CHEST X- RAY ALGORHITHM - GUIDE BASIC CHEST X- RAY INTERPRETATION FRONTAL VIEW

Transkript

1 CHEST X- RAY ALGORHITHM - GUIDE Remember to go through all steps of the algorithm to avoid overlooking pathology! BASIC CHEST X- RAY INTERPRETATION Air appears black. Tissue appears white the higher the density, the whiter it appears. X- rays is a two- dimensional illustration of a three- dimensional body. You are not able to recognize the left and right side of the human body in a lateral X- ray. Therefore, you ll have to use your knowledge of the human anatomy to assess left and right positions. 1) Identify patient Start by checking that the chest X- ray belongs to the patient you are examining. 2) View and quality FRONTAL VIEW To interpret the image correctly you need to know how the chest X- ray has been taken. It will usu- ally be written on the X- ray how it is taken (standing/supine position, PA/AP view, right/left side): a) Has the patient been standing or lying down (supine position)? Standing is the golden standard. You have to be careful when interpreting an X- ray of a patient in supine position because the quality of the chest X- ray is not as good: the heart might look larger, the lung structure more rough, and it is hard to ensure maximal inspiration. b) Is it a posterior- anterior (PA) view or an anterior- posterior (AP) view? PA view is the standard. It means that the X- ray beam passes through the patient from posterior to ante- rior. A supine chest X- ray is always AP. If the image is AP the mediastinum and heart seem enlarged. c) Identify the right and left side of the patient. The patient s right side needs to be on the left side of the image. d) Is the image rotated? The spinous processes must be centered on the vertebrae and the sternum must be right in front. The clavicles need to be leveled. e) Was the image taken during full inspiration? You should be able to identify the 10 upper posterior ribs. Now you are finally ready to interpret the frontal view of the chest X- ray 3) Mediastinum and trachea Locate the trachea, which you will find in front of the spine as an air- filled tube. It needs to be in the center of the picture but might diverge slightly to the right because of the aortic arch (Image 1). 1

2 The important and recognizable structures of the mediastinum are the heart, ascending and de- scending aorta, the aortic arch and lymph nodes (Image 1). Displacement, unclear boarder lines or abnormal densities might indicate disease. 4) Heart Again, look for clear contours of the heart. Abnormalities in the lungs can cover up the edges of the heart. Next, look for the cardio- thoracic ratio which is the cardiac width divided by the thoracic width. The cardiac width should be between 1/3 and 1/2 of the thoracic width on a PA projection. Re- member that you cannot rely on the heart size on an AP projection! IMAGE 1 5) Diaphragm (subdiaphragm) Check if each hemi- diaphragm appears as a well- defined, rounded, domed structure. The right hemi- diaphragm is slightly higher than the left due to the liver. The left hemi- diaphragm should be visible behind the heart. The gastric ventricle or the intestines will be visible as dark spots below the diaphragm if they are filled with air (Image 1). Be aware that a black rim of air underneath the diaphragm is a sign of abdominal pathology, pneumoperitoneum (Image 2). IMAGE 2 2

3 6) Costophrenic angle Locate the costophrenic angle where the diaphragm and the chest wall meets. It should be clear and sharp on both sides and forms an acute angle (Image 1). 7) Hilar region Assess the hilar regions by checking the position, density, and size. The left hilum is usually higher than the right. The density and size should be similar on each side (Image 1). Differences in size and density are indications of an underlying pathology e.g. enlarged lymph nodes. 8) Lung fields Divide each lung into three zones to assess the lung fields: an upper, middle and lower zone. Be aware that these zones do not equate the lung lobes! Compare the right and left of each zone and look for any asymmetry that is not explained by the normal structures: Is an area of the lung either too black or too white? Is there an area of the lung with a different tissue structure? Remember that some pathology might affect both lungs symmetri- cally so keep in mind the look of a normal chest X- ray. Here are some important things to look out for: IMAGE 3 a) Pneumothorax: 1) Follow the chest wall from the costophrenic angle and to the apices. Does the lung tissue reach the wall all the way, or do you find com- pletely black areas? A pneumothrorax can be any- thing from a thin black rim (Image 3) to an entirely black lung field. 2) Is the mediastinum pushed to- wards the opposite site as a sign of a tension pneu- mothorax? IMAGE 4 b) Consolidation and atelectasis: Both conditions make the lung tissue dense hence whiter (Image 4). An atelectasis is collapsed lung tissue. When the lung tissue or the small airways are filled with mate- rial/liquid it can be a sign of e.g. infection or edema. It can be hard to differ the two but look for the air bronchogram characteristic for consolidation. In ad- dition, the atelectasis might pull the surrounding structure such as the mediastinum and diaphragm, whereas a consolidation pushes them away. IMAGE 5 3

4 c) Pleural effusion: A pleural effusion is an excess of fluids in the pleural cavity. It accumu- lates at the bottom part of the cavity due to gravity (Image 5). A pleural effusion might push the surroundings like the consolidation. d) Lung stasis and edema: Lung stasis is character- ized by enlarged vessels visible all the way to the chest wall. Look for apical flow shift normally the vessels are more apparent in the lower lung zones. Edema is the next step when the fluid fills the lung tissue as well giving the lung fields a cloudy appearance (Image 6). e) Emphysema: Due to destruction of the lung tis- sue, the lungs will look darker. To compensate you will often find a barrel shaped thorax and the diaphragm flattened with a less acute costo- phrenic angle. 9) Ribs IMAGE 6 Follow the edges of each rib, looking for signs of fractures or any dark areas in the bones. 1) Diaphragm: LATERAL VIEW Identify the right and left hemi- diaphragm. The right hemi- diaphragm is situated higher than the left due to the liver. 2) Costophrenic angle As in the frontal plane the costophrenic angles should be clear and sharp. Remember to look at both the anterior and posterior angle. The posterior angle is lower than the anterior and effusions will often ac- cumulate here first (Image 7). 3) Retrosternal region IMAGE 7 Look at the area between the sternum and the heart. It should be a slim rim. A larger dark area indicates emphysema while a white area indicates a consolidation. 4) Hilar region Check the density (Image 8). 4

5 5) Lung fields Compare the lung fields in front and above the heart with the ones behind the heart. They should have equal density (Image 8). 6) Vertebrae The vertebrae should get darker as you follow the spine caudally. Look for the shape, size, collapsed vertebras and areas that are darker or lighter than the surrounding bone (Image 8). IMAGE 8 One last thing: remember the patient! Don t get lost in the X- ray 5