Lorenzo Crosta, Dr. med. vet.
Since when, in the early seventies, modern rigid arthroscopes were firstly used to determine the gender of monomorphic birds, it became clear that birds are ideal patients for endoscopy. In fact, the absence of a diaphragm and the presence of the airsacs system render useless the insufflation of air into the coelomic cavity. This makes laparoscopy (or better celioscopy), much more easy in birds, compared to other zoological classes. So it was a natural process that brought endoscopy to be both a primary diagnostic and therapeutic tool in avian medicine and surgery. To date, we can assess that a modern approach to avian veterinary science cannot be made without the help of an endoscope.
Rigid endoscopy: the basic equipment for avian endoscopy includes a light source, a fiberoptic cable, a small diameter (1.9-2.7 mm) rigid endoscope, and a simple sheath into which the endoscope may be inserted, if needed. If our purpose is simple observation, a 150 W light source may be enough, but if we need to take endoscopic pictures or movies, a more powerful, or better a xenon light source is needed. If possible, the light source should be equipped with air pump, for the few maneuvers that require it. Other wise a separate air pump will be acquired. The fiberoptic cable will transfer the light, without transferring the heat generated by the light source.
The rigid endoscope exploits a system of rod lenses: this makes the major difference between rigid and flexible endoscopy. In the latter, the fiberoptics are built in the endoscope itself. Rigid endoscopes may have different lens angle offset. Generally speaking, when operating with birds a 30° offset is the standard offset. This angle will allow for a direct, but also slightly lateral vision and rotating the endoscope on its major axis will widen the field of vision.
A more advanced equipment will include also an examination sheath, with a built-in working channel. The most common tools to be used with the working sheath are the flexible biopsy forceps, the flexible grasping forceps and the semi-rigid endoscopy scissors. All the work, especially the advanced one, will be made easier and the operator's skill enhanced, by the use of a video-camera and monitor.
Flexible endoscopy has more or less the same applications in birds as in mammals: it is especially used for the observation of the upper respiratory tract, proximal digestive apparatus and distal parts of the latter (in the largest bird species). Equipment for flexible endoscopy is basically formed by a light source and a flexible fiber-optic endoscope (fiberscope). Length and diameter of the fiberscope are depending on the size of the patient. The experience of the author is based on the use of two fiberscopes: a 6 mm bronchoscope, to be mostly used in esophagoscopy and gastroscopy of medium sized to large birds (geese, ducks, largest psittacines and small penguins) and a larger human colonoscope, the classic "all-round" fiberscope for the zoo veterinarian. This will be used in ostriches and other ratites and also in large penguins, raptors and swans.
1) Respiratory system
Rhino-choanoscopy: birds are small patients and the magnification allowed by the endoscope will add valuable information for the clinician.
Patient is in dorsal recumbency, the beak will be opened and the endoscope introduced directly into the choanal slit.
Tracheo-syringoscopy: is one of the commonest endoscopic maneuvers in avian medicine. Diseases of the upper respiratory tract are frequent in birds and a tracheoscopy often has a enlightening diagnostic value. For a simple observation, the patient will be anesthetized and brought to a deep anesthetic level. The bird can be either be in sternal recumbency, or held vertically by a helper. The endoscope is introduced into the trachea and the syrinx is rapidly reached. This is important as the syrinx is the place where the majority of the focal lesions will take place. Then the endoscope is slowly retrieved, allowing the clinician to observe the entire length of the trachea. If a longer work is needed, such as for a biopsy, or retrieving a foreign body, or a granuloma, then the anesthesia will be delivered through the airsacs.
2) Alimentary system
Inspection of the oral cavity: the observation of the oral cavity is run more or less for the same reasons and with the same technique used for the rhino-choanoscopy.
Esophago-ingluvioscopy: is one of the few maneuvers that require air to dilate the anatomic tract to be inspected. Observation of the esophagus and ingluvies, or crop (in the avian species that have it), is a routine procedure, because it is common to suspect crop traumas, infections or neoplasm. So esophagoscopy is done for a direct inspection of the crop, for taking biopsy samples and also for retrieving foreign bodies. The patient will preferably be fasted 2 or 3 hours before the procedure. Then it will be anesthetized and, if possible intubated. The rigid endoscope, or a flexible fiberscope, has to be connected to an air pump, in order to dilate the esophagus and crop. The endoscope will then be inserted into the oral cavity and down into the esophagus. The patient can be in dorsal, or ventral recumbency, depending on bird species and purpose of the procedure. If some fluid is still in the crop, this will be aspirated, to make the inspection easier and more effective. The amount of air to be delivered will be just enough for a good observation.
Gastroscopy (proventriculo- and ventriculoscopy): is still a common procedure, even if less frequent than the previous one. Indications for a gastroscopy are a simple inspection, to confirm a diagnosis, but also for taking biopsy samples and retrieving foreign bodies. A good knowledge of the anatomic differences between the various bird species is a must. Proventriculus and ventriculus (gizzard) can have different shape, appearance, structure and anatomic relationships. Gastroscopy is the natural consequence of an esophagoscopy: once in the crop (or in the distal part of the cervical esophagus, in the species that do not have a crop), the cavity will be gently dilated with air and the ostium that connects the crop to the thoracic esophagus, located. Once entered into the distal part of the esophagus, proventriculus and ventriculus are easily reached and inspected. For this procedure, both rigid and flexible endoscopes can be used. If a flexible fiberscope of the right size is not available, but our rigid scope is too short, then an esophagotomic access should be used. The anesthetized patient is in dorsal recumbency. A small cut is made at 4/5 of the neck length, in the ventral side of the cervical esophagus. In this way the proventriculus and ventriculus will be easily examined.
Cloacoscopy: cloaca, or the combined terminal opening of the alimentary, urinary and reproductive systems, is often involved in local and generalized disease processes. The endoscopic inspection of this organ can have great diagnostic value. Also this maneuver needs a dilatation of the organ, but this will be obtained with a sterile saline solution, and not with air. Normal saline, or Ringer's Lactate Solution, will be warm and delivered through the sheath of the rigid endoscope. Also this procedure needs a perfect knowledge of the anatomic differences between the various bird species.
3) Auditory system
Otoscopy: birds do not have external auricles, but their ears appear like two small openings, located laterally on the head and caudally to the eyes. A small rigid endoscope will facilitate the observation of the ear and the magnification that can be achieved is extremely helpful.
4) Laparoscopy (Celioscopy)
Since birds do not have two separated thoracic and abdominal cavities, but instead a single coelomic cavity, laparoscopy in birds should be named celioscopy. However we want to call it, there is no doubt that laparoscopy is the queen of the endoscopic techniques in avian medicine. This is because there is no other zoological class in which laparoscopy is made so easy by the natural anatomical situation of the patient.
Although several accesses to the avian coelom have been described, there are only two that are routinely used: the lateral approach (especially the left one) and the ventral midline one. Although the author has been using a pre-femoral access (with the upper leg pulled caudally), for many years, to date the preferred approach is the post-femoral. The pre-femoral approach may still be useful when a right lateral approach is required, or when the cranial movement of the left leg is limited by a disease process. The patient is placed in right lateral recumbency, with the wings extended dorsally. The left leg is flexed cranially, while the right leg is maintained in its normal position. The flank area is prepared for surgery. A small incision is made in the skin where the caudal thigh muscle (semi-membranous muscle--M. flexor cruris medialis) crosses the last rib. The abdominal muscles are then bluntly dissected, with an Adson, or small, curved mosquito forceps and the endoscope is inserted.
Organs and systems that can be accessed through a left lateral approach are the left lung, left abdominal, caudal thoracic and cranial thoracic air sacs, heart, liver, spleen, outer walls of the proventriculus, ventriculus and intestines, left kidney and ureter, left adrenal gland, left testicle (and often also the right one), left deferens duct, or left ovary and oviduct, in the case of a female patient. Through a right lateral approach there is a similar vision, but the female reproductive system can be inspected only in the few bird species that possess a right functional one. The only organ that needs to be accessed from the right side is the duodenal part of the pancreas.
To determine the gender in monomorphic species was the first practical application of avian endoscopy: in fact, although other techniques of sex determination are widely used by now, endoscopy still gives information of paramount importance, especially when selecting birds for breeding purposes. The surgical access is always left lateral, since in almost all the bird species, only the left part of the feminine reproductive system develops. Further, in the few species that have a developed right part, also the left one is developed.
Morphological diagnosis of reproductive abnormalities: during a routine sex determination, or for any other reason, is not uncommon to spot focal pathologies, or abnormalities of the reproductive tract. The most frequently observed are metaplasia of the gonad, neoplasm, abscess, or mycotic granuloma. Those lesions will be treated accordingly to their nature, and often can be removed during the same endoscopy, otherwise biopsy or microbiology samples can be taken for further examination.
The examination of the distal part of the respiratory system is a very useful technique, in avian endoscopy.
Inspection of the air sacs and pulmonary base: this may be considered a "natural procedure", since the lateral approach to the coelom is into the caudal thoracic air sac,. Main indication is when pathology of the distal respiratory system is suspected, or if a radiograph is showing abnormal shadows in the air sacs. Immediately after entering through the body wall of the patient, the endoscope is directed cranially, into the caudal thoracic air sac. In this way the walls of the air sac can be inspected, as well as the air sac itself, the base of the lung, and the ostium that connects the lung to the air sac.
INSPECTION OF THE LIVER
This is also a common procedure, either for a simple observation, or to take biopsy samples. The liver can be accessed through two approaches. When the routine left lateral approach is used, the endoscope will be directed into the peritoneal cavity. Once the thoracic esophagus and proventriculus are located, the endoscope will be driven dorso-laterally to the latter, until the caudo-lateral border of the liver is encountered. If the liver has to be accessed through the ventral, midline approach, the patient has to be in dorsal recumbency, and the abdomen carefully disinfected. A small incision is made few mm. caudally from the distal end of the sternum. Then the muscles are bluntly dissected, with and the endoscope is inserted. The endoscope will be driven parallel to the body main axis and the caudal borders of the liver are easily identified.
Inspection of the heart: due to the lack of a diaphragm, the avian heart, like the liver, can be observed for two different surgical approaches. After a left lateral access, from the caudal thoracic air sac, the endoscope is passed into the cranial thoracic air sac, where the dorso-lateral portion of the heart can be easily spotted. If the distal part of the heart needs to be inspected, then the access will be similar to the ventral one described for the liver. After passing the ventral surface of the liver, the cardiac apex can be observed in the groove formed by the two hepatic lobes.
Indications for the inspection of the kidneys and also for a renal biopsy, are linked to the suspicion of a nephropathy that cannot be ascertained in a different way. So this procedure is indicated in case of PU/PD, chronic hyperuricemia, and swelling of the kidneys, when this is diagnosed by radiography, ultrasounds, or even during the same endoscopic examination. Access to the kidney follows exactly the same route described for the gonads.
Inspection and sampling of the spleen can be very important in avian diagnostics. Unfortunately, access to this organ is not always easy, as it depends on the conditions of the surrounding organs. Surgical approach is the same described for the gonads and kidneys. Once the cranial lobe of the left kidney is located, the endoscope is driven ventrally, in the groove formed by the kidney and mesentery on one side, and the proventriculus on the other. There the red spleen, spherical in psittacines and elongated in most passerines and pigeons, will be located.
This is possibly the most difficult organ to be accessed in the avian coelom. This because it has to be reached through a right lateral approach, a less common procedure, compared to the left lateral approach, and also because the pancreas is hidden between several intestinal loops. Only the endocrine part of the avian pancreas can be observed endoscopically.
Endoscopy and other linked techniques are constantly growing in avian medicine. Some maneuvers use a natural access to the body cavities; while other ones require a surgical access to the avian coelomic cavity. This latter procedure is greatly facilitated by the presence of the air sacs, which, maintaining a constant airflow inside the avian body, make useless the artificial insufflation of air. Although the reduced size of most avian patients make impossible some endoscopic procedures, such as arthroscopy, it is clear that also this field of avian medicine is becoming highly independent. For this reason it is more common that an avian veterinarian is running endoscopies on his/her patients, instead of the general veterinary endoscopist. In fact, avian endoscopy cannot be applied without the perfect knowledge of the normal avian anatomy in the different species.
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