Measurement of the intersiphon distance for normal skull base development and estimation of the surgical window for the endoscopic transtuberculum approach in children.

Objective: Due to the underdeveloped skull base in children, it is crucial to predict whether a sufficient surgical window for an endoscopic endonasal approach can be achieved. This study aimed to analyze the presumed surgical window through measurement of the intersiphon distance (ISD) and the planum-sella height (PSH) on the basis of age and its correlation with the actual surgical window for the endoscopic transtuberculum approach.

Methods: Twenty patients of each age from 3 to 18 years were included as the normal skull base population. ISD and PSH were measured and compared among consecutive ages. Additionally, 42 children with craniopharyngiomas or Rathke's cleft cysts who underwent treatment via the endoscopic transtuberculum approach were included. ISD and PSH were measured on preoperative images and then correlated with the dimensions of the surgical window on postoperative CT scans. The intraoperative endoscopic view was classified as narrow, intermediate, or wide based on operative photographs or videos, and relevant clinical factors were analyzed.

Results: In the normal skull base population, both ISD and the estimated area of the surgical window increased with age, particularly at 8 and 11 years old. On the other hand, PSH did not show an incremental pattern with age. Among the 42 children who underwent surgery, 24 had craniopharyngioma and 18 had Rathke's cleft cysts. ISD showed the strongest correlation with the actual area of the surgical window [r(40) = 0.69, p < 0.001] rather than with age or PSH. The visual grade of the intraoperative endoscopic view was narrow in 17 patients, intermediate in 21, and wide in 4. Preoperative ISD was 14.58 ± 1.29 mm in the narrow group, 16.13 ± 2.30 mm in the intermediate group, and 18.09 ± 3.43 mm in the wide group (p < 0.01). There were no differences in terms of extent of resection (p = 0.41); however, 2 patients in the narrow group had postoperative complications.

Conclusions: Normal skull base development exhibited age-related growth. However, in children with suprasellar lesions, the measurement of the ISD showed a better correlation than age for predicting the surgical window for the endoscopic transtuberculum approach. Children with a small ISD should be approached with caution due to the limited surgical window.