Bony defects and dehiscences of the roof of the ethmoid cells.

Endonasal sinusectomy is one of the most useful operations for treatment of chronic sinusitis. A previous study by the author on the incidence of complications of sinusectomy revealed that injuries to the base of the skull occurred in 0.15% and acute meningitis in 0.01% in a total of 450,000 sinus operations performed in Japan. In the present study a close observation of 17 (34 sides) skull specimens by the operating microscope revealed five major dangerous areas in the roof of the ethmoid sinus where anatomical structures present unusual vulnerability to injury during operations because of dehiscences and bony defects. The author found frequent bony dehiscences, where submucous connective tissue was in direct contact with the dura mater and also unusual structure of intimate adhesions between the bone and connective tissue of the dura mater. It is stressed that utmost care should be used in the operation of the ethmoid sinus and that microscopic surgery is a useful means for meticulous surgery and for prevention of side injuries.