The Veteducation International Online Veterinary Conference 2011

Transcription

1 The Veteducation International Online Veterinary Conference 2011 Part of the Veteducation Live Online Web-Seminar Series The Artefacts of Life! With Dr Angela Hartman DVM Dipl. ACVR Massey University New Zealand August 2011 Dr. Angela Hartman 2011 Distributed with Permission by Veterinary Education Australia

2 Course notes: The Artefacts of Life: Common radiographic artefacts and variations of normal in small animals. Angela Hartman DVM, DACVR Massey University August 2011 Slide 1 The Artefacts of Life: Common radiographic artefacts and variations of normal Angela Hartman, BS, DVM, DACVR Veterinary Radiologist Massey University Many variations of anatomy or common radiographic artefacts are misinterpreted as lesions. This presentation is designed to prepare the practicing veterinarian to recognize these so that they do not divert you from an accurate radiographic diagnosis. Slide 2 Variations of normal Thanks to selective breeding, tremendous variation occurs amongst the canine species. It pays to have a background knowledge, radiographs of the contralateral limb or normal studies of various breeds with which to compare.

3 Slide 3 The similarities between breeds and species are far greater than the differences. From an imaging standpoint, basic radiographic principles can be used on any species with a high likelihood of providing a useful interpretation. As a radiologist, I interpret studies on all species except humans, and having normal studies with which to compare and applying my understanding of radiographic principles allows useful input even when species are unfamiliar. Slide 4 Pug Labrador Cat Selective breeding and species variation has led to a variety of radiographic appearances that are not necessarily abnormal for particular breeds. For instance, the absence of frontal sinuses in a Labrador would be alarming and possibly affect the expected use of a Lab, although this is normal in a Pug and other brachycephalic dogs. My generic image of a dog usually is a mid-sized Shepherd mix and this does not fit a pug or even a Mastiff, at least from a radiographic perspective. Familiarity, or a good normal comparison, is priceless. Slide 5 Neonatal Shar Pei Normal 3 month mid sized dog Normal 5 year GSD elbow Variation in anatomy also varies with stage of development. The apophyses and epiphyses are often invisible radiographically in neonatal patients because they are not yet ossified. Notice the lack of visualization of the anconeal process, olecranon tuberosity and the medial epicondyle of the humerus in the neonatal dog. The joints appear narrow in mature dogs, as compared to neonatal dogs, due to complete formation of the subchondral bone plate.

4 Slide 6 Physeal development 3 days 3 months 3 years Notice the incompletely ossified cuboidal bones of the carpus. The cuboidal cartilage structure is present, although the ossification centre is elliptical with the ossification being incomplete early in development. Also notice the variation in the physes of the distal radius. It is wide in neonatal dogs, has extensive metaphyseal sclerosis and periosteal bone flaring in juvenile and form a discrete sclerotic scar in young adults. The physeal scar diminishes with age in most dogs. Slide 7 Notice the variation of normal in the distal ulnar physis of small breed dogs. In most rapidly growing dogs, the physis is lucent with the distal metaphysis being very densely sclerotic (calcified cartilage and primary spongiosa). This gets remodeled to trabecular and cortical bone leading into the diaphysis with the trabecula in the medulla of the bone appearing more lucent than the metaphysis. Only the chondrodystrophied small breed dogs normally have a lucent line through their metaphyseal region. In any other type of dog, a lucency in this area would be abnormal and be suspicious of HOD or trauma. Slide 8 Physeal and epiphyseal development Neonatal dog Normal 2 month old cat 3 month old Labrador During epiphyseal ossification, the leading edge of the ossification centre can appear rough and irregular. This can be misconstrued as OCD or septic arthritis if the patient has effusion or lameness. Caution in interpreting the articular surface of dogs should be utilized until they have subchondral bone has clearly developed. Remember, osteolysis from OCD or sepsis is usually multifocal or focal not widespread in a joint.

5 Slide 9 Neonatal pelvis One month old canine Old dog (bone mets) It can be difficult to assess a juvenile pelvis for signs of femoral head subluxation due to the normal lack of complete ossification of the dorsal acetabular rim. Femoral heads can appear subluxated due to this lack of ossification. Ileal sutures can also appear similar to fractures through the acetabulum. Interpreting the non-lame hips for conformational features of dysplasia should wait until they are skeletally mature. Sometimes severe cases are obvious earlier. Distraction methods are useful for early identification of loose hips which are predisposed to arthritis. Slide 10 Slide 11 Starting with an ACCURATE exposure, both kvp AND mas must be changed to improve contrast or latitude 40 kvp 40 mas 85 kvp 3 mas Which is best? Normal thorax 125 kvp 0.5 mas Thorax When using film/screen as a detector, a diagnostic exposure can be accomplished at a variety of kvp settings by adjusting the mas. If your Xray generator is capable of high kvp settings, then high settings (75-85 in small, in medium, 100+ in large dogs) should be used to optimize the fine detail of the lung. This high latitude setting is most useful due to the inherent contrast of the thoracic tissues and the need to document them all in one exposure setting. With a high kvp setting, there is a normal interstitial pattern of the lung due to the epithelial structures, vessels, nerves and lymphatics of the tissue. This varies with exposure settings or variety of digital detector. Also notice the appearance of the heart in this mid-sized dog. The dorsoventral height of the heart of a midto large breed dog should take up no more than 60% of the height. On the DV, the heart should be no wider than 50% of the width at the level of the ninth rib.

6 Slide 12 Breed conformation Normal Dachshund In normal chondrodystrophied dogs, the dorsoventral height of the thorax is diminished and the normal heart appears to take up 75% or more of the thoracic height. On the DV view, the normal heart often appears more round and takes up more than 50% of the thoracic width. These rules of thumb can fail in dogs with a shallow dorsoventral dimension. These dogs often measure the same in DV as they do laterally when measuring for radiographs. Slide 13 Breed conformation Normal German Shepherd Normal Small Breed It is common for right sided cardiomegaly to be overinterpreted in small breed dogs based upon sterna contact. Remember that sternal contact is as much a factor of the degree of sternal concavity and dorsoventral thoracic height as it is heart size. Remember, if the right heart is big it will appear big on both views. Slide 14 Normal deep chested dog With deep chested dogs, the heart often appears small in the thorax, appearing suspended from the carina. The cardiac apex may not fully reach the sternum on the lateral view. Due to this upright position, the heart appears round on the DV view normally.

7 Slide 15 Interstitial pattern Edema from near drowning 5 month Poodle An increased interstitial pattern from disease can occur commonly in vet patients. Determining if the observed interstitial pattern is a normal variation versus pathology can be extremely challenging if only present to a mild or moderate degree. Loss of the normal vascular pattern and the loss of detail of the cardiac silhouette can assist in correctly interpreting interstitial lung disease. Slide 16 Fat dog Normal variations can masquerade as interstitial lung disease especially in obese patients. The Xrays are attenuated and scattered by the increased abdominal wall fat. Also, the patient is poorly inflated due to Pickwickian syndrome (decreased caudal diaphragmatic excursion due to increased abdominal fat). Slide 17 Inspiratory Expiratory Notice the difference in opacity of the lung in a dog that is fully inspired versus partial expiration. When assessing the interstitial opacity of any lung, first noting the degree of thoracic inflation is necessary to know what degree of lung interstitial opacity is due to degree of lung inflation. If using a film/screen system, also determining if the apparent increased interstitial pattern is due to underexposure is necessary for an accurate interpretation.

8 Slide 18 Degree of inspiration In this dog with poor thoracic inflation due to collapsing trachea and obesity, the lung appears artifactually increased in interstitial opacity. Collapsing trachea in a dyspnea, coughing dog Slide 19 Tracheal deviation Deviation of the trachea in the cranial mediastinum can be a normal finding in dogs with their head ventrally positioned or if a mass is pushing the heart cranial from behind. If a mass is present causing the tracheal deviation, there will be increased opacity of the cranial mediastinum underneath the deviated trachea. Slide 20 Tracheal deviation Also, the cranial mediastinum will appear wide on the VD view. The tracheal deviation to the right is clearly visible on the VD view when a mass is present. Normal Cranial mediastinal mass

9 Slide 21 Pleural space The fat cat fake out Now considering the pleural space, there can be artefactual appearances of fluid that occur due to abundant pericardial fat. Notice that the cardiac silhouette can be seen despite the abundant tissue in silhouette with the heart. That is due to the differential attenuation of Xrays between fat and soft tissue/fluid. Learn to expect the fat opacity cranial to the heart on the lateral thoracic view of fat cats. Slide 22 Pleural space Ventrodorsal Dorsoventral This is the same cat as above. If the increased thoracic opacity was due to pleural effusion, the fluid would move between VD and DV positions giving a very different appearance between views. Notice that the DV and VD does not vary in appearance when pericardial and mediastinal fat are causing the increased opacity. Slide 23 Pleural space Another pleural disease which can be mimicked by artefacts is pneumothorax. This is a very obvious case of pneumothorax with classic radiographic findings of air under the heart (mediastinal shift of the heart due to the air shifting to the non-dependent hemithorax), lung lobes retracted from the thoracic wall and lucent regions outlining the lung margins compatible with pleural air.

10 Slide 24 Pleural space Notice that the lung margin has a discrete lobation visible between the right middle and caudal lung lobes similar to pleural fissure lines in pleural effusion. This lobation pattern will nearly always be present when the lungs are retracted from the wall due to pleural disease. Lung infiltrates and skin fold artifact will not have this lobation pattern. Slide 25 Pleural space Deep chested dog artifact This is a deep chested dog. On many detector systems, to penetrate the mid thorax on the DV view, the periphery of the lung gets overexposed and no visible pulmonary vasculature can be seen. This can be mistaken for pneumothorax. Notice there is no lobation pattern seen associated with the thicker, more opaque portions of the lung. Slide 26 Pleural space Pseudopneumothorax (i.e. fakeout) Also occurring in deep chested dogs, air under the heart can occur as a normal finding especially in the left lateral projection. When a patient is placed in lateral recumbency, the dependent lung collapses allowing the heart to swing very close to the thoracic wall. Since the cardiac apex is already leftward positioned, when this recumbency atelectasis occurs, the cardiac apex shifts further towards the left thoracic wall away from the sternum and causes a rounded appearance to the heart that can mimic cardiomegaly and pneumothorax.

11 Slide 27 Hypovolemia Thoracic Trauma Severe pneumothorax Over the years, I have been tricked by a few hypovolemic patient s whose thorax mimicked pneumothorax. Notice on the right in the patient with severe pneumothorax, the opaque, collapsed lobes will always be visible if a pneumothorax is present. The hypovolemic patient has no vasculature visible, although no collapsed lung lobes are visible either. Slide 28 Normal young cat thorax In cats, the heart is angled at an approximately 65 angle to the dorsoventral plane. This is normal. This elongates the heart on the VD view. As cats age, this angle increases with more sternal contact visible and an apparent lengthening of the aorta. Cats usually appear well inflated and have very lucent lungs. Slide 29 Atelectasis Recumbency atelectasis is a common artifact that greatly compromises the diagnostic quality of a thoracic radiographic study. If radiographs are performed in anaesthetized patients, the recumbent lung lobe will collapse. Collapse is evident due to mediastinal shift of the heart and increased opacity of the collapsed lobe. Infiltrative disease can be obscured due to the lack of contrast resolution in this lobe. Notice the lobar sign overlying the heart in the upper (left lateral) projection when the collapsed lung is placed in a non-recumbent position. Placing the patient sternal or in left lateral positioning and ventilating the patient can

12 reinflate the lung and the radiographs should be retaken to yield the maximum diagnostic results from the study. Recumbency atelectasis can happen fast and resolves fast with positive pressure ventilation or positioning the collapsed lung in a non-dependent position. Slide 30 Metastasis check for oral melanoma This is a metastasis check for oral melanoma. Notice the endotracheal tube (anaesthetized patient), leftward medistinal shift of the heart and increased opacity of the left cranial lung lobe. This is non-diagnostic for a metastasis check due to the inability to assess all of the lung lobes. This represents collapse of the caudal subsegment of the left cranial lung lobe due to recumbency atelectasis. Slide 31 Metastasis check sedated only The same patient was awakened from anaesthesia and was sedated for a study the following day. Notice the reinflated lung lobe and the resolution of the mediastinal shift. The mediastinal shift is key to interpreting if lung opacity is due to infiltrates or collapse.

13 Slide 32 Allergic bronchitis with lung lobe collapse Notice in this cat there is leftward and cranial medistinal shift of the heart. Also, there is an elliptical shaped opacity overlying the pulmonary hilus on the right lateral view. This is a classic sign of lung lobe collapse of the left cranial lung lobe. This patient is dyspneic and has an airway pattern concurrently typical of allergic bronchitis. Lung lobe collapse is common in feline allergic bronchitis although it is usually the right middle lobe that collapses. Slide 33 Slide 34 Bronchopneumonia kitten Bronchial mass This is a very dyspneic, geriatric, feline patient with a chronic cough. Notice the leftward mediastinal shift of the heart and the increased lung opacity of the left lung lobes. This is lung lobe collapse. Also notice the apparent mass overlying the heart on the lateral view. If you look closely, this mass is invading the distal trachea causing a right mainstem bronchial obstruction and secondary collapse. Recognising lung lobe collapse is vital in interpretation of these challenging cases. In this kitten with bronchopneumonia, there is increased lung opacity of the right cranial and caudal subsegment of the left cranial lobe. No volume loss is noted. Air bronchograms are seen typical of alveolar infiltration. Air bronchograms can be seen with atelectasis although they appear bunched or collapsed together due to volume loss.

14 Slide 35 Slide 36 Osseous metaplasia (osteomas) The abdomen This patient has pneumonia seen cranial to the heart on the right lateral view. There is an additional nodular pattern visualized throughout the lung. These small nodules are easily visualized despite their small size. These are too opaque to represent soft tissue nodules and metastasis rarely mineralize. For this reason, they are diagnosed as osseous metaplasia of the lung also known as pulmonary osteomas. These are benign nodules that are not associated with disease. They are seen in medium to large breed dogs especially Collies. Abdomen 40 kvp 40 mas 85 kvp 3 mas 125 kvp 0.5 mas With film/screen systems, the energy of the Xray will affect the contrast resolution of the image. Low Xray settings tend to discriminate between fat and soft tissue better than high energy. The abdomen, as opposed to the thorax, is inherently low contrast so we have to shoot the radiograph to increase contrast. This is a non-issue in most digital systems with the Xray energy chosen to optimize the detector efficiency instead of patient X-ray interaction. Slide 37 Normal abdomen In the normal dog taken at an appropriately low to mid kvp, most parenchymal organ serosal surfaces should be visible in the peritoneum. The kidneys are often not seen due to overlying bowel gas in dogs. The spine can also be interpreted although, if spinal disease is suspected, a lower kvp, collimated image would improve bone quality even more and this should be done to optimize the chance for accurate diagnosis.

15 Slide 38 Neonatal abdomen Due to the type of fat and the presence of a small amount of free fluid in the abdomen of neonatal and juvenile patient s, poor serosal detail is normal. Mild abdominal distension is also normal. Slide 39 Lean dog abdomen The fat surrounding the soft tissue organs of the abdomen is what gives contrast resolution. If the patient is lean, then poor serosal detail is expected. I assess body condition by viewing the epaxial muscles of the lumbar spine and the amount of subcutaneous fat along the caudal thoracic wall on the VD view. Slide 40 Fat dog abdomen Fat ol Labrador with stifle and LS concerns Fat dogs can be hard to penetrate with standard film/screen systems and, there is a lot of forward scatter so we tend to get poor serosal detail despite voluminous abdominal fat in some dogs. Many digital systems use scatter reduction post processing software and therefore these digital images tend to have less image degradation secondary to obesity.

16 Slide 41 Neonatal puppy abdomen When animals have fluid in their abdomens, the serosal detail is diminished and the abdomen tends to distend with the degree of both dependent on the amount of fluid present. Poor serosal detail Slide 42 Fat cat abdomen Exquisite serosal detail Fat cats tend to compartmentalize their intra-abdominal fat and it can act like a mass. Notice the dorsal elevation of the liver by the falciform fat and the ventral deviation of the colon by the retroperitoneal fat. Cats are too small to allow much forward scatter so fat provides exquisite serosal detail. Slide 43 Acutely vomiting cat When a foreign body is mineral opaque, it is obvious due to enhanced contrast resolution with the surrounding soft tissue and fat. Proximal GI obstructions can be less obvious when the obstruction is radiolucent. No significant intestinal dilation is seen with proximal GI obstructions.

17 Slide 44 Stomach This vomiting dog has obvious gas distension of the stomach and a small amount of metal opaque gravelling in the region of the stomach. Gravelling is a finding to pay close attention to because it is usually just upstream of the obstruction. See the offending foreign body? Slide 45 Stomach Pyloric ball foreign body causing gastric outflow obstruction See the radiolucent ball at the entrance to the pyloric canal now? The pyloric contrast is dissecting around the ball when there is a strong wave of peristalsis orad to the point of obstruction. Just a wisp of duodenal contast is seen overlying the fundus. Slide 46 Recommended text Veterinary Diagnostic Radiology D.E. Thrall Publisher: W.B. Saunders Have plenty of resources at hand. Online resources are also available. Two are listed below. Normal radiographs: _anatomy/index.html Radiographic case library (norm and abnormal) t.aspx

18 Slide 47 Thank you! Very interesting case presentations: