Transverse sections of thorax at levels T2,3,5,8 and 9

Question 1

Cross section at T2- Cutting the superior mediastinum above the aortic arch

Answer 1

Here we are above the level of the Aortic Arch, at the point where the main branches (Brachiocephalic, Left Common Carotid & Left Subclavian) have emerged.

In the Respiratory System the Trachea lies postero-medial to the Brachiocephalic Artery as a midline structure, anterior to the Oesophagus, which causes a relatively flattened posterior aspect on the Trachea.

Both the Oesophagus and Trachea lie anterior to the body of the Vertebra.

Note the presence of the Thoracic Duct medial to the Left Subclavian Artery and the Brachiocephalic Veins anterior to the Arterial structures and the absence of the Manubrium Sterni (we are above it!).

Question 2

Crosssection at T3- superior mediastinum ( little lower than the one above)

Answer 2

We are looking at a slightly lower level that is inferior to the Aortic Arch giving its major branches. The Arch is visible as a structure that commences near the median plane before deviating postero-laterally to the left.

See how the Manubrium Sterni is the most anterior structure if the thorax in the midline.

One may also see the openings of: *Brachiocephalic; *L.Common Carotid; *L.Subclavian A.

Observe the presence of the Left Phrenic and Left Vagus Nerves, lateral to the Aortic Arch; and the Right Vagus Nerve just visible near the Trachea. The Right Phrenic Nerve is not shown here, but lies alongside the Right Brachiocephalic Vein and then the SVC.

Question 3

Cross section at T5- Through anterior, middle and posterior mediastina.

Answer 3

NB: T4-T5 Intervertebral Disc is the Angle of Louis an exciting area anatomically with much happening! Remember that the Angle of Louis is where the Ascending Aorta officially becomes the Aortic Arch, and then the arch becomes the Descending Aorta. It is also the level at which the Trachea bifurcates into the Left and Right Main Bronchi.

At this level shown (a fraction below the Sternal Angle) one may see the Thymus very clearly posterior to the Manubrium but anterior to the Ascending Aorta.

Note the prominent Pulmonary Trunk found posterior to, and slightly left of the Ascending Aorta, but also dividing into its Left and Right Pulmonary Arteries.

Posterior to the Pulmonary Trunk are the Right and Left Main Bronchi which lie anterior to Oesophagus.

Observe the position of the SVC touching the lateral aspect of the Aorta on the Right side and lying anterior to the Right Pulmonary Artery. The Right Phrenic Nerve lies immediately lateral to the SVC.

Question 4

Cross section at T8 - Through the heart

Answer 4

At last all 4 Cardiac Chambers are visible! Note how the Heart lies primarily to the Left of the Midline.

One may differentiate Anterior, Middle & Posterior Parts of Inferior Mediastinum and also the coronary arteries may be seen.

The Descending Aorta is posterior to the Left Atrium and slightly to the left of the midline; where as the Oesophagus (posterior to the Left Atriun) extends across the median plane just to the right.

Question 5

Cross section at T9 - Showing the heart and upper abdominal contents

Answer 5

Here we are just barely below the section above, but note that we are now cutting through the abdomen.

On the right side note the Liver (just inferior to the Diaphragm)

The Dome of Right Diaphragm is usually higher than the left due to the Liver below it.

Note the now prominent Inferior Vena Cava extending posterior to the Right Atrium (just before entering it) and lying medial to the Liver on its descent beyond the Diaphragm.