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An Urban Experience
more opaque than to be expected for a true pulmonary nodule of similar size. Pulmonary osteomas are punctate mineralized foci within the lung, especially seen in older dogs. These are small (1-2 mm) and are more opaque than pulmonary soft tissue nodules of this size. Skin nodules, nipples, parasites (ticks) on the skin and surface debris can mimic pulmonary nodules when superimposed over pulmonary parenchyma. Remedies include close examination of orthogonal radiographs to identify the “nodule”, physical evaluation of the patient surface, and marking of any super cial skin tags with positive contrast medium prior to repeating radiographs.
Radiology of the Abdomen
Technique: Unlike for thoracic radiographs, high contrast is desirable for an abdominal radiograph
to maximize margin de nition between soft tissue opaque organs and abdominal fat. This is achieved by choosing a technique relatively low in kVp. With very few exceptions, each radiographic study should include at least one lateral and a ventrodorsal view, and especially for evaluation of the gastrointestinal tract opposite lateral views are very valuable.
Anatomic Variations and Physiologic Status:
Optimally, animals should be fasted prior to a radiographic examination of the abdomen as a large amount of food within the stomach and faeces within the colon can obscure other abdominal organs, result in visceral crowding by displacing organs from their normal position, and create pseudo-lesions by superimposition of gastrointestinal contents over abdominal organs.
Serosal Margin Detail: Failure to choose adequate exposure factors may affect serosal margin detail
and may lead to a misdiagnosis of peritoneal effusion (underexposure or high kVp-low mAs technique) or pneumoperitoneum (overexposure). Serosal margin detail is greatly affected by presence of abdominal fat. Young animals have physiologically poor serosal margin detail as brown fat appears radiographically similar to soft tissue. Similarly, lack of abdominal fat in very thin animals may give the impression of abdominal effusion.
Liver: Deep chested dogs often have a subjectively small liver, and in some older dogs the liver becomes “saggy” resulting in the caudal ventral liver margin extending beyond the costal arch with maintained sharp margination and normal alignment of the gastric axis. These deviations from “normal” liver size should be evaluated in light of laboratory analysis  ndings.
Gastrointestinal Tract: On a right lateral view  uid within the stomach will accumulate in the pylorus which is frequently mistaken for a cranial ventral abdominal mass. A left lateral view will aid in distinguishing pylorus from mass as the normal pylorus will now  ll with air. Luminal contents within the gastrointestinal tract greatly affect its appearance. It is important to understand that
measurements of intestinal wall thickness on survey radiographs are unreliable as luminal  uid silhouettes with the wall which gives the impression of wall thickening.
Urinary Tract: Skin nodules/nipples and external debris superimposed over kidneys, retroperitoneal space or urinary bladder may mimic mineralization or calculi. The deep circum ex iliac artery arises ventral to the L5-6 vertebrae. Seen end-on it may mimic a ureteral calculus. Additional end-on vessels arising from the aorta are occasionally seen on digital radiographs and should also not be mistaken for pathologic  ndings.
Radiology of the Musculoskeletal System
Technique: High contrast radiographs are desirable
for the musculoskeletal system to highlight differences between fat, soft tissue and bone. Almost all indications require acquisition of at least 2 orthogonal views, and oblique views or special techniques such as stress views may be needed for full patient evaluation. “Mach lines” are an optical phenomenon which can be misinterpreted as  ssure lines. An important artefact to be familiar with in digital radiography is the “Ueberschwinger” or rebound artefact which appears as a dark halo around structures with a large density difference to surrounding tissues and which can mimic loosening of metallic implants.
Anatomic Variations and Physiologic Status:
There are numerous normal anatomic variations of the musculoskeletal system in small animals, and any potentially abnormal  nding has to be interpreted in light of history, signalment and clinical  ndings. Examples include vertebral anomalies (e.g., block vertebrae, transitional vertebrae
or hemivertebrae) and variability in conformation of the antebrachium between large breed and chondrodystrophic dogs. Open physes in young animals frequently lead to confusion when trying to identify the reason for a patient’s lameness. Nutrient foramina can be misinterpreted as fracture or  ssure lines. Purchase of a normal radiographic anatomy textbook, establishment of an in-house case library in which normal cases are stored for reference,
and obtaining comparison radiographs (either in a normal dog of similar age and breed, or of the contralateral limb
in the same animal) can all be helpful to develop a sense
of normal. Finally, degenerative changes are common especially in older dogs and may or may not be associated with clinical signs. Examples include spondylosis deformans and degenerative joint disease.
References/Suggested Reading:
1. Drost WT, Reese DJ, Hornof WJ. Digital radiography artifacts. Vet Radiol Ultrasound 2008;49 (1 Suppl 1):S48-56. Review.
2. Nuth EK, Armbrust LJ, Roush JK, Biller DS. Identi cation and effects of common errors and artifacts on the perceived quality of radiographs. J Am Vet Med Assoc 2014; 244:961-7.
3. Thrall DE. Introduction to Radiographic Interpretation. In: Textbook of Veterinary Diagnostic Radiology, 6th. Ed. Thrall DE, ed. St. Louis: Elsevier Saunders; 2013.
4. Thrall DE, Robertson I. Atlas of Normal Radiographic Anatomy and Anatomic Variants in the Dog and Cat. 2nd ed. St. Louis: Elsevier Saunders; 2015.

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