THORACIC CAGE

Radiological anatomy of Chest including Lungs,Mediastinum & Thoracic cageDr. Pankaj KairaJR I RadiodiagnosisSRMSIMS Bareilly,India

ChestThe chest consists of bony skeleton of the spine and ribs, chest wall and diaphragm, the mediastinum and great vessels, the airways, lung parenchyma and pulmonary vessels.

COMPONENTS OF THORACIC CAGE:

SternumManubrium, Body (Gladiolus), Xiphoid process

Ribs7 True Ribs5 False Ribs (including 2 floating ribs)

Clavicle PectoralScapula girdle

12 Thoracic Vertebrae (T1 - T12)

Thoracic CageIt forms a conical enclosure for the lungs and heart and provides attachment for the pectoral girdle and upper limb.It has a broad base and a narrower superior apex; it is rhythmically expanded by the respiratory muscles to create a vacuum that draws air into the lungs.The inferior border of the thoracic cage is formed by a downward arc of the ribs called the costal margin.The ribs protect the thoracic organs and spleen, most of the liver, and to some extent the kidneys.

Sternum/Breast boneFlat bone, with 3 parts:

Manubrium sterniBody/GladiolusXiphoid process

PARTS OF STERNUM:Manubrium sterniJugular/suprasternal notchArticulates with Clavicles and Ribs 1 and 2Lies opposite to T3 and T4 vertebraeManubriosternal joint inferiorly called Sternal Angle/Angle of Louis opposite articulation with 2nd rib at the level of intervertbral disc between T4 and T5 vertebrae(imp. for counting the ribs)

PARTS OF STERNUM:

2. Body/GladiolusArticulates with Ribs 2-7Xiphisternal joint inferiorly- opposite to T9 vertebra

3. Xiphoid processCartilaginous - calcifies through timeAllows attachment of musclesTip of xiphoid at level of T10

RibsTypical Ribs 2-7HeadNeckTubercleAngleShaftSubcostal groove

Atypical Ribs 1, 8 -10Rib 1 - short, flat and supports Subclavian vessels Ribs 1, 10-12 - articulate with only 1 vertebra Ribs 11 and 12 floating ribs do not articulate with Transverse processes of Vertebrae or Sternum

Typical ribs:1 7 pairs of ribs are attached anteriorly to the sternum by their costal cartilages.

Atypical ribs:8th, 9th and 10th pairs of ribs are attached anteriorly to each other and to the 7th rib by means of their costal cartilages and small synovial joints.

Floating ribs:The 11th and 12th pairs have no anterior attachment. They are embedded in the abdominal muscles.

Typical Ribs (2 -7)Long, twisted, flat boneThe anterior end of each rib is attached to the corresponding costal cartilage A rib has ahead, neck, tubercle, shaft, andangle Head located posteriorly -has 2 facets for articulation one for the numerically corresponding vertebral body and the other for the vertebral body immediately above it. Neckis a constricted portion - between the head and the tubercle. TheTubercleis a prominence on outer surface of the rib - at the junction of the neck with the shaft. It has a facet for articulation with the transverse process of the numerically corresponding vertebra. The Shaft is thin, flat and twisted on its long axis.It has a rounded, smooth superior border and a sharp, thin inferior border which hascostal groove (it accommodates the intercostal vessels and nerve (VAN ) The angle is where the shaft of the rib bends sharply forward.

Atypical Rib (1st Rib)The first rib has a close relationship to the lower nerves of the Brachial plexus, Subclavian artery and vein.

This rib is shortest with a prominent tubercle for the attachment of Scalenus anterior muscle.

Anterior to the attachment of Scalenus anterior, the Subclavian vein crosses the rib.

Posterior to the attachment of Scalenus anterior, the Subclavian artery and the lower trunk of the Brachial plexus cross the rib and lie in contact with the bone.

JOINTS OF STERNUM1. MANUBRIOSTERNAL JOINT:cartilaginous joint, symphysisbetween Manubrium and body of Sternum

2. XIPHISTERNAL JOINTcartilaginous jointbetween Xiphoid process and body of SternumThe Xiphoid process usually fuses with the body of the Sternum during middle age

JOINTS OF RIBS1. COSTOVERTEBRAL JOINTS:2 joints between heads of the Ribs and bodies of Vertebrae (corresponding and upper)- Synovial joints1st, 10th, 11th and 12th rib has 1 synovial joint with the corresponding vertebra, the rest have 2 each; one for the corresponding vertebra and the other for the vertebra above it1 joint between tubercle of Ribs and transverse process of Vertebra (corresponding) - Synovial joint (1st-10th Rib)Intra articular ligament connects head of Rib to the intervertebral disc

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Cervical Rib (Accessory Rib)Occurs in 0.5% populationThere is an extra pair of ribs just above the 1st ribThey arise from the transverse process of C7 vertebraeAnteriorly, they may be attached to 1st Rib or may be freeClinical Anatomy: Cervical Rib may compress Brachial plexus/Subclavian artery; causing Klumpkes paralysis/Ischemia

Intercostal MusclesExternal intercostalsInternal intercostalsInnermost intercostal muscles which is separated from the internal intercostal muscles by neurovascular bundle with the vein lying in a groove on the under surface of the corresponding rib and the artery and nurve lying more inferiorly (VAN).

Blood SupplyAnterior intercostal arteries arise from internal thoracic artery.The posterior intercostal arteries of first two space arise from the costo-cervical trunk (branch of subclavian artery) and posterior intercostal arteries of lower nine spaces arise from the descending thoracic artery.Intercostal veins drain into azygous and hemiaygous veins, except 1st on right drains into vertebral or brachiocephalic vein and 2nd and 3rd on left form the superior intercostal vein to drain into left brachiocephalic vein.

Intercostal Veins

DIAPHRAGMSeperates the thorax from the abdomen.It consists of1)A peripeheral muscular part arising from margins of thoracic outlet.2)Right crus arises from the front of vertebral bodies of L1-3.3)Left crus from the lateral aspect of vertebral bodies of L1-2.4)Arcuate ligament from the fascia of the psoas and guadratus lumborum.5)Central tendon which is partly fused with the fibrous layer of pericardium.

Main openings in DiaphragmAortic opening (T12) transmitting the aorta, thoracic duct and the azygous vein.

Oesophageal opening (T10) Oesophagus,oesophageal branches of left gastric artery, vein and B/L Vagus nerve.

Vena caval opening (T8) Inferior vena cava and right phrenic nerve.

TRACHEAThetracheaconnects the upper respiratory tract to thelungsvia the bronchial tree, enabling gas exchange.The trachea extends from the larynx at the level of thecricoid cartilage(C6)and branches into the right and left main bronchus at thecarina(T4/5)There are 12-16 incomplete cartilaginous rings.The posterior wall is fibrous tissue.Rings may calcify in older people.

Usually situated in a midline position and is slightly deviated to the right .

length : 9 12 cms . intrathoracic portion about 6-9 cm.

Trachea bifurcates into right & left main bronchus .

Normal Carina Angle : 60 to 70 Degrees.

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BRONCHOPULMONARY SEGMENTSBronchopulmonary segments are anatomic, functional and surgical units of lung.

Well defined areas of lungs, each of which is aerated by a segmental/ tertiary bronchus

These segments are pyramidal in shape with apex towards the root of lung

Each segment is an independent respiratory unit.

In each bronchopulmonary segment the segmental bronchus is accompanied by a branch of pulmonary artey, lymphatics and autonomic nerve supply.

Pulmonary veins run in intersegmental planes between adjoining segments

Broncho-Pulmonary Segments of the Right LungSuperior Lobe Apical (1)Anterior (2)Posterior (3)Middle Lobe Lateral (4)Medial (5)Inferior Lobe Superior (6) Medial basal (7)Anterior basal (8)Lateral basal (9)Posterior basal (10)

Broncho-Pulmonary Segments Of The Left LungUpper Lobe :Apico -posterior (1-3)Anterior (2)

Superior lingular (4)Inferior lingular (5)

Lower Lobe :Superior (6)Anterior basal (8) Lateral basal (9) Posterior basal (10)

Right Main Bronchus (Eparterial)

Wider, Shorter, and more Vertical

25 degrees to the median plane

2.5 cms long

Enters the right lung nearly opposite the T5 vertebra

It lies inferolateral and posterior to pulmonary artery.

The azygos vein arches over it from behind; and the right pulmonary artery lies at first below and then in front of it. 39

Left Main Bronchus (Hyparterial)

40 degrees to the median plane

5 cms long

1.2 cms wide

Courses below the arch of aorta entering the hilum at T6 then courses inferolaterally to the pulmonary artery.

Nearly 5 cm long Enters root of left lung at level of T6 vertebrae

Passes beneath the aortic arch, crosses in front of the esophagus, the thoracic duct, and the descending aorta, and has the left pulmonary artery lying at first above, and then in front of it The left bronchus has no eparterial branch, and therefore it has been supposed by some that there is no upper lobe to the left lung, but that the so-called upper lobe corresponds to the middle lobe of the right lung

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HILUM It is a large depressed area that lies near the centre of the medial surface of lung.

Various structures enter and leave the lung via its root.

Each hilum contains major bronchi, pulmonary vessels and lymph nodes.

The left hilum is higher than the right in 97% of people and equal in 3%.

Both have clearly defined concave lateral borders

Lymph nodes are also present on each side but are not visible unless abnormal

LUNGS Lungs are a pair of respiratory organs situated in thoracic cavity

Right lung is larger than the left

Right lung has 3 lobes

Left lung has 2 lobes

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PULMONARY FISSURES & LOBES

FISSURESACCESSORY FISSURES :

Azygous fissure

Superior Accessory fissure

Inferior Accessory fissure

Left transverse FissureMAIN FISSURES :

RIGHT LUNG :-

Horizontal fissure

Oblique fissure

LEFT LUNG :-

Oblique fissure

HORIZONTAL fissure is usually seen incompletely on a pa view, running from hilum to the region of 6th rib in the axillary line and may be straight or have a slightly downward curve.Fissures are more clearly seen on a lateral film.HORIZONTAL fissure runs ant. And often slightly downward.OBLIQUE fissures commence posteriorly at the level of T4 /T5, passing thru the hilum. Left oblique fissure is steeper and finishes 5cm behind the ant costophrenic angle, whereas right one ends just behind the angle.Azygous fissure is a comma shaped, with a triangular base peripherally, nearly always rt sided. Froms in apex of the lungs

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Oblique ( Major ) Fissure :

Right oblique fissure separates the lower lobe from the middle and upper lobes where as left oblique fissure separates lower lobe from upper lobe.

Extends from T4/T5 posteriorly to the diaphragm anteroinferiorly.

The left oblique fissure is more vertically oriented than the right.

ends just behind the anterior costophrenic angle, passing through the hilum.

is usually visible on a lateral radiograph and on a high resolution CT scan as a curvilinear band from the lateral aspect to the hilum.

Horizontal ( Minor ) Fissure :

Separates upper lobe from the middle lobe of the right lung. Is short as compared to oblique fissure

Runs horizontally from the hilum to the anterior and lateral surface of the right lung at the level of the 4th costal cartilage.

The posterior limit is the right oblique fissure which it meets at the level of 6th rib in midaxillary line.

Anatomically complete on in 1/3rd of the subjects.

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FISSURES AND LOBES OF THE RIGHT LUNG

FISSURE OF LEFT LUNG

Accessory fissures of the lung

Accessory fissures of the lungusually occur at the borders ofbronchopulmonary segments.

Azygous fissureInferior accessory fissureSuperior accessory fissureLeft minor fissure

Azygous fissureOn the right side.Occurs due to anomalous development of azygous vein and terminates in tear drop opacity.Consists of 4 layers of pleura and supplied by right apical bronchus or its branches.Seen in 0.5% of CXR with male:female ratio of 2:1.

SUPERIOR ACCESORY FISSURESeparates the apical from the basal segments of the lower lobe.It is commoner on right side.It is seen in 5% of the PA chest radiograph.

INFERIOR ACCESSORY FISSURE It seperates the medial basalbroncho pulmonary segment from the rest of the lower lobe.Common on the right than left

This fissure may also be referred to asTwining's lines.

It is seen in 8% of PA chest radiographs.

LUNG ZONESLungs are assessed by dividing them into 3 zones:

Upper zone : upto 2nd rib

Middle zone: 2nd to 4th rib

Lower zone: 4th and below

LOBES OF THE LUNGSRight lung has three lobes : a) upper lobe b) middle lobe c) lower lobe

Azygos Lobe :Not a true accessory lobe (rather a normal variant appearance of the right upper lobe)

Formed by a laterally displaced azygos vein which makes a deep fissure (Invaginates) in the upper part of the lung during embryological development

Seen on a chest radiograph where it is limited by the azygos fissure .

Azygos vein is a unilateral vessel that ascends in thorax to the right side of vertebral column, carrying deoxygenated blood from posterior chest and abdominal walls , arching over the right hilum to enter into superior vena cava

Forms a part of normal cardiomediastinal contour on chest x ray , normally measure