Transnasal Sinus Endoscopy (TSE)

Take Home Message—Transnasal endoscopy of the sinuses (TNSE) is a non-invasive technique to examine and treat selected cases of chronic sinusitis. Flexible endoscopes of variable diameter may be utilized for this purpose. However, it is possible to access all structures in normal horses.

I. Aim of the presentation

To explain how to perform transnasal endoscopy of the conchal recesses of the dorsal and ventral conchae and the rostral and caudal sinus systems in horses affected by sinonasal disease.

II. Introduction

Endoscopy and endoscopic surgery of the equine paranasal system has been described in several publications;^1-6 however the sinuses were accessed through surgical ports in these studies. A non-invasive transnasal approach was not described until recently. This technique was developed in Germany by Nowak.⁷ An accurate knowledge of the anatomy of nasal structures is imperative for the clinical application of transnasal sinus endoscopy using this technique. This novel technique is likely to be of increasing clinical importance in the future.⁸ Anatomical^8,9 and computed tomographic studies¹⁰ describing key landmarks of the nasal, conchal and sinusoidal anatomy have facilitated comprehension of the complicated three-dimensional structures and are recommended readings prior to implementing transnasal sinus endoscopy.

III. Materials and methods

Endoscopic Equipment

Flexible video- or fiberoptic endoscopes of 3-8 mm diameter may be utilized.⁷ For visualization of the narrow recess of the dorsal concha and the sinus systems however, endoscopes with a diameter of less than 5 mm are required.⁷

Preparations

Transnasal sinus endoscopy is usually performed in the standing sedated horse. Repeated topical application (rinsing or spraying) of 2% lidocaine into the nasal meatus before and during the endoscopic examination helps to desensitize the nasal mucous membranes, thus minimizing evasive head movements of the horse.⁷

Examination Technique and Anatomical Land Marks

Four separate conchal and paranasal sinus compartments and the nasomaxillary aperture can be examined using a transnasal approach. These are the:

• rostral recess of the ventral concha
• rostral recess of the dorsal concha
• rostral and caudal opening of the nasomaxillary aperture
• rostral paranasal sinus system
• caudal paranasal sinus system

Anatomical Landmarks

The ventral conchal bulla (Bulla conchae ventralis) is located in the caudal third of the   ventral conchal recess. It divides the ventral conchal recess in two narrow passages:
The medial passage is located between the medial wall of the ventral conchal bulla and the medial ventral conchal wall.
The lateral passage is located between the ventral conchal bulla and the medial wall of the maxilla.
The caudal end of the ventral conchal recess is formed by a translucent and thin epithelial membrane. Perforation of this membrane can easily be performed. The ventral conchal sinus can be approached through this artificially created orifice.

Endoscopic Access

The endoscope is inserted into the middle nasal meatus and directed caudo-laterally along the dorsal and lateral aspects of the ventral concha. It is then directed into the space between the dorsal aspect of the ventral concha and the medial wall of the maxillary bone. Bending the tip of the endoscope in ventral direction, it is guided into the recess of the ventral concha. The elastic properties of the conchal lamella in this area facilitate the insertion of flexible endoscopes of up to 8 mm diameter.⁷
While the medial passage is wide enough to allow the insertion of even large bronchoscopes until its caudal end, the 7lateral passage cannot be accessed completely.⁷

Rostral Recess of the Dorsal Concha

Anatomical Landmarks

In contrast to the rostral aspect of the ventral concha, the spiral lamella of the dorsal concha is supported by conchal bone which reduces the elastic properties of this structure. Consequently is cannot be compressed as easily during endoscope insertion as the cartilage-supported rostral aspect of the ventral concha.⁷

Endoscopic Access

The rostral recess of the dorsal concha can be accessed with low-diameter endoscopes (< 5mm) resting in the middle nasal meatus about 6-8 cm caudal to the nostrils. At this location the gap between the dorsal concha and the medial wall of the maxilla expands over a distance of 2-3 cm which facilitates the insertion of a small endoscope into this conchal recess.⁷

Rostral and Caudal Openings of the Nasomaxillary Aperture

Anatomical Landmarks

Approximately 20-25 cm caudal to the nostrils the ventral concha increases in height and width, gradually expanding to form the caudal ventral conchal bulla which protrudes into the caudal maxillary sinus. The dorsal aspect of the ventral concha resembles a ridge rising in dorso-caudal direction.
The name of the nasomaxillary aperture is partially misleading as it consists of two openings, one into the rostral sinus compartment (rostral maxillary sinus, ventral conchal sinus) and one into the caudal maxillary and it’s communicating sinuses.
Looking in caudal direction from a location on the dorsal aspect of the ventral concha in the middle nasal meatus, the rostral opening resembles a curved, horizontally orientated slit on the lateral side which is only 3 mm wide in normal horses. From this aperture a 2-3 cm long, ventrally orientated canal connects the middle nasal meatus with the rostral maxillary sinus. Moving in caudo-dorsal direction on the ascending ridge of the dorsal aspect of the ventral concha, the sickle-shaped caudal opening is reached. The dorsal aspect of the ventral concha (caudal bulla of the ventral conchal sinus) forms the base of this ventrally orientated aperture which enables access to the caudal maxillary sinus.

Endoscopic Access

In normal horses the passages through the nasomaxillary apertures are constricted and may only be accessed with low diameter (< 5 mm) endoscopes.⁷ Resting on the dorsal aspect of the ventral concha in the middle nasal meatus, the endoscope is directed in lateral direction and inserted about 20-25 cm, depending on the horse’s size.⁷
The rostral opening of the nasomaxillary aperture is located lateral between the ventral conchal lamella and the medial wall of the maxilla. It is hardly possible in normal horses to pass an endoscope through this narrow opening to examine the rostral sinus system. However, the apertures are significantly widened in sinusitis-affected horses. Then endoscopy of the rostral maxillary sinus with a < 5 mm diameter endoscope is possible.⁷

From its position on the dorsal crest of the ventral concha, the endoscope can be advanced caudally along this crest. The sickle-shaped, 3-5 mm wide caudal opening can be visualized. Passing a small-diameter endoscope through the caudal opening into the caudal maxillary sinus is frequently possible also in healthy animals.

Rostral Maxillary Sinus and Ventral Conchal Sinus

As mentioned above, transnasal visualization of the rostral maxillary sinus and the ventral conchal sinus is only possible in sinusitis-affected animals. Following endoscope-insertion through the rostral opening, it can be advanced through a 2-3 cm long, narrow slot in ventral direction.⁷ The slot opens into the rostral maxillary sinus where the buccal alveolar wall of the equilateral maxillary -09 is located. A characteristic anatomic landmark is the infraorbital canal. It is aligned in caudo-rostral direction and partially separates the rostral maxillary sinus from the ventral conchal sinus. Dorsal to the infraorbital canal these two sinuses communicate via the conchomaxillary aperture.⁷

Caudal Maxillary Sinus and Communicating Sinuses of the Caudal Sinus System

Passing the caudal opening of the nasomaxillary aperture, the ethmoid is clearly visible in caudo-medial direction. In dorsal direction the large oval frontomaxillary aperture connects the caudal maxillary sinus to the concho-frontal sinus. Angling the endoscope ventrally, the caudal part of the infraorbital canal is visible. The entrance to the sphenopalatine sinus is located in caudo-ventral direction between the infraorbital canal and the ethmoid. Lateral of the infraorbital canal the caudal maxillary sinus contains the alveoli of the equilateral maxillary -10 and -11 which can be clearly distinguished.⁷ [...]