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Author: Gretchen Kaufman, DVM
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OCW Zoological Medicine 2008
Avian Radiology (2008)
G. Kaufman, DVM
Cummings School of Veterinary Medicine at Tufts University

1. Learning Objectives

  • Understand the clinical application of diagnostic imaging in avian medicine

  • Be familiar with the normal radiographic anatomy of the bird

  • Be able to recognize organ displacement or enlargement in a lateral or VD radiograph of the body of a bird

Color coded topics indicate some of the learning objectives that the student should become familiar with.

2. Introduction

Diagnostic radiology is one of the most important diagnostic tools in avian medicine. The physical examination of the bird is not nearly as informative as it is in a mammal. The clinician is unable to palpate many internal organs, such as kidneys, loops of bowel, spleen, abdominal masses, etc. Auscultation in the bird is also very limiting due to the anatomy of physiology of the bird respiratory tract. In contrast, radiographic evaluation of the abdominal organs and especially the respiratory tract of the bird is perhaps more informative than it is in mammals. The bird's system of air sacs provides enhanced contrast in areas poorly visualized in mammals. Consequently the avian radiograph is often part of a routine workup involving a bird with somewhat obscure clinical signs, as well as in cases where radiographs are directly indicated.

3. Radiographic Technique

3.1. Equipment

Standard modern radiographic equipment is perfectly adequate for producing avian radiographs. The radiographs can be greatly enhanced with the use of high detail film/screen combinations however. Dental and mammography radiographic equipment can also be used to produce very high quality films on very small animals.

Positioning equipment may consist merely of "bird-friendly tape" (nylon, paper, or masking tape which will not damage the feathers) used to tape the bird in position on the cassette. However, the use of bird positioning or restraint boards make the process much easier and reduce the time required to correctly position the animal. Sand bags can be used very carefully in conjunction with tape.

3.2. Positioning

Accurate positioning of the patient is absolutely essential for correct interpretation of avian radiographs. Any deviation from near perfect alignment will produce artifacts and lead to misinterpretation or render a film completely unreadable. Conventions have been developed for correct positioning which allows some very specific information to be taken from the radiograph. In general, as in mammals, two views are taken in most situations.

Positioning an animal for the evaluation of distal extremities is very simple. One must simply be sure the body part of interest is on the plate and in the field of exposure! Two views may or may not be required, but are desirable. For very quick extremity views, manual holding the animal may be the most efficient technique. Positioning a bird for internal or "whole body" radiographs is very precise. Two views are always taken, unless one is looking for an obvious finding such as lead particles in the GI tract. A standard ventral-dorsal (VD) view requires an animal to be fully stretched out with the keel overlying the vertebrae. The right lateral view is usually taken as the complimentary view. In this position the animal must again be stretched out with the wings held back. The acetabulum and shoulders should fall directly one on the other, with the legs slightly scissored.

Anesthesia is used by many clinicians to reduce the stress on the bird and to assist in accurately positioning the patient. In general this is not absolutely necessary and is a matter of personal choice. Isoflurane anesthesia is by far the safest anesthetic to use for taking radiographs since the induction and recovery time are both very rapid and there is minimal compromise of even the very ill patient. Anesthesia is generally indicated in birds that are very depressed and likely to succumb to stress, birds that are extremely high strung and cannot be adequately restrained manually, birds with fractures, or in cases where cervical or head radiographs are required.

3.3. Technique

Specific techniques will be dictated by the instrument being used. In general all avian films are taken as " table-top" technique with the patient positioned directly on the radiographic plate. MaS and Kvp settings are at the lowest end of the scale since the subjects are all very small. Due to the rapid respirations and possible fine muscle movements, exposure time should be minimized to avoid movement artifact or blur.

Sample Radiographic Technique for Birds

Animal/Size

MS

KVP

Comments

Canary/Finch

32

42-45

Filter out, table top, high detail

Parakeet

40

50

High detail, table top

Cockatiel/Sm. parrot

50

54

High detail, table top

Cockatoo/Lg. parrot

64

58

High detail, table top

4. Radiographic anatomy

Radiographic anatomy of the avian skeleton is very straightforward. Consult avian anatomy review material and radiograph review material.

Radiographic anatomy of the internal structures of the bird is complicated and will be reviewed in class. Since the bird does not have a diaphragm ( only mammals have diaphragms ), there is no true division of thoracic and abdominal structures. However, for the sake of organization we will be considering the coelom to be divided into "thoracic" and "abdominal" regions. One must always remember, however, that this division is not real and that cross-over between these two areas is common. Birds and reptiles might be considered to have a superior design without a diaphragm. This particular feature gives them the option of allowing something from the "abdomen" to expand easily into the space usually occupied by the respiratory system (air sacs), without necessarily causing major compromise.

Avian radiographic anatomy of the "thoracic" region

STRUCTURE

VIEW BEST VISUALIZED

cervico-cephalic air sacs

both views

clavicular air sacs

VD view

cranial thoracic air sacs

both views

caudal thoracic air sacs

both views

abdominal air sacs

both views

lungs

lateral view

heart and great vessels

lateral view

trachea and syrinx

both views

esophagus

lateral view

Avian radiographic anatomy of the "abdominal" region

STRUCTURE

VIEW BEST VISUALIZED

proventriculus

lateral view

gizzard/ventriculus

both views

intestines

both views

liver

both views

spleen

lateral view

gonad/adrenal

lateral view

kidney

lateral view

5. Ultrasound

The use of ultrasound in birds is becoming more common. One major impedance is the great deal of air present throughout the bird. Air interferes with penetration of the ultrasound beam and renders this technology useless in many cases. However, very specific sites can be used to visualize internal structures. The best "window" is through the liver , just under the sternum. In cases of disease, particularly involving masses or fluid accumulation which obliterates an air sac, ultrasound is very useful. Ultrasound is most often utilized to assess problems related to reproductive disorders in female birds. Ultrasound guided biopsy of the liver is also possible.

6. Radiology review

A radiology review will be presented in class.

7. References and Resources

7.1. Resources mentioned in the text

Silverdust Bird Positioner, Silverdust, PO Box 159, El Branada, CA 94018.

An Avian restraint and positioner is also available from Henry Schein Inc., 5 Harbor Park Drive, Post Washington, NY 11050

Miami vise restraint device, Veterinary Specialty Products, Inc. PO box 812005 Boca Raton, FL 33481, (800) 362-8138. www.vet-products.com

7.2. Texts and Articles

Altman, Robert B., et al. Avian Medicine and Surgery . Philadelphia. W.B. Saunders Co., 1997. Chapter 13, 14

Harrison, Gregg J. and Teresa L. Lightfoot. Clinical Avian Medicine . Palm Beach, FL : Spix Pub., c2006. Chapter 25.

Krautwald-Junghanns, M.E. et al. Diagnostic use of ultrasonography in birds. Proceedings of the 1991 Annual Conference of the Association of Avian Veterinarians, Chicago, Illinois, September 23-28, 1991, pp.269-175.

McMillan, Marjorie C. Avian radiology. In Petrak, M.L . Diseases of Cage and Aviary Birds . 2nd ed. Philadelphia: Lea & Febiger, 1982, pp.329-360.

Nordberg, Cynthia, et al. Ultrasound examination and guided fine-needle aspiration of the liver in amazon parrots ( Amazona species ), Journal of Avian Medicine and Surgery , 14(3), 2000: 180-184.

Ritchie, Branson W., et al. Avian Medicine: Principles and Application . Lake Worth, Fla., c1994: Chapter 12.

Rubel, G. Alexander, et al. Atlas of Diagnostic Radiology of Exotic Pets . Philadelphia: W.B. Saunders Co., c1991

Smith, Stephen A., and Bonnie J. Smith. Atlas of Avian Radiographic Anatomy . Philadelphia: W.B. Saunders Co., c1992.

Zebisch K, Krautwald-Junghanns ME, Willuhn J. Ultrasound-guided liver biopsy in birds. Veterinary Radiology & Ultrasound , 45 (3), 2004 : 241 - 246.