Anatomic description of the middle meatus and classification of the hiatus semilunaris into five types based upon morphological characteristics.

Anatomical variation of the lateral nasal wall, including the pathway from the frontal, ethmoidal, and maxillary sinuses may affect the communication between the paranasal sinuses and the nasal cavity. The middle meatus and hiatus semilunaris are areas where variations can occur which predispose patients to recurring sinusitis. Endoscopy allows for visualization of the entire nasal cavity, for both diagnostic and therapeutic uses. The purpose of this study was to provide an accurate characterization of the middle meatus and hiatus semilunaris for the purposes of endoscopic procedures. Ninety seven cadaveric lateral nasal walls were observed. The middle meatus was measured at three distinct points. Cranial length was also recorded. A 3D digitizer was used to record spatial relationships for the openings of the paranasal sinuses and the morphology of the hiatus semilunaris. The average widths for the middle meatus were 1.69-mm anteriorly, 2.83 mm at the transition angle, and 4.74-mm posteriorly. The posterior width was significantly larger than either of the two other measurements. The length of the hiatus semilunaris was found to be shorter on both left-sides and in females. The hiatus semilunaris was categorized into five types according to the varying morphologies. Given that the middle meatus was significantly wider posteriorly, our findings support the recommendation that entering the middle meatus posteriorly may allow an endoscopic surgeon easier access to the structures of the lateral nasal wall. Knowing the discrepancy of hiatus semilunaris lengths between right and left sides and males versus females may guide advancement of endoscopic instruments into the nasal cavity. Describing the five distinct types of the hiatus semilunaris allows the distinction of normal variation in this anatomic space versus pathologic condition.