Clinical Sinus Anatomy

Take Home Message—Knowledge of paranasal sinus anatomy, their intercommunication and drainage; and their relationship to the maxillary cheek teeth is critical for creation of the complete three dimensional image of the horse’s head. This image is needed for effective diagnosis and treatment of primary and dental related sinus disease. Most references describe horses as having 7 paired sinuses.^1-3 Inclusion of the ethmoid sinus raises the number to 8.⁴ Clinically the rostral and caudal maxillary sinuses are the focus. Respectively they communicate with the ventral conchal and all the rest of the sinuses. The rostral and caudal maxillary sinuses on each side of the head drain into the middle nasal meatus via a shared slit like nasomaxillary aperture.^1,4 

I. Introduction

Anatomy: Horses have eight pared sinuses^1-5

1. Frontal
2. Dorsal conchal
3. Middle conchal
4. Ventral conchal (VCS)
5. Caudal Maxillary (CMS)
6. Rostral Maxillary (RMS)
7. Sphenopalatine
8. Ethmoid

⇒ The frontal and dorsal conchal sinuses are continuous with one another to form the Conchofrontal sinus (CFS)

General Features

The paired sinuses form through the extension of the nasal cavity lining between the frontal, maxillary, sphenoidal and palatine bones within the skull. Sinuses also invade the dorsal, ventral and ethmoid conchae. The exact purpose for the formation of the sinuses is unknown. Theories include: 1) to lighten the head as it expanded to house large hyposodont teeth, 2) to allow heat exchange and 3) to modulate vocalization.¹ The right and left sides do not communicate.

The sinuses are lined by pseudostratified columnar ciliated epithelium and goblet cells. This lining produces a layer of mucous that is moved by mucociliary transport towards the two sino-nasal apertures, then caudally to the nasopharynx where it is swallowed. The small drainage apertures prevent ascending infections but also make drainage difficult.¹

II. Discussion

Conchofrontal Sinus^1-5

The conchofrontal sinus (CSF) is formed through the excavation of the frontal bone (frontal sinus) and the dorsal concha (dorsal conchal sinus). No maxillary cheek teeth communicate with this sinus. The caudal limit of this sinus is an imaginary line drawn through the superorbital foramina while the rostral limit is an imaginary line perpendicular to the facial crest, halfway between the infraorbital foramen and the medial canthus of the eye. This corresponds to the point when your thumb and forefinger diverge when you move your hand caudally along the nasal bones (Fig. 1). The conchofrontal sinus communicates ventrally with the caudal maxillary sinus through the frontomaxillary aperture (Fig. 2). 
 

The conchofrontal sinus can be accessed via a portal or a bone flap. Trephination allows direct access to the caudal maxillary sinus through the frontomaxillary aperture for lavage or sinoscopy. Access to the rostral maxillary and ventral conchal sinuses can only be achieved through perforation of the ventral conchal bulla. The landmarks for this portal are halfway between the medial canthus of the eye and the midline septum and halfway between the caudal and rostral aspects of the eye (Fig. 3). [...]