A new approach to the classification of maxillary sinus hypoplasia with relevant clinical implications.

The purpose of this study was to discover the prevalence of maxillary sinus hypoplasia (MSH) and associated malformations. A total of 490 consecutive axial and coronal computerized tomographic (CT) scans of the paranasal sinuses were obtained from patients with chronic sinusitis. CT scans were assessed for the presence of MSH and associated anatomic variations. A new classification of MSH was made, and the diagnostic criteria listed. The frequency of anatomic variations coexisting with MSH was also estimated. MSH was encountered in 21 (4.2%) of the 490 patients. Unilateral types I, II and III MSH were seen in 7 (1.4%), 6 (1.2%) and 8 (1.6%) respectively. MSH was bilateral only in 3 (0.6%) patients, one of which was a bilateral type II. In the remaining two bilateral MSH cases, there was a type II MSH on one side and type III MSH on the other in each patient. Middle conchal pneumatization was the most common coexisting anatomic anomaly in MSH, followed by agger nasi cell, secondary middle concha, paradoxical middle concha and superior conchal pneumatization. A patient with MSH should be carefully evaluated prior to any sinus surgery in order to avoid surgical complications. With precise CT assessments, an MSH can be diagnosed and distinguished from other maxillary sinus anomalies. With the additional criterion of orbital enlargement, and the help of reproducible measurement techniques explained in this study, an objective diagnosis and classification can be made in further investigations of MSH.