V. Matejcik, G.Penzesova
Department of Neurosurgical Clinic of the Medical Faculty of Comenius University, Limbova 5, Bratislava, Slovak Republic
Outcome: The history of anatomical variations is tightly linked with the history of the anatomy itself, with the history of the search and constitution of the images of normal structure and composition of human body. Aberrations observed during surgical treatments inspired us to initiate the investigation of variations in the formation of brachial plexus.
Material and methods: We examined 55 adult cadavers in order to find out the incidence of neural variations. We observed the plexiform but not spinal roots. We saw the pretrunkal part of plexus including segment of spinal nerve in sulcus spinal nerve and anterior branch of the spinal nerve. Motoric innervation particularities in relation to diagnostics are emphasized as well, apart from the anatomic variability. Attention is put on the mechanism and the morphologic reasons of particular types of injuries.
Results: We did not observe any particular anomaly in the formation of the plexus in only 9 cases. There was one anomaly present in 11 cases and in 35 two or more anomalies in the same time. The anomalies were usually of anatomic character in the area of the formation of the terminal branches. Least number of anomalies was present in the area of neural roots.
Conclusion: In the present work we focused on the deviations from the normal formation of brachial plexus and its terminal branches and their relation to surrounding structures that often determine the outcome of surgical treatment. The results of such anatomical studies are necessary for a more concise interpretation of peroperational as well as clinical findings.
Key words: brachial plexus, supraclavicular part, infraclavicular part, variations.
Already the ancient Greek and medieval anatomists Galenus (129-200 B.C.) and Vesalius have drawn the attention to individual variation. Therefore we often find in their works expressions like always, often, sometimes, rarely and very rarely. Vesalius Andreas (1514-1564) in his work Humani corpori fabrica (1542) described anatomic variations of human bones, muscles and arteries. He used dissection as the major instrument in his attempt to understand the structure of human body.
Several centuries were necessary for the establishment of concepts of normality, abnormality and variability of human body. These results are based on works of many anatomists, biologists and clinicians. Corresponding studies continue also in the presence and result in scientific books and papers aimed at the anatomical variations that under normal circumstances do not affect the functionality of human organism.
Medicine needs more exact knowledge of the variability in the organization of human body to improve the diagnostics and treatment. New imaging methods such as echography, endoscopy, computer tomography, magnetic resonance imaging paved the way for the research in anatomical variations.
Information about the structure represent the means how to reach the final goal - the perfect treatment of peripheral nerve injuries and the correction of partial or total lesions in sensory and motoric functions. Lesions of peripheral nerves differ from all other injuries in the fact that their clinical course and outcome are substantially determined by the complexity of the processes of degeneration and regeneration.
The study is concerning 50 cadavers, in which the brachial plexus was observed bilaterally. The body was in a lying position with limbs slightly pulled out. The skin incision was performed from the upper third of the lateral side of sternocledomastoid muscle to the median third of the clavicle and from there along with the clavicle to its lateral part and through the deltoid-pectoral sulcus to the medial surface of the shoulder to its inferior third. Skin and subcutaneous tissues were moved to side. In the beginning we dealt with the supraclavicular part of the plexus.
The visualization of the spinal nerves in the intraforaminal level up to the border of dura mater was performed using a resection of the endings of the transverse processes.
When it was necessary to isolate the inferior plexus as C7 spinal root and C7 root as the middle trunk or C8 and Th1 of the inferior trunk, we have removed the insertion of the anterior scalenus muscle up to the anterior tubercle or we have cut a part of the scalenus muscle. The origin of the long thoracic nerve was found by pulling the C6 root to the front.
After the trunks and branches were exposed, we have proceeded to the next stage. It concerned a separation of the major pectoral muscle from the clavicle in the area of 2-3 cm and then a separation of the clavicle from medial to ist lateral third. This stage exposed the clavi-pectoro-axillary aponeurosis, subclavial and minor pectoral muscle, with enabled to observe the inferior trunk and medial fascicle. In the area covered with the minor pectoral muscle were the nerves of the plexus in close contact to each other around the artery. Discission of the minor and major pectoral muscles finally enabled to observe the infraclavicular part of the brachial plexus and all pectoral nerves as well as the terminal nerves in full integrity.
We have exposed the lateral fascicle, which was fixed with fibers of connective tissue to the fascia of the subclavius muscle, using a more proximal preparation. The middle fascicle was present more inwards from the lateral and deeper. A close preparation near the middle fascicle enabled localization of the posterior fascicle. A bifurcation of the posterior fascicle to the radial and axillary nerve is in the level of the origination of the coracobrachial branches from the lateral fascicle. A deeper preparation downwards to the inferior border of the minor pectoral muscle projection enabled an exposure of the median nerve.
Working upwards, the preparation of the proximal part of the median nerve led to the lateral and medial root of bifurcation of the median nerve.
The level of the origination of the axillary nerve from the posterior fascicle was used as an orientation point. Proximally from this level were located fascicles, distally then nerves originating from them.
The formation of fascicles took place usually not above the projection of the lower margin of the clavicle.
When anomalies were detected, we continued the preparation using a magnifying lens. Under the term root we define plexiform root not spinal root. It means pretrunkal part of plexus including segment of spinal nerve in sulcus spinalis nerve and anterior branch of the spinal nerve up to the plexiform trunk.
(Fig.1) Brachial plexus, left side: root C5 (1), root C6 (2), root C7 (3), root C8 (4) splits into several branches, the root Th1 (5) is thicker than the root C8.
(Fig.2) Brachial plexus, left side: root Th1 (1), root C8 is splitted into two branches (2,3), root C7 (4), root C6 (5), root C5 (6). A branch of the root C8 (2) joins the root Th1 (1); another branch of the root C8 (3) joins the root Th1 over the arteria subclavia.
(Fig.3) Brachial plexus - convergence of the root C7 (1) with truncus superior (2), root C8 (3), root Th1 (4).
(Fig.4) Brachial plexus, right side. Lateral branch to n. medianus (1) is thicker than the median root (2), n. medianus (3) branches to m. biceps (4,5,6), n. musculocutaneus (7).
(Fig.5) Branch from lateral root to median root of n. medianus (1,2). The lateral root is not thicker, n. musculocutaneus (3) is joined with n. medianus (4).
(Fig.6) Brachial plexus n. musculocutaneus (1) is joined with n. medianus (2), lateral root of n. medianus is thicker (3).
(Fig.7) Arteria axillaris (1) is located over the bifurcation of n. medianus (2).
(Fig.8) Brachial plexus, right side. Root C5 (1), root C6 (2), root C7 (3), root C8 (4), root Th1 (5), nervus axillaris (6) extension of the posterior branch of truncus superior.
(Fig.9) Brachial plexus complex cluster of trunks and fasciculi before the preparation under the binocular microscope.
The variations of the formation of the brachial plexus are of a clinical and surgical importance. Knowledge of its anatomical variations may contribute on the explanation of inconceivable clinical pictures. It is supposed that the variations of the formation of the brachial plexus are caused by a deviation of the normal development. Some anatomical peculiarities are important especially for surgeons engaged in the reconstruction of plexus injuries.
It is important to be aware of these variations but also of their relation to the great vessels, because the topographic relations of fascicles and arteries may be various and they can lead to problems during an urgent surgery [1, 6]. There was not always the same type of variation in case of bilateral variations.
The main supraclavicular variations described in literature concerned the contrubution of C4 or Th2 [9, 10]. We havent encountered any study in literature available to us concerning the variations of the formation of the neural roots, trunks and fascicles.
We have only detected the actual origination of the terminal branches of the plexus in 6 cases after a preparation of the variation of the trunk and fascicle formation. Attention deserves sparse connective tissue foming sleeves, often multiplayer, which was greatest in the level of the trunk branching and fascicle formation, especially medial. Less of this tissue was present in the area of terminal branches formation. Its function is probably to prevent a damage of nerves among each other or by arteries or bone structures in these sites during movements with the upper limb. We have detected fibrotic changes in this tissue in several cases. The greatest fibrotic changes were in individuals heavily physically working, former sportsmen and in cases of postcaval catheters.
Our results concerning the variations of the formation of the terminal branches of the brachial plexus often corresponded with previously described findings [2 - 8].
The described variations of the musculocutaneous nerve concern ist origination. It can originate on the apex of the median nerve bifurcation, from the apex of the bifurcation between the median and ulnar nerve or finally from the median nerve [2, 3, 6, 9, 10].
Described variations of the median nerve:
Variations of the ulnar nerve concerned:
Described variations of the axillary nerve concerned:
The described variations of the radial nerve concerned its origination: from two roots formed variably from the posterior branches of the trunks .
Variations of the cutaneus brachii medialis nerve concerned:
Described variations of the cutaneus antebrachii medialis nerve concerned:
The information about variability in the formation of brachial plexus and its terminal branches is important for traumatic damage and for reconstruction surgery.