Anatomical Variations of the Trigeminal Nerve, Trigeminal Ganglion and Foramen Ovale: A Systematic Review

Introduction: The trigeminal nerve is principally responsible for controlling the sensory modalities of the face. The Foramen Ovale (FO) is one of the apertures present in the skull base, through which the mandibular nerve, a branch of the trigeminal nerve passes. Aim: To deliver a thorough understanding of the anatomical variations of the trigeminal ganglion and FO that would be beneficial to neurologists and neurosurgeons when performing various treatments involving these structures. Materials and Methods: The present systematic review was formulated according to Preferred Reporting Items for Systematic Reviews (PRISMA) guidelines. Major electronic databases were screened and all types of studies including descriptive studies, surveys, full-text literature providing information about the variations in trigeminal ganglion and FO, were incorporated in the current review. Studies from 2001 to 2022 were included in this review. The risk of bias evaluation in the present study was conducted by using the review manager software (Rev Man version 5.4) and risk assessment domains were classified as high, indeterminate, or low risk. The recommended approach to check biases such as selection, performance, attrition, reporting, and other biases was done. Results: A total of 12 studies were examined. The studies measured the proper location and the size (diameter) of the trigeminal ganglion and FO using the MRI-based findings in 1,341 subjects in total. It was observed that the length of the trigeminal nerve was found to be about 9.66 mm in the cistern (range 6.04-20.74 mm) in 50% of studies, whereas in 16.67% of the studies trigeminal nerve was longer in the older patients as compared to the normal anatomy. Additionally, the distinctive form of the FO was noted in the current investigation. In total, (n=4) 66.66% of the studies demonstrated the oval shape of the FO, and (n=3) 50% of studies noticed an almond shape, 50% identified a round shape; (n=2) (33%; n=2) displayed a slit form. Only one investigation demonstrated a bony bridged of FO whereas 33% showed tubercle and triangular shapes. Conclusion: Majority of the studies showed that the length of the trigeminal nerve was found to be about 9.66 mm. Whereas, only one author reported that the trigeminal nerve is longer in the older patients as compared to the normal anatomy. The majority of studies demonstrated that the variations were observed in the shape of the FO, i.e., oval, round, almond, slit, spine.