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CHAPTER 21
Sinus Trephination
David A. Wilson
approximated by a line from the medial canthus
INDICATIONS of the eye to the infraorbital canal. This line
should be avoided when creating entrance portals
Sinus trephination can be performed for both to the sinuses. The location of the sinuses are illus-
diagnostic and therapeutic purposes to confirm trated in Figures 21-1 through 21-3 and the
the presence of purulent exudate; to obtain sinus approximate boundaries of the sinuses are
contents for cytology, biopsy, or culture; and to described below. 6
provide a portal for sinus irrigation or tooth
repulsion. 1-3
Maxillary Sinuses
The dorsal boundary corresponds to a line drawn
EQUIPMENT caudad from the infraorbital foramen parallel to
the facial· crest. The ventral boundary varies with
A Steinmann intramedullary pin of 3/16- or 1/4-i11cl1 the age of the horse. The last three or four cheek
diameter or a trephine instrument is used for this tooth roots project into the ventral aspect of the
procedure. maxillary sinus to an extent that varies with age.
The rostral boundary is at the level of the infraor-
bital foramen, and the caudal border is at the level
POSITIONING AND PREPARATION of the ventral portion of the orbit. The maxillary
sinus is divided into rostral and caudal portions by
The procedure is performed in the standing, an oblique septum, whose lateral margin is com-
sedate horse with local anesthesia."? The trephine monly about 5 cm caudal to the facial tubercle, but
site is clipped and prepared for surgery. Instilla- can be quite variable (see Figure 21-1). The infra-
tion of local anesthesia should create a skin bleb orbital canal separates the maxillary sinus into a
and infiltrate the underlying periosteum. lateral bony compartment occupied by the roots
of the cheek teeth and a medial compartment
within the ventral conchal sinus.
ANATOMY
Frontal Sinus
Important landmarks for defining the boundaries
of the sinuses and determining entrance portals The frontal sinus is roughly triangular-shaped
include the infraorbital canal, the facial crest, the with the base on midline. The right frontal sinus
facial tubercle, the orbit, and the nasolacrimal is separated from the left sinus by a complete
duct. The course of the nasolacrimal duct can be septum. The rostral limit of the frontal sinus is at
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