Anatomy of The Thoracic Region Mahmoud Alshirbini, MD, PHD

Basic Anatomical Planes Anterior VS. Posterior Superior (cranial, beak of spine) VS. Inferior (caudal- tail of spine) Midline (median) means the mid-sagittal The para-sagittal plane (lateral to the midline) Medial (towards the midline) VS. Lateral (away from the midline)

Proximal (think proximity ) VS. Distal (think distance) Superficial (outside e.g. skin) VS. Deep (inside e.g. organs) Sagittal Frontal (coronal) Horizontal (transverse or axial)

Regional anatomy The thorax is an irregularly shaped cylinder with a narrow opening ( thoracic inlet) superiorly and a relatively large opening (thoracic outlet) inferiorly. The thorax consists of: ■ Thoracic wall (cage) ■ Two pleural cavities ■ The lungs ■ The mediastinum.

Muscles attached to the anterior thoracic wall provide some of this support, and together with their associated tissues, nerves, and vessels, and the overlying skin and superficial fascia, define the pectoral region.

The thorax is the body cavity enclosing and protecting the heart, lungs, and great vessels a conduit for structures passing between the neck and the abdomen plays a principal role in breathing. The thorax also provides support for the upper limb.

The thoracic skeleton Thoracic skeleton consists of: -12 thoracic vertebrae (posteriorly) - 12 pairs of ribs (on either sides) - 12 pairs of costal cartilages - Sternum (anteriorly)

The Sternum It is a flat dagger-shaped bone which Supports and articulates with the clavicles & the upper 7 pairs of ribs Consists of: it is formed of 3 parts : (1) manubrium (2) body (3) xiphoid process 1st costal cartilage forms articulation with manubrium 2nd costal cartilage forms articulation with manubriosternal joint 3rd- 7th costal cartilage forms articulations with the body of the sternum

The ribs 1st thoracic vertebra associated with the 1st rib 1-7 form direct articulations with the sternum via costal cartilage (true) Ribs 8-10 reach costal cartilage above, forming indirect articulations (false ) 11 and 12 lack anterior attachment (floating) Articulations (= joints) with vertebral column – heads (inferior to anterior articulations with costal cartilage) with costal cartilages – tubercles

The 7th rib forms its articulation at the body-xiphoid joint Ribs 11 and 12 do not form articulations with the sternum, and are known as floating ribs The costal cartilage forms articulations with the sternum via articular facets The attachment site for rib 1 is different than the rest (a NON-synovial joint) Superior of the sternum is the articular site for the clavicle, as well as the jugular notch

Thoracic vertebrae 2- Vertebral Arch 3- Vertebral Foramen They are 12 "rib bearing vertebrae _each vertebra is formed of 2 main parts 1- Vertebral Body 2- Vertebral Arch 3- Vertebral Foramen

1- Vertebral Body It is the ventral strong 'part of the vertebra it transmits the body weight downwards

2- Vertebral arch it is the dorsal part which surrounds the spinal cord - it is formed of the following parts (a) Pedicle (b) lamina (c) Transverse process (d) Spinous process (Spine) (e) 2 Superior articular processes (f) 2 Inferior articular processes

3- Vertebral foramen lies between the vertebral body and the vertebral arch The successive vertebral foramina form the vertebral canal which lodges the spinal cord

How Vertebrae are connected together 1) Vertebral bodies: are Connected together by (a) the inter-vertebral discs (2ry Cartilaginous joints). (b) the ant-longitudinal Iig. : Connecting the ant.surface of the vertebral bodies. (c) the post. longitudinal Iig.: Connecting the post, surfaces of the vertebral bodies. (2) Laminae : are Connected together by ligamenta flava (Contain yellow elastic fibres). (3) transverse processes: are connected by inter transverse ligaments

(4) the Spines: are connected by (a) interspinous ligaments: Connecting the adjoining spines (b) supraspinous ligament: Connecting the tips of spines ( from c7 to sacrum) (5) Articular processes : of adjoining vertebrae are Connected by the fibrous capsules of the intervertebral joints

Classification of thoracic Vertebrae Typical vertebrae (2nd-8th) Atypical vertebrae (1st,9th,10th,11th,12th)

Characters of the typical thoracic vertebrae The body is heart-Shaped and has sup. and inf. Demifacet for articulation with heads of. ribs The foramen is narrow and circular The transverse process is directed posterolaterally and has an articular facet near Its tip anteriorly, for articulation with the tubercle of the numerically corresponding rib the transverse process becomes progressively shorter from T1 to T 12

Intercostal spaces The spaces between each 2 successive ribs 11 spaces exist between the 12 ribs on each side Structure: (a) Intercostal muscles and membranes arranged in 3 layers (b) a neurovascular bundle (VAN)

Intercostal muscles Arranged in 3 layers in each space: 1-Outer layer : external intercostal muscle 2-Middle layer: internal intercostal muscle 3- Inner layer: transversus thoracic muscle , incomplete muscle formed of 3 separate muscles; (a) Sternocostlis m. (b) Innermost intercostal m. (c) Subcostalis m.

Intercostal neurovascular branches Consist of: Vein – most superior Artery Intercostal nerve – most inferior Runs just inferior to each rib, deep to the internal intercostal mm. superficial to the innermost intercostal mm.( between the internal and innermost)

The intercostal muscles External intercostals – form inferiorly and laterally from lower border of rib above to rib below (lateral if considering origin to be vertebral column), Replaced by anterior external intercostal membrane at costo-chondral (rib-cartilage) junction Internal intercostals – attachments begin anteriorly at the sternum- from lower border of rib above to rib below - fibres directed at right angles to external intercostals, Replaced by membrane posteriorly Innermost intercostals.

Muscles expanding chest and lung volume The inferior thorax is larger in size to the superior thorax Most lung tissue and capacity for lung expansion lies in the inferior thorax The diaphragm has a flat central tendon with muscle radiating to costal margin and vertebrae. On inhalation: Dome flattens to increase vertical diameter of chest Costal margin is pulled up to increase transverse (horizontal) and antero-posterior diameters

The intercostal muscles have another role: they stiffen the chest wall to improve efficiency of breathing movements The ribs move in ways to either increase or decrease chest volume. In order to increase chest volume: The sternum moves superior and anterior The lateral shaft of the ribs is elevated

Thoracic inlet (superior aperture) It is the upper opening of the thoracic cage at its junction with the root of the neck Boundaries &structures : Discussed in details later in this section

Thoracic outlet (inferior aperture) It is the lower opening of the thoracic Cage at its junction with The abdomen Boundaries and structures passing through it will be discussed later

Intercostal Nerves They are the ant. 1ry rami of the thoracic nerves. 11 pairs (relating to thoracic vertebrae 1-11) 1 subcostal nerve which relates to T12 May be motor and/or sensory Consists of two main branches: Lateral cutaneous branch – which then subdivides into the posterior and anterior branch Anterior cutaneous branch – which then subdivides into the medial and lateral branch Supply the intercostal spaces and muscles

Classification of intercostal nerves 1) 2 special nerves : 1st nerve, most of its fibers ascend to join the brachial plexus The last (subcostal), runs all its course in the abdominal wall 2) 5 typical intercostal nerves : from 2nd to 6th intercostal nerves, they run all their course in the thoracic wall 3) 5 non-typical nerves: from 7th to 11th , part of their course in the thoracic wall and part in the abdominal wall

Branches of the intercostal nerves 1- Ganglionic branches 2-Collateral branches (motor) 3-Lateral cutaneous branch 4-Anterior cutaneous branch 5-Muscular branches 6-Pleural and peritoneal branches 7-Articular branches

Vascular Components Each intercostal artery joins (anastomoses) with a major artery at each end of the intercostal space Posteriorly the intercostal arteries are branches of the aorta anteriorly the intercostal arteries are branches of the internal thoracic artery

The Thoracic cavity Filled laterally by the lungs - each lying in its pleural cavity Space between the pleural cavities = mediastinum Heart (lying in its pericardial sac) Great vessels Oesophagus Trachea Thymus Thoracic duct and other major lymph trunks Lymph nodes Phrenic and vagus nerves

The thoracic inlet Also known as the superior thoracic aperture Ring formed of: T1 (body of first thoracic vertebra) (post.) 1st ribs (on either side) Manubrium (ant.)

Contents of Thoracic Inlet Great vessels heading for neck and upper limb: Common carotid artery Internal jugular vein Subclavian artery and vein (vein anterior to artery) Esophagus Trachea Nerves and lymphatic system Also apex of the right lung is superior to the clavicle

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