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

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

Rib

Vertebra

Scapula

Chest Radiograph – Lateral View

Chest Radiograph (PA View) – Ribs

Intercostal muscle Rib Sternum

Vertebral body

Spinous process Vertebral canal with spinal cord

Transverse process

CT Scan of the Chest

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)

Parietal Pleura

Visceral Pleura

Pleural Cavity

Visceral Pleura

Parietal Pleura

Pleural Space

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 sides4. Right Oblique

Fissure10. Left Oblique

Fissure

• 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

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

Thymus

Superior Mediastinum on Chest Radiograph

Superior Mediastinum on Chest Radiograph - Thoracic Duct

CT Scan of Superior Mediastinum

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 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 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 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 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 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 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 Left brachiocephalic vein crosses to join vein crosses to join right brachiocephalic right brachiocephalic veinvein

Azygous vein

Superior vena cava 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

Left Subclavian artery

Trachea

Esophagus

Arch of aorta

Superior vena cava

Brachiocephalic trunk

Common carotid artery

Subclavian artery/vein

Trachea

Esophagus

Azygous vein

Superior vena cava

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 Mediastinum

This is where the action is Important group of lymph nodesAortaPulmonary arteriesSuperior vena cava

Mediastinum 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 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 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 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 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 Mediastinum

Below the level of the carinaAzygoesophageal recess

Part in association with the esophagus and azygous vein

Important due to adjacent subcarinal lymph nodes and esophagus

Mediastinum 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 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 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 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 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

Pretracheal space

Prevascular 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

Left atrium

Right atrium

Aortic sac Pulmonary trunk

Descending aorta

Aortic sac

Superior vena cava

Descending aorta

Left Pulmonary artery

Left Pulmonary Artery Level

Right pulmonary artery

Pulmonary trunk

Left pulmonary artery

Right Pulmonary Artery Level

Left Atrial Left Atrial Level Level

Left atrium

Superior Vena Cava entering Right atrium

Aortic sac Pulmonary trunk

Descending aorta

1.Right Atrium 2.Left Atrium3.Right Ventricle 4.Left Ventricle 5.Descending Aorta 6. Transverse Process of T77.Right pulmonary artery branch 8.Left pulmonary artery branch

Four Chamber Level

Left Ventricle

Interventricular Septum

Right atrium Right Ventricle

Three Chamber Level

Azygoesophageal recess Azygoesophageal recess

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