Mediastinum: must know SAQs

Mediastinum

1. Define mediastinum with different subdivision.
2. Give the boundary of superior / inferior (anterior/ middle/ posterior)  mediastinum and list their content. 
3. how many vertebra present just behind the menubrium sternae 
4. sternal angle present in which level of vertebra  
5. which tumor involve superior , middle and posterior mediastinum ? 
6. which pathological condition widen mediastinum? 
7. what do you mean by pneumomediastinum? 
8. discuss cranial and caudal communication of mediastinum :  The mediastinum communicates cranially with the fascial planes of the neck via the thoracic inlet. Caudally the mediastinum communicates with the retroperitoneal space through the aortic hiatus. These communications provide the means for the spread of mediastinal disease to the neck and abdomen and vice versa.
9. how many mediastinal reflections are present in our body? There are three mediastinal reflections (Figs 1, 2, and 3) two of which are frequently identified in normal thoracic radiographs: (1) the cranioventral mediastinal reflection; (2) the caudoventral mediastinal reflection; and (3) the vena caval mediastinal reflection or the plica vena cava.
   The cranioventral mediastinal reflection is caused by extension of the right cranial lung lobe across the midline, pushing the mediastinum to the left. It is usually visible on the ventrodorsal or dorsoventral projection as a curvilinear soft tissue opacity extending from T1 or T2 to the cranial left border of the heart (approximately the level of the pulmonary artery segment). The thymus lies in this reflection. On the lateral projection, the cranioventral mediastinal reflection and the margin of the right cranial lobe may frequently be identified immediately cranial to the heart.
   The caudoventral mediastinal reflection is caused by extension of the right accessory lung lobe across the midline and is only seen on some ventrodorsal or dorsoventral radiographs. It is seen as a relatively straight, soft tissue opaque line extending from the left apex of the heart caudally to approximately the middle of the left diaphragm.
   The caudal vena caval mediastinal reflection, or plica vena cava, is not visible.
10.  DISCUSS RADIOGRAPHIC ABNORMALITIES OF THE MEDIASTINUM:
    
    Radiographic abnormalities of the mediastinum are related to:
    1.  Positional abnormalities (mediastinal shift)
    2.  Mediastinal effusion
    3.  Mediastinal masses
    4.  Abnormal visualization of mediastinal structures (pneumomediastinum)
11.  Discuss cause of mediastinal shift :
    
    A mediastinal shift occurs when the mediastinum is displaced by pressure differences between the right and left pleural cavities.
    Mediastinal shift is diagnosed by evaluating the position of the heart, trachea, aorta and caudal vena cava or the mediastinal reflections on dorsoventral or ventrodorsal views.
    When a mediastinal shift is seen on a radiograph, we must:
     Examine for a technical artifact, because rotation of the animal will mimic mediastinal shift
     Check for underlying lung disease (atelectasis or bronchial obstruction)
     Look for signs of a previous or present pleural disease
     Look for concomitant changes of the diaphragm, the spine or the thoracic wall.
12.  what do you mean by mediastinal effusion ?
    Free mediastinal fluid is usually of soft-tissue opacity; therefore, it may appear radiographically as a mediastinal mass or as cardiomegaly if it collects around the heart, or both.
    Mediastinal fluid may results in reverse fissures lines as fluid dissects into the interlobar fissures from hilar region. The reserve fissures line are wide centrally and narrow peripherally.
    The more common causes of mediastinal fluid are:
    1.  Feline infectious peritonitis
    2.  Trauma
    3.  Coagulopathy
    4.  Oesophageal perforation
    5.  Mediastinal masses
    
    
    
    
    

Thoracic Wall, thoracic cavity : must know SAQs

Thoracic Wall, thoracic cavity

1. Give the skeletal boundary of thoracic cage. Write content of thoracic cavity
2. Give the boundary of thoracic inlet. Discuss the name of structures passing through it.
3. Give the  boundary of thoracic outlet. Which structure cover the outlet?
4. What do you mean by typical intercostals space? Discuss blood and nerve supply of it
5. What do you mean by intercostals nerve ?
6. Discuss the difference between spinal nerve and intercostals nerve
7. Mention the name of intercostal muscles with origin, insertion & nerve supply
8. What do you mean by innermost intercostalis?
9. Identify sternal angle and write importance of sternal angle.
10. Joint: sternocondal jt & costochondal jt formation & type.
11. What do you mean by i) True ribs ii) False rib iii) Floating ribs
12. How can you inserting a chest tube without damaging intercostal vessels and nerves?
13. A needle inserted into the 9th intercostal space along the midaxillary line would enter which space?
14. Discuss branches of subclavian artery, intercostals artery , descending thoracic aorta
15. Which  line of the thorax is formed by the pectoralis major muscle
16. Give posterior relation of sternum and intercostals groove
17. Give relation of superior surface of 1^st rib

Mediastinal part of right and left lung

Mediastinal part of lung:

the impression and relation of mediastinal surface differ in two lungs

Mediastinal surface of right lung:

Cardiac area is related with   Anterior surface of Right auricle, Anterior and right surface of right atrium,  Part of anterior surface of right ventricle  

In front of hilum upper part : Groove for SVC

In front of hilum lower part groove for  IVC are present

Above the hilum : groove for azygous vein

Behind the hilum : osophagus except upper and  lower part

From apex to groove for azygous vein:Anterioposteirly

Right brachiocephalic vein,Trachea,Osophagus

Three neural structures:right phrenic nerve, Right vagus nerve, Right sympathetic chain

Mediastinal surface of left lung

Cardiac area is related withAnterior and left surface of left ventricle and left auricle, Anterior surface of a part of the right ventricle

In front of hilum : upper part impression for ascending aorta

Just below and little in front  the ascending aorta , the impression for pulmonary trunk is present

Above the hilum : arch of aorta

Behind the hilum: descending thoracic aorta and osophagus present just above  and below the descending aorta

So osophagus is related twice with the left lung  

From apex to groove for arch of aorta  

Anterioposteirly

Left common carotid arter,Left subclavian artery,Trachea,Osophagus,Thoracic duct

Four neural structures

Left  phrenic nerve

Left  vagus nerve

Left recurrent laryngeal nerve

Right sympathetic chain

Summary of pleura

pleura

Pleura, plural

Pleurae , singular

Origin of word : Greek   [Gr.]

The serous membrane investing the lungs (visceral p.) and lining the walls of the thoracic cavity (parietal p.); the two layers enclose a potential space, the pleural cavity. The two pleurae, right and left, are entirely distinct from each other.pleu´ral cavity .

The glistening surface of the pleura is made up of a sheet of flat cells, the mesothelium, which covers an underlying layer of loose elastic tissue. The pleura exudes a thin fluid that keeps it moist and lubricated.

Major disorders of the pleura include pleurisy, the inflammation of the pleura; pleural effusion, the accumulation of excess fluid between the visceral and parietal pleurae; empyema, the collection of pus in the pleural space; mesothelioma and other tumours of the pleura; chylothorax, the rupture of the thoratic duct; hemothorax, the accumulation of blood in the pleural space; and fibrothorax, the encasement of the lung in fibrin following a severe pleural inflammatory process such as empyema.

Normally, there is no air in the pleural space and, if air should enter, perhaps as the result of a stab wound or a diseased lung, the increase in pressure causes the lung to collapse. Air in the pleural space is known as pneumothorax. If the pleural space becomes continuous with the air outside, after a piercing injury for example, this is called an open pneumothorax.

Pleura: /pleu·ra/ (ploor´ah) pl. pleu´rae   [Gr.] the serous membrane investing the lungs (visceral p.) and lining the walls of the thoracic cavity (parietal p.); the two layers enclose a potential space, the pleural cavity. The two pleurae, right and left, are entirely distinct from each other.pleu´ral cavity .

 

Parietal pleura : it is the outer part of serous sac which lines the thoracic wall and mediastinum.

It develops from somatopleuric layter of lateral plate mesoderm .Innervated by somatic nerves

It is sensitive to pain

Blood supply and lymphatic draianage is same as that of thoracic wall 

Visceral pleura

Lines the surfeces of lung except hilum.  It develops from splanchnopleuric layter 

of lateral plate mesoderm. Innervated by autonomic nerves

It is insensitive to pain. It  is only sensitive to stretch.

Blood supply and lymphatic drainage is same as that of the lung