Avian Anatomy Aids Endoscopic Procedures

by Veterinary Practice News Editors | April 17, 2009 4:06 pm

Birds' unique anatomy and physiology make them perfect candidates for endoscopy. They have air sacs in addition to lungs but they don't have diaphragms. Mammals must have carbon dioxide pumped into their peritoneal cavities in order to more easily identify organs through endoscopy. This is not required, nor advised, in avian species, because of the natural inflation of the air sacs. 

Equipment and Care

Many types of equipment are used to visualize birds' internal organs. Otoscopes with small cones designed for canine and feline ear canals have been employed; however, these provide a low level of light, poor magnification and are not recommended. A tubular endoscope that utilizes an otoscope/ophthalmoscope base may be upgraded with a halogen light source. Endoscopes designed for human medicine have played a role in avian medicine. However, the best systems have been designed specifically for the needs of avian and exotic animal veterinarians. For most general practices, a 2.7 mm rigid endoscope between 170 and 190 mm long is probably the most useful. This telescope can be used for birds weighing between 55 and 4,000 grams. A 1.9 mm diameter telescope is the smallest device used in small birds (less than 100 grams) and for tight spaces (choana, trachea, oviduct and sinuses).

Most endoscopic systems use a halogen or xeon light source. 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.

Instruments are fairly delicate and must be cleaned, sterilized and stored properly. Care must be taken not to bend or torque a rigid telescope, which can damage the optics.

Endoscopes must be sterilized before each use. Most practitioners use a 2 percent gluteraldehyde solution, although ethylene oxide can also be used. For sterilization, equipment must be soaked for a minimum of 15 to 20 minutes between uses.—M.W.

Understanding of birds' respiratory system is vital, since when performing endoscopy, the surgeon will enter different air sacs or cavities, depending on the purpose of the procedure and the location of any lesions present.

Bird anatomy doesn't include a peritoneal cavity 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 after hatching or soon after 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.

Preparation and Procedure

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 performed as frequently. Today, endoscopy is most commonly used to visualize internal organs and tissues, perform tissue biopsies, collect samples for culture, remove accessible foreign bodies, remove granulomas and monitor treatment response. 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 and proventriculus), oropharynx, choanal slit, trachea, crop, cloaca, external ear canal and nares.

While it's ideal for each avian patient to have pre-surgical bloodwork completed prior to undergoing endoscopy, it's not always practical or possible. At minimum, a complete history and physical exam (including weighing the bird in grams) should be performed. To be safe, fast psittacines for at least three hours (up to eight hours) prior to endoscopy. Raptors should be fasted for 24 to 36 hours. Unweaned baby birds should not undergo endoscopy because of 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 the crop is empty and intubate the bird to minimize risk of aspiration. Lories often have a larger proventriculus, which can make endoscopy more difficult. Birds with 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 endoscopic procedures should include some form of anesthesia. 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.

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.

Ensoscopic Skill Savvy

Before making endoscopy available to avian patients, it is important to obtain good equipment skills. Several associations offer continuing education courses in avian endoscopy, including the Association of Avian Veterinarians and the North American Veterinary Conference. These associations offer in-depth courses, often with differing levels of expertise, both for beginners and those learning and advanced techniques. Drs. Michael Taylor and Michael Murray offer courses throughout North America in endoscopic techniques, including biopsy techniques.—M.W

There are many approaches to the avian coelom. During the most commonly used procedure, the endoscopist enters 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 is 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.

Prior to surgery, the skin is prepped as for aseptic surgery and the bird is draped with clear drapes. The skin is incised with a small blade; 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 complete, 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 seal naturally.

Other approaches may be used, depending on the goals of the procedure. A ventral midline approach is best for liver biopsies; other approaches include 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 quick 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.

Dr. Wissman owns the Icarus Mobile Veterinary Service in Wesley Chapel, Fla., and is a frequent contributor to Veterinary Practice News.


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