Imaging the respiratory system from the tip of the nose to the diaphragm (Proceedings)

General comments

·         The respiratory system extends from the tip of the nose to the diaphragm.

·         Take good quality radiographs.

·         Take as many radiographs as needed to make the diagnosis or to determine that other diagnostic methods are needed.

·         Take sequential radiographs to monitor a disease process and response to therapy.

·         .Have the radiographs reviewed by the radiologist if you are not sure what is happening.

·         CT imaging is a more “robust” technology to assess the lungs especially for “mass” lesions.

·         Ultrasound is a more “robust” technology to assess the cardiac silhouette and heart.

·         Intervention may be required to obtain a definitive diagnosis.

·         Some animals never get completely better and others die despite your best efforts

Head

·         Nasal passages

·         Sinuses

Neck

·         Pharynx

·         Larynx

·         Trachea

Thorax

·         Lungs-

o    Bronchi

o    Alveoli

o    Interstitium

o    Vessels

·         Heart

·         Mediastinum

o    Lymph nodes

o    Ectopic tissue

o    Thymus

·         Esophagus

·         Pleura

·         Diaphragm

·         Soft tissues body wall

·         Fat

·         Osseous structures

The airways and the lungs

The number of radiographic projections required to define a lesion will depend on the extent and location of the lesion. The common views are:

Upper airway

·         Lateral

·         Oblique

·         Open mouth VD

·         Rostro-caudal

Neck

·         Lateral

·         Oblique

Thorax

Ventrodorsal projection

·         Sternum towards the X-ray tube;  vertebrae against cassette or on the table.

·         Used to evaluate the cranial mediastinum, ventral contour of the heart, and ventral lung region.        

Dorsoventral projection

·         Vertebrae towards the X-ray tube;  sternebrae against cassette or on the table.

·         Used to evaluate the caudal mediastinum, overall contour of the heart, the aorta, and the dorsal lung region.        

·         In both projections, the beam is centered on the fifth thoracic vertebra; the vertebrae and sternebrae are superimposed; the elbows are adducted, and the skin folds are moved laterally.        

Right lateral projection

·         Left lateral surface of the torso is toward the X-ray tube; the right lateral surface of the torso is against the cassette.

·         Used to evaluate the left lung field, mediastinal structures, left side of the diaphragm, esophagus,  and pericardial sac.   

Left lateral projection

·         Right lateral surface of the torso is toward the X-ray tube; the left lateral surface of the torso is against the cassette.

·         Used to evaluate the right lung field, mediastinal structures, right side of the diaphragm , and pericardial sac.

·         Used to evaluate for a hiatal hernia after barium administration. 

In both projections the beam is centered on the fifth intercostal space;  the sternum is lifted slightly away from table; the forelimbs are pulled forward, and the skin folds are moved dorsally and/or ventrally.

Radiographs of the thorax are usually obtained during inspiration unless you suspect pneumothorax or free pleural fluid. Free gas or fluid is easier to define when the animal is in expiration.

The lung, when viewed in expiration, is often mistakenly diagnosed as being pathologic. When the animal is in expiration, there is less gas in the lung, and the lung becomes more opaque. This physiologic change results in increased lung opacity that mimics many disease processes that also cause the lung to become more opaque.

Air/gas is the natural contrast agent of the lung; take advantage of this contrast agent by radiographing the animal in inspiration when you wish to evaluate lung parenchyma. The pericardial sac, mediastinal structures and the diaphragm.

When the animal is in expiration, the pulmonary vessels are closer together, the diaphragm overlaps the heart; the cranial lung lobes do not extend to the thoracic inlet, (comma) and the pericardial sac appears larger.

Lung lobes

 Right:     Cranial (Apical)                       Left:         Cranial (Apical & Cardiac)

                Middle (Cardiac)                                     Cranial Segment-Apical

                Caudal (Diaphragmatic)                          Caudal Segment-Cardiac                  Accessory (Intermediate)                               Caudal (Diaphragmatic)

·         Radiographic findings when disease processes involve the alveolar:

o    Air bronchograms

o    Air Alveolograms

o    Ill-defined infiltrates

o    Lobar border visualization

·         Radiographic findings when disease processes involve the interstitial tissues:

o    Interstitial Pattern:

o    Short linear opacities crisscross randomly

o    Nodular densities round or irregular in contour with well-defined borders, admixture linear and nodular densities.

·         Radiographic findings when disease processes involve the bronchi and vessels

o    Bronchovascular Pattern:

o    Vessel or conducting airways change in appearance

o    Increased prominence

o    Decreased prominence

·         Vessels

o    Cranial lung lobe vessels (artery or vein) at edge of cardiac silhouette shouldbe approximately 3/4 diameter of the 3rd or 4th rib at approximately the level of the trachea; the transverse diameter of the vessels should be equal to each other.

  Changes seen in vessel size with disease Disease Artery Vein Patent ductus arteriosus Increased Increased Septal defect Increased Increased Pulmonic stenosis Decreased Decreased Left heart failure Increased Increased Shock Decreased Decreased Dirofilariasis Increased Decreased

Changes normally seen as animal ages (“normal for age”)

·         Pleural thickening

·         Increased linear markings - interstitial fibrosis

·         Nodular densities - occasionally calcified – metaplastic mineralization-alveolar microlithiasis, osteomata

·         Increased density of tracheal and bronchial walls - mineralized cartilages

·         Hyperlucency -emphysema, air trapping

The lung - radiographic assessment

·         Like any other organ, the lung can respond to noxious stimuli in a finite number of ways. One can try to memorize a distinctive radiographic appearance for each type of lung lesion; however, the final result will  probably be utter frustration as the lung changes all begin to look alike.

·         As such, a systematic approach based on morphoanatomic structures is suggested. The basis for this system is pattern recognition; once the pattern is recognized, then a list of differential diagnoses can be made. Subsequent tests can be performed to exclude or confirm a diagnosis.      

When evaluating the lungs, you should know

·         Pattern of involvement

·         Lung lobes/regions involved

·         History

You must make sure you can distinguish hyperinflated lung from pneumothorax.  When a pneumothorax is present, the lung is collapsed, and it is therefore more opaque. Free gas is present in the pleural space so the edge of the collapsed lung can be seen. The vessels in the collapsed lung do not extend to the parietal pleural, and the heart may be displaced away from the sternum. When hyperinflated lung is present, the lung is less opaque. Free gas is not seen in the pleural space; vessels can be seen extending to the parietal pleural, and the heart may be lifted away from the sternum.  If you insert a transthoracic needle into a chest that you believe is a pneumothorax and it is truly a hyperinflated lung, you may kill the animal!!!