Visceral fascia

Chapter 1.8


Visceral fascia




Introduction


The organ systems of the body, whether visceral or somatic in nature, are composed of highly differentiated tissue and require an elaborate support system for their maintenance. This sustentacular system is a connective tissue network comprised of irregularly arranged collagen and elastin fibers with their supporting cells embedded in a matrix of glycoproteins, all of which is termed fascia. The density of fibrous elements is highly regionally variable as well as individually variable. The role of fascia as a packing or investing tissue, surrounding and protecting organ systems, seems well accepted in the textbook literature (Gardner et al. 1986; Drake et al. 2010).


Although fascia has been described in several academic treatises (Gallaudet 1931; Singer 1935), there still remains much confusion regarding distribution and naming surrounding the fascias of the body cavities (Skandalakis et al. 2006). A previous chapter in this text suggested that there are four primary fascial layers in the body: (1) pannicular (often termed superficial), (2) axial and appendicular (often termed deep or investing or muscular fascia), (3) meningeal fascia surrounding the central nervous system, and (4) viscera (or splanchnic) fascia surrounding the body cavities and packing around the internal organs (Chapter 1.2). This current chapter will examine the visceral fascias of the body and attempt to present a unifying concept concerning their organization and continuity.



Visceral fascia


Extending from cranial base to pelvic basin and lining the body cavities, visceral fascia is by far the most complex of the four main layers of fascia. Embryologically, this layer of fascia, termed mesenchyme, is derived from the splanchnic tissue and it is into this loose matrix that the body cavities – pleural, pericardial, and peritoneal – expand in size. As this expansion occurs, the visceral fascia becomes compressed outward against the somatic body wall as well as consolidated medially along the midline. In the adult, the composition of visceral fascia is typically described as loose, irregular, connective tissue containing a varying amount of adipocytes (Plate 1.8.1).


Functionally, visceral fascia provides the packing tissue for the midline structures of the body. The midline fascia forms a column that extends from its attachments to the cranial base, through the cervical region into the thorax, where it occupies the mediastinum. At the diaphragm, this column passes through the aortic and esophageal openings to enter the abdomen. Descending through the abdomen into the pelvic basin, the midline fascia forms a continuation of the mediastinum. In the pelvic basin, the visceral column of fascia surrounds the midline structures. This entire mediastinal region of the body contains the major vasculature, such as the aorta, the caval venous systems, and the thoracic duct, as well as the great abdominopelvic plexus of autonomic nerves. These structures and their branches become invested in fascia layers, which accompany the neurovascular bundles as they extend outward to reach individual organ systems (Anderson & Makins 1890).


Early studies had suggested four layers of visceral fascia are present in the walls of the body cavities: (1) muscular fascia surrounding the body wall muscles (at one time termed “parietal fascia”; see discussion in Thompson 1901; Derry 1907a,b); (2) the fascia forming neurovascular sheaths; (3) fascia surrounding individual organs; and (4) fascia underlying the pleural and peritoneal linings (reviewed in Hollinshead 1961). The muscular or “parietal” fascia is essentially the axial and appendicular fascia described in Chapter 1.2. In general, the remaining fascial layers can be considered to form an extensive visceral fascial matrix.


Sentinel descriptions of visceral fascia can be found in the Journal of Anatomy and Physiology by Anderson & Makins (1890). These original descriptions emphasized the continuity of visceral fascia from the nasopharyngeal and cervical region, through the thorax and abdomen, to levator ani in the pelvic region. However, most of the recent anatomical research concerning visceral fascia has been done from a surgical perspective designed to solve clinical problems involving access into a specific region or excision of tissue in cases of neoplastic growth (for example, see Garcia-Armengol et al. 2008). Although the fine-grained analysis of individual fascial planes is necessary from a surgical perspective, the narrow focus of these studies tends to obscure the overall picture of this continuous fascial matrix in the body. In the remainder of the chapter, the general organization of visceral fascia in the cervical, thoracic, abdominal and pelvic areas will be presented. Although in any of these regions there are multiple and complex arrangements, for the sake of an overview, we will attempt to generalize as much as possible.



Cervical visceral fascia


In the cranial region, visceral fascia surrounds the pharynx and its attachment to the cranial base. Superiorly, visceral fascia includes the pharyngobasilar and pharyngobuccal fascia and, as such, fuses to the cranial base surrounding the attachments of the superior constrictor muscles (Last 1978). Cervical visceral fascia extends inferiorly into the neck, surrounding the nasopharynx, oropharynx, and remaining cervical viscera. Thus at the cranial base, cervical fascia has a flared opening surrounding the nasal passageways and the mouth (Plate 1.8.2, Section 22 and 46).


In the neck, visceral fascia incorporates such regional fascias as pretracheal, retropharyngeal, and alar (carotid sheath) fascias as well as the fascia surrounding the thyroid cartilage and thyroid gland (Plate 1.8.2, Section 66 and 86). Thus, visceral fascia can be conceived of as a continuous vertical sleeve lying internal to the hyoid muscles, anterior to the longus muscles, and extending into the thorax.

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Aug 24, 2016 | Posted by in ORTHOPEDIC | Comments Off on Visceral fascia

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