Thorax

Thorax

1. Thoracic cavity

   • contains the lungs, heart, aorta, part of the trachea and the oesophagus
     • the contents of the thoracic cavity is protected by the thoracic wall
       • the thoracic wall consists of the sternum, thoracic vertebrae (T1-T12), 12 pairs of ribs with their costal cartilages, intercostal muscles that fill the intercostal spaces and the arteries and nerves that supply the wall
         • the pectoral muscles are considered upper limb muscles, not part of the thoracic wall
         • ribs
           • true ribs
             • costal cartilage attaches directly to the sternum
               • the first rib that can be felt during physical examination is the second pair of ribs
               • costal cartilage provides flexibility and absorbs shock
             • ribs 1-7
           • false ribs
             • costal cartilage attaches to the cartilage above
             • ribs 8-10
           • floating ribs
             • do not attach to the sternum at all
             • ribs 11&12
           • articulates with demifacets of vertebrae
             • on the transverse processes of the vertebrae there is a facet for articulation with the tubercle of the rib
             • there are 4 demifacets on most vertebrae and each demifacet is for articulation with the rib
               • typical ribs: the head of the rib articulates with the superior demifacet of the corresponding vertebra and the inferior demifacet of the vertebra superior to it
               • atypical ribs: the head of the first rib only articulates with T1, the head of ribs 10-12 only articulate with their corresponding vertebra and ribs 11&12 do not articulate with the transverse process
             • the symphathetic chain runs lateral to the verbal bodies
               • bilateral
                 • composed of ganglia, cell bodies of post-ganglionic neurons and these are joined together by the ascending and descending pre-ganglioni neurons
                   • extends from the base of the skull to the coccyx where they form the unpaired coccygeal ganglion
                     • 22-23 pairs of ganglion in the cervical region
                       • 11 in the thoracic region
                         • 4 in the lumbar region
                           • 4-5 in the sacral region
                     • preganglionic nerves from the spinal cord synapse at one of the ganglia and the postganglionic fibres will come out and extend to the visceral organ
                       • as a general rule, the nerve fibres of the sympathetic NS begin at the spinal cord
                         • they arise from the thoracolumbar regions (T1-L2) and they arise at the lateral horn of the spinal cord
                           • they emerge via the ventral roots of the spinal cord
                             • they pass into the ganglion via the white ramus communicans
                               • preganglionic sympathetic fibres can either run up the chain to synapse further up, they can synapse at the level they enter/are already at, they can pass straight through the chain and synapse somewhere else or they can run down the chain and synapse further down the chain
                                 • once the preganglionic nerve has synapsed, we then have a postganglionic neuron, which goes through the grey ramus communicans and passes out of the chain to the effector organ
         • the thoracic cage is open superiorly and inferiorly
           • the diaphragm separates the thoracic and abdominal cavities
             • there are two domes of the diaphragm: left and right
               • the dome projects upwards to reach the level of the 5th rib
                 • the dome shape means that the abdominal organs are also protected by the ribs
                   • the central tendon is at the top and medial part of the diaphragm
                     • when the diaphragm contracts it becomes flatter due to the central tendon
                       • contraction of the diaphragm increased the superoinferior dimensions of the thorax, while elevation of the ribs increases the anteroposterior and lateral dimensions
             • apertures in the diaphragm
               • a hiatus hernia is the protrusion of an organ, typically the stomach, through the oesophageal opening (oesophageal hiatus), the part of the organ that passes through the hiatus will be compressed, it differs from congenital diaphragmatic hernia which is a congenital malformation of the diaphragm, concengital diaphragmatic hernia causes lung hypoplasia (underdevelopment) as the pushing of the organ gives little space for development and can push the heart over to the right side
               • hiatus hernia often causes reflux as stomach acid moves into the oesophagus more easily, this is more common in those over 50, the risk factor for a hiatus heria includes anything that increases intra-abdominal pressure
               • T8
                 • inferior vena cava goes through the diaphragm
                   • caval hiatus
               • T10
                 • oesophagus goes through the diaphragm
                   • oesophageal
               • T12
                 • aorta goes through the diaphragm
                   • aortic hiatus
               • paradoxical breathing occurs due to the diaphragm moving in the opposite direction to normal
                 • inspiration: ribs move inwards as there is no muscle tone to resist the decrease in intrapleural pressure expiration: ribs are pushed outwards by increasing the pressure reduces vital capacity
                 • attachments of the diaphragm
                   • L1-L3 vertebrae
                   • inferior 6 costal cartilages and adjacent ribs
                   • xiphoid process
                 • when breathing quietly, the diaphragm moves 1-2cm but when breathing if forced it can move 6-10cm
                   • nerve supply to the diaphragm
                     • motor
                       • phrenic nerve (C3,4,5 keeps the diaphragm alive)
                     • sensory
                       • phrenic nerve centrally
                       • lower intercostal nerve (T6-11)
                       • subcostal peripherally (T12)
                     • a spinal cord injury at the level of C1 or C2 would cause paralysis of the diaphragm and the person would require mechanical vetilation
           • in the thoracic cavity, the medial part is the mediastinum and the two lateral sides are the pulmonary cavities
             • the pericardial cavity surrounds the heart while the pleural cavity surrounds the lungs
               • as the organ (heart or lung) develops, it pushes into the serous memrbane
                 • there are potential spaces between the costal and diaphragmatic pleura that the lungs can move into during inspiration
                   • pleural recesses
                     • costodiaphragmatic recess
         • there are 3 layers of intercostal muscles
           • external
             • occupies the ribs from the posterior of the ribs to the costochondral junction
               • anteriorly it becomes the external intercostal membrane
             • most active during inspiration
           • internal
             • occupies spaces from the most medial part of the costal cartilage up to the angle of the ribs
             • most active during expiration
           • innermost
             • deep part of the internal intercostal muscles that form an incomplete layer which is most obvious laterally
             • the intercostal neuromuscular bundle lies between the internal and innermost intercostals
               • the sharper edge of the ribs protects the neuromuscular bundle
                 • the anterior rami of T1-11 spinal neves form the intercostal nerves and the anterior ramus of T12 spinal nerve forms the subcostal nerve
                   • posterior roots of the spinal nerves innervate muscles of the back but anterior roots innervate the intercostal muscles
                     • collateral vessel branches are located more inferiorly
                       • collateral branches are organised as NAV instead of VAN, like the vessels in the neuromuscular bundle
                         • the safest route to insert a needle to perform a thoracentesis is superior to the rib, just enough to avoid damaging the neurovascular bundle and collateral branches
                           • thoracentesis exraction of liquid from the pleural cavity pericardialentesis - extraction of liquid from the pericardium
                     • the posterior intercostal artery originates from the aorta while the anterior intercostal artery originates from the internal thoracic artery or its branches
                       • upper 6 anterior intercostal arteries originate from the internal thoracic artery and the musculophrenic artery gives off the lower anterior intercostal arteries
                       • posterior and anterior intercostal arteries anastomose
                         • these forms alternative roots doe the blood to get to and from the heart if there is a blockage
                         • the internal thoracic artery (mammary artery) originates from the subclavian artery
                           • it bifurcates into musculophrenic and superior epigastric arteries
                           • if there is restriction of the proximal aorta, the internal thoracic arteries and anterior intercostal arteries can expand to maintain the blood supply
                       • most of the posterior intercostal arteries arise from the back of the thoracic aorta but the 1st and 2nd posterior intercostal arteries arise from a branch of the subclavian artery (the supreme intercostal artery)
                         • blood flow
                           • subclavian artery
                             • internal thoracic artery
                               • anterior intercostal arteries
                                 • posterior intercostal arteries
                                   • aorta
                                     • rest of body
                     • dorsal thoracic ramus innervates intrinsic muscles of the back
                     • ventral thoracic ramus innervates a variety of component like the brachial plexus and the intercostal muscles
                     • SAME DAVE
                       • sensory afferent, motor efferent - dorsal afferent, ventral efferent
         • abdominal muscles and the pectoral girdle are accessory muscles for respiration
   • the left vagus nerve gives off the left recurrent laryngeal branch nerve as it goes over the aorta
     • the nerve travels inferior to the aorta, on the posterior part of the hilum
     • the left recurrent laryngeal nerve passes posteriorly to the ligamentum arteriosum
       • innervates all the intrinsic muscles of the larynx allowing breathing and speaking, on the left it goes around the aorta and on the right it goes around the subclavian artery, on the left it goes under the ligamentous arteriosus
   • the left phrenic nerve passes over the aorta an then over the more anterior part of the heart

2. Cardiac tamponade

   • clinical syndrome where there is accumulation of fluid or blood in the pericardial cavity

3. Pectus deformities

   • pectus excavatum
   • pectus carinatum

4. Sternum

   • jugular notch is also called the suprasternal notch
   • sternal angle is also called the angle of Louis
     • inferior border of the manubrium and superior border of the sternal body
       • it indicates the border between the superior and inferior mediastinum and corresponds to the 2nd pair of ribs
         • the top of the manubrium (T1) and the sternal angle (between T4&5) make up the superior and inferior borders of the superior mediastinum
           • the transverse thoracic plane passes through the bifurcation of the trachea, superior limit of the pericardium, the start and end of the aortic arch and the superior vena cava
           • the inferior mediastinum is split into 3 parts: anterior, middle and posterior inferior mediastinum
             • the posterior inferior mediastinum contains the oesophagus, descending thoracic aorta, azygous and heme-azygous vein and the thoracic duct
             • the heart is the largest organ in the middle inferior mediastinum
             • the lungs are separated from each other by the mediastinum
               • the root of the lung contains structures that attach the lung to the mediastinum
                 • the hilum is the area where these structures enter and leave the lung
                   • the lymph nodes, if enlarged, can occlude the blood vessels and bronchi
                   • 1cm away from the hilum is the root of the lung
               • the pulmonary artery becomes lobular lobular and segmental arteries in the lungs
               • the arch of the descending aorta, the descending thoracic aorta, the superior vena cava and the azygous vein are some of the structures that have impressions on the mediastinal surfaces of the left and right lung
   • xiphoid process
     • composed of hyaline cartilage (like costal cartilages)
     • with age it gradually becomes bone
       • calcification does not usually occur until >40 and can present as a lump

5. Heart

   • veins are always more superficial than arteries of the heart region
   • great vessels of the heart are the pulmonary trunk and the aorta
   • external features
     • between the atria and ventricles, anteriorly, lies the atrioventricular groove
       • also called the coronary sulcus
     • between the ventricles lies the anterior interventricular artery
     • anteriorly, only the auricle of the left atrium can be seen
       • auricle is the rough part of the atrium
     • posteriorly, the posterior interventricular artery lies between the ventricles
     • coronary arteries
       • variations
       • there are sparse anastomoses between coronary artery branches
   • cardiac veins
     • most drain to the coronary sinus
       • lies in the atrioventricular groove posteriorly and drains to the right atrium
         • other veins
           • the azygous venous system is found on either side of the vertebral column
             • they drain the visceral within the mediastinum as well as the posterior abdominal wall and thoracoabdominal walls
               • right posterior intercostal veins, the hemi-azygous and accessory semi-azygous veins and the right ascending lumbar veins are all tributaries to the azygous vein
                 • the azygous vein drains to arches over the right lung root and it forms a communication between the inferior and superior vena cava
                   • this means that if the inferior vena cava or superior vena cava is blocked, then venous blood has an alternative route to the heart
     • some small veins on the anterior surface will drain directly into the right atrium
     • 3 main coronary veins
       • the great coronary vein
       • middle coronary vein
       • small cardiac vein
   • cardiac referred pain
     • visceral sensory nerves on the heart and somatic sensory nerves in dermatomes T1-4
   • the sinus centrum is the smooth wall of the heart and the pectinate muscles is the rough wall of the heart
     • the crista terminals is a vertical ridge/boundary of smooth myocardium within the right atrium and it makes the boundary between the smooth and rough wall
   • both ventricles of the heart have trabecular carnae (rough muscular wall), papillary muscles and chordae tendinae
   • nerve fibres reach the heart from the cardiac autonomic plexus which is situated at the base of the heart
     • this contains sympathetic and parasympathetic nerves
       • it is divided into a superficial, which lies beneath the aortic arch and in front of the right pulmonary artery, and a deep part
         • the superficial part is formed by the superior cervical cardiac branch of the left sympathetic trunk and the inferior branch of the left vagus nerve
           • there is also a small ganglion that is sometimes visible in this area called the cardiac ganglion of Wrisberg
             • both parts are in quite good communication with each other
         • the deep part of the cardiac plexus is situated in front of the bifurcation of the trachea (carina)
           • it is derived from the cervical ganglia of the sympathetic trunk and also branches of the vagus and recurrent laryngeal nerves
       • the sympathetic nerves originate from T1-4 and the parasympathetic nerves originate from the vagus nerve
         • in heart transplants the sympathetic and parasympathetic nerves are severed but the heart will continue to beat as it is auto rhythmic

6. Lungs and pleura

   • superiorly, the pleural cavity extends 2-3cm above the medial clavicle
     • therefore, a possible consequence of a neck puncture wound could be a haemothorax or a pneumothorax
       • pneumothorax
         • air in the pleural cavity
       • haemothorax
         • blood in the pleural cavity
       • chylothorax
         • chyle in pleural cavity
           • chyle is lipid rich lymph fluid
       • empyema
         • pus in pleural cavity (e.g. pneumonia)
   • physical examination with stethoscope
     • above medial clavicle
       • apex of the lung
     • 2nd intercostal space
       • superior lobe of the lung
     • 4th intercostal space (midclavicular line)
       • middle lobe of the right lung
     • 6th intercostal space (lateral clavicle)
       • inferior lobe
   • atelectasis is a partial or incomplete inflation of the lung which is caused by obstruction of the lung
   • respiratory system can be divided into the conducting and respiratory portions
     • conduction: nasal cavities - terminal bronchioles respiratory: respiratory bronchioles to alveoli

7. Left internal jugular veins joins the left subclavian vein to form the left brachiocephalic vein

   • superior vena cava
     • azygous vein lies posterior to the superior vena cava and drains directly into it

8. Lymphatics

   • the body produces 10L of interstitial fluid per day
     • 3L of this fluid enters the lymphatic system
       • the thoracic duct drains chyle from most of the body and it is the main lymphatic duct of the system
         • it originates at the cisterna chyle in the abdomen (at L2) and enters the thorax through the aortic hiatus
           • the thoracic duct enters the venous system at the left venous angle
             • junction of the internal jugular and subclavian veins
           • chyle is a milky form of lymph that contains emulsified fats and other by-products of digestion
             • comes from the abdominal region and passes into the thoracic duct
               • most of the body, apart from the right side of the head, neck, thorax and right arm, is drained by the thoracic duct
                 • other areas are drained by the right lymphatic duct into the right venous angle
         • the left supraclavicular lymph node is commonly referred to as Virchow's node
           • this is the last shared common pathway of lymph originating from the abdomen
           • swelling of Virchow's node is often the first sign of abdominal malignancy
             • swelling is called Trosier's sign
             • swelling of the right supraclavicular lymph node suggests malignancy in the thoracic region

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