As a small animal practitioner, aren't there times, after the radiographs have been taken and evaluated, and after the palpations have been performed, and after the ultrasound images have been recorded, that we would just love to actually take a peek inside an animal to indeed visualize a suspicious lesion? While in dogs and cats, that isn't always possible unless an exploratory is performed, visualization of internal organs can be easily undertaken in birds. What is so different about a bird that makes endoscopy so practical?
The unique anatomy and physiology of birds makes them perfect candidates for endoscopic procedures. Birds do not have a diaphragm and they have air sacs in addition to lungs. Mammals must have carbon dioxide pumped into the peritoneal cavity in order to more easily identify organs by endoscopy. This is not required, nor advised, in avian species, due to the natural inflation of the air sacs.
Birds don't have a peritoneal cavity that is analogous to that found in mammals. There are 16 separate and distinct cavities enclosed within the body wall of an adult bird. Eight are cavities of the air sacs and the other eight cavities are those of the coelom proper. There are five peritoneal cavities formed by peritoneal partitions that are not found in mammals. These are the left ventral hepatic peritoneal cavity (pc), right ventral hepatic pc, left dorsal hepatic pc, right dorsal hepatic pc and intestinal pc. The remaining three cavities are formed essentially as in mammals, and they are the left pleural cavity, right pleural cavity and the pericardial cavity. In bird embryos, there are six pairs of air sacs. In the great majority of birds, two pairs have fused at or soon after hatching to form a single median sac, called the clavicular air sac. In the domestic fowl and a number of other species, another pair fuses at about this time to form another single median sac, the cervical air sac. In many species of adult birds, there are eight air sacs altogether: one cervical, one clavicular, two cranial thoracic, two caudal thoracic and two abdominal air sacs. There are some species variations in the air sacs, however.
It is important to have a good understanding of the anatomy of a bird's respiratory system, since when performing endoscopy, the surgeon will be entering different air sacs or cavities, depending on the purpose of the procedure and the location of any lesions present.
There are many common uses of the endoscope in avian medicine. In the past, endoscopy was used primarily for surgically sexing sexually monomorphic birds. Since the advent of DNA blood sexing and chromosome sexing, surgical sexing is not as frequently performed. Endoscopy is most common utilized to visualize internal organs and tissues, to perform tissue biopsies, to collect samples for culture, to remove accessible foreign bodies, to remove granulomas and to monitor response to treatment. It is possible to access many different sites in most birds, and it is possible to even perform endoscopy in birds as small as finches. Sites commonly accessed are the coelomic cavity (gonads, air sacs, liver, lungs, spleen, kidneys, ventriculus, proventriculus), oropharynx, choanal slit, trachea, crop, cloaca, external ear canal and nares.
There are many different types of equipment that historically have been used to visualize internal organs of birds. Otoscopes with small cones designed for canine and feline ear canals have been employed, however, these provide a low level of light and poor magnification and are not recommended. A tubular endoscope that utilizes an otoscope/ophthalmoscope base has been designed, and may be upgraded with a halogen light source (Focuscope). Endoscopes designed for human surgical use have also been used. The best systems available for veterinarians have been designed specifically for the needs of avian and exotic animal veterinarians. For most general practices, a 2.7 mm rigid endoscope that is between 170 and 190 mm in length is probably the most useful. This telescope can be used for birds weighing between 55 and 4000 grams. A 1.9 mm diameter telescope is available, and is the smallest one that is useful in small birds (less than 100 grams in weight) and for tight spaces (choana, trachea, oviduct, sinuses). Most endoscopic systems use a halogen or xeon light source. (*Note to editors: it IS xeon, not xenon). A beveled distal lens element allows for a larger viewing field, for less traumatic passage through the tissues and air sacs and for better visualization when other instruments are used (for example, when biopsy forceps are utilized during endoscopy). Light quality, size, clarity of image and degree of magnification are all important considerations when choosing an endoscopy system for avian and exotic animal practice.
Before offering endoscopy to avian patients, it is extremely important that avian vets obtain good surgical skills with endoscopic equipment. There are several associations that offer excellent continuing education courses in avian endoscopy. The Association of Avian Veterinarians and the North American Veterinary Conference offer in-depth endoscopy courses, often with differing levels of expertise, both for those just beginning to learn the skills and those wishing to learn new and advanced techniques. Dr. Michael Taylor and Dr. Michael Murray, two brilliant endoscopists, offer courses throughout North America in endoscopic techniques, including biopsy techniques. It is helpful to practice on culled pigeons (ask local pigeon breeders) or dead birds (but the air sacs and tissues are not the same as those found in live birds).
Instruments are fairly delicate and must be cleaned, sterilized and stored properly. Rigid telescopes must be handled carefully and care must be taken not to bend or torque the scope, which can damage the optics. The endoscope must be sterilized before each use. Most practitioners use a 2% gluteraldehyde solution, although ethylene oxide can also be used. For sterilization, equipment must be soaked for a minimum of 15-20 minutes between uses.
For all endoscopic procedures, some form of anesthesia should be used. Most practitioners use isoflurane because of its safety and rapid induction and recovery. Injectables such as ketamine combined with diazepam or xylazine can be used when the use of gas is impractical. While it would be best if each avian patient would have pre-surgical blood-work prior to undergoing endoscopy, this is not always practical or possible. As a minimum data base, a complete history and physical exam (including weighing the bird in grams) should be performed. To be on the safe side, it is best to fast psittacine birds for at least three hours (up to eight hours) prior to endoscopy. Raptors should be fasted for 24-36 hours. It is best if unweaned baby birds not undergo endoscopy due to the great risk of aspiration of crop contents and because the proventriculus is comparatively larger and softer than that found in adult birds. If endoscopy or surgery must be performed in baby birds, ensure that the crop is empty and intubate the bird to minimize risk of aspiration. Lories also often have a larger proventriculus, which can make endoscopy more difficult. Birds with the disease, proventricular dilatation disease (PDD), usually have a grossly dilated proventriculus and soft ventriculus, so endoscopy or biopsies of tissues of the gastrointestinal tract can be dangerous and are difficult to heal. All birds undergoing endoscopy should be provided with supplemental heat during and after the procedure until the bird is standing. Unless there has been excessive bleeding, birds do not usually require parenteral fluids during endoscopy.
Many approaches to the avian coelom have been described. The most commonly used approach has the endoscopist enter the bird's coelom on the left lateral side. Since psittacines have one ovary usually located on the left side, this approach allows easy visualization of gonads, air sacs, liver, spleen, lungs, kidneys, adrenal glands, proventriculus, ventriculus and pericardium. The anesthetized bird is placed in right lateral recumbency and well restrained. The wings are extended and taped to a restraint board, and the left leg extended cranially. The entry site is easily visualized and palpated just caudal to the last rib and just ventral to the flexor cruris medialis muscle. The skin should be prepped as for aseptic surgery and the bird should be draped for surgery. The use of clear drapes is recommended. The skin incised with a small blade, then the muscle is either punched through with a hemostat or with a trochar provided with the endoscopy equipment. Once the body wall is penetrated, the scope is inserted in a craniomedial direction into the caudal thoracic air sac. To better view the gonad, the membranes between the caudal thoracic and abdominal air sacs usually are penetrated by gently but firmly sweeping the tip of the scope through an avascular area of the membrane. Organs or lesions are then visualized. Abnormalities of organs, fluid accumulation, exudates, granulomas, opaque air sacs or foreign bodies can be visualized, biopsied, cultured or excised.
Once the procedure is completed, the telescope is extracted and the skin may be closed with tissue glue or a suture. The muscle need not be sutured since once the leg returns to normal position, the hole will naturally seal.
Other approaches may be employed, depending on the goals of the procedure. A ventral midline approach is best for biopsy of the liver. Other approaches include the prepubic and the postischial. The tracheal lumen can be scoped. For extended procedures, it is best to insert an abdominal air sac breathing tube prior to tracheal endoscopy, but it is not necessary for short peeks into the trachea. The telescope can be passed down the esophagus and into the crop. To visualize lower structures, an incision into the crop can be made, and the telescope inserted through the crop and into the esophagus to examine the proventriculus or ventriculus. This can be used to attempt retrieval of foreign bodies within the gastrointestinal tract. The telescope can also be inserted in the choanal slit, external ear canal, infundibular cleft and cloaca.
Endoscopy is a wonderful addition to avian practice. While it is not a mandatory addition, it will enhance and improve the level of care for avian patients. It is important, however, to get the necessary training and correct equipment to best serve our clients and patients.
Copyright © 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
All Rights Reserved
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