Hidden unilateral aplasia of the frontal sinus: a radioanatomic study

BACKGROUND: Hidden unilateral frontal sinus aplasia is the absence of 1 frontal sinus with increased pneumatization of contralateral sinus toward the aplastic side. It may give the false impression of the presence of 2 separate frontal sinuses, creating potential for complications during the surgery. The aim of this study was to evaluate the prevalence and morphology of this anatomical variation using multiplanar reconstruction of computed tomography (CT) results. METHODS: A total of 305 CT examinations were analyzed. Hidden unilateral frontal sinus aplasia was defined as lack of pneumatization of 1 frontal sinus beyond the level of the orbital roof, with increased pneumatization of the contralateral sinus, extending to the sagittal plane, crossing the lamina papyracea on the side of the aplastic sinus. RESULTS: Eleven patients (3.6%) with hidden unilateral frontal sinus aplasia were identified, 5 on the left and 6 on the right side, in 5 female and 6 male patients. Twenty-four (7.8%) patients with "regular" frontal sinus aplasia (without hyperplastic contralateral frontal sinus) were found, 4 with bilateral aplasia and 20 with unilateral aplasia. CONCLUSION: Hidden unilateral aplasia of the frontal sinus is a relatively uncommon anatomical variation. Its presence should be considered during routine preoperative CT evaluation because it poses the risk of intraoperative complications.