Thoracic Wall and Mediastinum Anatomy

• Students should understand the muscles and bones of the thoracic wall
• Students should a general understanding of the mediastinum boundaries
• Students should understand the anatomy of the anterior and superior mediastinum

Surface Landmarks

• The jugular notch is at the level of the T2 vertebra, where the trachea is palpable
• The sternal angle is at the articulation of rib 2 and the level of the T4 vertebra
• The nipple marks the T4 dermatome and the approximate location of the dome of the diaphragm
• The xiphoid process is at the inferior aspect of the sternum and the anterior attachment point of the diaphragm

Breast Anatomy

• Breasts consist of alveolus', suspensory ligaments, fat lobules, lactiferous sinus, areola, and nipple
• Breasts contain a retromammary space (bursa) and subcutaneous tissue
• The pectoralis minor and major are both related to the breasts
• The intercostal space is also related to the breasts
• Mammary gland lobules are present when resting and lactating
• Pectoral fascia form part of the breasts
• Lactiferous ducts make up part of the breasts and connect to the mammary gland lobules

Blood Supply and Lymphatics of the Breasts

• The breasts receive blood supply from the subclavian a, axillary a, brachial a, and the lateral thoracic a.
• Other blood supplies are the thoraco-acromial trunk, lateral mammary branches, the lateral mammary branches of the lateral cutaneous branches of the posterior intercostal aa.
• Arteries of the mammary gland are also part of the breasts

Bony Thoracic Wall

• The bony thorax consists of the sternum, 12 pairs of ribs with costal cartilages, and 12 thoracic vertebrae
• The superior thoracic aperture and inferior thoracic aperture also contributes

Superior Thoracic Aperture

• The superior thoracic aperture consists of the body of the T1 vertebra, the first pair of ribs and costal cartilages, and the manubrium of the sternum
• Structures passing through are the trachea, esophagus, and nerves & vessels for the head, neck, & upper limbs

Inferior Thoracic Aperture

• The inferior thoracic aperture consists of the body of the T12 vertebra, rib pairs 11 & 12, costal margins, and the xiphisternal joint
• Inferior thoracic aperture is closed in life by the diaphragm

Ribs

• There are different classifications of ribs, based on bony features and connection with the sternum
• Typical ribs (3rd-9th) have a wedge-shaped head with 2 articular facets separated by a crest
• The neck connects the head and body at the tubercle
• Ribs have articular and non-articular tubercles, a thin, flat, and curved body
• Atypical ribs are 1st, 2nd, 10th-12th
• True ribs (1st-7th) connect directly via their own cartilage
• False ribs (8th-10th) connect indirectly via cartilage of ribs above
• Floating ribs (11th, 12th) have no connection to the sternum and end in the posterior abdominal wall musculature

Typical Rib Articulations

• The head articulates with the body of its own vertebra and the vertebra above
• The tubercle has an articular part for the transverse process and a non-articular part for the costotransverse ligament
• The costal angle is the most curved part of the body
• The costal groove is on the internal surface of the inferior border of the body and protects intercostal vessels and nerves

Atypical Ribs: 1st Rib

• Has a single facet on the head
• It articulates with T1 only
• Has grooves for subclavian vessels on the superior surface
• The grooves are separated by the scalene tubercle (anterior scalene muscle)

Atypical Ribs: 2nd Rib

• Has a rough area on the upper surface
• It has tuberosity for the serratus anterior muscle

Atypical Ribs: 10th-12th Ribs

• Have a single facet on the head
• They articulate with a single vertebra

Atypical Ribs: 11th and 12th Ribs

• Short, with no neck or tubercle

Intervertebral Joints

• Synovial plane joints connect articular facets (zygapophyseal joints)
• 2° cartilaginous joints connect bodies

Costovertebral Joints

• The joints connect the vertebrae, ribs, and surrounding ligaments

Respiratory Movements: Pump Handle

• Ribs 1-6 demonstrate a pump handle movement

Respiratory Movements: Bucket Handle

• Ribs 7-12 demonstrate a bucket handle movement

Respiratory Movements: dimensional changes

• In anterior-posterior dimension the sternum moves anteriorly and superiorly
• In the lateral dimension the lower ribcage moves laterally
• In the vertical dimension the diaphragm descends
• The diaphragm is the primary muscle of resting inspiration

Sternocostal Joints

• For rib 1, there is a 1° cartilagenous joint(synchondrosis)
• For ribs 2-7, there are Synovial Plane Joints
• Between 6&7, 7&8, 8&9, there are Interchondral Joints made with Synovial Plane Joints
• Between 9&10, there is a Fibrous Joint

External Intercostal Muscles

• Fibers pass downwards and forwards
• Attach to tubercles at the costochondral junction
• Replaced anteriorly by the external intercostal membrane
• They raise the ribs in inspiration

Internal Intercostal Muscles

• Fibres pass downwards and backwards
• Goes from the sternum to the angle of the ribs
• Replaced posteriorly by the internal intercostal membrane
• The Interosseous part depresses the ribs and the Interchondral part raises ribs

Innermost Intercostal Muscles

• Located deep to the lateral part of the internal intercostal muscles
• Fibres pass downwards and backwards

Subcostal

• Near the angle of the ribs
• Spans 1 or 2 Intercostal spaces
• Fibres may blend with the Innermost Intercostal muscles

Transversus Thoracis

• Radiates from the sides of the sternum to costal cartilages 2-6

Scalenes

• Attach to the Serratus Posterior

Major Muscles

• Pectoralis major (medial and lateral pectoral nerves)
• Pectoralis minor (medial pectoral nerve)
• External oblique (anterior rami)
• Rectus abdominis (anterior rami)
• Serratus anterior (long thoracic nerve)

Intercostal Space

• Innermost intercostal, subcostal muscle, and the posterior intercostal (vein, artery, nerve)
• External intercostal present

Neurovascular Structures: Anterior Ramus (intercostal nerve)

• Muscular branch, internal intercostal membrane, external intercostal and internal intercostal are related to it

Intercostal Arteries: Posterior

• 1&2 from Supreme Intercostal a. (branch of costocervical trunk from subclavian a) and 3-11, subcostal from Thoracic Aorta

Intercostal Arteries: Anterior

• 1-6 Direct from Internal Thoracic a. 7-9 from Musculophrenic a.

Venous Drainage

• Anterior Intercostal veins drain into the Internal Thoracic Vein
• Posterior Intercostal veins drain into the Azygos/Hemiazygos Venous System

Divisions of the Thoracic Cavity

• Right Hemi-thorax and Left Hemi-thorax separate by the Mediastinum
• Divisions include: Superior, Anterior, Middle lungs

Anterior Mediastinum

• The boundaries are the Body of sternum, Pericardium, Transverse thoracic plane and Diaphragm
• It is Larger in children due to the thymus

Middle Mediastinum

• Consists of the Heart and Pericardium
• Adjacent structures are Great vessels, Phrenic nerves, and the Lung root structures

Superior Mediastinum Boundaries

• Consists of the Manubrium, Bodies of T1-T4 vertebrae, Transverse thoracic plane, Thoracic inlet, and Parietal Pleura

Contents of the Superior Mediastinum

• Anterior to posterior contents: Thymus, Brachiocephalic veins and SVC, Arch of Aorta, Trachea, Oesophagus, Associated nerves (phrenic and vagus), Thoracic duct and lymphatics

Great Vessels

• LCC, Brachiocephalic Trunk, Right Subclavian a, 1st rib, Right Brachiocephalic v, SVC, Left Subclavian a, Arch of Aorta, Left Brachiocephalic v

Trachea

• Begins below the larynx (C6/7) to Carina (Transverse thoracic plane; T4/5)
• Has C-shaped cartilages anteriorly and the Trachealis muscle posteriorly

Oesophagus

• The esophagus Begins at C6 and pierces the diaphragm at T10, taking a short abdominal course
• It has 3 Constrictions: Arch of aorta, the Left bronchus, and the Diaphragm

Vagus Nerve (X) Right:

• Anterior to the right subclavian a
• Loops to the Right recurrent laryngeal n. under the RSC

Vagus Nerve (X) Left:

• The nerve located Between the left common carotid and left subclavian aa
• Has looped recurrent laryngeal n. under the arch of aorta

Vagus Nerve (X) Contribution

• Contributes to the Cardiac Plexus deep to arch of aorta
• Contributes to the Right and Left Pulmonary plexus on right and left main bronchi

Oesophageal Plexus

• Formed from Vagus Nerve (X)
• Also Continue as Anterior and Posterior Vagal Trunks (mainly left and right nerves respectively)

Phrenic Nerves - Right

• Runs alongside right brachiocephalic v., SVC and pericardium over right atrium
• Anterior to the root of the right lung and pierces the diaphragm near the caval opening

Phrenic Nerves - Left

• Lies between the left subclavian a. and v. and to the left of the arch of aorta anterior to vagus onto surface of pericardium over left atruim and ventricle
• Anterior to the root of the left lung onto pierces diaphragm to the left of pericardium