OSCE: Learning chest X-ray

X-ray is a form of ionizing radiation having more energy than UV waves passed through patient and onto a detector mechanism, which produces image. Chest radiography is most commonly done procedure in critically sick children. Thus, a basic knowledge of chest radiograph interpretation is essential for intensivist. If we follow the systematic approach for interpretation, we will not miss the diagnosis. Variable size of mediastinum in same child may pose difficulty in assessment. Thymus grows until puberty but radiologically visible up to three years of age. Three classical signs have been described while reading thymus structure. These are wave sign, sail sign and cardio-thymic incisure. During stress state in children thymus size may reduce in size and can grow ≥50% once stress is removed. In children film taken in supine position and AP view in expiratory phase show heart enlargement. One third of heart is present on right side from midline and two-third on left. Trachea proximal to subglottic area show bilateral convexities “described as shouldering of air column” and distally the diameters remains constant. During tracheal inflammation this shouldering is lost. Due to less space in upper mediastinum, vessels may indent the trachea. Because of large size and flexibility of trachea in small children below 5years angulation may be seen. Trachea may be physiologically deviated to right side. Tracheal narrowing beside above-mentioned reason is always abnormal. Left hilum is higher than right hilum. Arteries and veins branch vertically in upper and lower lobe and also upper lobe vessels have smaller diameter. Right dome of diaphragm is higher than left (1cm approximately). Age specific changes are appreciated by reading developmental anatomy. Q. What are various imaging modalities of thorax in children? Answer: Various modalities are; Conventional chest ray: Conventionally PA and lateral view are preferred. The distance from source is usually kept by 6 feet and kilovoltage (140kVp) radiation. Portable chest x-ray: During portable x-ray longer duration of exposure is required. Distance usually kept is 40 inches. This will change magnification of structure (Heart by 15-20% and decrease in lung volume due to shift of diaphragm). Digital radiography: Increased dose efficiency and quality image but poor spatial resolution. Dual-energy subtraction and digital tomosynthesis are more advanced techniques. Ultrasound: Preferred for assessment of fluid, air Computed Tomography and High-Resolution Computed Tomography Magnetic Resonance Imaging Positron Emission Tomography Ventilation/Perfusion Lung Scanning Diagnostic Pulmonary Angiography Thoracic Needle Biopsy Percutaneous Catheter Drainage Q. What are the positions or view for x-ray chest? Answer: Various position or views are: Principle is to keep site in examination close to the film. Postero-anterior View (PA) or frontal view: Most commonly used with low radiation exposure Antero-posterior View (AP): If scapulae overlap the lung, picture is AP and also if clavicle projected over lung field. Level of diaphragm is higher in AP view compare to PA view. Lateral View: Rarely used with higher dose of radiation, helpful in analysing posterior costophrenic and lower lobe area Obliques View Apical Lordotic View: X-ray beam is angled superiorly 15-20 degree Penetrated postero-anterior Inspiration / expiration postero-anterior: Expiratory film to assess air trapping Q. What is best position or view for x-ray chest? Answer: Best view is PA taken in standing position keeping hands on posterior aspect of hip, elbow rolled forward, shoulder touching the x-ray film to keep scapula away from lung fields. Also, film size should be adequate to cover lateral lung field, dome of diaphragm during inspiration, and 5-8cm above patient shoulder. The size of heart and pulmonary vessels is related to distance from film. Pulmonary vessels are not equally perfused in standing position. Supine position causes accentuation of apical and upper zone vessels. Apical zones seem smaller from clavicle in supine position. Depth of respiration and phase of respiration also contributes to size of heart and pulmonary vessels perfusion. In children below 5years AP is common. Thus, PA view is superior over AP view. During AP view smaller film-focus distance also contributes to magnification. Also, during supine position higher position of diaphragm contributes to cardiac enlargement. But in intensive care settings AP view taken commonly. Lateral radiograph if needed is taken from right to left beam projection. The rays should be projected at the level of fourth thoracic vertebra in midline in PA view and sternal notch in AP view at right angle during inspiration at a distance of 180-200cm approximately. Q. What are various pattern of chest diseases? Answer: Congenital Inflammatory: Bacterial, viral, fungal, parasitic Traumatic Neoplastic Vascular Idiopathic Iatrogenic Q. Describe radiographic appearance of thoracic structures. Answer: The differential absorption of radiation by different tissues or diseases is responsible for all radiographic shades of grey. Tissue which has good penetration will produce black picture while with poor penetration will have white picture. Attenuation depends tissue density, thickness, composition, phase of respiration, and distance from film. Tissue of different density must strike tangentially by roentgen beam to produce well defined boundary line. Air, fat, soft tissue (muscle, fluid), and metal (bone) absorb progressively more radiation. The thicker the tissue, the more it absorbs. Q. What are principle division of lungs? Answer: Various practical division of lung on PA view are; Apical zone: Area above the clavicle Upper zone: Inferior border of clavicle to superior border of pulmonary hilum or apex to upper boarder of second costal cartilage anteriorly Middle zone: Superior border to inferior border of hilum or between second and fourth costal cartilage anteriorly Lower zone: Inferior border to diaphragm or below fourth cartilage anteriorly Central lung Peripheral lung Anatomical division based on fissure Right lung is divided by oblique or major (run from anteriorly from diaphragm to posteriorly fourth thoracic vertebra dividing upper and lower lobe) and horizontal or minor fissure (run from right hilum to sixth rib in axillary line dividing lung into upper and middle zone) Left lung is two lobes by oblique fissure Q. Discuss steps of interpretation of Chest radiograph Answer: Pattern approach should be: -Systematic -Begin with the less important areas -Focus on the region of interest. -Completed a systematic review Review periphery of chest. Start at neck and include shoulders, ribs, clavicles, and diaphragms Evaluate heart size and mediastinal contours, edges, and shape Follow trachea to carina and main bronchi Evaluate peripheries of lungs for air and fluid Study lungs up and down and side to side. Include lung volumes and symmetry of markings Check for gastric bubble, free air, and abnormal air collections Check for devices Points to be appreciated during reading chest x-ray are; Identification number, name, age or date of birth, and date of exposure Type of view or projection: PA/AP/Lateral. If the scapulae lie over lung field, film is AP view. Orientation: Left or right marking Rotation: Spinous process between the clavicle and at equidistance and clavicles lie on first rib. During rotation medial end of clavicle moves closure to spinous process of that side. This is most commonly used in adults and less reliable in children. Abnormal rotation may show hyperlucent lung. Also, distance between anterior costal arches and spine is equal in non-rotated film and more reliable in children. Adequate penetration: Superior thoracic vertebral bodies behind heart are visible. Clearly visible vertebral behind indicate over exposure. Both the lungs field should have equal translucency. Horizontal fissure should run from hilum to 6th rib in axillary line. Position of the patient: Ideal is standing and in full inspiration. Depth of inspiration: 9th posterior rib visible above dome of diaphragm, well defined costophrenic angles, heart and diaphragm. Also, the anterior end 6th rib is seen above the diaphragm. In inadequately ventilated film vessels at lung base look like consolidation or collapse. Type and quality of radiograph: Misalignment results in unilateral hyperlucency. Poorly inspired film child results in increase lung density, poor definition of vessels, and widening of mediastinum. ABCDFEFG's Sequence: Airway (trachea, bronchi, alveoli)& Aorta, Breathing & Bone cage, Circulation (blood vessels)& Cardiac (cardiothoracic ratio, borders, chambers, position), Diaphragm (level, shape, tenting, costo-phrenic and cardio-phrenic angles)) & Deformity (shape of thorax, ribs, borders, intercostal space, pleura level), Soft; tissues (emphysema, tumour), Extrathoracic structures, Fissures, Gastric air bubble, Hilum (ABCDEFGH). Pleura: Both costophrenic angles are visible Mediastinum: Trachea in midline, left hilum is slightly up to right hilum and concave in shape Look for four silhouettes: Loss of right heart border indicates of air in middle lobe and loss of left heart border points towards loss of air in lingula. Similarly, loss of both the hemidiaphragm indicates loss of air in lower lobe or something between diaphragm and lower lobe. Lung parenchyma: Apices are visible 2.5- 5cm above the clavicle in adults. Foreign materials: ET tube, Feeding tube, central line, pace maker, artificial valve, PIG tail catheter, ICD tube etc. Diagnosis includes identifying and localizing abnormalities, defining appearance, categorizing grades or pattern, and differential diagnosis. Different tissue absorbs difference in amount of x-ray beam leading to different attenuation of tissues. Q. What are review areas in x-ray chest? Answer: Various areas are; Behind heart, Cardio-phrenic angles, Costophrenic

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