Anatomic variation in the pterygopalatine angle of the maxillary sinus and the maxillary bulla.

Bulges of the most posterior ethmoid air cells into the maxillary sinus were termed maxillary bullæ by Onodi. With few exceptions, they have since been ignored by anatomists through time. Likewise, Sieur cells-the spheno-ethmoido-maxillary air cells-are uncommonly found in anatomical texts. We therefore aimed to perform a retrospective cone beam computed tomography study on 50 patients to document the possibilities of anatomic variation in the situs of the orbital process of palatine bone-a variation related anatomically with the pterygopalatine fossa (PPF) and the respective angle of the maxillary sinus. Commonly occurring pneumatizations in this situs were the Sieur cell (58 %/64 % right/left side), and the maxillary recess of the sphenoidal sinus (20 %/22 % right/left side). Alone or in combination, these determined, but not exclusively, the maxillary bullæ. Uncommon pneumatizations in the anterior wall of the PPF were also found, such as a sphenoidal recess of the maxillary sinus, and lateral (maxillary, or pterygopalatine) recesses of the middle and superior, respectively, nasal meatuses. In two different cases, non-Haller, and non-Sieur posterior ethmoid air cells were found extruded posterior to the maxillary sinus. Significant statistical association indicated bilateral symmetry of Sieur's cell and of the maxillary recess of the sphenoidal sinus. It is important to identify such variant pneumatizations on a case-by-case basis in different surgical procedures and endoscopic corridors.