Lower esophageal sphincter

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The LES is a 3-4 cm segment of tonically contracted smooth muscle in the distal esophagus. Among normal individuals basal LES tone varies from 1030 mmHg relative to intragastric pressure and exhibits substantial temporal variation. Studies utilizing concurrent fluoroscopy and manometry, localize the proximal aspect of the EGJ high-pressure zone 1-1.5 cm proximal to the SCJ and the distal aspect extending about 2 cm distal to it (1) (Fig. 1). Anatomical studies suggest that the EGJ component distal to the SCJ is largely attributable to the sling and clasp fibers of the middle layer of gastric musculature in the cardia [2], [3]. In this region, the lateral wall of the esophagus meets the medial aspect of the stomach at an acute angle, defined as the angle of His.

Large fluctuations of LES pressure occur during phase III of the migrating motor complex during which LES pressure may exceed 80 mmHg during this phase. Minor fluctuations occur throughout the day with pressure decreasing in the post-prandial state and increasing during sleep [4]. Basal LES tone is a property of both the smooth muscle itself and of its extrinsic innervation [5]. Consequently, LES pressure may be altered by myogenic factors, intra-abdominal pressure, gastric distention, peptides, hormones, various foods, and many medications. To maintain the delicate

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Hiatal hernia

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Fig. 1. Pressure topography of the EGJ of normal subjects (left) and hiatus hernia patients (right). Position zero on the axial scale is the midpoint of the diaphragmatic hiatus.The proximal clip indicates the position of the squamocolumnar junction (SCJ) and the distal clip marks the median position of the intragastric aspect to the EGJ as imaged endoscopically. All values of length and pressure are the medians of seven subjects in each subject study group.The bottom tracings represent maximal radial pressure for normals (left) and hiatus hernia subjects (right). Note the two peaks in the hiatus hernia group correlating to the above axial topography figures. (From [1]: Kahrilas PJ, Lin S, Chen J et al (1999) The effect of hiatus hernia on gastro-oesophageal junction pressure.Gut 44: 476-482,with permission)

Fig. 1. Pressure topography of the EGJ of normal subjects (left) and hiatus hernia patients (right). Position zero on the axial scale is the midpoint of the diaphragmatic hiatus.The proximal clip indicates the position of the squamocolumnar junction (SCJ) and the distal clip marks the median position of the intragastric aspect to the EGJ as imaged endoscopically. All values of length and pressure are the medians of seven subjects in each subject study group.The bottom tracings represent maximal radial pressure for normals (left) and hiatus hernia subjects (right). Note the two peaks in the hiatus hernia group correlating to the above axial topography figures. (From [1]: Kahrilas PJ, Lin S, Chen J et al (1999) The effect of hiatus hernia on gastro-oesophageal junction pressure.Gut 44: 476-482,with permission)

balance between antegrade and retrograde flow, the LES has a complex neurological control mechanism involving both the CNS and peripheral enteric nervous system. LES pressure is modulated by reflexes involving both vagal and sympathetic nerves [6]. Efferent function is mediated through neurons of the myenteric plexus that can effect either LES contraction or relaxation. Synapses between the efferent vagal fibers and the myenteric plexus employ a cholinergic system. The post-ganglionic transmitter effecting contraction is acetylcholine while several studies suggest that NO is the dominant inhibitory nonadrenergic-noncholinergic transmitter with VIP serving some type of modifying role [7], [8].

Crural diaphragm

The hiatal orifice is an teardrop shaped opening through the diaphragm through which the esophagus and vagus nerves gain access to the abdomen. Although minor variants are recognized, the most common anatomy is for the hiatus to be formed by elements of the right diaphragmatic crus with partial contribution from the left crus [9]. The crura arise from tendinous fibers emerging from the anterior longitudinal ligament over the upper lumbar vertebrae (Fig. 2). The crura pass upward in close contact with the vertebral bodies for most of their course and only incline anteriorly as they arch around the esophagus [9]. Once muscle fibers emerge from the tendinous origin of the right crus, they form two overlying ribbon-like bundles separated from each other by connective tissue. The dorsal bundle forms the left limb of the right crus and the ventral bundle becomes the right limb of the right crus. As they approach the hiatal canal, the muscle bands diverge and cross each other in a scissor-like fashion and merge anterior to the esophagus. The lateral fibers of each hiatal limb insert directly into the central tendon of the diaphragm but the medial fibers, that form the hiatal margins, incline toward the midline and decussate with each other in a trellis-like fashion anterior to the esophagus (Fig. 3) [9]. Normally there is about a centimeter of muscle separating the anterior rim of the hiatus from the central tendon of the diaphragm.

Under normal circumstances, the esophagus is anchored to the crural diaphragm by the phrenoesopha-

geal ligaments (membranes) and the stomach cannot be displaced through the hiatal canal into the thoracic cavity [10], [11]. The phrenoesophageal membrane is formed from the fascia transversalis on the under surface of the diaphragm and fused elements of the endothoracic fascia. This membrane inserts circum-ferentially into the esophageal musculature, close to the squamocolumnar junction, and extends for about a centimeter proximal to the EGJ at which point it merges with the perivisceral fascia of the esophagus [12]. Thus, the axial position of the squamocolumnar junction is normally within or slightly distal to the diaphragmatic hiatus [13].

Independent control of the crural diaphragm can be demonstrated during esophageal distension, belching and vomiting when electrical activity in the crural diaphragm is selectively inhibited [14], [15]. This reflex inhibition of crural activity is eliminated with vagotomy. On the other hand, crural diaphragmatic contraction is amplified during abdominal compression, straining or coughing [16]. Additional evidence of the sphincteric function of the hiatus comes from manometric recordings in patients after

Squamocolumnar junction

Squamocolumnar junction

Normal Hiatal hernia

Fig. 2. Anatomy of the diaphragmatic hiatus. The right crus makes up the muscular component of the crural diaphragm. Arising from the anterior longitudinal ligament overlying the lumbar vertebrae. A single muscle band splits into an anterior and posterior muscular band, which cross each other to form the walls of the hiatal canal and then fuse anteriorly. With hiatus hernia the muscle becomes thin and atrophic limiting its ability to function as a sphincter. ([53]: Pandolfino JE, Kahrilas PJ (2001) Esophageal motility abnormalities in Barrett's esophagus. In: Barrett's esophagus and esophageal adenocarcinoma (Sharma P, Sampliner RE, eds). Malden: Blackwell Science, pp 35-44, with permission)

Normal Hiatal hernia

Fig. 2. Anatomy of the diaphragmatic hiatus. The right crus makes up the muscular component of the crural diaphragm. Arising from the anterior longitudinal ligament overlying the lumbar vertebrae. A single muscle band splits into an anterior and posterior muscular band, which cross each other to form the walls of the hiatal canal and then fuse anteriorly. With hiatus hernia the muscle becomes thin and atrophic limiting its ability to function as a sphincter. ([53]: Pandolfino JE, Kahrilas PJ (2001) Esophageal motility abnormalities in Barrett's esophagus. In: Barrett's esophagus and esophageal adenocarcinoma (Sharma P, Sampliner RE, eds). Malden: Blackwell Science, pp 35-44, with permission)

distal esophagectomy for esophageal cancer [17]. These patients still exhibited an EGJ high-pressure zone of about 6 mmHg within the hiatal canal despite having had the entire smooth muscle intrinsic sphincter removed.

Hiatus hernia

Hiatal hernia is a perturbation of EGJ anatomy such that elements normally confined within the abdomen traverse the hiatal canal. The most comprehensive classification scheme recognizes 4 types of hiatal hernia and the main distinction is the difference between types-I and II (Fig. 4). Type-I or sliding hiatal hernias are associated with a widening of the muscular hiatal tunnel and circumferential laxity of the phrenoesophageal membrane, allowing a portion of the gastric cardia to herniate upward. Due to the inherent subjectivity in defining type-I hiatal hernia, estimates of prevalence vary substantially, from 10% to 80% of the adult population in North America [18]. Most type-I hiatal hernias are asymptomatic and, even with larger type-I hernias, the main clinical implication is the predilection to develop reflux disease, the likelihood of which increases with increasing hernia size. With a well de-

Transverse membrane

Transverse membrane

Competent hiatus Hiatus with hernia

Fig. 3. The most common anatomy of the diaphragmatic hiatus in which the muscular elements of the crural diaphragm derive from the right diaphragmatic crus.The right crus arises from the anterior longitudinal ligament overlying the lumbar vertebrae. Once muscular elements emerge from the tendon, two flat muscular bands form which cross each other in scissor-like fashion, form the walls of the hiatus, and decussate with each other anterior to the esophagus. (Modified from Marchand P (1959) The anatomy of esophageal hiatus of the diaphragm and the pathogenesis of hiatus herniation. Thorac Surg 37:81-92, with permission)

Competent hiatus Hiatus with hernia

Fig. 3. The most common anatomy of the diaphragmatic hiatus in which the muscular elements of the crural diaphragm derive from the right diaphragmatic crus.The right crus arises from the anterior longitudinal ligament overlying the lumbar vertebrae. Once muscular elements emerge from the tendon, two flat muscular bands form which cross each other in scissor-like fashion, form the walls of the hiatus, and decussate with each other anterior to the esophagus. (Modified from Marchand P (1959) The anatomy of esophageal hiatus of the diaphragm and the pathogenesis of hiatus herniation. Thorac Surg 37:81-92, with permission)

veloped hernia, the esophageal hiatus abuts directly on the transverse membrane of the central tendon of the diaphragm and the anterior hiatal muscles are absent or reduced to a few atrophic strands [9]. The hiatus itself is no longer a sagittal slit but a rounded opening whose transverse diameter approximates its sagittal diameter in size (Fig. 3). This change in caliber of the hiatus is most apparent during distention (Fig. 5) [19]. Associated with the widening of the hiatal orifice, the phrenoesophageal membrane also becomes attenuated. However, the phrenoesophageal membrane remains intact and the associated herniated gastric cardia is contained within the posterior mediastinum [18].

Although there are instances in which trauma, congenital malformation, and iatrogeny can be implicated, most evidence suggests that type-I hiatus hernia is usually an acquired condition. Allison observed that the typical age of onset was in the fifth decade of life [20] and pregnancy has long been suspected to be an inciting factor [21]. Marchand theorized that the compounded stresses of age-related degeneration, pregnancy, and

Type-I hiatal hernia Type-I I hiatal hernia

Type-I hiatal hernia Type-I I hiatal hernia

Phrenoesophageal Membrane

Fig. 4. Alteration of the hiatal anatomy associated with sliding hiatal hernia. Note that the main change is a widening of the hiatal canal. Associated with this there can be substantial atrophy of the abutting muscular elements, thinning and elongation of the phrenoesophageal membrane, and axial displacement of the gastric cardia. Sliding verses paraesophageal hiatal hernia. With sliding or axial hiatal hernia there is thinning and elongation of the phrenoesophageal membrane leading to herniation of the stomach into the posterior mediastinum. As such, there is no potential for incarceration or strangulation. With paraesophageal herniation, visceral elements herniate through a focal weakness in the phrenoesophageal membrane with the potential to lead to the usual array of complications associated with visceral herniation through a constricted aperture [Modified from Skinner DB (1985) Hernias (hiatal, traumatic, and congenital). In: Gastroenterology (Berk JE, ed). Philadelphia: Saunders, p 705, with permission]

obesity take their toll on the supporting structures of the EGJ. The positive peritoneo-pleural pressure gradient acts to push the abdominal contents into the chest and is opposed by the entire surface of the diaphragm. In this respect, only the esophageal hiatus is vulnerable to visceral herniation because it faces directly into the abdominal cavity. Furthermore, since the esophagus does not fill the entire hiatal canal, the integrity of this opening depends upon its intrinsic structures, especially the phrenoesophageal membrane [22]. Add to this susceptibility the repetitive stresses of deep inspiration, Valsalva, vomiting, physiologic herniation with swallowing, and tonic contraction of longitudinal muscle induced by gastroesophageal reflux, and then compound this stress by filling the abdominal cavity with adipose tissue or a gravid uterus and eventually the integrity of the hiatus is gradually compromised.

The type-I, or "sliding", hiatal hernia described above accounts for the vast majority of hiatal hernias, while less common types (II, III and IV) are varieties of "paraesophageal hernias." Together, paraesophageal hernias account for approximately 5-15% of all hiatal hernias [24]-[26]. Although these hernias may also be associated with significant gastroesophageal reflux their more worrisome clinical consequence lies in the poten-

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Fig. 5. (A) Dimensions and radial symmetry of the EGJ. Measurements of EGJ opening diameters were made from PA and lateral fluoroscopic projections and are plotted for each intra-bag pressures relative to intragastric pressure distention pressure. Some degree of radial asymmetry of the hiatus was seen in all three groups; the lateral diameters were similar among the three groups but the hiatal hernia (HH) and non-hiatal hernia (NHH) GERD patients had increased PA diameters compared to normal subjects (NLS) (From [51]: Pandolfino etal (2003) Gastroenterology 125(4): 1018-1024, with permission)

Fig. 5. (A) Dimensions and radial symmetry of the EGJ. Measurements of EGJ opening diameters were made from PA and lateral fluoroscopic projections and are plotted for each intra-bag pressures relative to intragastric pressure distention pressure. Some degree of radial asymmetry of the hiatus was seen in all three groups; the lateral diameters were similar among the three groups but the hiatal hernia (HH) and non-hiatal hernia (NHH) GERD patients had increased PA diameters compared to normal subjects (NLS) (From [51]: Pandolfino etal (2003) Gastroenterology 125(4): 1018-1024, with permission)

tial for mechanical and ischemic complications. A type-II paraesophageal hernia results from a localized defect in the phrenoesophageal membrane while the EGJ itself remains fixed to the preaortic fascia and the median arcuate ligament (Fig. 4) [18]. The gastric fundus then becomes the leading point of herniation and the natural history of a type-II hernia is progressive enlargement so that the entire stomach eventually herniates into the chest, inverting as it does so with the pylorus juxtaposed to the gastric cardia. Type-III, or mixed, paraesophageal hernias have elements of both types-I and -II hernias with both axial displacement of the EGJ above the diaphragm and a focal defect within the phrenoesophageal membrane adding a paraesophageal element (Fig. 3). Type-IV hiatus hernia is associated with a large defect in the phrenoesophageal membrane, through which other abdominal organs, such as colon, spleen, pancreas and small intestine to enter the hernia sac. Type-IV hernias are usually encountered only in individuals with prior surgical procedures involving the left upper quadrant. In general, paraesophageal hernias are associated with abnormal laxity of structures normally preventing displacement of the stomach; the gastrosplenic and gastrocolic ligaments and are a recognized complication of surgical manipulation of the hiatus.

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