Overview

Radiographs are an integral part of the diagnostic workup for any sick animal. Most of the diagnostic imaging equipment used in canine and feline practice is appropriate for avian radiography.

Avian radiographic technique requires low KVP to maximize contrast of the soft tissue organs of the coelomic cavity and typically, high mA to allow short exposure times, which minimizes inherent motion artifact due to tremoring and breathing.

Non-screen films provide better resolution but require increased exposure time, increasing the risk for motion artifact. The use of fast screens can decrease motion artifact. Slower screens used for extremity orthopedic radiographs in humans and cats and dogs can be very useful for avian patients. Single emulsion mammography film screen combinations or non-screen dental film can provide excellent resolution, particularly for smaller passerine patients.

Digital radiology is widely available and provides certain post-processing advantages over standard radiographs, specifically the ability to alter contrast and manipulate size of images. The ease of storing images as well as sharing images are other advantages of digital radiology. It is recommended to fast patients before performing radiographs to minimize risk for regurgitation and aspiration.

Patient Positioning

Good positioning of the patient is vital for providing quality diagnostic images. In many cases, sedation or anesthesia will be required. In ill patients, restraint can be achieved in various ways, including the use of tape, sandbags, and specially designed avian restraint devices. In some instances, most commonly in whole-body screening for ingested metallic foreign material, positioning may not be vital.

For a ventrodorsal (VD) radiograph, birds are restrained on their backs with both wings equally extended and both feet equally extended. Symmetry in positioning of the wings and feet yield better radiographs. In lateral radiographs, the wings are extended dorsally (behind the back) and the feet are extended towards the tail. In general, the leg closest to the film is placed slightly cranial to the other leg.

Radiographic Assessment

An approach to systems, similar to what is used for feline and canine patients, is required. Knowledge of avian anatomy is a necessity. While for the most part, basic anatomy is similar between different species, there are certain anatomic differences that may affect diagnostic accuracy. For example, in psittacines, differences exist between species in relative sizes of the hepatic and cardiac silhouettes. Another example is the presence of syringeal bullae in male ducks.

Respiratory System

Lung parenchyma: The reticular/honeycombed lung parenchyma is best assessed on lateral radiographs. With pulmonary disease (pneumonia, abscess, granuloma), the fine reticular appearance of the lung is lost and there is increased opacity pole of parenchyma, more diffuse with pneumonia and more discrete with abscesses or granulomas (often aspergillosis).

Air sacs: Most psittacines have nine air sacs, four paired (cervical, cranial thoracic, caudal thoracic, abdominal) and one unpaired (clavicular air sac). The clavicular air sac is located dorsal and caudal to the crop at the thoracic inlet. The normal air sac is not visible radiographically. It is normal to see mineralization of the cartilage tracheal rings. Inflammation or infection causes increased opacity, which should be classified as diffuse, focal, or striated. Trauma can cause disruption of the air sac wall integrity, resulting in subcutaneous (SQ) emphysema. Aspergillosis infection of air sacs can also result in loss of wall integrity and secondary SQ emphysema. Syrinx granulomas can occur with aspergillosis and are often identifiable radiographically.

Coelomic Organs

Crop: The crop is an extracoelomic structure located at the level of the thoracic inlet and often contains gas food material.

Esophagus:The esophagus connects the crop to the proventriculus and is not typically visualized on radiographs.

Proventriculus:The proventriculus is usually identified on lateral views dorsal to the cardiac silhouette, coursing in craniodorsal to caudoventrally. On VD, the proventriculus is usually to the left of the liver and more difficult to identify on survey radiographs. Pathologic distension can occur with foreign body obstruction and proventricular dilatation disease, among others. Proventriculus to keel ratios have been developed in order to differentiate normal from distended proventricular diameter.²

Ventriculus:The ventriculus can be identified often on both views and in many species, there is a normal finding of ingested mineral opaque material that is typically incidental. Ingested metallic foreign material is usually identified in the ventriculus.

Small intestines: Intestines are located in the caudal coelomic cavity and are typically difficult to evaluate due to superimposition.

Kidneys and gonads: Both the kidneys and gonads are located in the dorsal coelomic cavity. The gonads are usually located more cranial and sometimes more ventral. Gonadal enlargement commonly occurs during reproductive activity and there can be concurrent displacement of adjacent organs. Renal enlargement can be seen with carcinomas among other disease processes.

Spleen:The spleen can be identified on the lateral views dorsal to the ventriculus. Splenic enlargement can occur with infectious diseases and neoplasia, particularly lymphoma.

Cloaca: The cloaca can be visualized in the most caudal aspect of the coelomic cavity.

Liver: The liver and heart form an hourglass on VD views and have a noticeable waist at their junction. The relative size of heart and liver varies between species and comparisons to individuals of the same species should be made when attempting to determine the presence of abnormal cardiac or hepatic size. In raptors and macaws, the cardiac silhouette is typically larger than the hepatic silhouette. In other species, this relationship is typically reversed. Hepatomegaly can occur with infectious diseases, neoplasia, lipidosis, and artifactually with pathology of the intestinal tract and reproductive organs. Coelomic effusion can also mimic hepatomegaly on VD views.

Heart: Enlargement of the cardiac silhouette can occur with primary cardiomegaly and pericardial effusion. Increased opacity of major vascular structures, including the aorta, can occur with atherosclerosis.

Skeletal Structures

Some vertebrae are fused into notarium, synsacrum, and pygostyle. Some long bones of the pelvic limbs are fused (tibiotarsus, tarsometatarsus). Pneumatic bones (femur, humerus) are often relatively lucent when compared to other bones. The ulna is larger than the radius in birds.The shoulder girdle, composed of the coracoid, clavicle, scapula, humerus, a complex anatomic and functional region, is a common site of injury in raptors and other wildlife species.¹ Increased opacity of long bones in females commonly occurs secondary to reproductive activity (hyperostosis).

Upper Gastrointestinal Tract Contrast Study

Should be used more frequently than in cat or dog practice. It is useful for identifying alimentary tract lesions (e.g., obstruction, etc.) and essential in helping differentiate hepatomegaly from pathology of the gastrointestinal tract, reproductive tract and other coelomic organs.

 25 ml/kg 30% w/v barium

 25 ml/kg 1:1 iohexol:water (faster transit time than barium³)

 Rough estimates: 1–3 ml for budgie, 10–15 ml for cockatoo

 Timing - barium: 5, 30, 60, 90, 120 minutes and longer

 Timing - iohexol:water: 1, 5, 15, 30, 60, 90 minutes and longer

 Always obtain lateral and VD views for each

Summary

The ability to obtain quality radiographs and make accurate interpretations is essential for the avian practitioner. As part of the diagnostic process, knowledge of the unique anatomic structures of the avian patient is mandatory.

References

1.  Chitty J, Lierz M. BSAVA Manual of Raptors, Pigeons and Passerine Birds. Quedgeley, England: British Small Animal Veterinary Association; 2008.

2.  Dennison SE, Paul-Murphy JR, Adams WM. Radiographic determination of proventricular diameter in psittacine parrots. J Am Vet Med Assoc. 2008;232:709–714.

3.  Ernst S, Goggin J, Biller D. Comparison of iohexol and barium sulfate as gastrointestinal contrast media in mid-sized psittacine birds. J Avian Med Surg. 1998;12:16–20.