CHAPTER 4 Oral and Nasal Cavities, Pharynx, Guttural Pouches, and Paranasal Sinuses
Clinical signs associated with pathologic conditions of the oral cavity include ptyalism, quidding, foul odor, dysphagia, and depression. Conditions of the nasal passages may result in nasal discharge, epis-taxis, dyspnea, inspiratory stridor, and foul breath. Involvement of the nasopharynx can be associated with dysphagia, dyspnea, abnormal respiratory noise, and exercise intolerance.1
Horses have four pairs of paranasal sinuses: frontal, maxillary, sphenopalatine, and ethmoidal. Pathologic conditions of the paranasal sinuses may result in unilateral purulent nasal discharge, facial distortion, foul breath, dullness on percussion of the involved sinus, and formation of a chronic fistula.
Clinical signs associated with guttural pouch disease include nasal discharge (usually unilateral), unilateral epistaxis, and swelling and/or pain in the area of the parotid salivary gland. The amount of nasal discharge often increases when the head is lowered. Because cranial nerves IX (glossopharyngeal), X (vagus), XI (spinal accessory), and XII (hypoglossal), the sympathetic trunk, and the cranial cervical ganglion are associated with the wall of the guttural pouch, neurologic disease caused by inflammation of the guttural pouch wall (Horner’s syndrome, etc) also may be present.
If disease of the oral cavity is suspected, a thorough examination can usually be conducted in the standing animal. Sedation is often necessary. Food material in the oral cavity may conceal the lesion and should be removed by flushing with water before examination. A mouth speculum also may facilitate visualization. Lesions near the base of the tongue are often difficult to visualize, and careful digital palpation may be necessary. Radiographic evaluation is sometimes helpful, especially if teeth or bony structures are involved.
Diseases of the nasal passages and nasopharynx often require endoscopic examination for adequate visualization.1 Sedation may distort the nasopharynx by relaxation of the soft tissues. Therefore, initial endoscopic examination of this area should be conducted without the aid of sedation if possible. Radiography may also help define the extent of lesions in this area.
The paranasal sinuses on each side communicate and drain into the middle meatus via the nasomaxillary opening. The nasomaxillary opening is not visible endoscopically. However, if nasal discharge is observed endoscopically to originate at the caudal portion of the middle meatus, paranasal sinus disease should be suspected. Confirmation of paranasal sinus involvement requires percussion and often radiography. Once primary sinus involvement is confirmed, the involved sinus can be aspirated for culture and cytologic evaluation.
The guttural pouches can be evaluated by palpation, endoscopy, and radiography. Two different methods may be used to insert a flexible endoscope into the guttural pouch. In the first method, place a biopsy instrument or cleaning brush in the biopsy channel of the endoscope and extend it 2 or 3 cm past the end of the endoscope. Then insert the biopsy instrument or cleaning brush into the guttural pouch opening and rotate the endoscope to open the guttural pouch flap. Then advance the endoscope into the guttural pouch. With the second method, place a Chambers mare catheter into the guttural pouch and rotate to open the flap (Fig. 4-1). Pass the flexible endoscope dorsal or ventral to the catheter and into the pouch as the Chambers catheter is withdrawn.
Lesions in the oral cavity, nasal passages, nasopharynx, paranasal sinuses, and guttural pouches may be defined by cytologic evaluation, histopathologic examination, and culture (bacterial, fungal). Cytologic samples from the oral cavity are usually limited to fine-needle aspirates of masses or imprints for cytologic examination from excised tissues (see Chapter 1 for a discussion of slide preparation techniques). Cytologic preparations from ulcerative lesions may be collected by imprinting, swabbing, or scraping.
Cytologic samples from nasal passages and nasopharynx are collected directly via the external nares or with a flexible endoscope. Atheromas are accessible for percutaneous aspiration, and fungal polyps often are close enough to the external nares to make direct imprints, biopsy, and/or fine-needle aspiration possible. Samples of exudates in nasal passages can be collected via polyethylene tubing passed through the biopsy port of a flexible endoscope. Masses and fungal plaques can be sampled with the endoscopic biopsy instrument.
Though exudate from paranasal sinuses can sometimes be detected endoscopically in the middle meatus, samples for cytologic evaluation and culture should be taken directly from the involved sinus. Sinus aspiration is usually possible in a standing horse using sedation and local anesthesia. The landmarks for frontal sinus aspiration are 2.5 cm caudal to the point at which the nasal bones start to diverge and 2.5 cm lateral to the midline. For superior maxillary sinus aspiration, the landmarks are dorsal to the facial crest and about 2 cm rostral to the bony orbit. To avoid the lacrimal canal, the practitioner must not perform trephining more dorsally than a line drawn from the medial canthus to the infraorbital foramen.2
After surgical preparation and local anesthetic infiltration, make a stab incision in the skin and use a small Steinmann pin to drill into the sinus. Anatomic landmarks and the technique for trephination of paranasal sinuses are described in detail elsewhere.1 Retrieve exudate by aspiration with a male canine urinary catheter or intravenous catheter. If exudate is not easily obtained, infuse and aspirate 30 to 40 ml of physiologic saline. If sinus contents are too thick for aspiration, use the eyed end of a large suture needle for sample collection.
The technique for endoscopic entrance into the guttural pouches is described above. To collect cytologic samples from the guttural pouch, pass polyethylene tubing through the biopsy port of the endoscope and into the guttural pouch. In most instances, exudate is present on the floor of the pouch and is easily aspirated into the tubing. If exudate is not present, infuse 20 to 30 ml of physiologic saline through the tubing and onto the lesion. The saline pools on the floor of the guttural pouch and is easily aspirated.
To make smears from swabbed samples, the practitioner gently rolls the swab across a clean glass microscope slide and allows it to air dry. Rolling the swab avoids the rupturing of cells that often occurs if the swab is rubbed or dragged across the slide. Samples collected by brushing can be impressed on the slide. Rubbing or dragging the brush across the slide surface should be avoided to prevent excessive damage to cells.
Cells collected by washes can be harvested by centrifugation in a clinical centrifuge using the same speed as is used for urine sedimentation. The supernatant is poured off, the pelleted material is gently resuspended, and a drop of the suspension applied to a clean glass microscope slide with an applicator or pipet. The sediment is then spread using a blood smear technique (see Chapter 1) and allowed to air dry.
Preparation of fine-needle aspirate smears and impressions of biopsied samples is covered in Chapter 1. Staining with hematologic stains is satisfactory for cytologic examination of samples from the oral cavity and upper respiratory tract. A more complete discussion on sample collection, slide preparation, and staining is given in Chapter 1.
The oral cavity and upper respiratory tract are composed of several mucous membrane–lined, communicating passages and cavities: the oral and nasal cavities, pharynx, guttural pouches, and paranasal sinuses. Cytologic samples of the normal oral cavity or upper respiratory tract, collected by washing, swabbing, or brushing, consist of the exfoliated epithelial cells characteristic of the area sampled.
The epithelium of the mucous membranes lining the oral cavity and rostral portion of the nasal passages consists of keratinized and nonkeratinized stratified squamous epithelium; therefore, these surfaces exfoliate squamous epithelial cells (Fig. 4-2). Squamous epithelial cells appear cytologically as large flattened cells with angular borders and abundant, pale-staining cytoplasm and a condensed to pyknotic central nucleus.
(Courtesy Oklahoma Veterinary Diagnostics.)