Anatomic measurements for the endoscopic modified Lothrop procedure

Background: The aim of this study was to introduce preoperative radiographic frontal recess and sinus anatomic measurements to assist in the selection of patients considered for the modified Lothrop procedure. Methods: Data were collected from sagittally reconstructed computed tomography (CT) scans of seven cadaver heads. Four anatomic parameters for measurement were defined as follows: (1) thickness of the nasal beak (desirable <10 mm); (2) midsagittal distance from nasal beak to skull base (adding 1 and 2 provides the anterior posterior (AP) space at the cephalad margin of the frontal recess; desirable, >= 15 mm); (3) accessible dimension (in a parasagittal plane through the frontal ostium; the distance between two lines drawn parallel to the plane of the anterior skull base and perpendicular to the line of the insertion of the nasal endoscope during surgery; the posterior line is drawn at the skull base and the anterior line is drawn at the posterior margin of the nasal beak; the distance between the lines indicates the space available for instrumentation; desirable, >5 mm); (4) AP dimension of each frontal sinus. Results: The average and the range of each parameter measured were as follows: (1) nasal beak thickness = 8.0 mm (5.0-10.4 nun); (2) nasal beak-skull base = 7.9 mm (2.5-14.1 mm); (3) accessible dimension, 6.1 mm (0.9-9.6 mm); (4) AP diameter of the frontal sinus, 9.7 mm (5.2-14.1 mm). Four specimens were considered candidates for modified Lothrop and three were not. Conclusion: Preoperative radiographic frontal recess and sinus anatomic measurements may assist in the selection of patients considered for the endoscopic modified Lothrop procedure.