(1234) Hidden Frontal Sinus Aplasia: A Single Institution Radioanatomic Study

Introduction: Hidden unilateral frontal sinus aplasia is the absence of the frontal sinus on one side, with an increase in pneumatization of the contralateral sinus. Previous literature shows that these frontal sinus variations carry a significant surgical impact by creating a misleading representation of the anatomy; however, they remain underreported and a detailed analysis is essential to assess the morphology of these variants and to raise awareness of this finding.

Methods: Retrospective chart review of patients with hidden frontal sinus aplasia from 2019-2024. Aplasia was defined as a lack of pneumatization of one frontal sinus below the level of the supraorbital line with increased pneumatization of the contralateral side. The sinus was classified as hypoplastic if it extended from the supraorbital line. Demographics, clinical presentation, and imaging data was collected.

Results: Overall, 28 patients were identified with hidden frontal sinus developmental anomalies, of which 21 (75.0%) were classified as aplastic and 7 (25.0%) hypoplastic. The total cohort had a mean age of 53.7 years (SD 18.4) and was predominantly female (71.4%) and White (78.6%). The right side was affected in 18 (64.3%) patients and the left in 10 (35.7%). Chronic rhinosinusitis was present in 21 (75.0%), nasal polyps in 11 (39.3%), septal deviation in 19 (67.9%), frontal recess obstruction in 15 (53.6%), and concha bullosa in 6 (21.4%). Of the total cohort, 16 (57.1%) had at least one endoscopic sinus surgery, and of the 24 CT scan reports available, only 5 (17.9%) reported frontal sinus variation.

Conclusions: Frontal sinus aplasia and hypoplasia are rare anatomical variations. However, they carry great surgical significance and should be evaluated preoperatively.