“Do not despise your own place and hour. Every place is under the stars, every place is the center of the world.” 
John Burroughs, Studies in Nature and Literature

PositionThe Common Vein copyright 2009

“Not invisible but unnoticed Watson.You did not know where to look so you missed all that was important.” said  Sherlock Holmes  in “A Case of Identity”.

A sign with this quote remained on my reading board for 16 years and its message is embedded in my psyche.

The position of the parts of the body and particularly positioning of parts in relation to each other  is another critical aspect of structure.  In the clinical realm, the position of the internal organs is determined by external landmarks; this is called surface anatomy.

The heart has a very characteristic position in the chest.  It is a little off midline toward the left, with the left ventricular apex pointing down and slightly out and leftward.  It can be palpated in the left midclavicular line in the fifth rib interspace.  When the left ventricle is enlarged, the position of the apex shifts down and more leftward. The right ventricle is anterior to the left ventricle and lies just leftward of the sternum.  Since it is a low pressure structure, it cannot be palpated under normal circumstances.   When it enlarges a left parasternal heave is palpated.

The aortic valve lies on the right sternal border in the second rib interspace.  One would have thought that as a left sided structure it would be on the left, but in fact it sits to the right of the pulmonary valve and to the right of the sternum.  Thus the aortic valve it is best heard auscultated in the second interspace on the right side of the sternum.  The pulmonary valve, on the other hand, is best evaluated in the second interspace on the left side.  Odd, but true and important.

The reason for describing the surface anatomy of the heart is not to expect rote memorization, but rather to reiterate the principle of understanding the position of structure.  This information carries important clinical relevance.

A few other examples demonstrating the relevance of position of structure at the bedside and even in life saving maneuvers follow.

There is no more critical time to know the position of structures than when performing resuscitative measures.  Knowing the position of key structures and their neighbors is essential in a host of critical circumstances: when placing a femoral venous line or internal jugular line for rapid infusion of fluids during uncontrolled hemorrhage when blood pressure is falling; when positioning an endotracheal tube in the airway and avoiding the esophagus during airway maintenance in acute respiratory failure; when catheterizing the left coronary ostium during thrombolytic administration for acute coronary thrombosis; and  when performing an emergency cricothyrotomy through the cricothyroid membrane for acute airway obstruction.  These procedures all require knowledge of position of the structure and or knowledge of easily identified surface structures that are used as reference landmarks.

Situs inversus is a condition where all or some of the bodily organs are inverted in location across the midline.  For some patients this condition represents a mere incidental anomaly which they may not be aware of, nor affected by.  When associated anomalies are present in some patients, particularly when cardiac anomalies are present, death can ensue.  Kartagener’s syndrome (immotile cilia syndrome) is characterized by situs inversus, bronchiectasis, chronic sinusitis and infertility.  The most severe form of situs inversus is seen in the asplenia syndrome which is usually a fatal condition in infancy because of associated severe forms of congenital heart disease.

Central Gallbladder in Situs Ambiguus

82222.8s liver gallbladder bilateral right lobe asplenia syndrome Ivemark syndrome central gallbladder situs ambiguus congenital position gross pathology Courtesy Ashley DAvidoff MD copyright 2008

More scientifically challenging and deeply perplexing than malpositioned organs are the diseases associated with a  single misplaced, displaced, or replaced amino acid in the DNA strand.  These positional defects can result in devastating disease including thallasemia, sickle cell anemia, cystic fibrosis, or Huntington’s chorea.  In these congenital disorders the most seemingly minor malposition of a single amino acid has far reaching clinical implications.  The challenge of treating such disorders is on the horizon for the coming generations of scientists and doctors.

Position also infers and implicates the concept of space.  Cells organs, people, families and nations need their own space in order to function and contribute to the society at large.    One of the most significant consequences of malignant disease is that cancer occupies space but does not contribute to the well being of the “society” in which it resides.  Malignant disease can be viewed as an aggressive and foreign group of cells (“squatters”) that embed in a mother organ, grow off the fat of the land, contribute nothing to the function of the society at large, and by multiplication take over space and displace normal and well functioning tissue.  This is the nature of malignancy.  Eventually it either impedes the function of the mother organ, or it sends seedlings directly into the surrounding tissues, into the lymph nodes, and or via the circulation to distant organs where it takes up more space and impedes the function of other organs.  Eventually orderly society succumbs, together with the parasite, and all is lost.

The difficulty again relates to how a medical student can know which of the detail provided in the structural courses in medical school have clinical relevance.  Is it important to know a seemingly minor anatomical point like “the intercostal arteries, veins and nerves run inferior to the ribs”?  How can the medical student know or understand the relevance of this dry fact?  How does one continually integrate the vast array of information with its practical relevance and make the dry knowledge come alive?  An arborized integration with a computer program written by the basic scientists and subsequently integrated with clinical science and medicine written by practicing physicians is the solution to this problem.  With current systems in place the best advice is for educators to point out as much as possible. It is important to know how the information can be applied.  Failing this difficult task of continued integration of basic and clinical faculty, the student has to be aware that the principles being outlined here (parts, size, shape, and position so far), do have clinical relevance and will at some time be revisited  in a clinical career.

Principles

 

 

 

 

Kartagener’s syndrome TCV page in the Heart module

 

Critical Location

 

Position in Treatment