA were measured in the closed and open positions on the coronal MRI images. The location of the main trunk of the IMA was classified with respect to the lateral pterygoid muscle, as follows: as the lateral type when the main trunk ran superficial to the lateral pterygoid muscle, or as the medial type when the main trunk ran deep to the lateral pterygoid muscle ( Fig. 3 ). On each cross-section, a line tangent to the bilateral mandibular exterior region and a line horizontal to the bilateral external acoustic meatus were drawn on the coronal MRI and the distance to S-IMA and MN-IMA measured in the closed and open positions ( Fig. 4 ).
