Abstract
The aim of this study was to display the lingual artery superimposed on the anatomical image and to confirm its course and relation to the adjacent structures, noninvasively. Nineteen volunteers participated in the magnetic resonance imaging (MRI) study and one was excluded for excessive movement during scanning. A three-dimensional phase-contrast sequence (3D-PC) of magnetic resonance angiography (MRA) was used for vessel images, and a 3D-T1 high-resolution volume examination (THRIVE) was used for anatomical images. Colour-coded vessel images from 3D-PC MRA were superimposed on the 3D volume anatomical images, and the arterial course and relation to the adjacent structures were confirmed with multiplanar reconstructed cross-sectional (MPR) images. 3D-PC MRA images visualized the lingual artery in all 18 subjects and the sublingual artery in 14 subjects. In seven of 18 cases the bilateral sublingual arteries were shown to run side by side but had no contact with the sublingual veins. They ran together with the sublingual veins in four cases. Three cases showed irregular patterns. The bilateral sublingual arteries could not be identified in four cases. 3D-PC MRA images of the lingual artery superimposed on the anatomical images may be clinically useful to confirm its course and relationship to the adjacent structures before surgery, in order to prevent haemorrhage.
Life-threatening haemorrhage and hematoma formation in the floor of the mouth secondary to injury of any of the lingual or facial arterial branches is particularly serious. The recent increase in dental implant treatment has resulted in an increased incidence of complications. Therefore, obtaining prior image information on the lingual and sublingual arteries and their relation to the adjacent structures is very useful for surgeons performing maxillofacial surgery.
Sublingual hematoma during surgical placement of mandibular dental implants has been reported in previous case studies. Bleeding, which potentially leads to fatal airway obstruction, can result from damage to the lingual or facial arterial branches. Many studies have examined the vessels in human cadavers to clarify the variations in the vessels. In general, the sublingual artery that branches from the lingual artery, and the submental artery from the facial artery, run antero-posteriorly above and below the mylohyoid muscle, respectively ; however, there are variations in their courses. Hofschneider et al. reported that 71% of specimens had a sublingual artery in the mandibular anterior region, while 41% had a branch of the submental artery perforating the mylohyoid muscle into the same region. On the other hand, Bavitz et al. found that a perforating submental artery was present in 60% of the cases, while the sublingual artery was small or missing in 53% of the cases. Cadaver reports are useful for surgeons to determine where there is a need to pay special attention when placing implants, however, the information is categorized and does not apply directly to the individual patient’s situation.
Tagaya et al. assessed the frequency of the foramina on the lingual surface of the mandible using computed tomography (CT) and reported that the frequency of the lingual foramina in the medial region was 100% and that in the lateral region was 80%. They recommended CT examinations before implant surgery to reduce severe haemorrhage in the anterior region of the mandible. CT examination is indeed useful in providing the image information of the mandibular lingual foramina of each patient, and conveniently it is currently widely performed to examine bone thickness and the mandibular canals. However, CT cannot visualize the vessels themselves without contrast medium, which is invasive and can lead to side effects such as an anaphylactic reaction or contrast-induced nephropathy, especially in elderly patients. In addition, ionizing radiation is harmful to the patient.
Magnetic resonance imaging (MRI) has become widespread in clinical use due to its superior soft tissue imaging and spatial resolution. MRI does not use ionizing radiation, but rather magnetic fields and radio waves, to produce an image that is dependent on the distribution of hydrogen in the body. The MRI signal intensity depends on many factors, including the sequence used. There are many different types of sequence, however, they all have timing values that can be modified to obtain the required image contrast.
The purpose of this study was to display the lingual artery superimposed on the anatomical image, noninvasively using MRI, and to confirm its course and relation to the adjacent structures, such as mandible and muscles, which would aid the surgeon in avoiding serious complications.
Materials and methods
Nineteen healthy volunteers participated in this study (11 males and eight females, mean age 29.8 years, age range 24–43 years). One of the original subjects was excluded because of excessive movement during scanning. Institutional review board approval was obtained for all experimental procedures. The participants were informed in detail about the nature of the experiment, and all gave their written informed consent to participate in the study.
All experiments were performed using a Gyroscan Intera Achieva 1.5-T Nova Dual device (Philips Medical Systems, Eindhoven, The Netherlands) with a neurovascular coil. Two different sequences were used: a three-dimensional phase-contrast sequence (3D-PC) of magnetic resonance angiography (MRA) for vessel images, and a 3D-T1 high-resolution volume examination (THRIVE) for the anatomical images.
The imaging parameters used in the 3D-PC MRA sequences consisted of 60 slices, 3D-T1 turbo-field echo sequence (T1 TFE). The representative parameters were: a repetition time (TR) of 17 ms, echo time (TE) of 6.2 ms, flip angle (FA) of 12°, field of view (FOV) of 180 mm, acquisition pixel = 0.9 × 0.9, reconstruction pixel = 0.56 × 0.56, number of excitations (NEX) = 1, and reduction factor of SENSE = 2. The slice thickness was 2.0 mm and the slice gap was −1.0 mm. A velocity encoded gradient was applied along the posterior-to-anterior (PA), right-to-left (RL), and superior-to-inferior (SI) directions with a velocity encoding number (VENC) of 8 cm/s. The scan time was 8 min 12 s.
The THRIVE sequences were: TR of 11 ms, TE of 6.4 ms, FA of 10°, FOV of 180 mm, acquisition pixel = 0.9 × 0.9, reconstruction pixel = 0.56 × 0.56, NEX = 1, reduction factor of SENSE = 2, and the scan time was 4 min 41 s.
The DICOM data obtained were imported into a personal computer and maximum intensity projection (MIP) images for 3D-PC MRA were created to verify the depiction of the lingual and sublingual arteries. Then colour-coded phase images from 3D-PC MRA were superimposed on the 3D volume anatomical images, and the arterial course and relation to the adjacent structures were confirmed with multiplanar reconstructed (MPR) cross-sectional images.
Two specialists in oral and maxillofacial radiology performed the data processing and image assessment using the Osirix free software package. The results were used with the consent of the two observers. The images were examined again after 1 week using the same procedure.
The lingual artery arises from the external carotid artery between the superior thyroid and facial arteries, and the deep lingual and the sublingual arteries are main branches. The lingual artery releases the sublingual artery anteriorly in the oral floor and rises into the tongue as the deep lingual artery ( Fig. 1 ). The vessel that originates directly from the external carotid artery and then runs into the oral floor horizontally was defined as the lingual artery, and its consecutive course was extracted.
Results
3D-PC MRA images visualized the lingual artery and its terminal branch (deep lingual artery) clearly, without contrast medium, in all subjects. The sublingual artery could be identified in 14 of the 18 cases. A representative MIP image for 3D-PC MRA is shown in Fig. 2 . The anatomic relationships between the lingual arteries and the adjacent structures were observed on fusion images of 3D-PC MRA and anatomical images of THRIVE ( Fig. 3 ).
