Surface anatomy of thoracic organs

Surface anatomy of thoracic organs - Practical Handout

Surface lines 

For clinical purposes, and for convenience of description, the surface of the thorax has been mapped out by arbitrary lines. On the front of the thorax the most important vertical lines are the midsternal, the middle line of the sternum-, and the midclavicular, which runs vertically downward from a point midway between the centre of the jugular notch and the tip of the acromion. This latter line, if prolonged, is practically continuous with the lateral line on the front of the abdomen. Other vertical lines on the front of the thorax are the lateral sternal along the sternal margin, and the parasternal midway between the lateral sternal and the midclavicular.
On either side of the thorax the anterior and posterior axillary lines are drawn vertically from the corresponding axillary folds: the midaxillary line runs downward from the apex of the axilla.
On the posterior surface of the thorax the scapular line is drawn vertically through the inferior angle of the scapula.

Surface marking of pleurae

The lines of reflection of the pleurae can be indicated on the surface of the chest. Surface mark the pleurae on a volunteer student according to the following description.
It projects 2.5 cm above the medial third of the clavicle. It passes behind the sternoclavicular joint to reach the midsternal line at the level of the 2nd rib. It passes vertically down along the midsternal line to the level of the 6th costal cartilage on the right side. On the left side it passes only up to 4th costal cartilage from where it curves out laterally halfway towards the apex of the heart. From these points each turns laterally and downwards, meeting the 8111 rib at the midclavicular line, 10th rib at the midaxillary line, 12th rib at the lateral border of the erector spinae and from there they run horizontally to the spinous process of the 12th thoracic vertebra. Refer the table to locate the important points.

Surface marking of lungs

Surface marking of the lungs coincide with that of the pleurae on each side at the apices and their upper parts. The anterior borders of lungs lie just lateral to the midsternal line but within the lateral sternal borders. Lower borders of lungs overlap 6th rib at the midclavicular line, 8th rib at the midaxillary line and 10th rib at the lateral border of the erector spinae.
A line joining the spine of 3rd thoracic vertebra to the 6th rib in the midclavicular line indicates the position of the oblique fissure on each side. This is approximately the line of the 5'h rib or the vertebral border of the scapula when the arm is fully abducted.
On the right side a line passing through the 4th costal cartilage to meet the oblique fissure at the midaxillary line indicates the horizontal fissu

Midsternal line

Pleura
2nd to 6th( 2nd to 4th on left) costal
cartilages
Lung
Just lateral to midsternal line

Miciclovicular line

Pleura
8th rib
Lung
6th rib

Midaxillary line

Pleura
10th rib
Lung
8th rib

Lateral border of erector spinae

Pleura
12th rib
Lung
10th rib


Note that the lungs do not extend as fly down as the pleurae, and below the level of the lungs the costal and the diaphragmatic pleura are separated by a narrow space called costodiaphragmatic recess.

Surface marking  of heart 

About one-third of the heart lies to the right of the midline. Surface mark the heart on a volunteer student according to the following description. The apex of the heart is first determined, either by its pulsation or as a point in the fifth interspace 9 cm to the left of the midsternal line (or the midclavicular line). The right border extends from the lower border of the right 3rd costal cartilage to the lower border of the right 6th costal cartilage just lateral to the lateral sternal margin. This line is slightly convex to the right. The inferior border passes from the right 6th costal cartilage to the apex. From the apex the left border extends upwards to the lower border of the left 2nd costal cartilage about 2 cm from the lateral sternal margin. These are the borders that are seen in a typical radiograph of the heart. If percussion was used as a means or determining the borders of the heart, you v■ould get a smaller area than this due to the lungs overlapping the borders of the heart giving a resonant note.

Surface marking and auscultation areas of heart valves  

All valves of the heart lie behind the sternum in an almost vertical line. In the given diagram they are represented in circles drawn in continuous lines. The arrows indicate the directions in which the sounds of the closing valves are propagated and the circles in dotted lines are the preferred sites for auscultation. 

Tricuspid 

Last's Anatomy, 10th ed. Page 196, Figure 4.21 

Prepared by Dr. Sanjaya Adikari Dept. of Anatomy Faculty of Medicine University of Peradeniya