Anatomical variations of the frontal sinus and its relationship with the orbital cavity.

The anatomy of the frontal sinus is highly variable and its variations affect the occurrence/course of pathological processes. We investigated its size and relationship to the orbit, searching for patterns that would allow it to be classified anatomically. Cone beam computed tomography was applied to 91 skulls (age range 21-86 years) to determine sinus height, width, length, and length of contact with the orbit in the coronal and sagittal planes. In addition, orbital roof pneumatization in the coronal plane was categorized as: none; only medial part pneumatized; the medial and a portion of the central part pneumatized; roof predominantly pneumatized. Sinus dimensions varied widely (mm): height 6.2-50.0; width 3.7-54.0; length 2.4-45.0; frontal orbital contact 4.0-41.6; sagittal orbital contact 0.0-41.2. Pneumatization of the orbital roof (coronal plane) mostly affected the medial and a portion of the central part (50%), or the roof was predominantly pneumatized (32%). Three "types" of sinus (cluster analysis) were distinguished by the extent of pneumatization of the orbital roof in the coronal plane: "small", pneumatization absent or only of the medial part; "medium-sized", pneumatization of the medial and a portion of the central part; "large", roof predominantly pneumatized. All dimensions were significantly different among the types (P < 0.001). Sinus type was fairly predictive of the extent of contact with the orbit in the sagittal plane (not routinely assessed clinically). The data confirm the variability of frontal sinus anatomy and suggest a simple and straightforward classification with potential clinical relevance. Clin. Anat. 31:576-582, 2018.