Morphometric study of the medial aspect of the human maxillary sinus with special reference to the nasal fontanelle

Objective: The purpose of this study was to clarify configurations of the nasal fontanelle (NF) from the morphometrical point of view, especially variations of its four margins (anterior, posterior, superior, and inferior), for clinical application. Methods: We used 136 sides of hemi-sectioned heads that were obtained from 119 donated Japanese cadavers (66 men and 53 women with an average age of 77.6±12.0). After mucosal examination, the specimens were boiled with a small amount of powdered soap and treated with protease. The residual mucous membrane was then gently removed. These specimens were originally made for our previous study describing variations of the uncinate process (Isobe M, Murakami G, Kataura A. Variations of the uncinate process of the lateral nasal wall with clinical implications, Clin. Anat. 1998;11:295–303). Different series of measurements were conducted based on surgical approaches and angles of observation. Results: The superior margin of the NF is difficult to identify because the ethmoidal infundibulum, which leads the anterior end of the margin upward, often interrupts the superior margin. Because the inferior and posterior margins are modified by thin paper-like bony structures and because the anterior margin is disturbed by variations of the lacrimal bone and/or the inferior turbinate, they are also difficult to identify. Knowing these variables, we evaluated the NF morphometrically. The NF was located 12.6±4.3 mm posterior to the anterior nasal spine and 6.6±2.2 mm anterior to the sphenopalatine foramen. The size of the NF was 17.9±3.2 mm (anteroposterior axis)×11.5±3.0 mm (inferosuperior axis). The lowest orbital floor was located 10 mm below the superior margin of the anterior NF (−10 mm), and the distance was therefore measured as −3.7±2.4 mm on average. Viewed from the maxillary sinus, the location of the NF varied along the anteroposterior axis, whereas it was located consistently at the most superior portion of the medial aspect of the sinus wall. Conclusion: During endoscopic sinus surgery for tumor resection in the maxillary sinus, a large and primary window should be prepared in the posterior NF, including partial removal of the uncinate process. Preparation of an additional window in the inferior meatus is preferable to enlargement of the primary window. Approaching the anterior NF should be avoided, if possible, due to its complicated configuration as well as its proximity to the orbital floor.