Anatomical Principles

One should have a clear understanding of anatomy of the respiratory system to perform a proper physical exam. Some of the important anatomical details are outlined below. For details review the link provided to Dr. McNulty's lesson on Thorax by clicking on anatomic principles.

  1. Starts from cricoid cartilage to sternal angle anteriorly and T4 spinous process posteriorly, where it divides into left and right main stem bronchi. This information is important in understanding D'spine sign seen in patients with large Mediastinal mass.
  2. Trachea is slightly slanted to right. Bronchovesicular breathing heard in right infraclavicular region is due to this phenomenon.
  3. Trachea has intra and extra thoracic components. This has important bearing in the understanding of physiology of variable obstruction.
Manubrium Angle
The angle between the body and Manubrium. Many important land marks occur at this level. It is called Louis Angle.

In the surface anatomy exercise we arbitrarily divide the thorax into various spaces and create lines. Localization of abnormal finding is achieved and described using the ribs, interspaces, spaces, and lines.

Anteriorly ribs are counted down starting from 2nd rib. There are 12 ribs and 11 interspaces. You can also count up from 12th rib. Inferior angle of scapula sits on 7th rib posteriorly.
Anteriorly there are supra clavicular, infraclavicular, precardiac and Traube's space. Posteriorly we have interscapular, supra, and infra scapular spaces.
There are following vertical lines around chest. Midsternal, parasternal, midclavicular, anterior axillary, mid-axillary, posterior axillary, infrascapular and vertebral lines.
Surface Anatomy of Lungs
Right Lung: With a marking pen start 3 centimeters above clavicle in midclavicular line, come down along right parasternal line , join to 6th rib in midclavicular line, to 8th rib in mid-axillary line, to 10th rib posteriorly, to vertebral line posteriorly.

Left Lung: At angle of Louis, follow the outer margin of heart to 6th rib in mid-clavicular line.

Appreciate that apex of lung is just under the skin easily palpable in the supraclavicular space.

Pancoast tumor and TB occur at this site. Hence, the apex of lungs should be routinely examined.

Surface Anatomy of Lobes
Draw oblique fissure by drawing a line strait from 6th rib in MCN. to 5th rib in mid axillary line and along the medial margin of scapula (with the patients hands on head) to 3rd spinous process.

Transverse fissure can be drawn by drawing a line from 5th rib in mid-axillary line to 4th rib anteriorly.

Once the fissures are drawn over the outline of lungs, one can easily recognize the surface anatomy of lobes of lungs. One can then appreciate the importance of examining the patient all around the chest to cover the lobes. Most of lower lobe is in back, upper lobe is in front and all of middle lobe is in front. In the axilla all of the three lobes can be seen.

Pleura: Once the diaphragm has been outlined you can appreciate that the pleural gutter is deep posteriorly. Fluid thus tends to accumulate posteriorly.
Mediastinum is the space between lungs from inlet to outlet of thorax. Anteriorly it is between parasternal lines. Posteriorly it is at vertebral line. Mediastinum is narrow posteriorly and widens anteriorly. Inferiorly it extends to xiphisternum. Superiorly it starts at suprasternal notch. Since the inlet of thorax is slanted, only posterior Mediastinum extends to neck.

Sternal angle separates superior from inferior Mediastinum. The inferior Mediastinum is divided into anterior, middle and posterior compartments. The space in front of heart is anterior Mediastinum and behind is posterior Mediastinum. Heart itself defines the middle Mediastinum. The posterior Mediastinum is divided into paravertebral and prevertebral space. Superior Mediastinum extends into the neck and is called cervico-Mediastinal space.

It is important to know the structures in each compartment. In the differential of masses in the Mediastinum one uses this knowledge.

Costal Angle
Costal angle is formed by the 10 rib with Costal cartilage on either side and xiphisternum in the middle. The normal angle is . Both sides are symmetrical. Volume changes in each hemithorax will alter this relationship. Hyperinflated lungs will increase the Costal angle. Diaphragmatic paralysis also alters the symmetry of Costal angle.
Spinous Process
The most prominent spinous process is 7th cervical vertebra. You can count down the thoracic vertebra and the ribs using this landmark.