The value of 3D-iMSDE MR neurography in the determination of the anatomical relationship between intraparotid facial nerve and parotid ducts and parotid tumors

Abstract

Objective To investigate the spatial relationship between intraparotid facial nerve and parotid ducts in different types of parotid neoplasms with 3D improved motion-sensitized driven-equilibrium pulse (3D-iMSDE) MR neurography, and to guide the operation plan. Methods By means of prospective research methods, the sequences of 3D-iMSDE and 3D-T2-fast field echo (3D-T2-FFE) were obtained in 30 healthy volunteers and 40 patients with parotid gland tumors, respectively. All patients with parotid mass were found by physical examination, by maxillofacial surgeons or by ultrasonography or other imaging examinations. Facial nerve trunk with its first branches and parotid ducts were evaluated independently on images of iMSDE and T2-FFE sequence for volunteers. The signal intensity ratio (SIR) of both facial nerve and parotid ducts were compared respectively in two sequences The relationship between intraparotid facial nerve and parotid ducts with the lesion were analyzed on images of iMSDE and T2-FFE sequences for 40 patients. The results were compared with intra-operative anatomy and post-operative pathological findings.Wilcoxon symbolic rank test, t test and chi-square test were used Results The image scores of intra-parotid facial nerve and parotid ducts in iMSDE sequence were higher than that of T2-FFE sequence in all 30 healthy volunteers. The difference was statistically significant (Z=-6.197,P<0.05). Both the facial nerve and parotid duct on images of iMSDE sequence had higher SIR than that of T2-FFE. The differences were statistically significant (t=10.772,11.586, respectively;P<0.05). Forty patients with parotid gland tumors had a total of 41 lesions. Compared with the intraoperative anatomy, the accuracy of iMSDE and T2-FFE sequences in showing the relationship between the facial nerve and its primary branches with the mass were 36/41 (87.8%), and 22/41 (53.7%) respectively, and the accuracy of the two sequences in showing the relationship between the dominant duct of the parotid gland and the mass were 38/41 (92.7%) and 30/41 (73.2%), respectively.The accuracy rate in showing the relationship between facial nerve and its primary branch and the mass on images of iMSDE sequence were higher than that of T2-FFE sequence, and also in showing the relationship of parotid duct and the mass. The statistical differences were significant (χ2=9.725, 5.513;P<0.05,respectively). In the iMSDE sequence, the relationship between the facial nerve and its first branches (temporofacial and cervicofacial division) with the tumor was correctly demonstrated in 36 cases. 38 cases of parotid ducts were satisfactorily displayed on image of iMSDE sequence. Conclusions The 3D-iMSDE MRN sequence can correctly show the relationship between intraparotid facial nerve and parotid duct and the parotid gland neoplasms. Key words: Parotid neoplasms; Facial nerve; Magnetic resonance imaging; Parotid duct