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How to take and interpret avian radiographs

The right positioning and anaesthesia can vastly improve the diagnostic outcomes when radiographing birds

11 September 2019, at 9:00am

Radiographs can be an excellent tool to assess avian patients, given their non-invasive nature and ease of acquisition. A basic knowledge of avian anatomy can result in radiographs becoming incredibly useful and easy-to-interpret diagnostic tools. Radiographs can be helpful for diagnosis of conditions in captive birds such as lameness, regurgitation, coelomic distension, dyspnoea, general malaise and countless other clinical presentations. They can also be used to assess for fractures or other trauma in wild birds, which are commonly presented to clinical practice. Radiographs can be taken with any standard small animal radiography set up, ideally with a high frequency unit and digital radiography.

Sedation and general anaesthesia

Radiographs should be taken with appropriate restraint and positioning. The author recommends the use of general anaesthesia or sedation to allow for appropriate positioning. It is never appropriate to hold the patient down to the plate, straddle the X-ray beam or have the handler’s own hands within the radiographic view.

Conscious radiographs usually result in superimposed anatomy and non-diagnostic radiographs. There are times in which conscious radiographs can be indicated, such as in collapsed and debilitated patients when trying to rule in or out certain diagnoses, for example egg binding (Figure 1) or the presence of heavy metals. Routine or planned radiographs should be performed after a small period of starvation – enough to allow the crop to empty and decrease the risk of regurgitation and subsequent aspiration.

FIGURE (1) A conscious radiograph taken to assess for the presence of an egg. The remainder of this radiograph is non-diagnostic due to superimposition of structures
FIGURE (1) A conscious radiograph taken to assess for the presence of an egg. The remainder of this radiograph is non-diagnostic due to superimposition of structures

Isoflurane inhalational anaesthesia provides quick anaesthetic induction and recovery, due to the efficiency of avian respiratory systems. Mask induction of birds can take as
little as 30 seconds and patients can be maintained either with the face mask left in place or by intubating. Birds have a large glottis, located at the base of their tongue, which makes them simpler than most exotic and mammalian species to intubate. Bards placed in dorsal or sternal recumbency for prolonged periods of time can develop
apnoea, and so intubation is ideal to allow for intermittent positive pressure ventilation.

Inspiration and expiration are active processes in birds, by which their ribs and keel bone expand cranially and ventrally on inspiration. This increases the volume of their air
sacs and allows air to pass through the respiratory system. If the patient is placed in sternal recumbency, they need to lift their dorsal body in order to inspire, which can be difficult in larger, heavier birds. If an avian patient is placed in dorsal recumbency, some of the more dorsal air sacs are compressed by internal organs, resulting in reduced air flow. This is one of the reasons that the author prefers ventrodorsal views to dorsoventral views, and ideally, once this image has been taken, the patient is moved to lateral recumbency in order to allow for more efficient ventilation.

FIGURE (2) A Severe Macaw positioned for a ventrodorsal radiographic view
FIGURE (2) A Severe Macaw positioned for a ventrodorsal radiographic view

© Courtesy of Stacey Vickery

Positioning for radiographs

It is important to consider the area for interpretation when taking a radiograph. Similar to a canine or feline patient, if a bird is lame then the field of view should be focused on the limb of interest. Whole-body radiographs are used more frequently in exotics practice, due to the small size of the patients and the ease of acquisition; however, collimation should be considered. In avian patients, adequately positioned contralateral radiographs can yield a myriad of diagnostic findings and can help narrow down diagnosis and point the practitioner in the direction of the next diagnostic step.

Limbs can be restrained with tape, light sandbags or ties. Ventrodorsal views are taken with the bird in dorsal recumbency, with the wings extended laterally and the legs extended caudally (Figure 2). It is not necessary for the wings to be fully extended, as long as they do not superimpose the coelomic cavity. The keel should be superimposed over the spine and the two sides of the pelvis should be symmetrical. Lateral views are taken with the patient in left or right lateral recumbency with both wings extended dorsally (Figure 3). Care must be taken when restraining the wings as too much pressure on the humeri can result in an iatrogenic fracture. The legs should be pulled ventrally and caudally to reduce superimposition on the coelomic cavity.

FIGURE (3) A Severe Macaw positioned for a lateral radiographic view
FIGURE (3) A Severe Macaw positioned for a lateral radiographic view

© Courtesy of Stacey Vickery

Orthopaedic radiographs should also consist of orthogonal views, in a similar fashion to those taken for canine or feline patients. This is especially important when investigating fractures, dislocations or osteomyelitic lesions.

Interpreting avian radiographs

The normal anatomy of birds varies greatly depending on the species, age and sex of the patient; however, a general interpretation should follow the same pattern every time to ensure nothing has been overlooked when assessing the images (Figures 4 and 5).

Axial skeleton and appendicular skeleton

All bones should be assessed for any abnormalities in lucency, obvious fractures, arthritic changes or abnormalities. Flighted birds have a number of pneumatised bones
which, depending on the species, can include the humerus, coracoid, ribs, pelvic girdle and femur. Pneumatised bones have thin, radiopaque cortices with fine bony trabeculae with the medulla. More distal bones are not pneumatised and are often more radiopaque in appearance.

During times of increased reproductive stimulation, an increase in circulating oestrogen leads to an increase in radiopacity of the long bones of females, due to the deposition of calcium within the medullary cavity. The pectoral girdle of birds consists of the scapula, clavicle and coracoid. Fractures of the coracoid can be common in wildlife cases, and sometimes evaluation of this requires a 45 degree caudoventral-craniodorsal oblique radiographic view to assess, as described by Visser et al. (2015).

Cardiovascular system

The heart can be visualised in the cranial coelomic cavity on ventrodorsal and lateral views. In captive psittacines, the heart base should be within 51 to 61 percent of the maximum width of the thorax on ventrodorsal view (Crosta et al., 2018). However, species-specific values should be referenced when assessing for cardiomegaly. In the VD
view, the cardiac silhouette contributes to the “hourglass figure” described by many resources. The great vessels can be identified on both views as soft tissue opacities, as round “dots” on the ventrodorsal view and as more recognisable longitudinal structures on the lateral views.

Respiratory system

Birds have fixed, dorsal lungs, which are best evaluated on a lateral view. These sit dorsal to the heart and have a characteristic honeycomb appearance, due to the presence of parabronchi. The trachea can be easily traced from the skull down to where it bifurcates at the syrinx. The syrinx is a common place for fungal lesions to form in captive psittacines, so the area should be assessed for any abnormal soft tissue opacities. Air sacs are thin and should be empty of anything other than air, and so are best evaluated by their borders with other organs. They are visible on the ventrodorsal views lateral to the hepatic silhouette. The walls of air sacs should not be identifiable, so increase in wall thickness should rouse suspicion of air sacculitis.

Digestive system

The avian digestive system consists of the crop (with the exception of some species), proventriculus, ventriculus or gizzard, intestines, caecum and cloaca. It is best examined by use of contrast media, due to superimposition of the caudal coelomic contents. Ideally, patients are starved long enough before general anaesthesia to allow food to move distally from the crop; however, sometimes food can be visualised inside. The proventriculus sits dorsally and caudal to the heart on the lateral view. Abnormal distention of the proventriculus can be an indication of proventricular dilatation disease (PDD) and should be followed up with contrast radiographs.

The ventriculus or gizzard normally contains some grit with opacity similar to that of bone. Metal opacity particles within the ventriculus should not be present and should result in a suspicion of metal ingestion (Figure 6). The ventriculus sits caudoventrally to the proventriculus on the lateral view and slightly to the left of midline on a ventrodorsal projection. The intestines, caecum and cloaca are superimposed on other coelomic organ and so can only be fully evaluated with contrast media.

Other coelomic viscera

The liver is best assessed on the ventrodorsal view, where it should form a rough hourglass shape when viewed in conjunction with the heart. As a general rule, the edges of the hepatic silhouette should not extend laterally past an imaginary line between the shoulder joints and the acetabulae of the hips.

The spleen is best visualised on a lateral view, where it is seen as a round, soft tissue opacity dorsal to the liver and proventriculus. The kidneys are also best visualised on
the lateral view, sitting dorsally within the pelvis. They are often only seen as soft tissue opacities, so any increase in radiopacity should be further investigated.

The gonads of birds are internal and superimpose upon the cranial pole of the kidneys. Their size depends on the reproductive status of the patient at the time. Males have bilateral testes and in females only the left ovary is functional. Appropriate positioning and adequate anaesthesia can vastly increase the diagnostic capacity of avian radiographs. These techniques can be utilised to improve patient outcomes and help direct further testing if required.

References
Author Year Title
Crosta, L., Melillo, A. and Schnitzer, P. "Basic radiography" in Chitty, J. and Monks, D. (eds.) 2018 BSAVA Manual of Avian Practice A Foundation Manual. Gloucester: British Small Animal Veterinary Association, pp. 269-285
Harcourt-Brown, H.N. "Diagnostic Imaging", in Harcourt-Brown, N. and Chitty, J. (eds.) 2005 BSAVA Manual of Psittacine Birds, 2nd ed. Gloucester: British Small Animal Veterinary Association, pp. 97-106.
Krautwald-Junghanns, M.E., Schroff, S. and Bartels, T. "Birds" in Krautwald-Junghanns, M.E., Pees, M., Reese, S. and Tully, T. (eds.) 2011 Diagnostic Imaging of Exotic Pets. Hannover: Schlütersche Veragsgesellschaft mbH & Co. KG, pp. 1-26.
Visser, M., Hespel, A.M., de Swarte, M. and Bellah, J.R. 2015 Use of a caudoventral-craniodorsal oblique radiographic view made at 45° to the frontal plane to evaluate the pectoral girdle in raptors. Journal of the American Veterinary Medical Association, 247, 1037-1041.

Ashton Hollwarth, BSc, BVMS, MRCVS, studied in Western Australia. Since graduation she has worked in exotic practices in England and is currently enrolled in her CertAVP Zoo Med certificate. Ashton recently started an ECZM residency in Avian Medicine and Surgery at Great Western Exotics.

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