Body tissues/organs are compartmentalized by sleeves of fascias and
interfascial spaces. The term "fascia" is used
for a sheet or layer of condensed fibroelastic connective tissue, and
the term "interfascial space" is used for loose connective tissue
between fascias. These planes are just potential spaces, not actual
cavities. Fascias separate tissues into groups of
structures. Thus, an understanding of fascial anatomy and interfascial planes is crucial for a safe surgical dissection.
A grasp of how the fascias are formed will be helpful in understanding the
compartmentalization of the particular body regions. When nerves, blood vessels, bones, muscles, and other organs are first
formed, they are surrounded by mesenchymal tissue. As they grow and move
relative to adjacent structures, lines of force are set up in the
mesenchyme causing it to condense. The pulsation of the vessels and the
contraction of muscles cause the formation of an adventitia around
blood vessels and an epimysium around muscles. Thus, each structure has
its own protective minor fascia.
When a group of structures move during embryological development as a
unit with respect to adjacent structures, they develop a major
fascia which surrounds them. These major fascias anatomically
compartmentalize the region. For example, the common carotid
artery, internal jugular vein and vagus nerve move up or down as a
group; similarly, the viscera of the neck (esophagus and trachea)
move as an another group. Each group of tissue is thereby compartmentalized
within a major fascia.
To allow this movement, some mesenchymal tissue between major fascias
remains very loose, thus forming an interfascial space. All the fascias
and interfascial spaces develop from early mesenchyme, and thus,
they are all continuous. The degree of relative movement determines the
eventual strength of the fascias and the looseness of the interfascial
spaces. Vessels and nerves passing through major fascias and
interfascial spaces have their own minor fascias and will tend to join
major fascias together.
There
may be significant difference between drawings of fascias in different
anatomy and surgical books. Diagrams of major fascias are usually
oversimplified, and diagrams from
different sources vary because each author's interpretation of what
he/she has observed differs. Major fascias that are easily identified
at one level may be difficult to identify at other levels, as in the
case of the carotid sheath. Moreover, as fascias directly cross bone
or cartilage, they typically fuse to the periosteum or perichondrium.
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