Radio Anatomy Of The Thorax And Medias Tin Um 9-17

RADIOANATOMY OF THORAX AND MEDIASTINUM

VINITA SHARAN MD

Objectives  To identify the ribs, sternum and thoracic

spine  To identify the muscles of the chest wall  To evaluate the diaphragm and costophrenic sulci  To identify the lungs, heart and great vessels  To identify the trachea, carina and right and left main stem bronchi

Imaging modalities  Plain X-Ray  CT scan

Chest radiograph- Views Required  Most commonly done

Posteroanterior view (PA View)  Lateral view  Others  Lordotic view – to look at the apical segment  Right anterior oblique view to evaluate heart and 

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Left anterior oblique view ribs Anteroposterior view – for bed ridden patients and children Decubitus view – for evaluating pleural effusion or pneumothorax

Chest Radiograph  Look for symmetry and technique  Structures

Fissures  Lung Parenchyma  Trachea and bronchi  Heart  Pulmonary vasculature  Bony structures  Soft tissues  Costo-phrenic angle 

Chest Radiograph - Posteroanterior View

Chest Radiograph - Lateral View

Bony Thorax  The bony thorax comprises of

Ribs  Vertebral column  Sternum 

Ribs  12 ribs on each side – may vary occasionally  Forms greater part of the thoracic cage  Bony arches arranged one below the other  Gap between two ribs is the intercostal space  Upper ribs less oblique than lower ribs  The length of the ribs increase from 1st to 7th

and then decreases from 7th to 12th  The breadth of the ribs decreases from up downwards

Ribs  The upper 7 ribs are connected through their

cartilages to the sternum – true ribs  The cartilages of the 8th,9th and 10th ribs are joined to the cartilage of the rib above – false ribs  The 11th and 12th ribs are free – floating ribs

Sternum  Flat bone  Forms anterior median part of the thoracic

cage  Upper part is called the manubrium  Middle part is called the body  Lower tapering part is called the xiphoid process

Sternum  Manubrium is the quadrilateral upper part  Thickest and strongest part  Upper level of manubrium is at the upper

level of the 3rd thoracic vertebra  Body is longer, narrower and thinner than the manubrium  Xiphoid process is the smallest part of the sternum

Vertebral Column  12 thoracic vertebra and intervening

intervertebral discs  Thoracic vertebra recognized by presence of costal facets on the sides  There are two facets in most ribs  The upper being near the upper border and articulates with the numerically corresponding rib  The lower facet is near the lower border and articulates with the next lower rib

Vertebral Column  Body of the vertebra is heart shaped  Pedicels are directed straight backwards  Laminae overlap each other from above  Transverse processes are large and directed laterally

and backwards from the junction of the pedicles and laminae  Spine is long and directed downwards and backwards  5th to 9th spine are longest and overlap each other  Vertebral foramen is comparatively small and circular

Walls of the Thorax  Coverings of the thoracic wall

Skin  Superficial fascia  Deep fascia  Extrinsic muscles 

 Thoracic wall proper is formed by the

intercostal muscles

Chest Radiograph - PA View Clavicle Scapula

Rib Vertebra

Chest Radiograph – Lateral View

Chest Radiograph (PA View) – Ribs

Rib

Sternum

Intercostal muscle

CT Scan of the Chest Vertebral body Transverse process

Vertebral canal with spinal cord

Spinous process

Soft Tissues And Spaces

Aorticopulmonary Window

Aorticopulmonary Window and Retrosternal Space

Between the ascending and descending aorta is the aorticopulmonary window Aorticopulmonary window level

Diaphragm Right hemidiaphragm is slightly higher than left hemidiaphragm

Right hemidiaphragm is slightly higher than left hemidiaphragm

Diaphragm

Right hemidiaphragm is slightly higher than left hemidiaphragm

Costophrenic Angle

Pleura  Serous membrane lined by flattened

epithelium  Two pleural sacs – one either side of mediastinum  Lungs have two layers Outer layer- parietal pleura  Inner layer- visceral pleura 

 Space between the – pleural cavity (potential

space)

Visceral Pleura

Pleural Cavity

Parietal Pleura

Visceral Pleura

Pleural Space

Parietal Pleura

Oblique Fissures Indicated by a line that runs from the spinous process of T2 vertebra around the thorax to the sixth costochondral junction Similar on both sides 4. Right Oblique Fissure 10. Left Oblique Fissure

Oblique Fissures

• Indicated by a line that runs from the spinous process of T2 vertebra around the thorax to the sixth costochondral junction • Similar on both sides

Oblique Fissures

Transverse Fissure Runs from the anterior border of the lung along the fourth costal cartilage to the oblique fissure

Fissures

Runs from the anterior border of the lung along the fourth costal cartilage to the oblique fissure

MEDIASTINUM

MEDIASTINUM  Superior  Anterior  Middle  Posterior

Superior Mediastinum  Located superior to the pericardium  Above the horizontal plane passing through the

sternal angle to the intervertebral disc space between T4-T5  Contents      

Thymus Great vessels Phrenic and vagus nerve Esophagus Thoracic duct Prevertebral muscles

Trachea and Bronchi •Angle of Carina (angle between the two main stem bronchi) •Should be less than 60 degrees

Superior Mediastinum on Chest Radiograph Thymus

Superior Mediastinum on Chest Radiograph - Thoracic Duct

CT Scan of Superior Mediastinum

Superior Mediastinum  First of all identify the trachea

Easy to recognize as it is air-filled , central in location  Consistent in position and round or oval in shape  Many other structures have fairly consistent relation to it  Esophagus  Lies posterior to the trachea  Depending on the position of the trachea in relation to the vertebra it may be on one side – usually on the left  Appears as a flattened structure of soft tissue attenuation  Small amounts of air or air and fluid may be seen 

Superior Mediastinum  Great arterial branches of the aortic arch and great

veins  At the thoracic inlet  Brachiocephalic veins

Most anterior and lateral vascular branches visible  Lying immediately behind the clavicular head  Vary in size but positions are relatively constant 

 Brachiocephalic , left common carotid and left

subclavian arteries 

Are posterior to the veins and adjacent to the anterior and lateral walls of the trachea

Superior Mediastinum  Below the thoracic inlet  Left brachiocephalic vein  Crosses

from left to right anterior to the arteries  Joins the right brachiocephalic vein to form the superior vena cava

Suprerior Mediastinum  Left subclavian artery  Posterior most in location  Adjacent ot the left side of the trachea – at 3 or 4 o’clock position from tracheal lumen  Left common carotid artery  Anterior to the left subclavian artery – at 1 or 2 o’clock position from tracheal lumen  Variable in position  Brachiocephalic artery  Anterior and to the right of the tracheal lumen – about 11 o’clock position  Variable size and shape

Suprerior Mediastinum  Brachiocephalic artery  Oval at origin and somewhat bigger than other braches  On higher level may be oval or elliptical – because of its bifurcation into the right suclavian and right common carotid artery  May be tortuous  Other than these structures – some veins and

lymphnodes , lower part of thyroid gland may sometimes be visible

Mediastinum  At the aortic arch level  Aortic arch  Anterior aspect of arch is anterior to the trachea  Arch passes to the left of the trachea  Posterior arch is lying anterior and lateral to the spine  Posterior part of arch is smaller  Superior vena cava  Anterior and to the right of the trachea  Oval in shape  Esophagus  Similar appearance and position as at a higher level

Brachiocephalic vein Internal jugular vein joins subclavian vein to form brachiocephalic vein

At the Thoracic Inlet (six vessels level) RBV

LBV

Five vessels level

Left brachiocephalic vein crosses to join right brachiocephalic vein

Superior vena cava

Azygous vein

Left Brachiocephalic Vein crossing over to the right to join the right Braciocephalic vein to form the SVC

Superior vena cava

Brachiocephalic trunk

Left Common carotid artery

Trachea Esophagus

Left Subclavian artery

Arch of aorta

Superior vena cava

Brachiocephalic trunk

Common carotid artery

Trachea Esophagus

Subclavian artery/vein

Superior vena cava

Azygous vein

Arch of aorta

Azygos Vein draining into the SVC

Anterior mediastinum  Smallest division of the mediastinum  Located anterior to the pericardium or

pericardial sac  Contains the thymus in childhood

Middle Mediastinum  Contains the pericardium and heart and

immediately adjacent part of the great arteries  Phrenic nerves  Main bronchi  Root of the lungs

Posterior Mediastinum  Located posterior to the pericardium  Anterior to the body of the inferior eight

thoracic vertebrae  Contents Esophagus  Thoracic aorta 

Chest Radiograph – Anterior Mediastinum

Chest Radiograph - Middle Mediastinum

Chest Radiograph - Middle Mediastinum

Posterior Mediastinum Esophagus (Esophagogram)

CT Scan of Mediastinum  Anterior  Middle  Posterior

Mediastinum  This is where the action is  Important group of lymph nodes  Aorta  Pulmonary arteries  Superior vena cava

Mediastinum  Pretracheal or anterior paratracheal space Aortic

arch on left, superior vena cava and mediastinal pleura on the right and trachea posteriorly  Triangular fat filled space contains important middle mediastinal lymph nodes of the pretracheal chain

Mediastinum  Prevascular space – anterior mediastinum  Anterior

to the aorta and superior vena cava  Roughly triangular  Part of the anterior mediastinum and contains the thymus, lymph nodes and fat

Mediastinum  At level slightly below the aortic arch  Ascending

and descending aorta are two separate

structures  Ascending aorta (25-35 mm) is slightly larger than descending aorta (20-30mm)  Trachea bifurcates at the carina into right and left mainstem bronchus  At carina trachea assumes oval or triangular shape

Mediastinum  On right side  the

arch of the azygous vein joins the posterior wall of the superior vena cava and passes above the right main-stem bronchus and hence is seen at a higher level than the bronchus  Passes along the mediastinum to the right and anterior of the spine

Mediastinum  On the left side  Aorticopulmonary

window  Under the aortic arch but above the pulmonary artery  Contains fat, middle mediastinal lymph nodes and recurrent laryngeal nerve  Aorticopulmonary window lymph nodes freely communicate with the pretracheal lymph nodes

Mediastinum  Below the level of the carina  Azygoesophageal recess  Part

in association with the esophagus and azygous

vein  Important due to adjacent subcarinal lymph nodes and esophagus

Mediastinum  The main pulmonary artery divides into the

right and left arteries  Left

is slightly higher than the right – usually 1 cm above  Left appears as a continuation of the main artery and is directed posterolaterally and to the left  Right arises at an angle of 90 degrees to the main artery and crosses in front of the carina or main bronchi

Mediastinum  The main pulmonary artery is most anterior arising

from the right ventricle  Right ventricle is anterior and to the right of the left ventricle  Superior vena cava is seen entering the right atrium  Between the right atrium and the main pulmonary artery the aortic root arises from the left ventricle

Mediastinum  Left atrium is located posteriorly appearing

larger than the right atrium  On each side the pulmonary veins can be seen entering the left atrium  Esophagus is seen in the retrocardiac area

Mediastinum  Near the level of the diaphragm the inferior

vena cava is seen as an oval structure entering the posterior right atrium  Azygous vein is seen in the same location as higher up  Hemiazygous vein is seen on the left side behind the descending aorta  Paravertebral nodes lie in association with the azygous and hemiazygous veins

Mediastinum  Normal pericardium and pericardial contents

is visible as a 1 to 2 mm stripe of soft tissue attenuation paralleling the heart and outlined by mediastinal fat and epicardial fat

Prevascular space

Pretracheal space

Between the ascending and descending aorta is the aorticopulmonary window Aorticopulmonary window level

1.Superior vena cava 2. Ascending aorta 3. Descending aorta 4. Trachea 5. Right lung 6. Left lung 7. Sternum

Aortic sac

Pulmonary trunk

Right atrium

Left atrium

Descending aorta

Aortic sac

Left Pulmonary artery

Superior vena cava

Left Pulmonary Artery Level

Descending aorta

Right pulmonary artery

Pulmonary trunk

Left pulmonary artery Right Pulmonary Artery Level

Left Atrial Level

Aortic sac

Pulmonary trunk

Superior Vena Cava entering Right atrium

Left atrium

Descending aorta

1.Right Atrium 2.Left Atrium 3.Right Ventricle 4.Left Ventricle 5.Descending Aorta 6. Transverse Process of T7 7.Right pulmonary artery branch 8.Left pulmonary artery branch

Four Chamber Level

Right atrium

Right Ventricle

Interventricular Septum

Left Ventricle

Three Chamber Level

Azygoesophageal recess

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