Avian radiographic normals (Proceedings)

Proper positioning is critical. Use of anesthesia and/or restraint boards will reduce the human exposure to radiation, but may pose increased risks to the compromised patient. These risks should be assessed prior to obtaining radiographs.

For a ventro-dorsal radiograph, proper positioning will be reflected by alignment (superimposition) of the vertebral column and the carina of the keel. To thoroughly examine lateral aspects of the cranial and mid-coelom, the wings should be extended symmetrically. The acetabula and scapulae should be symmetrical.

In positioning for the lateral position, the carina of the keel should be parallel to the table. On viewing the radiographs, the acetabula, scapulae and coracoids should be superimposed.

Digital radiography has made communication between practitioners, referring veterinarians and radiologists much more efficient. The image detail with digital radiology is not as great as with some available films but there is increased image contrast and ability to manipulate the image. However, with some structures in smaller birds, the greater detail inherent in mammography and dental films still has advantages.

Identifying normal structures on avian radiographs is the first step toward utilizing these for diagnosis of illness or injury. A list of structures that will be identified in radiographs and in line drawings during the Power Point presentation follows. Some bullet points regarding these structures are included below:

Skeletal:

     1. Head/skull

          a. Scleral ossciles of the orbit

          b. Jugal bone

     2. Hyoid apparatus Shoulder girdle

          a. Coracoids

               i. (Commonly fractured in free-ranging raptors)

          b. Clavicles – In psittacines these are not fused into a furcula

          c. Scapulae

          d. Sternum (keel)

          e. Carina of the keel

     3. Thoracic limb

          a. Humerus

          b. Radius/ulna

          c. Radial and ulnar carpal bones

          d. Digits

               i. Alular (I) or bastard wing

               ii. Major (II)

               iii. Minor (III)

     4. Vertebrae

          a. Cervical (ribs present)

          b. (Fused notarium present in some species)

          c. Thoracic (ribs present)

          d. (Synsacrum)

          e. Free caudal vertebrae

     5. Pygostyle (fused caudal vertebrae) Pelvic Limb

          a. Femurs

          b. Tibiotarsi

          c. Tarsometatarsi

          d. Digits (numbered one through four in psittacines - each containing one more phalange than the digit number)

Cardiovascular

     1. Heart and great vessels including the aorta

          a. Average measurement parameters

Respiratory

     1. Trachea

     2. Syrinx

          a. difficult to visualize – usually between 2nd and 3rd thoracic vertebrae

     3. Lungs

          a. honeycomb pattern and location

          b. Air sacs (borders of ii-iv below only visible if abnormal)

               iv. cervicocephalic

               v. clavicular

               vi. cranial thoracic

               vii. caudal thoracic

               viii. abdominal

Gastrointestinal

     1. Ingluvies (crop) (in species where present)

     2. Esophagus

     3. Proventriculus

     4. Isthmus

     5. Ventriculus

     6. Intestines

     7. Cloaca

Other organs

     1. Liver (note cardio-hepatic waist and species variation)

     2. Spleen

     3. Uropygial gland (when present)

     4. Note: Pancreas is not radiographically visible but is present in the duodenal loop

Species /gender differences

     1. Macaw and some cockatoos - smaller liver

     2. Ducks and geese

          a. Syringeal bulla in males

          b. Reduced cardio-hepatic waist

     3. Penguins bifurcated trachea

     4. Trumpeter swan redundant trachea

     5. Testicles

     6. Ovaries

     7. Pneumatic bones (with species variation)

     8. Hyperostotic polyostosis (estrogen stimulation in females)

Thanks to Dr. Jon Rubinstein for use of material from his presentation at the Florida Veterinary Medical Association Conference, 2009 and to Dr. Majorie C. MCMillan for the incredible radiographic examples provided in her chapter "Imaging Techniques" in Avian Medicine, Principles and Application, currently available through Iowa State University Extension.

References/recommended reading

Silverman S, Tell LA, Radiology of Birds: An Atlas of Normal Anatomy and Positioning, Saunders/Elsevier, St. Louis, MO, USA, 2010.

Helmer P, Advances in Diagnostic Imaging, in Clinical Avian Medicine, Harrison GJ, Lightfoot TL, (eds) Spix Publishing, Lake Worth, FL, USA, 2006

Rubel GA, Isenbugel, Wolvekamp P, Atlas of Diagnostic Radiology of Exotic Pets, Saunders, Philadelphia PA, 1991.

Smith SA, Smith BJ, Atlas of Avian Radiographic Anatomy, Saunders, Blackberry, VA, USA, 1992.