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