General Medical Information

Frontal Sinus

Ronald G. Amedee
Andrew J. Miller

The frontal sinus develops from anterosuperior ethmoidal cells in the area of the frontal recess. The frontal recess is a complex structure that can take many different forms. The middle turbinate functions as the medial wall, and the lamina papyracea makes up most of the lateral wall. The posterior wall is the anterior face of the bulla ethmoidalis (also known as the second basal lamella), and the agger nasi cells help to form the anterior wall. If pneumatization of the bulla ethmoidalis and the agger nasi cells is minimal, the frontal recess develops into a wide area. If pneumatization of these areas is extensive, the frontal recess becomes narrow and appears tubular.

The structure of the frontal sinus can be quite variable from person to person. The height varies between 5 and 66 mm, and the width ranges from 17 to 49 mm. An intrasinus septum usually is present, and the distal borders of the sinus often spread to form an irregular pattern, which makes mucosal removal difficult during frontal sinus obliteration. The anterior wall is the strongest of the sinus walls and is twice as thick as the posterior wall. Each sinus wall has an anterior and posterior table with intervening diploë, although the diploë is minimal in the posterior wall. The posterior wall separates the frontal sinus from the anterior cranial fossa. The floor of the sinus also functions as the supraorbital roof, and the drainage ostium is located in the posteromedial portion of the sinus floor. The frontal infundibulum is a more narrow area within the sinus that leads to the ostium. The frontal sinus-ostium-frontal recess complex is shaped like an hourglass. The size of the bottom half depends on the dimensions of the frontal recess.