Discovery of Invasion Routes for Nasopharyngeal Adenoid Cystic Carcinoma

The aim of this study is to discover regional invasion routes for nasopharyngeal adenoid cystic carcinoma (NACC) through analyses of the magnetic resonance (MR) images and comparison with keratinizing squamous cell carcinoma (KSCC). Both MR results and clinical records were retrospectively reviewed for 18 patients with NACC and 182 patients with KSCC. The metastasis routes of NACC were identified by analysis of MR images of patients who underwent magnetic resonance imaging (MRI). There were significant differences in skull base invasion and cavernous sinus invasion (p = 0.020 and 0.028, respectively) while parapharyngeal space invasion rate was not. The laryngopharynx invasion rate and external pterygoid muscle invasion rate were higher in NACC patients than that in KSCC patients (16.7% vs. 0.5 %, p = 0.002; 27.8% vs. 11.0%, p = 0.040, respectively). Paralysis of the cranial nerves had a significant higher incidence in the NACC group compared to the KSCC group (66.7% vs. 8.2%, p < 0.001). There was significant difference in invasion to the neural foramen between the NACC and KSCC groups (66.7% vs. 36.3%, p = 0.020). Foramen ovale was a common invasion site, significantly higher in NACC patients than in KSCC patients (50.0% vs. 24.1%, p = 0.018). Based on the MRI findings, a regional invasion model of NACC with two possible routes has been built, including aggressive local infiltration along submucosa to laryngopharynx or external pterygoid muscle, and extension from pharyngonasal cavity, through cranial nerve canal to cavernous sinus. The significant difference in overall survival (OS) time between the two different invasion routs and the recurrent rates in different regions also supported the validity of the invasion model.