The anatomy of nasopharyngeal carcinoma spread through the pharyngobasilar fascia to the trigeminal mandibular nerve on 1.5 T MRI

Purpose To analyze, from 1.5 Tesla (T) MRI clinical cases, anatomical accessibility of nasopharyngeal tumors through the pharyngobasilar fascia (PBF) to the mandibular nerve for potential perineural spread. Methods A 6-year retrospective review of 1.5 T MR images were rated for tumor involvement of fascial planes and perineural spread in 15 consecutive patients (10 female, 5 male; mean age 45.8 years, range 19-86) with histopathologically proven tumors of the nasopharynx and referrals for radiotherapy due to intracranial extension. Results Nasopharyngeal tumors were best appreciated on T1 fat-saturated, post-gadolinium MRI. Tumors extended through the sinus of Morgagni in all cases. This sinus is a defect in the PBF through which the Eustachian tube and levator veli palatini muscle gain access to the nasopharynx. In six patients, the PBF and tensor veli palatini fascia were breached anteriorly with tumor infiltration of the tensor veli palatini and medial pterygoid muscles. In 13 cases, tumor breached the posterolateral PBF with extension into the poststyloid parapharyngeal space. In three subjects, 3 T images were also acquired and exhibited superior delineation of the anatomy and perineural tumor spread. Conclusions At 1.5 T, images showed nasopharyngeal tumors extending through the PBF into the masticator and parapharyngeal spaces, with access to the mandibular nerve and potential for perineural spread. At 3 T, soft tissue resolution appeared superior to 1.5 T. This may reflect not only the increased Weld strength, but an improved technique and matrix, and future studies are necessary to confirm this observation. Awareness of this anatomy for radiation and surgical planning is essential and may improve the ability for obtaining negative margins, and increasing overall survival.