Fascias and Interfascial Planes

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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