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.