Predicting the limits of the endoscopic endonasal approach in children: A radiological anatomical study

Objective The endoscopic endonasal approach (EEA) has been established as an alternative approach to craniovertebral junction (CVJ) pathology in adults. The authors have previously described the nasoaxial line (NAxL) as an accurate predictor of the lower limit of the EEA to the CVJ in adults. The surgical anatomy limiting the EEA to the pediatric CVJ has not been well studied. Furthermore, predicting the lower limit of the EEA in various pediatric age groups is important in surgical planning. To better understand the anatomy affecting the EEA to the CVJ, the authors examined the skull base anatomy relevant to the EEA in children of different age groups and used the NAxL to predict the EEA lower limit in children. Methods Axial brain CT scans of 39 children with normal skull base anatomy were reconstructed sagittally. Children were divided into 4 groups according to age: 3-6, 7-10, 11-14, and 15-18 years old. The intersection of the NAxL with the odontoid process of C-2 was described for each group. Analyses of variance were used to estimate the effect of age, sex, interaction between age and sex on different anatomical parameters relevant to the endonasal corridor (including the length of the hard palate [HPLe]), dimensions of choana and piriform aperture, and the length of the NAxL to C-2. The effect of the HPLe on the working distance of NAxL to the odontoid was also estimated using analysis of covariance, controlling for age, sex, and their interaction. Results The NAxL extended to the odontoid process in 38 of the 39 children. Among the 39 children, the NAxL intersected the upper third of the odontoid process in 25 while intersecting the middle third in the remaining 13 children. The measurements of the inferior limits did not differ with age, varying between 9 and 11 mm below the hard palate line at the ventral surface of C-2. Significant increases in the size of the piriform aperture and choana and the HPLe were observed after age 10. The HPLe predicted the length of the NAxL (p < 0.0001). Conclusions The caudal limit of the EEA extends as far as the middle third of the odontoid process in children, as predicted by the NAxL. The most prominent increase in the size of the choana and piriform aperture occurs after age 10. The HPLe is a significant predictor of the working distance to C-2. Utilizing the NAxL preoperatively may help in planning the EEA to the CVJ in children.