basic chest radiology

BASIC

CHEST

RADIOLOGY

Views for standard chest radiography

POSTERIOR ANTERIOR VIEW

• The patient's chest is placed against the film cassette.

• The x-rays enter the patient posteriorly and exit ventrally.

• The PA view minimizes cardiac magnification which can be a complication of other views.

LATERAL VIEW

• A lateral view is ordered in conjuction with a PA view.

• By convention, the left side of chest is placed against the film cassette.

• Since the right side of the body is closer to the source of the x-rays, the right side is magnified greater than the left side. This will help separate structures. For example, the right costophrenic margin appears larger than the left costophrenic margin in this image.

APICOLORDOTIC VIEW

• It is similar to a PA view except the x-ray beam is angled cranially.

• It is performed to evaluate upper lobe pathology.

• This view removes the clavicular shadows seen in the PA view.

ANTERIOR POSTERIOR VIEW

• It is performed on patients who are unable to stand for the PA exam.

• AP radiographs are performed at bedside. The film cassette is placed under the patients back and a portable x-ray machine is positioned over the patients chest.

• Difficult to interpret due to many potential technical problems.

• May cause cardiac magnification as demonstrated in this comparison.

*Chest x-rays are designed specifically for heart and lung anatomy. Do not order chest x-rays to examine rib or vertebral

anatomy.

FISSURES– Right major fissure

separates the right upper lobe, and right middle lobe from the right lower lobe.

– Right minor (horizontal) fissure separates the right upper lobe from the right middle lobe.

– Left major fissure separates the left upper lobe from the left lower lobe

– Also note that the lower lobes extend behind the outline of the diaphragm on a PA view.

• Right upper lobe – Segments: apical,

posterior, anterior

• Right middle lobe – Segments: lateral,

medial

• Right lower lobe – Segments: medial

basal, anterior basal, lateral basal, posterior basal and superior.

• Left upper lobe – Segments:

apicoposterior, anterior, superior lingular, inferior lingular

• Left lower lobe – Segments: superior,

anteromedial basal, lateral basal, posterior basal

CARDIAC ANATOMY

PA CARDIAC VIEW

• The right cardiac border is formed by the right atrium

• the left cardiac border is formed by the left ventricle.

• The right ventricle and left atrium are superimposed structures and are not border forming.

• The Superior vena cava: forms a right paramedian border.

LATERAL CARDIAC VIEW

• On the lateral projection, the anterior cardiac border is the right ventricle while the posterior cardiac border is composed of both the LV and LA.

• The right atrium is not a border-forming structure.

LATERAL CARDIAC VIEW

• The inferior vena cava is seen best on lateral projection.

• The posterior border is evident in contrast to the air-filled lungs.

Hilar Anatomy

• The "hilum" is composed of the pulmonary artery and its branches, and adjacent airway and pulmonary veins.

• Since airways do not produce a significant shadow on plain film radiography, the majority of the detectable "hilar" structures are vascular.

HILAR ANATOMY• On the left side, the

left pulmonary artery is directed posterolaterally, toward the left scapula and goes over the left main stem bronchus. The left pulmonary artery is therefore located higher than the right pulmonary artery.

HILAR ANATOMY

• On the lateral projection, the left pulmonary artery is posterior to a line drawn down the tracheal air column.

HILAR ANATOMY• The right pulmonary

artery (RPA) courses underneath the left main stem bronchus.

• The right hilar shadow is inferior to the left on the PA projection ( 70%). Hilar shadows are equal in height (30%).

• The right hilum is never superior to the left hilum.

HILAR ANATOMY

• On the lateral projection, the right hilum is anterior to a line drawn through the tracheal air column.

• The right pulmonary artery is approximately 3 times larger than the LPA, due to the more horizontal course of the RPA.

Tracheobronchial Anatomy

TRACHEA

• The trachea appears as an air-shadow coursing down the midline of the chest and terminating at the carina. The left and right mainstem bronchus may be evident as well as the lobar bronchi.

PULMONARY VENOUS ANATOMY

• Pulmonary veins course more horizontally than pulmonary arteries, are ultimately directed toward the left atrium and best seen on a lateral projection.

• Pulmonary venous anatomy should not to be confused with a retrocardiac infiltrate.

MEDIASTINUM

ANTERIOR MEDIASTINUM

• Borders include the sternum anteriorly, and the ventral cardiac surface posteriorly.

• Includes fat, ascending aorta, lymph nodes, internal mammary artery and vein, adjacent osseous structures (ribs and sternum), thymus. Knowledge of the mediastinal contents can aid in your differential diagnosis.

• This thymoma has spread throughout the Anterior Mediastinal compartment.

MIDDLE MEDIASTINUM

• Borders composed of the anterior mediastinal compartment ventrally, and the anterior surface of the spine, posteriorly.

• Structures include the esophagus, vagus nerve, recurrent laryngeal nerve, heart, proximal pulmonary arteries and veins (hilar), trachea and root of the bronchial tree, and superior and inferior vena cava

POSTERIOR MEDASTINUM

• Borders: Anterior surface of the spine posteriorly to the ribs.

• Structures include the descending aorta, adjacent osseous structures (the spine and ribs) and nerves, roots, spinal cord, and the azygous and hemiazygous veins.

SUPERIOR MEDASTINUM

• It is located above a horizontal line drawn from the angle of Louis posteriorly to the spine.

• Structures include the thyroid gland, aortic arch and great vessels, proximal portions of the vagus and recurrent laryngeal nerves, esophagus and trachea.

AORTOPULMONARY WINDOW

AORTOPULMONARY WINDOW

• A "space" located underneath the aortic arch and above the left pulmonary artery.

• Contains fat.

• On the PA projection, it appears as a concave shadow. If adenopathy is present, it manifests as a convex shadow.

DIAPHRAGM

• The left and right diaphragm appear as sharply marginated domes.

• The peripheral margins of the diaphragm define the costophrenic sulci.

• The right diaphragm is higher than left due to the position of the liver. Will appear larger on a lateral chest film

OSSEOUS STRUCTURES

• Ribs

• Anterior and posterior ribs.

• Spine

• Pedicles

• Transverse processes

• Spinous Processes

• Sternum

X-ray densities

• Density is related to the structures ability to block photons. Air, for example, allows a greater number of photons to pass through and subsequently exposes more film generating a black image. More dense structures, such as bone or metal, reflect or absorb photons. Therefore, the film absorbs less photons and appears white.

• Five different densities are represented on plain films: air, fat, soft tissue (fluid), bone & metal (contrast material)

Sensitivity and specificity of plain films.

• Plain films are not very sensitive.

• A great deal of pathology is missed on plain films.

• They are also not very specific since the majority of possible pathology falls under the catagory of fluid or soft tissue density making it difficult to differentiate.

Detection rates of abnormality.

• Plain films are poor screening exams.

• Studies looked at patients with documented lung disease approximately 10% of the patients had normal looking plain films.

Basic Pulmonary Pathology

• Concept of the silhouette sign– able to distinguish anatomical margins

when two structures of different density abut one another. When two structures of similar density abut one another, their margins are lost.

ATELECTASIS

• Right upper lobe: up and in

• Right middle lobe: like a fan.

• Right lower lobe : inferior and posteriorly

• Left upper lobe: medial and anterior

• Left lower lobe :inferior and posteriorly

Pleural effusions

• Pleural efusions may be caused by a number of possible etiologies. Some of the most common causes are congestive heart failure, trauma, or blood.

• One cannot determine the nature of the pleural fluid based solely on the plain film (blood, pus, transudate, or exudate, etc).

Pleural effusions

• The pleural fluid collects first in the posterior gutters. As the amount of fluid increases, plain films will reveal a blunting of the posterior and lateral gutters

• The build up of fluid will apply pressure to the lung causing a decrease in air intake.

• Treament - drain pleural fluid.

PSEUDOTUMOR

• The fissures are in continuity with the pleural space.

• Fluid can fill the fissures.

• This phenomenon is often refered to as pseudotumor due to its strong resemblance to a tumor.

Fluid has filled the minor fissure creating a density that resembles a tumor (arrow).

LATERAL DECUBITUS VIEW

• It is often difficult to determine the size of a pleural effusion based on a plain film.

• The patient lies on their affected side and gravity causes the pleural fluid to coalesce in the lateral margin.

• A Decubitus chest film can detect as little as 5 cc's of fluid.

PNEUMONIA

• Pneumonia causes pus (bacterial, viral, fungal) to accumulate in the lungs causing increased density of the lung.

• It is possibly confused with blood, water or even tumor.

• Clinical history is necessary to help differentiate pneumonia from other possible pathology.

• Radiographic appearance predicated on infiltrate location, i.e. broncho-pneumonia vs. lobar pneumonia.

CAVITATION

• The infection causing the pneumonia may lead to cavitation or destruction of the lung tissue, forming abscesses.

• The three most common organisms that cause pulmonary abcesses are staph aureus, strep pyogenes, and Klebsciella.

• Gram negatives are also very common causes of abscesses.

Pulmonary NodulesCan be benign, malignant primary or metastatic nodules.

• Carcinoma can resemble other pathology such as pneumonia.

• Criteria for malignancy: presence of calcification, size, margins-not defined, growth, patient age/sex, and smoking history.

• Metastatic disease is hematogenously disseminated from another primary source such as colon or ovary which usually present as multiple nodules.

• If the nodule is highly calcified, it is a benign process and is not life-threatening and typically is a granuloma.

What should you do if you discover a nodule?

• The first step is to review the patient's old chest films. – No change over a two-year period then the

nodule is more than likely benign. – If there are no old chest films, then a CT should

be ordered. If the nodule is enlarging over time, then the nodule should be worked up.

Cardiac Pathology

• A buldge on left cardiac boarder is indicative of possible Mitral Valve Stenosis.

Left Ventricle Enlargement is evident on a PA view by distension of the lower left cardiac boarder.

Rigler's rule

• A line is drawn from the point where the inferior vena cava meets the heart border up 2 cm and then a second line is drawn posteriorly from this point 2 cm. If the cardiac boarder is beyond this point than the posterior cardiac boarder is enlarged.

Congestive Heart Failure

• Cardiomegaly. – determined by comparing the width of

the heart to the width of the thoracic cavity on a PA film. If the heart is greater than 50% of the width of the thoracic cavity, then the heart is enlarged.


• The upper lobe vessels become more prominent due to vascular congestion or interstitial edema - results from transudation of fluid through the capillary walls into the interstitium around the vessels which can render normally indistinct vessels distinct, and creates a shaggy appearance around the heart border on a chest film.


• The increased transudate burdening the lymphatic system results in interstitial edema , evident on chest films by the appearance of Kerley lines, which represent thickening of the interlobular septa which carry the lymphatics.

• As hydrostatic pressure continues to increase, fluid begins to accumulate in the pleural space resulting in pleural effusions. With continued pressure, transudate infiltrates the alveolar spaces causing pulmonary edema.

THE END