|
Exotic Animal Endoscopy Course
© Stephen Hernandez-Divers, The University of Georgia Small Mammal Endoscopy The endoscope can be used in small mammals, including rabbits, rodents, ferrets, as well as dogs and cats. The most common indications appear to be oral
exams and endoscope assisted tracheal intubation, although laparoscopy, thoracoscopy, otoscopy, rhinoscopy, coloscopy, cystoscopy and vaginoscopy are possible depending upon patient size and presenting signs.
Pic01: Endoscopic view of the ruptured tympanic membrane in a rabbit with otitis media and head tilt. Oral Cavity The very small oral commissure tends to preclude
thorough examination of the cheek teeth in small herbivores. As a result, malocclusion tends to proceed undetected until it reaches a point severe enough to elicit overt clinical signs. The rigid
endoscope is ideally suited to examine the oral cavity in these small mammals, and offers considerable advantages over the use of an otoscope (Taylor and Murray, 1999). With the patient appropriately
anesthetized, the mouth may be held open. It is suggested that small mammals be fasted for 1-4 hours to enhance visualization, as food material is often retained in the oral cavity after eating,
especially in guinea pigs. The author prefers to employ both a cheek gag and a self-retaining mouth gag (Spectrum Surgical Supply, Stow, Ohio, 330-686-4550). The telescope within a protective
sheath may then be inserted into the oral cavity for a detailed examination. The upper arcades may be examined with the endoscope in its normal position. In order to examine the lower arcades,
the endoscopist can take advantage of the 30 offset of the telescope. By rotating the telescope 180 (if a camera is in use, it should NOT be rotated, just the telescope) the lower teeth are well
visualized.Every tooth should be evaluated, including lingual, buccal, and occlusal aspects. Appropriately sized and curved dental probes may be used to palpate each tooth attempting
to elicit movement or other evidence of tooth pathology. Additionally, the clinician should pay particular attention to the gingiva. Chinchillas often present with a sub-gingival point on the
buccal aspect of the first upper pre-molar as the sole cause of "slobbers". The most commonly encountered malocclusions involve overgrowth to the lingual aspect on the lower arcades and overgrowth to the
buccal side on upper teeth. If left untreated, severe tongue injury and laceration may occur. In guinea pigs, it is not uncommon for the mandibular teeth to actually bridge and entrap the tongue.
Once identified the malocclusion should be trimmed with either a motorized dental hand piece or ronguers. When utilizing the latter, the clinician must take exceptional care to avoid
fracturing the tooth. For that reason, the dental hand piece is preferred. For obvious reasons, it is recommended that the telescope be removed (or further protected) during the trimming process.
It should then be re-inserted to evaluate the teeth following reduction of the malocclusion. Pic02: General endoscopic view of the oral cavity of a rabbit
Pic03: Close-up of dental spurs in a rabbit with molar malocclusion Pic04: Endoscopic view of maloccluded molars in a rabbit being surgically reduced using a dental burr. Tracheal Intubation In addition to limiting access to oral structures, the small oral commissure of the small herbivore drastically limits access to the caudal oropharynx, including
the glottis. As a result, tracheal intubation tends to be a "blind" procedure with varying degrees of success. This limited ability to routinely and consistently establish a patent airway may
pose significant problems during the anesthetic management of these species. Further complicating the problems associated with intubation is the significant trauma to which laryngeal structures may be
subjected during attempts to blindly pass an endotracheal tube. The larynx of the rabbit, consistent with other small herbivores commonly encountered in practice, is situated caudal and slightly ventral to
the angle of the jaw. Being obligate nasal breathers, the anatomy of the larynx is somewhat different than that encountered in the dog or cat. The epiglottis is a relatively large structure with
a "butterfly-shaped" distal aspect, which is normally located entrapped on the dorsal surface of the soft palate. This arrangement permits passage of air directly from the naso-pharynx into the larynx
and trachea without entry into the oral cavity. The rigid endoscope can be easily utilized as an aid in the placement of endotracheal tubes. This may be accomplished either by slipping the tube over
the endoscope or by passing the tube along side the scope. It must be remembered that only tubes with an inside diameter greater than that of the telescope, in most cases 3.0 mm and greater, can be fit
over the instrument. As the instrument is slowly advanced caudally, gentle dorsally directed pressure on the soft palate will free the epiglottis, revealing the glottal opening. An endotracheal
tube, the tip of which has been lubricated with a xylocaine gel, may then be slowly advanced between the arytenoids cartilages and into the trachea. The beveled tip of the endotracheal tube should be
manipulated in such a manner as to facilitate the movement of the tube between the vocal folds. The endoscope may then be removed and the tube secured to the rabbit in a normal fashion.
Pic05: Normal endoscopic view of the glottis following displacement of the epiglottis from the soft palate. Pic06: Endoscopic view of tracheal intubation using a stylet within an endotracheal
tube. Upper Respiratory Endoscopy In all cases general anesthesia greatly facilitates endoscopic examination and therefore the veterinarian must ensure that the patient has been stabilized and can
be safely anaesthetized. For rhinoscopy procedures the animal is orally intubated, but for endoscopic evaluation of the glottis and trachea, nasal intubation is often preferred. In addition, supplemental
oxygen and isoflurane/sevoflurane can be delivered via an anesthetic line connected to a sheath port. For detailed buccal examinations, naso-intubation or endotracheal intubation can be used depending upon
the size of the animal and space within the oral cavity. Respiratory and cardiovascular monitoring is essential and can include pulse oximetry, capnography, and blood gases. Clinicians should guard against
hypoventilation and hypothermia of small, anesthetized mammals.Depending upon animal size, a 2.7mm telescope, 1.9mm telescope, or 1.0mm semi-rigid endoscope can be used to examine of nasal
passages and turbinates of most rabbits. Examination of the nasal turbinates can be extremely useful for the characterization of rhinitis and the collection of tissue biopsies and microbiological samples,
which are essential to accurately attribute pathogenicity to a particular organism. Many different bacterial and fungal organisms cultured from nasal swabs or, worse still, nasal discharges may simply
represent commensal or environmental contaminants. With the head and neck held in full extension, the larynx can be approached via a buccal approach, however, the rabbit glottis is not
usually visible as (being a nasal breather) the epiglottis is engaged over the soft palate. Gently pushing the scope up against the soft palate will cause the epiglottis to fall ventrally revealing the
glottis and the obvious cuniform processes. Entry through the glottis permits the examination of the trachea, which in rabbits looks hyperemic. This intense red coloration is simply due to the brightly
colored smooth muscle that encloses the trachea. The pale dorsal ligament of the trachea is obvious. The trachea divides into two primary bronchi and very quickly subdivides into secondary bronchi. A rigid
scope can, with care, be inserted down to the level of the bifurcation and the primary and secondary bronchi can often be seen. For larger rabbits small diameter bronchoscopes may be required. Respiratory
exudates are not infrequently encountered and may be sampled through the endoscope operating channel. Pic07: Endoscopic examination of the nasal chambers in an anesthetized rabbit. Pic08: Normal nasal turbinates in a rabbit Pic09: Grossly abnormal nasal chamber in a rabbit with nasal mycobacteriosis. Gastrointestinal Tract Examination The endoscope
can be passed over the glottis and down the esophagus. Air insufflation is often required to visualize the esophagus for gross lesions and foreign bodies, but water irrigation provides much better mucosal
detail. Entry into the stomach is not usually possible with the rigid scope but a fiberscope can be used to enter the stomach. Even following 24 hours of fasting the rabbit stomach will still contain ingesta
and therefore the value of gastroscopy in the rabbit remains questionable.Following an enema, the scope can be used to examine the rectum and colon. On one occasion the author identified a
colonic intussusception in a dwarf rabbit that was then corrected at laparotomy. Urogenital Examination
The 2.7mm scope will enter the posterior vagina and with practice can be inserted into the bladder and
advanced to examined the twin cervices of rabbits. Although still in the early stages of clinical use, such techniques may help in the identification of uterine adenocarcinoma and characterisation of urinary
tract diseases.Pic10: Endosocpic view of the normal vagaina and urethral opening in a rabbit Laparoscopy Single and multipl-entry techniques are
continually being developed in small mammals. Carbon dioxide insufflation is essential and because of potential respiratory compromise all rabbits are intubated and are maintained on intermittent positive
pressure ventilation. The exact point of endoscopic entry will depend upon the particular organ of interest and the preferences of the operator, but the author currently prefers a umbilical approach for
examination of the right liver lobes, pancreas, right kidney/adrenal gland, pylorus, duodenum, caecum, colon and diaphragm. The biggest problem facing rabbit laparoscopy is obesity, and abdominal fat may
cover all organs rendering examination impossible. The biopsy instruments can be used to collect organ biopsies and certainly biopsies of the liver, spleen, and pancreas are straightforward.
Pic11: Endoscopic liver biopsy in a rabbit. Thoracoscopy Respiratory disease remains a major cause of morbidity and mortality in rabbits and rodents but a thoracoscopic examination of the lungs can permit the
evaluation and collection of biopsies without the need for a major thoracotomy. A paraxiphoid approach is preferred, but exact entry site will depend upon the suspected nature and position of lesions. Breach
of the pleural membrane causes collapse of the lung unless extensive adhesions are present. Intubation and positive pressure ventilation are essential. The scope can then be inserted and examination of the
pleural membrane, lung lobes and heart can be undertaken. In most cases such techniques are utilised for undertaking biopsies of masses identified on radiography. Following removal of the scope, as much air
as possible is evacuated from the thorax and the animal is held at maximum inspiration while the trocar is removed. Once the skin incision has returned to its normal position (distal to the thoracotomy entry
point) air rarely re-enters the thorax. Close observation is required during the immediate post-operative period, and if there is any suggestion of a deteriorating pneumothorax then fine needle aspiration
can be used to remove air, or in exceptional cases a chest drain can be inserted.Pic12: Endoscopic examination of the caudal lung of a rabbit with lung consolidation due to bacterial
pneumonia. Summary Rabbits and rodents are small animals that do not appreciate extensive surgical invasion. The use of endoscopy provides the exotic animal clinician with the means
of examining internal structures through key-hole approaches which greatly reduces operating time and improves success. |
