The Contribution of the Left Phrenic Nerve to Innervation of the Esophagogastric Junction

The contribution of the left phrenic nerve to innervation of the esophagogastric junction. The esophagogastric junction is part of the barrier preventing gastroesophageal reflux. We have investigated the contribution of the phrenic nerves to innervation of the esophagogastric junction in humans and piglets by dissecting 30 embalmed human specimens and 14 piglets. Samples were microdissected and nerves were stained and examined by light and electron microscopy. In 76.6% of the human specimens, the left phrenic nerve participated in the innervation of the esophagogastric junction by forming a neural network together with the celiac plexus (46.6%) or by sending off a distinct phrenic branch, which joined the anterior vagal trunk (20%). Distinct left phrenic branches were always accompanied by small branches of the left inferior phrenic artery. In 10% there were indirect connections with a distinct phrenic nerve branch joining the celiac ganglion, from which celiac plexus branches to the esophagogastric junction emerged. Morphological examination of phrenic branches revealed strong similarities to autonomic celiac plexus branches. There was no contribution of the left phrenic nerve or accompanying arteries from the caudal phrenic artery in any of the piglets. The right phrenic nerve made no contribution in any of the human or piglet samples. We conclude that the left phrenic nerve in humans contributes to the innervation of the esophagogastric junction by providing ancillary autonomic nerve fibers. Experimental studies of the innervation in pigs should consider that neither of the phrenic nerves was found to contribute. Clin. Anat. 33:265-274, 2020. © 2019 Wiley Periodicals, Inc.

[Anatomic research on the transposition of accessory nerve to phrenic nerve]

OBJECTIVE

To comprehend the anatomic characteristics and correlations between the accessory nerve and the phrenic nerve in the adult corpses.

METHODS

The bilateral accessory nerves, phrenic nerves, and their branches of 20 adult corpses (38 sides) were underwent exposure. The morphologic data of the accessory nerves and the phrenic nerves above clavicle were measured. In addition, the minimal and maximal distances from several points on the accessory nerve to the full length of the phrenic nerve above clavicle were measured. Then, the number of motor nerve fibers on different locations of the nerves utilizing the method of immunohistochemistry were counted and compared.

RESULT

The accessory nerves after sending out the sternocleido-mastoid muscular branches were similar in the morphologic data with the phrenic nerves. Meanwhile, the accessory nerve had a coiled appearance within this geometrical area. The possibly minimal distance between the accessory nerve and phrenic nerve was (3.19 ± 1.23) cm, and the possibly maximal distance between the starting point of accessory nerve and the end of the phrenic nerve above clavicle was (8.71 ± 0.75) cm.

CONCLUSIONS

The accessory nerve and the phrenic nerve are similar in the anatomic evidences and the number of motor nerve fibers. And the length of accessory nerve is sufficiently long to connect with phrenic nerve as needed. It is possible to suture them without strain directly.

An ultrasound study of the phrenic nerve in the posterior cervical triangle: implications for the interscalene brachial plexus block

BACKGROUND AND OBJECTIVES

Concomitant phrenic nerve block frequently occurs after brachial plexus block procedures in the neck and can result in substantial morbidity. In this study we sought to establish the anatomic basis using ultrasound imaging.

METHODS

We scanned the neck region of 23 volunteers with high resolution ultrasonography and identified the phrenic nerve in 93.5% of scans.

RESULTS

The phrenic nerve was monofascicular with a mean diameter of 0.76 mm. The phrenic nerve position was nearly indistinguishable from the C5 ventral ramus at the level of the cricoid cartilage (mean distance 1.8 mm). Separation between the phrenic nerve and the brachial plexus increased substantially at more caudal levels in the neck. Phrenic nerve identification was confirmed by percutaneous injection of methylene blue followed by open dissection in a cadaver. Furthermore its identity was confirmed by ultrasound-guided transcutaneous nerve stimulation.

CONCLUSIONS

This descriptive study found that the phrenic nerve and brachial plexus are within 2 mm of each other at the cricoid cartilage level, with additional 3 mm separation for every cm more caudal in the neck. Clinical trials with imaging guidance are needed to establish whether brachial plexus selective blocks can be consistently achieved above the clavicle.

The ansa subclavia: a review of the literature

The ansa subclavia, subclavian loop, Vieussens' ansa or Vieussens' loop is a nerve cord that connects the middle cervical and inferior cervical sympathetic ganglia, forming a loop around the subclavian artery. The structure of the ansa subclavia is evolutionarily conserved from rats, guinea pigs, the porcine species and dogs to humans. A common application in physiological studies is to electrically stimulate the ansa subclavia in animal models as a robust protocol to modulate stimulatory cardiac sympathetic input. Despite a large number of physiological studies utilizing the ansa subclavia, only very brief descriptions have been devoted to it in standard anatomy texts. An extensive search found only one report in the English language literature concerning the anatomy of the ansa subclavia. The aim of this report, therefore, was to provide a comprehensive review of the clinical anatomy of the ansa subclavia and to discuss its potential physiological functions.

Phrenic nerve conduction studies: technical aspects and normative data

In our clinical work we have occasionally encountered difficulties (e.g., no response, concomitant brachial plexus stimulation) in performing phrenic nerve conduction studies. The aim of this study was to overcome these difficulties and obtain our own set of normative data. In 29 healthy volunteers (15 men), aged 21-65 years, phrenic nerve conduction studies were performed using bipolar surface stimulation electrodes and a standard recording montage. Stimulation just above the clavicle, between the sternal and clavicular heads of the sternocleidomastoid muscles, elicited responses at the lowest stimulation strength, without concomitant brachial plexus stimulation. M-wave amplitude and duration changed with respiration, whereas latency and area did not. The normative limit for M-wave latency was 8.0 ms (upper), for amplitude it was 0.46/0.33 mV (lower: inspiration/expiration), and for area it was 4.4 mVms (lower). We suggest a slight modification of the generally used position for phrenic nerve stimulation, and the use of M-wave latency and area (unaffected by the respiratory cycle) in future phrenic nerve conduction studies.

Glutamatergic neurons in the Kölliker-Fuse nucleus project to the rostral ventral respiratory group and phrenic nucleus: a combined retrograde tracing and in situ hybridization study in the rat

Kölliker-Fuse nucleus (KF) neurons are considered to excite motoneurons in the phrenic nucleus (PhN) during inspiration through its projection to the PhN and/or to the rostral ventral respiratory group (rVRG), which in turn projects to the PhN, probably by releasing glutamate from their axon terminals. Using a combined retrograde tracing and in situ hybridization technique, here we demonstrate that most of the KF neurons projecting to the PhN and rVRG contain vesicular glutamate transporter 2 (VGLUT2) mRNA but not glutamic acid decarboxylase 67 (GAD67) mRNA, providing definitive evidence that these neurons are glutamatergic. Together with previous data by Stornetta et al. [Stornetta, R.L., Sevigny, C.P., Guyenet, P.G., 2003b. Inspiratory argumenting bulbospinal neurons express both glutamatergic and enkephalinergic phenotypes. J. Comp. Neurol. 455, 113-124], indicating that PhN-projecting rVRG neurons are VGLUT2 mRNA-positive, the present results suggest that the glutamatergic KF-PhN pathway and/or the glutamatergic KF-rVRG-PhN pathway transmit excitatory outputs of KF neurons to the PhN neurons during inspiration.

Detection of phrenic nerves and their relation to cardiac anatomy using 64-slice multidetector computed tomography

The improved temporal and spatial resolution allowed by multidetector computed tomography (MDCT) has facilitated the noninvasive assessment of cardiac anatomy before transcatheter electrophysiologic procedures. Clarification of spatial relations of phrenic nerves and key cardiac structures is important to decrease potential complications. The purpose of this study was to reconstruct the course of the right and left phrenic pericardiophrenic bundles and their relations to cardiac structures using 64-slice MDCT. One hundred six consecutive subjects (age 61 +/- 13 years; 39% women) who underwent self-referred coronary computed tomographic angiography using 64-slice MDCT underwent retrospective assessment of the phrenic nerves contained within the pericardiophrenic bundles. The course of the nerves was outlined in relation to the left atrial appendage, coronary sinus, and cardiac veins. The ability to individually detect the left and right phrenic nerves, as well as the frequency of direct contact between the left phrenic nerve and cardiac veins, was recorded. The left phrenic nerve was identified in 78 of 106 patients (74%). It crossed the left atrial appendage (n = 72, 91%), great cardiac vein (n = 63, 80%), posterior vein of the left ventricle (n = 39, 49%), posterior interventricular vein (n = 8, 10%), and anterior interventricular vein (n = 7, 9%). Mean Hounsfield units (HUs) of the left phrenic nerve was 81 +/- 25. The right phrenic nerve was identified in 50 of 106 patients (47%). Mean HUs of the right phrenic nerve were 94 +/- 26. In conclusion, cardiac imaging using 64-slice MDCT enabled adequate detection of the left and right phrenic nerves in relation to cardiac anatomy. In the setting of electrophysiologic interventions, MDCT before a procedure may elucidate anatomic relationships and help minimize inadvertent complications.

Surgical anatomy of innervation of the gallbladder in humans and Suncus murinus with special reference to morphological understanding of gallstone formation after gastrectomy

AIM: To clarify the innervation of human gallbladder, with special reference to morphological understanding of gallstone formation after gastrectomy.

METHODS: The liver, gallbladder and surrounding structures were immersed in a 10 mg/L solution of alizarin red S in ethanol to stain the peripheral nerves in cadavers (n = 10). Innervation in the areas was completely dissected under a binocular microscope. Similarly, innervation in the same areas of 10 Suncus murinus (S. murinus) was examined employing whole mount immunohistochemistry.

RESULTS: Innervation of the gallbladder occurred predominantly through two routes. One was from the anterior hepatic plexus, the innervation occurred along the cystic arteries and duct. Invariably this route passed through the hepatoduodenal ligament. The other route was from the posterior hepatic plexus, the innervation occurred along the cystic duct ventrally. This route also passed through the hepatoduodenal ligament dorsally. Similar results were obtained in S. murinus.

CONCLUSION: The route from the anterior hepatic plexus via the cystic artery and/or duct is crucial for preserving gallbladder innervation. Lymph node dissection specifically in the hepatoduodenal ligament may affect the incidence of gallstones after gastrectomy. Furthermore, the route from the posterior hepatic plexus via the common bile duct and the cystic duct to the gallbladder should not be disregarded. Preservation of the plexus may attenuate the incidence of gallstone formation after gastrectomy.

Phrenic nerve distribution in the rabbit diaphragm and morphometric analysis of nerve branches

The best method to evaluate the pathogenesis of diaphragmatic disorders is to demonstrate the distribution pattern of the phrenic nerve in the diaphragm. For this purpose the branching pattern and the microanatomic features of the phrenic nerve were observed in six rabbits. All diaphragms were stained by using Sihler's stain method. The phrenic nerve divided into three to four branches when entering the diaphragm. These branches were classified as sternal, anterolateral, posterolateral and crural. The crural branches were the thickest whereas the anterolateral branches were the thinnest. Knowledge about the distribution pattern of the phrenic nerve may be important in surgical approach to the diaphragm.

Surgical Anatomy of the Accessory Phrenic Nerve

BACKGROUND

Reports place the frequency of phrenic nerve injury after cardiac operations between 10% and 85%, emphasizing the importance of an accurate anatomic description of the diaphragm's innervating nerves to reduce iatrogenic injury, length of hospitalization, and associated costs. The aim of our study was to explore the anatomic variations of the accessory phrenic nerve and relate these findings to phrenic nerve injury.

METHODS

Eighty adult formalin-fixed cadavers were dissected, resulting in 160 nerve specimens. Fifty nerve specimens were also examined laparoscopically with findings later confirmed through gross dissection. All nerves contributing to the phrenic nerve after crossing the anterior scalene were considered to be accessory phrenic nerves.

RESULTS

The phrenic nerve was present in all specimens, and 99 (61.8%) also had an accessory phrenic nerve. The accessory phrenic nerve arose from the nerve to subclavius in 60 specimens (60.6%), ansa cervicalis in 12 (12.1%), and nerve to sternohyoid in 7 (7%). The accessory phrenic nerve joined with the phrenic nerve in the thorax anterior to the subclavian vein in 45 (45.5%) specimens and posterior in 17 (22.2%). A phrenic-accessory phrenic nerve loop was found around the subclavian vein in 45 (35 on the right, 10 on the left) specimens and around the internal thoracic artery in 38 (31 on the right, 7 on the left).

CONCLUSIONS

To reduce injuries to the diaphragm, the presence of an accessory phrenic nerve should be considered before mobilization and skeletonization of the internal thoracic artery above the second rib.

[Applied anatomic study on the repair of the facial nerve defect by the anastomosis of the facial nerve with the phrenic nerve]

OBJECTIVE

To explore of the anatomic basis of the anastomosis of the facial nerve with the phrenic nerve.

METHOD

Bilateral microsurgical dissection was performed on eleven human cadavers fixed with formalin. The following length data were measured with calipers: the distance between the bifurcation of the facial nerve trunk and the phrenic nerve root, the useful length of the facial nerve trunk and the phrenic nerve, and the distance between the overlapped nerve ends.

RESULT

The length from the root of the the phrenic nerve to the level of the subclavian vein was (7.2 +/- 1.6) cm. The length from the root of the phrenic nerve to the bifurcation of the facial nerve trunk was (7.23 +/- 0.9) cm. The length from the bifurcation of the facial nerve trunk to the level below the horizontal semicircular canal was 2.7-3.5 cm, 1.0-1.5 cm longer than that cut below the level of the stylomastoid foramen. The cutting nerve ends were placed side by side. The distance between the overlapped nerve ends was 0.4-1.8 cm.

CONCLUSION

In 20 specimens the tension-free anastomosis of the facial nerve with the phrenic nerve that cut in the subclavian vein level can be achieved, in 2 specimens the tension-free anastomosis can not be achieved.

Considerations on the phrenic ganglia

The phrenic ganglion is described as a small ganglion located at the junction of the right phrenic nerve and branches of the celiac plexus, on the diaphragm. The descriptions of this ganglion are few and incomplete and justify the present study which has been performed macroscopically by dissection and microscopically using silver stained (the method of Bielschowsky) drawn pieces. Dissections of 10 human adult specimens showed one or more ganglia located at the level of the terminal division of the right diaphragmatic artery; these ganglia belong to a trunk linking the right phrenic nerve and the celiac ganglion. In some specimens that nervous trunk was replaced by a ganglionated plexus. That trunk--the diaphragmatic nerve--attaches to a distinctive projection of the celiac ganglion; it may be double, but there is one ganglionated component. No left phrenic ganglia were detected. The macroscopic phrenic ganglia are distributed as follows: the lower to the adrenal gland and the upper to the diaphragm. Microscopically, the ganglia had autonomic characteristics; intrinsic microganglia were also detected within the diaphragmatic nerve. Moreover, periadventitial nervous cells were detected on the right inferior phrenic artery.

IN CONCLUSION

(1) the phrenic ganglia seem to be constant structures on the right-hand side; (2) their number is variable--it may be the result of individual fragmentation or coalescence during development; (3) these ganglia may be either adrenal vasomotor or diaphragmatic vasomotor, and functionally belong to the celiac plexus; (4) intrinsic neural and periarterial locations are also possible for macroscopically undetectable populations of autonomic nervous cells.

Phrenic nerve neurotization of the musculocutaneous nerve with end-to-side neurorrhaphy: A short report in a rabbit model

This experimental study was performed to evaluate the efficacy of end-to-side coaptation between the musculocutaneous nerve and the phrenic nerve for brachial plexus injuries with nerve-root avulsions. In an experimental rabbit model, neurotization of the musculocutaneous nerve with the phrenic nerve was compared using end-to-end and end-to-side neurorrhaphy. Preliminary results from electrophysiologic and histologic examinations indicate that end-to-side neurotization of the musculocutaneous nerve with the phrenic nerve is an effective means for musculocutaneous nerve repair. The effectiveness of the phrenic nerve is attributed to its large number of motor axons.

How close are the phrenic nerves to cardiac structures? Implications for cardiac interventionalists

BACKGROUND

Phrenic nerve injury is a recognized complication following cardiac intervention or surgery. With increasing use of transcatheter procedures to treat drug-refractory arrhythmias, clarification of the spatial relationships between the phrenic nerves and important cardiac structures is essential to reduce risks.

METHODS AND RESULTS

We examined by gross dissection the courses of the right and left phrenic nerves in 19 cadavers. Measurements were made of the minimal and maximal distances of the nerves to the superior caval vein, superior cavoatrial junction, right pulmonary veins, and coronary veins. Histologic studies were carried out on tissues from six cavaders. Tracing the course of the right phrenic nerve revealed its close proximity to the superior caval vein (minimum 0.3 +/- 0.5 mm) and the right superior pulmonary vein (minimum 2.1 +/- 0.4 mm). The anterior wall of the right superior pulmonary vein was <2 mm from the right phrenic nerve in 32% of specimens. The left phrenic nerve passed over the obtuse cardiac margin and the left obtuse marginal vein and artery in 79% of specimens. In the remaining specimens, its course was anterosuperior, passing over the main stem of the left coronary artery or the anterior descending artery and great cardiac vein.

CONCLUSIONS

The right phrenic nerve is at risk when ablations are carried out in the superior caval vein and the right superior pulmonary vein. The left phrenic nerve is vulnerable during lead implantation into the great cardiac and left obtuse marginal veins.

The triangle of the vertebral artery

OBJECTIVE

Neurosurgical procedures such as proximal brachial plexus repair, scalenotomy, and direct isolation of the proximal vertebral artery require a good working knowledge of the triangle of the vertebral artery. This deep triangle of the neck is bound by the subclavian artery and the anterior scalene and longus cervicis muscles. In addition to the vertebral artery, many important structures are found in this area, such as the ganglionated sympathetic chain and certain cervical spinal nerves.

METHODS

Twenty formalin-fixed cadavers were used for this study. Dissection of this triangle was performed, and measurements were made not only of parts of its borders, but also distances from these borders to neurologically important structures within its confines, such as the C8 spinal nerve.

RESULTS

In all specimens, the middle scalene muscle was noted to form part of the posterior wall of the triangle. The mean height of the triangle was found to be 3.2 cm, and the mean width of its base was 1.3 cm. We observed that the C8 spinal nerve had a mean distance of 1.2 cm inferior to the apex of the triangle and that the C7 spinal nerve was found inside the triangle in 5% of sides. If the phrenic nerve entered the triangle, it was never found more than 6 mm medial to the anterior scalene muscle. The vertebral artery always traveled intimately along the lateral border of the longus cervicis muscle, and its lateral edge ranged 5 to 8 mm medial to the medial edge of the anterior scalene muscle.

CONCLUSION

The C7 spinal nerve was observed in the triangle of the vertebral artery. In addition, the posterior border of the triangle of the vertebral artery was clearly defined in this study, and the middle scalene muscle could be used as a landmark. These data, coupled with our quantitation of parts and structures within the triangle, may assist neurosurgeons who operate on this area of the neck.

"Pes anserinus" of the right phrenic nerve innervating the serous membrane of the liver: a case report (anatomical study)

During the preparations of cadavers for educational purposes we followed the course of the right phrenic nerve. On one of them and especially a female cadaver aged 72-year-old we found a branch arising from the thoracic portion of the right phrenic and passing through the two layers of the falciform ligament distributed to the upper surface of the serous layer of the liver in the form of "pes anserinus". As it is known, pain referred from the diaphragmatic peritoneum is classically felt in the shoulder tip but pain from thoracic surfaces supplied by the phrenic nerve is usually located there albeit vaguely. We believe that the above anatomical finding is the explanation of distinct radiating pain from the hepatic region to the right shoulder in some patients. The stimulations is carried through the phrenic nerve to the fourth cervical neurotome from were arise the supraclavicular nerves which are distributed to the shoulder region.

Functional organization of respiratory neurones: a brief review of current questions and speculations

This article presents a short overview of current knowledge about the medullary respiratory neurones and the generation of breathing rhythm. The background respiratory neurophysiology of the medulla and pons is briefly reviewed, with some current ideas about the organization of the pontine-medullary respiratory control system and its development. Questions and speculations about the organization and generation of respiratory rhythm are included, with a view to stimulating experiments to provide answers.

Identification of the phrenic nerve in surgical exploration of the brachial plexus in obstetrical palsy

This report describes a simple technique for identifying the phrenic nerve at the beginning of exploration of the brachial plexus in obstetrical palsy. Both the phrenic and supraclavicular nerves originate from the C4 root; therefore, retrograde dissection of the supraclavicular nerve will end at the C4 root and identify the phrenic nerve. This technique is very useful to less experienced surgeons but may also be helpful when the experienced surgeon encounters excessive scarring of the anterior scalene muscle. Finally, the dissected supraclavicular nerve may be used as a cable graft in brachial plexus reconstruction.

Scalenus muscles in macaque monkeys

The attachment and innervation of the scalenus muscles in both sides of two Japanese monkeys and a rhesus monkey were observed to discuss their morphological significance while comparing their findings in humans. The scalenus ventralis muscle in macaques had almost the same attachments as the scalenus anterior muscle in humans and was innervated by the cervical nerve branches, which were lower in spinal segment than in humans and had a close relationship with the branches to the intertransversus ventralis muscles. Furthermore, the scalenus ventralis muscle was penetrated by the phrenic nerve in all cases observed. The posterior part of the scalenus muscle in macaques (the scalenus dorsalis muscle) was divided into short (the scalenus dorsalis brevis) and long (the scalenus dorsalis longus) parts according to their attachments. The former was attached to the transverse processes of the lowest two cervical vertebrae and the first rib, whereas the latter was attached to the 3rd-5th ribs. It is notable that the scalenus dorsalis muscles in macaques were innervated by branches from the long thoracic nerve in addition to direct branches from the cervical nerve roots. In addition, the scalenus dorsalis longus was supplied by twigs from the lateral cutaneous branches of the 2nd and 3rd intercostal nerves. This indicates that the scalenus dorsalis muscles contain a muscular component derived from the upper limb girdle musculature, unlike the human scalenus muscles, which have been considered to belong to the cervical trunk muscles.

Characterization of the human diaphragm muscle with respect to the phrenic nerve motor points for diaphragmatic pacing

Diaphragm pacing from laparoscopically placed electrodes is an alternative to conventional phrenic pacers that use electrodes placed in direct contact with the nerve in the neck or chest. The challenge with the laparoscopic approach is determining where to implant the electrodes, as the phrenic nerves are not visible from the abdomen. The objective of this study was to locate the phrenic nerve "motor points" in the human diaphragm muscle from an abdominal perspective. Twenty-five cadavers were examined by excising the diaphragm muscle and assessing for the thickness of the muscle, the motor point area, and the accessibility of the motor point from the abdominal approach. The data indicate the average thickness of the muscle in the motor point region was 3.0 mm for the left and 2.9 mm for the right hemidiaphragm. The average motor point area was 73 mm2 for the left and 58.7 mm2 for the right hemidiaphragm. The motor points were accessible from an abdominal approach, but the motor point on the right hemidiaphragm was located on the central tendon in many cases (12 of 25). Thus, although the nerves branch prior to entry into the muscle on the right side, several well-placed electrodes could still activate the entire nerve. In this study, we have characterized the human diaphragm muscle in the motor point region and found that it is feasible to place laparoscopically intramuscular electrodes in the motor point region. This is the foundation for the laparoscopically placed diaphragm pacing device that has been utilized in a small series of patients.

Anatomical variations of the phrenic nerve and its clinical implication for supraclavicular block

This paper reports a case of simultaneous diaphragmatic and brachial plexus stimulation followed by a successful nerve block using the supraclavicular approach. An explanation for the qualitative differences in phrenic nerve block between interscalene and supraclavicular block is postulated, based on known anatomical variations.

The phrenic ganglion in man

During educational dissections we observed a phrenic ganglion on the nerve of the phrenic artery originating from the upper pole of the right coeliac ganglion, which accompanied the right inferior phrenic artery on a female cadaver at the age of 34. In our case the left coeliac ganglion, the inferior phrenic artery, the right and left greater, lesser and least splanchnic nerves were present and normal. However, the left nerve of the phrenic artery and the phrenic ganglion were absent. We consider that this rarely reported neural formation may be of importance for anatomists and clinicians.

Anatomical study of the diaphragm of the opossum (Didelphis albiventris)

The anatomical characteristics of the South American opossum diaphragm were described. Five male and seven female adult opossums, weighing between 700 and 1110 g, were used. Animals were killed by ether inhalation saturation. The abdominal and thoracic walls were dissected and opened, the viscerae were removed and the diaphragm anatomy was described and photographed in situ. After diaphragm removal, some dimensional data were taken and tabled. Primary branches of the phrenic nerves were dissected under a surgical microscope. The secondary branches were studied and described by transillumination after clarification in acetic acid. The opossum diaphragm is domed and has a mean area of 54.33 +/- 3.8 cm2. Well-identified costal, sternal and lumbar parts form the peripheral muscular region. The central tendinous region presents with a V-like form. Three folioles comprise the phrenic centre and present different dimensions. The caudal vena cava passes through its foramen between the ventral and right dorsal folioles. Both right and left phrenic nerves present one ventral branch and one dorsolateral trunk in 50.0% and 66.67% of the cases, respectively.

[Applied anatomy for the reinnervation of posterior cricoarytenoid muscle by phrenic nerve for bilateral vocal cord paralysis]

OBJECTIVE

To study the anatomic basis for the anastomosis of phrenic nerve (PN) to the anterior branch of recurrent laryngeal nerve(RLN) for the treatment of the injured bilateral RLN.

METHODS

The origin and the nutritive arteries and the adjacent tissue construction of PNs in 46 cases were studied. The longest utilizable length of PNs and the distance from the root of PN to cricothyroid joint were measured. The sectional area and the number of myelinated fibers of PNs and the anterior branch of RLNs were measured by computer image processing system.

RESULTS

PNs coming from C4 comprised of 93.5%, 95.6% (44/46) of the nutritive arteries came from the ascending carotid artery and got into the cervical segment of PN from its root. The common trunk of PN was very deep, to the external of the common carotid artery and the vertebral vein, and deep to the internal jugular vein and thoracic duct (left), and in the superficies of the subclavian artery and in the deep of the subclavian vein when it was crossing the thoracic entrance. The distance from the root of PN to the level of the subclavian vein and to cricothyroid joint were (7.2 +/- 1.6) cm and (5.5 +/- 1.4) cm, respectively. The former was at least 1.5 cm longer than the latter. The average number of myelinated fibers and the sectional area of the PNs were 2.41 times and 2.15 times as many as those of the anterior branch of RLNs, respectively. The single-fasciculated PNs comprised of about 75.0% (18/24)).

CONCLUSION

Clinically, it may be safe and available for cutting PN off at the level of the subclavian vein. The length of PN is enough for the anastomosis of PN to the anterior branch of RLN.

[Anatomic and radiologic considerations of varied appearances of thoracic structures]

The purpose of this pictorial essay was to demonstrate normal chest anatomy and related pathologies on chest radiographs and chest CT images. It is important for the general practitioner to have a clear understanding of anatomy in order to avoid overestimating subtle radiologic findings and to be able to differentiate true pathological lesions. This pictorial essay includes various appearances of pleural fissures, companion shadows of the ribs, and minor structures of the chest walls and mediastinum.

The communicating branch of the 4th cervical nerve to the brachial plexus: the double constitution, anterior and posterior, of its fibers

Twenty-four adult cadavers (48 sides) were used to investigate the incidence of a branch arising from the ventral ramus of the fourth cervical nerve (C4) with the phrenic nerve and subsequently joining the brachial plexus. Six brachial plexuses with spinal cords and phrenic nerves were dissected under a surgical microscope to investigate localization of fibers contained in the C4 branch to the brachial plexus. The incidence of the C4 branch was 23% (11/48 sides). Branches from C4 to the brachial plexus divided into anterior and posterior divisions on four sides (4/6 sides). On two sides, the branch did not divide but consisted entirely of an anterior division (2/6 sides). In the brachial plexus, anterior division fibers of the C4 branch were intertwined with fibers from the anterior divisions of the ventral rami of the fifth and sixth cervical nerves. They then passed to the suprascapular nerve and the anterior division of the superior trunk (6/6 sides). On the other hand, posterior division fibers of the C4 branch were intertwined with fibers from the posterior divisions of the ventral rami of the fifth and sixth cervical nerves. They then passed to the suprascapular nerve (2/6 sides) and the posterior division of the superior trunk (4/6 sides). The anterior division of the C4 branch received fibers from the ventral rootlets of the entire fourth cervical segment, whereas the posterior division received fibers from the ventral rootlets of the caudal half of the fourth cervical segment only. The fact that the suprascapular nerve received fibers from both the anterior and posterior divisions of the C4 branch was considered to support our claim that the human suprascapular nerve belongs to both the anterior and posterior divisions of the brachial plexus.

Potential fascial dome made by the upper leaf of the phreno-esophageal membrane

We describe the configuration and size of the artificial fascial dome created in 57 cadavers. This dome protrudes into the thoracic cavity from the esophageal hiatus. This dome was a potential space realized by finger dissection (i.e., a specific but common surgical procedure during surgery of the upper part of the stomach). The vagus nerves penetrated the top of the dome and ran down along the esophagus. The height of the ventral wall of the dome ranged from 10-60 mm, while the dorsal wall was 10-40 mm longer than the ventral one since the dorsal wall attached to the lower, dorsal limb of the esophageal hiatus. Accordingly, the dorsal wall separated the "thoracic" aorta from the "abdominal" esophagus. We considered that the upper leaf of the phreno-esophageal membrane forms the fascial dome, although the lower leaf of the membrane was not identified in this study. According to the results, we proposed a schematic representation of the phreno-esophageal membrane.

Cervical anatomy of phrenic nerve roots in the rabbit. European Group for Research on the Larynx

The cervical anatomy of the different nerve contributions that constitute the phrenic nerve (phrenic nerve roots and accessory phrenic nerve) were studied in rabbits. In 55 dissections, 6 main root arrangement types were observed. The roots that issued from the fourth and fifth cervical nerves (C4 and C5 roots) were constant. The C4 root was either short or long. The C6 root was at times absent, or sometimes double. An accessory phrenic nerve was present in 43% of the right and 28% of the left dissections. The distribution of the phrenic nerve roots often displayed left-right asymmetry. We conclude that a better knowledge of the cervical anatomy of the phrenic nerve is useful both in physiological studies involving diaphragm denervation and in experimental laryngeal reinnervation.

Electrophysiological properties of rat phrenic motoneurons during perinatal development

Past studies determined that there is a critical period at approximately embryonic day (E)17 during which phrenic motoneurons (PMNs) undergo a number of pivotal developmental events, including the inception of functional recruitment via synaptic drive from medullary respiratory centers, contact with spinal afferent terminals, the completion of diaphragm innervation, and a major transformation of PMN morphology. The objective of this study was to test the hypothesis that there would be a marked maturation of motoneuron electrophysiological properties occurring in conjunction with these developmental processes. PMN properties were measured via whole cell patch recordings with a cervical slice-phrenic nerve preparation isolated from perinatal rats. From E16 to postnatal day 1, there was a considerable transformation in a number of motoneuron properties, including 1) 10-mV increase in the hyperpolarization of the resting membrane potential, 2) threefold reduction in the input resistance, 3) 12-mV increase in amplitude and 50% decrease duration of action potential, 4) major changes in the shapes of potassium- and calcium-mediated afterpotentials, 5) decline in the prominence of calcium-dependent rebound depolarizations, and 6) increases in rheobase current and steady-state firing rates. Electrical coupling among PMNs was detected in 15-25% of recordings at all ages studied. Collectively, these data and those from parallel studies of PMN-diaphragm ontogeny describe how a multitude of regulatory mechanisms operate in concert during the embryonic development of a single mammalian neuromuscular system.

Surgical anatomy of the diaphragm and the phrenic nerve

In this article, the anatomy of the diaphragm and phrenic nerves is discussed, together with related surgical implications. Since the major cause of phrenic nerve injury is surgery, usually for congenital or acquired heart disease, incisions in the diaphragm that do not injure major branches of the phrenic nerve are also discussed. Diaphragmatic plication is usually required in infants less than 3 months of age, and older children may be managed by ventilatory support if electrophysiologic studies document the possibility of return of nerve function. In adults with normal pulmonary function, unilateral diaphragmatic paralysis is usually asymptomatic.

Respiratory activity of the rat posterior cricoarytenoid muscle

An anatomic and electrophysiological study of the rat posterior cricoarytenoid (PCA) muscle is described. The intramuscular nerve distribution of the PCA branch of the recurrent laryngeal nerve was demonstrated by a modified Sihler's stain. The nerve to the PCA was found to terminate in superior and inferior branches with a distribution that appeared to be confined to the PCA muscle. Electromyography (EMG) recordings of PCA muscle activity in anesthetized rats were obtained under stereotaxic control together with measurement of phrenic nerve discharge. A total of 151 recordings were made in 7 PCA muscles from 4 rats. Phasic inspiratory activity with a waveform similar to that of phrenic nerve discharge was found in 134 recordings, while a biphasic pattern with both inspiratory and post-inspiratory peaks was recorded from random sites within the PCA muscle on 17 occasions. The PCA EMG activity commenced 24.6 +/- 2.2 milliseconds (p < .0001) before phrenic nerve discharge. The results are in accord with findings of earlier studies that show that PCA muscle activity commences prior to inspiratory airflow and diaphragmatic muscle activity. The data suggest that PCA and diaphragm motoneurons share common or similar medullary pre-motoneurons. The earlier onset of PCA muscle activity may indicate a role for medullary pre-inspiratory neurons in initiating PCA activity.

The brachial plexus in the chacma baboon (Papio ursinus)

The brachial plexus in each of ten embalmed, mature chacma baboons was dissected to document the structure and branching pattern of this nerve plexus in this increasingly used research animal. In general, the brachial plexus in the chacma baboon was similar to the plexuses in the vervet and other Old World monkeys. However, several aspects were comparable to those observed in domestic animals. Thus the bipedal and quadrupedal abilities of the chacma baboon were reflected in the structure of its brachial plexus.

[The structural bases of the tensile strength properties of nerves]

Morphological and mechanical properties of phrenic and vagal nerves cervical regions were studied in 51 cadavers of fetuses and newborns in 28 to 40 weeks gestation. Diameter and thickness of coats, porting of cross section area occupied by connective tissue and general tensile strength were found to increase in both nerves with the gestation period growth, while relative share of nerve bundles cross section reduces. Within the last trimester of intrauterine development nerve trunk rigidity grows smaller and tensile strength does not change significantly. Vagal and phrenic nerves possess an elongation reserve, safe for their structure due to nerve fibers tortuosity. Connection between the nerve trunk rigidity coefficient and epineurium thickness, porting of cross section of nerve and connective tissue is non-linear and statistically significantly approximates with hyperbolic equation of order 1 or 3.

The thoracic inlet: normal anatomy

The thoracic inlet is the junction between the neck and the chest. A number of neural structures traverse this region. A knowledge of the location of these various neural structures and their relationship to one another is important when interpreting cross-sectional images of this region. This article will review the normal anatomy of the major neural structures that are found in this region.

Variations in the formation of the cardiac plexus--a study in human foetuses

The origin and distribution of nerves forming the cardiac plexus and the subdivision of this plexus were studied in six human foetuses (2 male, 4 female) of gestational ages 30 to 40 weeks. The cardiac plexus was not divided into superficial and deep parts in any foetus. True plexiform arrangement of nerves forming the cardiac plexus was seen only after the nerves reached the walls of the heart. The sympathetic trunks, vagi, recurrent laryngeal nerves and phrenic nerves of both sides contributed to the cardiac plexus. The cervical sympathetic trunk showed only two ganglia bilaterally in one foetus; this has not been reported before. In one foetus on the right side, the middle cervical sympathetic cardiac branch joined the recurrent laryngeal and the phrenic nerves which has not been reported earlier. The sympathetic pathways to the heart were found to be very variable; no two foetuses showed the same arrangement. Awareness of these variations in the nerves forming the cardiac plexus would enhance the success of sympathectomy to augment cardiac blood flow or to relieve the severity of cardiac pain.

NMDA as well as non-NMDA receptors mediate the neurotransmission of inspiratory drive to phrenic motoneurons in the adult rat

The neurotransmission of bulbospinal respiratory drive is believed to involve primarily non-NMDA receptors located in the phrenic motonucleus (PMN). This conclusion is based on studies carried out mainly on in vitro brainstem-spinal cord preparations of the neonatal rat. The present study was undertaken to investigate the transmitter/receptor mechanisms in the PMN which are involved in the neurotransmission of inspiratory drive, using an in vivo adult rat model. Microinjections of glutamate, NMDA and AMPA into the PMN elicited an increase in the phrenic nerve (PN) background discharge. These injections did not alter significantly the frequency of spontaneously occurring PN bursts confirming that mechanisms responsible for respiratory rhythm reside in the supraspinal structures. Microinjections of an NMDA receptor blocker (AP-7), in concentrations that did not alter the responses to a non-NMDA receptor agonist (AMPA), reduced the PN amplitude significantly. Similarly, microinjections of a potent non-NMDA receptor blocker (NBQX), in concentrations that did not alter responses to NMDA, reduced the PN amplitude significantly. Sequential microinjections, within an interval of 5 min, of AP-7 and NBQX into the PMN, resulted in a dramatic reduction in the spontaneous PN bursts. The reduction of PN amplitude started immediately after the microinjection of AP-7 and NBQX, either alone or in combination, and reached a maximum within 5-10 min. These results indicate that, unlike in the neonatal rat, both NMDA and non-NMDA receptors located in the PMN play a significant role in the neurotransmission of the inspiratory drive in the adult rat.

Application of the Cavalieri principle in volume estimation using laser confocal microscopy

The Cavalieri principle, a well-established stereological technique, uses interpolation between samples to estimate volume of three-dimensional (3D) objects. Serial optical sectioning with the confocal microscope resembles certain aspects of the Cavalieri principle, albeit with no interpolation. However, reconstruction and analysis of finely spaced optical sections can be cumbersome and time consuming. Application of the Cavalieri principle to confocal sections may be advantageous in reducing the size of the data set required to obtain reliable estimates of volume. In the present study, somal volumes of phrenic motoneurons were estimated by applying the Cavalieri principle to confocal images. These estimates were compared to measurements of somal volume using on interpolation of confocal sections. Phrenic motoneurons in adult rats were retrogradely labeled with a fluorescent rhodamine dye. Confocal optical sections of 0.6 micron thickness were then obtained from 150-micron-thick spinal cord slices containing labeled neurons. These image sets were reoriented to represent transverse sections. The Cavalieri principle was applied to these confocal image sets at selected sampling intervals from 1.2 to 3.0 microns. Planimetric measurements of motoneuron somal cross-sectional area in the selected sections were made using a point-counting method. At sampling intervals less than 2.4 microns, individuals motoneuron somal volume estimates were similar for the noninterpolated confocal and the interpolated Cavalieri methods. At these sampling intervals, the distributions of motoneuron somal volumes were also similar for the two methods. At a sampling interval of 2.4 microns or greater, there was a greater variability in individual motoneuron somal volume estimates, although the population mean and median were similar to the noninterpolated confocal measurements. Therefore, a satisfactory agreement between noninterpolated confocal measurements and the Cavalieri estimates suggests that less-stringent optical sectioning parameters may suffice for individual cell volume measurements when using confocal microscopy, thus making it significantly more efficient.

A midline area in the nucleus commissuralis of NTS mediates the phrenic nerve responses to carotid chemoreceptor stimulation

The carotid body chemoreceptor afferents have been reported to project to a discrete area located in the nucleus commissuralis of nucleus tractus solitarius [A. Vardhan et al., Am. J. Physiol., 264 (1993) R41-R50]. The afore-mentioned study was done in spontaneously breathing rats and the afferents and efferents located in the chest wall and the respiratory tract of these animals were intact. In order to exclude the role, if any, of these afferents and efferents, in the present experiments respiratory changes were monitored by recording the phrenic nerve activity instead of tracheal airflow. Experiments were carried out in pentobarbital-anesthetized, bilaterally vagotomized, paralyzed and artificially ventilated rats with a pneumothorax. The carotid body chemoreceptors were stimulated with tracheal administration of nitrogen for 7-10 s. The chemoreceptor stimulation induced an increase in the frequency and amplitude of phrenic nerve bursts. A decrease in the duration of inspiratory (T1), expiratory (TE) and total cycles (TTOT) was observed in the phrenic nerve activity. Inhibition of neuronal cell bodies by microinjections of muscimol (140 pmol/20 nl) into a discrete area in the commissural subnucleus of the nucleus tractus solitarius (coordinates in mm: 0.3 rostral to 0.5 caudal, 0 to 0.5 lateral and 0.3 to 0.5 deep with respect to the calamus scriptorius), attenuated the phrenic nerve responses to the carotid body stimulation. On the other hand, control injections of saline (0.9%) into this site did not alter the phrenic nerve response to the carotid body stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Surgical anatomy of the phrenic nerve and internal mammary artery

Dissection of the thoracic inlet was performed on 22 cadavers to determine the relationship of the phrenic nerve to the internal mammary artery as it passes from lateral to medial behind the first rib. On the left the nerve was found to cross superior to the artery and then medial to it in 14 of 22 specimens; on the right this was found in ten of 22 specimens. In all other specimens, it crossed inferior to the internal mammary artery. These findings demonstrate that there is no constant relationship between these structures, and emphasize the need for caution when dissecting the internal mammary artery at or above the level of the first rib.

Anatomical interrelation between the phrenic nerve and the internal mammary artery as seen by the surgeon

Paresis of the diaphragm (especially left-side paresis) is a relatively frequent finding following cardiac surgery. While, usually, it is a rather benign condition, in exceptional cases it may lead to severe impairment to death of the patient. The supposed causes of damage to the phrenic nerve include: local myocardial cooling by ice slush; opening of the pleural cavity in connection with local cooling; cross clamp length; total hypothermia; central venous cannulation; traction-related damage; mammary artery harvesting. Perhaps the commonest cause of damage to the phrenic nerve, i.e., the effect of local myocardial cooling by ice slush, and the mode of phrenic nerve protection have been studied in considerable detail. The authors focused their attention on the interrelation between the phrenic nerve and the proximal segment of the mammary artery. Using anatomical preparations, the authors demonstrate the very intimate relationship of the above entities. The interrelation of the two anatomical structures basically differs depending on whether the left or right side is concerned. 1) On the left: The phrenic nerve, on entering the thorax, runs between the subclavian artery and vein laterally from the mammary artery crossing it medially; it parts the latter and continues in mediastinal adipose tissue to run on the pericardium toward the diaphragm. 2) On the right: The phrenic nerve passes between the subclavian vein and artery medially from the mammary artery. For another 3-4 cm, it runs along the medial and dorsal edges of the mammary artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurements of motoneuron somal volumes using laser confocal microscopy: comparisons with shape-based stereological estimations

Previous studies on motoneuronal morphometry have assumed the geometry and orientation of neuronal soma in estimating somal volumes based on two-dimensional measurements. In this study, the optical sectioning property of the confocal microscope was used to make direct measurements of phrenic moto-neuron somal volume. These measured volumes were compared to shape-based stereological estimates of volume. Phrenic motoneuron pools in adult rats were retrogradely labeled with fluorescent dye. Labeled motoneurons, in 150-micron-thick tissue sections, were imaged using a Bio-Rad MRC 500 confocal microscope. Somal volumes were directly measured using ANALYZE, a comprehensive image processing software package. These volumes were compared to volume estimates based on five geometrical shapes previously used to study spinal motoneurons. In the adult phrenic motoneuron pool, overestimations of somal volume up to 300% were observed in cases where the Z-axis dimensions of the neurons were not simply related to the X and Y dimensions. None of the five geometrical shapes were found to be suitable for estimating either mean or individual somal volumes of the phrenic motoneuron pool. Confocal microscopy allowed accurate reconstruction along X, Y, and Z axes, and therefore provided a more direct method of measuring motoneuron somal volumes. We conclude that significant and inconsistent errors can be introduced by using shape-based stereological methods for estimating neuronal somal volumes.

Diaphragm reinnervation by laryngeal motoneurons

Inspiratory activity of the paralyzed diaphragm was restored by reinnervation with brain stem laryngeal motoneurons. In 10 anesthetized cats, the right recurrent laryngeal nerve (RLN) was cut and anastomosed to the distal stump of either one or both roots (C5-C6) of the ipsilateral phrenic nerve. Three to four months later, reinnervation was assessed under deep anesthesia by the reappearance in the paralyzed diaphragm of 1) direct electromyographic (EMG) responses after electrical stimulation of the RLN and 2) spontaneous inspiratory bursts. Serial radiography, performed on five animals, revealed diaphragmatic excursions of comparable amplitude on the normal and reinnervated sides. Six to twelve months after anastomosis, laparotomy (performed under Nembutal anesthesia) allowed inspection and EMG recording of the spontaneous inspiratory contractions of the reinnervated areas and their sustained responses to tetanic RLN stimulation. Inspiratory discharges showed a ramplike recruitment similar to that of the normal diaphragm. Although the RLN contains a number of expiratory axons, multiple-site recordings disclosed expiratory EMG discharges only once. Histological analysis confirmed the substitution of phrenic axons by regenerating RLN fibers.

Thoracoscopic dissection of the esophagus in human cadavers

A technique for thoracoscopic dissection of the esophagus is described which gives a large and magnified view of the pleural cavity, the mediastinum, and the esophagus. This technique was developed on human cadavers which gives excellent technical resources for learning and practicing endoscopic surgical anatomy of the esophagus. It avoids the need to change the position of the patient to perform a total thoracoabdominal esophagectomy via a triple surgical approach.

Origin of the internal thoracic artery and its relationship to the phrenic nerves

The internal thoracic artery was studied because of its recent use in the revascularization of the myocardium in patients with coronary artery disease. The artery of 50 cadavers of adult individuals of either sex, whose age ranged from 20 to 84 years, was studied after neoprene latex injection. Its origin, relation to the phrenic nerve and origin of the pericardiacophrenic artery were investigated. The left and right phrenic nerves cross the artery anteriorly in 54% of the cases and posteriorly in 14%. The right nerve crosses the artery anteriorly and the left posteriorly in 22%, and the reverse occurs in 10%. The origin of the internal thoracic artery is much more frequent from the subclavian artery (80%) than from a common trunk with other arteries (20%). The pericardiacophrenic artery is a branch of the internal thoracic artery in 99% of the cases and the average distance between the origins of these two arteries is 3.9 +/- 1.3 cm.

Postnatal maturation of phrenic nerve in children

The phrenic nerve at the pericardial level was examined postmortem in 17 children, ages 3 days to 8 years. Detailed macroscopic and histologic examination of the central nervous system in all patients disclosed no abnormalities. Quantitative developmental studies demonstrated that myelinated axons doubled in number from birth to age 1 year when a plateau was reached. The main period of growth in diameter of myelinated axons also corresponded to the first year when median diameters increased from 1.75 microns at 3 days of age to 3.0 microns by 8 months of age. Unmyelinated axons also grew significantly in the first 11 months when median diameters reached 1.4 microns. There was no significant increase in axonal diameter at later ages. The slope of the regression line for the number of myelin lamellae on axonal diameters increased with age until 6 months of age, whereas the dispersion around the regression lines decreased in the same period. This finding suggests a direct relationship between myelination and axonal growth. Significant maturation of the phrenic nerve occurs during the first year of life.

Identification of the axon pathways which mediate functional recovery of a paralyzed hemidiaphragm following spinal cord hemisection in the adult rat

Despite extensive neurophysiological work carried out to characterize the crossed phrenic phenomenon, relatively little is known about the morphological substrate of this reflex which restores function to a hemidiaphragm paralyzed by spinal cord injury. In the present study WGA-HRP was injected into normal and functionally recovered hemidiaphragm muscle in rats during the crossed phrenic phenomenon. The retrograde transynaptic transport characteristics of WGA-HRP was utilized to delineate the source of the neurons which mediate the crossed phrenic phenomenon. The results indicated that the neurons which drive phrenic motoneurons in spinal hemisected rats during the crossed phrenic phenomenon are located bilaterally in the rostral ventral respiratory group (rVRG) of the medulla. No transneuronal labeling of propriospinal neurons was noted in either normal or spinal-hemisected rats. Thus, propriospinal neurons do not relay respiratory drive to phrenic motoneurons. The neurons of the rVRG project monosynaptically to phrenic motoneurons. The present results suggest that both crossed and uncrossed bulbospinal pathways from the rVRG collateralize to both the left and right phrenic nucleic and functional recovery of a hemidiaphragm paralyzed by ipsilateral spinal cord hemisection is mediated by supraspinal neurons from both sides of the brain stem. These results are important to our complete understanding of the mechanisms which govern motor recovery in mammals following spinal cord injury.