Paranasal Sinuses

The horse has seven pairs of paranasal sinuses, namely the rostral maxillary sinus (RMS), ventral conchal sinus (VCS), caudal maxillary sinus (CMS), dorsal conchal sinus (DCS), frontal sinus (FS), sphenopalatine sinus (SPS) and ethmoidal sinus (ES). The FS and DCS are very closely associated and often considered as a single sinus; the conchofrontal sinus (CFS). The position of each of the sinus compartments vary both between individual horses and with age, in particular there is great variation in the position of the maxillary septum and the position of the maxillary sinuses in relation to the cheek teeth apices. With increasing age, the reserve crowns of the cheek teeth become shorter, the maxillary septum enlarges and its rostral limit approaches the infraorbital foramen (Hillmann 1975).

Fluid within the paranasal sinuses drains by ciliary transport toward one of the two drainage ostia. The drainage ostia (NMAs) originate from the CMS and RMS separately, but combine together to form a common nasal exit of the nasomaxillary apertures (NMAs) at the caudal aspect of the middle meatus of the nasal cavity. In terms of drainage the paranasal sinuses can be considered as two functional compartments. One compartment consists of the RMS and VCS, the drainage of which is via the drainage ostia of the RMS. The other compartment is formed by all the other paranasal sinuses, which drain via the drainage ostia of the CMS. Knowledge of the anatomy of the two drainage ostia is vital in understanding the pathophysiology of disease in the paranasal sinuses.

Recently, Sinoscopic techniques have been utilized to diagnose and treat most diseases within the paranasal sinuses. An understanding of the different options for portal location enables easier access into the different sinus compartments.