134 - Replacement of the Esophagus with Jejunum

Editors: Shields, Thomas W.; LoCicero, Joseph; Ponn, Ronald B.; Rusch, Valerie W.

Title: General Thoracic Surgery, 6th Edition

Copyright 2005 Lippincott Williams & Wilkins

> Table of Contents > Volume II > The Mediastinum > Section XXV - Anatomy > Chapter 157 - Neurogenic Structures of the Mediastinum

Chapter 157

Neurogenic Structures of the Mediastinum

Thomas W. Shields

Phrenic and Vagus Nerves

Phrenic Nerves

The phrenic nerve on the right lies on the medial border of the anterior scalene muscle and enters the thoracic inlet as it continues with the anterior scalene muscle between the subclavian vein and artery. It crosses the origin of the internal mammary artery and is joined by the pericardiacophrenic branch of the artery. According to a study by Owens and co-workers (1994), there is no constant relationship between the phrenic nerve and the internal mammary artery on right or left sides as these structures cross behind the first rib. The vessel may be anterior or posterior to the nerve in any individual. These structures pass caudally over the cupula of the pleura on the lateral surface of the superior vena cava. In its caudad descent, the phrenic nerve passes ventrally to the hilar structures. The nerve lies deeper and has a more vertical course than the left nerve as it passes along the lateral aspect of the pericardium between the pericardium and the mediastinal surface of the pleura. Just above the diaphragm, it divides into two or more terminal trunks.

The left phrenic nerve is longer than the right. In the root of the neck, it is crossed by the thoracic duct, and in the upper portion of the visceral compartment, it lies between the left common carotid and subclavian arteries. The left phrenic nerve lies behind the left innominate vein lateral to the vagus nerve (Fig. 157-1). As the nerve crosses down, it moves ventrally; in the region where the left superior intercostal vein joins the left innominate vein, it comes to lie medial and anterior to the vagus nerve as these two nerves cross over the aortic arch. As on the right, the left phrenic nerve lies ventral to the hilus of the lung, and its remaining course and relationship to the pericardium, except for its longer route, are the same as on the right.

Vagus Nerves

The right vagus nerve enters the thoracic inlet within the carotid sheath between the internal jugular vein ventrally and the common carotid artery dorsally. It crosses the first part of the right subclavian artery. Here it gives off the right recurrent nerve, and this branch loops under the arch of this vessel and passes dorsal to it, traveling to the tracheoesophageal groove and upward to the larynx. Caudally, the main descending trunk comes to lie on the right side of the trachea and passes dorsal to the pulmonary hilus. The trunk forms the posterior pulmonary plexus, and below this, it forms a plexus of nerve fibers on the dorsal aspect of the esophagus. After receiving branches from the left vagus, it forms a single trunk, the posterior vagus nerve, and it lies slightly dorsal away from the wall of the esophagus before passing through the esophageal hiatus to enter the abdomen.

The left vagus nerve enters the thorax between the left carotid and subclavian arteries deep to the left innominate vein. It comes over the dorsal aspect of the left side of the aortic arch angling somewhat dorsally in its caudad descent. It passes between the aorta and left pulmonary artery just distal to the ligamentum arteriosum. At this site, it gives off the left recurrent branch, which loops from in front to behind the arch to lie on the side of the trachea (Fig. 157-2). The recurrent nerve then passes upward in the tracheoesophageal groove to the neck. As on the right, the major trunk of the left vagus passes dorsally to the pulmonary hilus, where the nerve flattens out into the posterior pulmonary plexus. It reaches the esophagus as a variable number of smaller trunks, which lie on the ventral aspect of the esophageal wall. After receiving branches from the right vagus, these branches form a single trunk called the anterior vagus nerve, which is closely applied to the esophagus as it passes through the diaphragmatic hiatus into the abdomen.

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SPINAL NERVES AND SYMPATHETIC TRUNKS

Each nerve emerges from the vertebral canal through the intervertebral foramen below the corresponding vertebra. Each nerve is in relation to the spinal rami of the artery and vein for the respective foramen. Essentially, the spinal nerve, as it leaves the vertebral foramen, divides into four branches: (a) posterior primary division (ramus posterior); (b) anterior primary division (ramus anterior); (c) ramus communicans, by which it connects to the sympathetic trunk; and (d) a smaller ramus meningeus, which returns to the spinal canal. The anterior ramus runs laterally to be joined by the respective intercostal artery and vein to run in the groove on the undersurface of each rib.

Fig. 157-1. Superior portion of the mediastinum. The ligamentum arteriosum holds the left recurrent nerve to the left, and the left phrenic nerve originally to the left passes anteriorly and medially to the vagus nerve. The right vagus nerve enters the mediastinum behind the great veins, whereas the right phrenic nerve passes anterolaterally to these vessels. From Anderson JE: Grant's Atlas of Anatomy 8th Ed. Baltimore: Williams & Wilkins, 1983. With permission.

The thoracic sympathetic trunk is made up of a variable number of ganglia connected by the sympathetic trunk, which lies ventral to the heads of the first through tenth ribs, at which site it passes more ventrally to lie on the bodies of the lower two thoracic vertebrae. Above, the sympathetic trunk is continuous with the cervical trunk and posterior to the vertebral artery, and inferiorly it passes out of the thorax just posterior to the medial lumbocostal arch. The trunk is external to the costal pleura and crosses ventrally to the aortic intercostal arteries.

Fig. 157-2. Course of the left vagus nerve with the recurrent nerve given off on the anteroinferior portion of the aortic arch just lateral to the ligamentum arteriosum and passing under and behind the arch to ascend to the tracheoesophageal groove. From Anderson JE: Grant's Atlas of Anatomy. 8th Ed. Baltimore: Williams & Wilkins, 1983. With permission.

Fig. 157-3. Four types of intrathoracic nerve of Kuntz (INK) and ramus communicans from the T2 nerve to the stellate ganglion. ICN, intercostal nerve; RC, ramus communicans; SG, stellate ganglion; ST, sympathetic trunk. From Chung I-H, et al: Anatomic variations of the T2 nerve root (including the nerve of Kuntz) and their implications for sympathectomy. J Thorac Cardiovasc Surg 123:498, 2002. With permission.

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The number of ganglia in the thoracic chain is variable, usually 10 or 11. The first thoracic ganglion is frequently fused with the inferior cervical ganglion, forming the stellate ganglion. The location of the ganglia may vary. They may lie on the heads of the ribs, the costovertebral articulation, or even the bodies of the vertebrae. Each ganglion receives a white ramus communicans from the respective thoracic nerve and gives off a gray ramus communicans to the same nerve.

With the increase of interest in and the performance of thoracic sympathectomy by the video-assisted thoracic surgery (VATS) approach for the management of craniofacial, palmar, and axillary hyperhidrosis, the anatomic variations in the origin and branching of the second thoracic nerve root, including the nerve of Kuntz and the adjacent structures of the sympathetic trunk, have become important to those surgeons who perform upper sympathectomy for the various manifestations of hyperhidrosis. Chung and associates (2002) dissected the upper symphatic trunk and upper symphatic ganglia in 39 adult cadavers bilaterally in 27 and on one side in 12 for a total of 66 dissections. The dissections were centered on the anatomy of the intrathoracic nerve of Kuntz (INK). This nerve is an inconsistent intrathoracic ramus described by Kuntz in 1927 connecting the first and second thoracic nerves. Chung and colleagues (2002) identified an INK in 68.2% of the specimens, and it was present bilaterally in 48.1% of the bilateral dissection group. These authors classified the INK into four types according to its connection to the adjacent nerves: (a) type A, connecting from the T2 to the T1 nerve (47%); (b) type B, connecting from the T2 to the first intercostal nerve (12.1%); (c) type C, connecting from the T2 nerve to ramus communicans between the stellate ganglion and the T1 nerve (7.6%); and (d) type D, the branching and connecting from the T2 nerve to the T1 nerve and the first intercostal nerve (1.5%) (Figs. 157-3 and 157-4). Twenty-one slides did not have a demonstrable INK but had a ramus communicans connecting from the T2 nerve to the stellate ganglion. Any ascending connection was absent in 7.6% of specimens, and an INK was noted connecting the T2 and T3 nerves in 7.6%. The location of the T2 sympathetic ganglion was most frequently located in (a) the second intercostal space (50%), followed in decreasing frequency by (b) the upper border of the third rib, (c) elongated from the second to the third rib where the T2 ganglion seemed to be fused to the stellate ganglion, (d) the lower border of the second rib, and (e) from the second to the third intercostal space over the entire width of the third rib where the second (T2) sympathetic ganglion appeared to be fused with the T3 sympathetic ganglion. In 7.6% of the specimens, Chung and associates (2002) could not identify a T2 sympathetic ganglion. The importance and significance of the location and the necessity of division of INK for a successful sympathectomy (the dissection needs to be extended at least 1.5 cm laterally from the sympathetic trunk) were discussed in detail by Chung and colleagues (2002).

Fig. 157-4. Upper thoracic sympathetic trunk. BP, brachial plexus; ICA, intercostal artery; RC, ramus communicans; SG, stellate ganglion; ST, sympathetic trunk. From Chung I-H, et al: Anatomic variations of the T2 nerve root (including the nerve of Kuntz) and their implications for sympathectomy. J Thorac Cardiovasc Surg 123:498, 2002.

Fig. 157-5. Intercostal nerves, sympathetic ganglia, sympathetic trunk, and splanchnic nerves. From Anson BJ, McVay CB: Surgical Anatomy. Philadelphia: W.B. Saunders, 1971, p. 441. With permission.

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Finally, numerous branches from the upper four or five ganglia pass to the visceral structures in the mediastinum. The branches from the lower group run caudally and form the greater and lesser splanchnic nerves; occasionally, the least splanchnic nerve arises from the last thoracic ganglion. These various trunks pass medially and ventrally on the sides of the vertebral bodies (Fig. 157-5). Numerous branchings and filaments give off these nerves as they descend caudalward to the diaphragm. The trunks pass into the abdomen through the crus of the diaphragm.

AORTIC BODIES AND MIDDLE MEDIASTINAL PARAGANGLIA

The paraganglia are collections of neural crest cells that are distributed throughout the body. They are composed of the adrenal medulla, the carotid and aortic bodies, the vagal body, and small groups of cells associated with the thoracic, intraabdominal, and retroperitoneal ganglia. The present concept regards all these paraganglia rests as having the same embryologic origins, but the functional capacity and histology vary from site to site (the chemodectoma as opposed to the pheochromocytoma). Alfred Kohn formulated this concept in 1903. Early anatomists and pathologists tried to further subdivide the extraadrenal paraganglia system by the reaction of these cells to chromate solutions, such as Zenker's fluid or potassium dichromate. When fresh tissue from a pheochromocytoma with a high content of epinephrine is immersed in chromate solution, it turns a mahogany brown color. This represents a positive chromaffin reaction and is not seen with norepinephrine-containing tumors. The chemoreceptors (aortic and carotid bodies) react weakly or not at all with chromate solutions, whereas the adrenal medulla and some other paraganglia react strongly with the chromate solutions. As a result of this reaction, the terms chromaffin paraganglioma and nonchromaffin paraganglioma have been used to describe tumors of these structures. Glenner and Grimley (1974) pointed out that the chromaffin reaction is not consistent even in the presence of catecholamines.

According to Maximow and Bloom (1942), the aortic body on the right lies between the angle of the right subclavian and carotid arteries. On the left, it is found above the aorta medial to the origin of the left subclavian artery. As early as 1942, Maximow and Bloom stated that neither of these bodies, nor the carotid body, contained chromaffin cells. Subsequent investigators, such as Lack and associates (1979a, 1979b), however, have demonstrated dense-core neurosecretory-type granules in these cells by electron microscopy. In contrast to secretory granules in other so-called paraganglia elsewhere in the body, the secretory nature of these granules remains obscure. It has not been established whether they are a polypeptide or a biological amine, such as norepinephrine, which is found in the electron-dense granules of the chromaffin cells of the paraaortic sympathetic and parasympathetic paraganglia. Of interest in this regard is that none of the 45 carotid body tumors described by Lack and associates (1979a) revealed any biochemical functional activity.

In addition to the aortic bodies in the mediastinum, however, small collections of readily identifiable chromaffin cells are found in connective tissue between the aorta and pulmonary artery. On the left, these cells are usually medial to the ligamentum arteriosum. On the right, they lie between the right side of the main pulmonary artery and the ascending end of the aorta near the origin of the left coronary artery (Fig. 157-6). According to Maximow and Bloom (1942), chromaffin cells are also found in the subepicardial connective tissue in the coronary sulcus, mainly along the left coronary artery. Similar tissue cells have been identified above the aortic arch on the lateral aspect of the innominate artery. Some of these cells react strongly to the appropriate chromaffin stains, whereas others stain poorly or not at all. As a consequence, the terms chromaffin paraganglioma and nonchromaffin paraganglioma have been used to describe these various collections of cells and the infrequent tumor associated with them.

The paraganglia are made up of two cell types: (a) compact microscopic nests of chief cells (Zellballen), and (b) sustentacular cells, which are similar to the satellite cells of the autonomic ganglia. The chief cells in all subgroups contain variable numbers of dense-core granules readily identified on electron microscopy. The granules contain

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amines, which in most granules are catecholamines. This may be demonstrated by formalin-induced fluorescence. The chief cells of the aortic bodies, similar to those of the carotid bodies, are chemoreceptors, and it has been suggested they might release dopamine or a related neurotransmitter rather than the norepinephrine that is released by the chief cells in the aorticosympathetic paraganglia or adrenal medulla. According to Enzinger and Weiss (1988), the sustentacular cells are modified Schwann cells that appear to conduct nerves to their synaptic terminations on the chief cells.

Fig. 157-6. Sites of aorticopulmonary paraganglia in human fetuses and newborn infants. Paraganglia of groups 2 and 3 persist in adults. From Glenner GG, Grimley PM: Tumors of the extraadrenal paraganglion system (including chemoreceptors). In Atlas of Tumor Pathology. Second Series, Fascicle 9. Washington, DC: Armed Forces Institute of Pathology, 1974. With permission.

In an exhaustive study of tumors of these cells, including the carotid and aortic bodies and the paraganglionic tissues of the abdomen, Glenner and Grimley (1974) classified all locations of the extraadrenal paraganglionic system into four divisions: (a) branchiomeric, (b) intravagal, (c) aorticosympathetic, and (d) visceral autonomic. Functionally, the aorticosympathetic paraganglia are thought to have an intermediate degree of differentiation between the chief cells of the adrenal medulla (the most active) and those of the branchiomeric and intravagal paraganglia (the least active functionally). However, tumors of branchiomeric and intravagal paraganglia may be biologically active or inactive. Incidentally, the distribution of these paraganglia is greater in the human fetus and newborn than in the adult. This probably accounts for the occurrence of tumors derived from these cells (paragangliomas) in locations where no conspicuous or constant paraganglia have been described as a normal location in the adult.

The aortic bodies and other paraganglionic tissue within the visceral compartment of the mediastinum are considered as a group to belong to the branchiomeric category, although some may belong to the intravagal group (Fig. 157-7). Glenner and Grinley (1974) further divided the mediastinal paraganglia into the aorticopulmonary (aortic body), the coronary, and the pulmonary paraganglia. Embryologically, these tissues arise at the level of the fourth and fifth, the fifth, and the fifth and sixth branchial arches, respectively. Functionally, the aortic body detects changes in blood pH and oxygen content. In reviewing the reported mediastinal paragangliomas in the literature up to that time, Olson and Salyer (1978) identified 39 tumors as arising from the mediastinal branchiomeric paraganglia. Numerous other reports have appeared since then (see Chapter 191). Some of these tumors, as would be expected, have been biologically active (pheochromocytomas), whereas others have been biologically inactive (chemodectomas). How often the aortic bodies give rise to the inactive tumors remains a conjecture. It is equally likely that the nonbiologically active chromaffin cells of the other aorticopulmonary paraganglia in the visceral mediastinum are the origin of such tumors. It would also appear that the biologically active branchiomeric and intravagal paraganglia are the sites of origin of the visceral mediastinal pheochromocytomas. Rarely, if ever, would it appear that the aortic bodies are the sites of origin of such biologically active tumors.

Fig. 157-7. Sites of branchiomeric and intravagal paraganglia. From Glenner GG, Grimley PM: Tumors of the extraadrenal paraganglion system (including chemoreceptors). In Atlas of Tumor Pathology. Second Series, Fascicle 9. Washington, DC: Armed Forces Institute of Pathology, 1974. With permission.

Fig. 157-8. Sites of aorticosympathetic paraganglia. Diagram of extramedullary chromaffin tissue in a newborn child. From Glenner GG, Grimley PM: Tumors of the extraadrenal paraganglion system (including chemoreceptors). In Atlas of Tumor Pathology. Second Series, Fascicle 9. Washington, DC: Armed Forces Institute of Pathology, 1974. With permission.

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Paraganglia of the Paravertebral Sulci

Small, scattered collections of chromaffin cells are found in both paravertebral sulci in association with the connective tissues around the spinal ganglia bilaterally. These are grouped under the term paraaortic sympathetic paraganglia, which corresponds to the aorticosympathetic group described by Glenner and Grimley (1974). No constant number is defined, but these collections of cells obviously are the sites of origin of the chromaffin tumors that occur in the paravertebral sulci (Fig. 157-8). Olson and Salyer reported 12 such tumors in their 1978 publication. The paraaortic sympathetic paraganglia contain two cell types: (a) the chief cells, and (b) the supporting (sustentacular) cells. The latter apparently are of no particular interest, whereas the former are chromaffin cells that on electron microscopy contain numerous electron-opaque granules that contain catecholamines (primarily but not exclusively norepinephrine), which are readily identified histochemically.

The chief cells of the paraaortic paraganglia that are associated with the branches of the parasympathetic nerves have little chromaffin reaction on light microscopy, even with appropriate staining. As a consequence, they formerly were termed achromaffin paraganglia. On electron microscopy, however, electron-opaque granules have been identified in these cells. According to Fawcett (1986), no distinction should be made between the two types of paraaortic paraganglia.

REFERENCES

Anderson JE: Grant's Atlas of Anatomy. 8th Ed. Baltimore: Williams & Wilkins, 1983.

Anson BJ, McVay CB: Surgical Anatomy. Philadelphia: W.B. Saunders, 1971, p. 441.

Chung I-H, et al: Anatomic variations of the T2 nerve root (including the nerve of Kuntz) and their implications for sympathectomy. J Thorac Cardiovasc Surg 123:498, 2002.

Enzinger FM, Weiss SW: Soft Tissue Tumors. 2nd Ed. St. Louis: CV Mosby, 1988.

Fawcett DW (ed): Bloom and Fawcet Textbook of Histology. 11th Ed. Philadelphia: WB Saunders, 1986.

Glenner GG, Grimley PM: Tumors of the extraadrenal paraganglion system. In Atlas of Tumor Pathology. Second Series, Fascicle 9. Washington, DC: Armed Forces Institute of Pathology, 1974.

Kohn A: Die paraganglien. Arch Mikrobiol 62: 263, 1903.

Kuntz A: Distribution of the sympathetic rami to the brachial plexus: its relation to sympathectomy affecting the upper extremity. Arch Surg 15:871, 1927.

Lack EE, Cubilla AL, Woodruff JM: Paragangliomas of the head and neck region. A pathologic study of tumors from 71 patients. Hum Pathol 10: 191, 1979a.

Lack EE, et al: Aortico-pulmonary paraganglioma: report of a case with ultrastructural study and review of the literature. Cancer 43: 269, 1979b.

Maximow AA, Bloom W: A Textbook of Histology. 4th Ed. Philadelphia: WB Saunders, 1942.

Olson JL, Salyer WR: Mediastinal paragangliomas (aortic body tumors): a report of four cases and a review of the literature. Cancer 41: 2405, 1978.

Owens WA, Gladstone DJ, Heylings DJ: Surgical anatomy of the phrenic nerve and internal mammary artery. Ann Thorac Surg 58:843, 1994.

Reading References

Anderson JE. Grant's Atlas of Anatomy. 8th Ed. Baltimore/London: Williams & Wilkins, 1983.

Clemente CD. Gray's Anatomy. 30th Ed. Philadelphia: Lea & Febiger, 1985.

Romanes GJ (ed): Cunningham's Textbook of Anatomy. 12th Ed. Oxford/New York: Oxford University Press, 1981.