The Surgical Dissection Of The Sterno-clavicular Or Tracheal Region And The Relative Position Of Its Main Bloodvessels Nerves &c

Sources: Surgical Anatomy

The law of symmetry governs the development of all structures which

compose the human body; and all organized beings throughout the animal

kingdom are produced in obedience to this law. The general median line

of the human body is characterized as the point of fusion of the two

sides; and all structures or organs which range this common centre are

either symmetrically azygos, or symmetrically duplex. The azygos organ

p esents as a symmetrical unity, and the duplex organ as a symmetrical

duality. The surgical anatomist takes a studious observation of this law

of symmetry; and knowing it to be one of general and almost

unexceptional occurrence, he practises according to its manifestation.



The vascular as well as the osseous skeleton displays the law of

symmetry; but while the osseous system offers no exception to this law,

the vascular system offers one which, in a surgical point of view, is of

considerable importance--namely, that behind the right sterno-clavicular

articulation, C, Plate 9, is found the artery, A, named innominate, this

being the common trunk of the right common carotid and subclavian

vessels; while on the left side, behind the left sterno-clavicular

junction, Q, Plate 10, the two vessels (subclavian, B, and carotid, A,)

spring separately from the aortic arch. This fact of asymmetrical

arrangement in the arterial trunks at the fore part of the root of the

neck is not, however, of invariable occurrence; on the contrary,

numerous instances are observed where the arteries in question, on the

right side as well as the left, arise separately from the aorta; and

thus Nature reverts to the original condition of perfect symmetry as

governing the development of even the vascular skeleton. And not

unfrequently, as if to invite us to the inquiry whether a separate

origin of the four vessels (subclavian and carotid) from the aorta, or a

double innominate condition of the vessels, were the original form with

Nature, we find her also presenting this latter arrangement of them. An

innominate or common aortic origin may happen for the carotid and

subclavian arteries of the left side, as well as the right. Hence,

therefore, while experience may arm the judgment with a general rule,

such generality should not render us unmindful of the possible

exception.



When, as in Plate 9, A, the innominate artery rises to a level with C,

the right sterno-clavicular junction, and when at this place it

bifurcates, having on its left side, D, the trachea, and on its right

side, B, the root of the internal jugular vein, together with a, the

vagus nerve, the arterial vessel is said to be of normal character, and

holding a normal position relative to adjacent organs. When, as in Plate

10, A, the common carotid, and B, the subclavian artery, rise separately

from the aortic arch to a level with Q, the left sterno-clavicular

articulation, the vessels having M, the trachea, to their inner side,

and C D, the junction of the internal jugular and subclavian veins, to

their outer side, with b, the left vagus nerve, between them, then the

arterial vessels are accounted as being of normal character, and as

holding a normal relative position. Every exception to this condition of

A, Plate 9, or to that of A B, Plate 10, is said to be abnormal or

peculiar, and merely because the disposition of the vessels, as seen in

Plates 9 and 10, is taken to be general or of more frequent occurrence.



Now, though it is not my present purpose to burden this subject of

regional anatomy with any lengthy inquiry into the comparative meaning

of the facts, why a common innominate trunk should occur on the right of

the median line, while separate arterial trunks for the carotid and

subclavian arteries should spring from the aorta on the left of this

mid-line, thus making a remarkable exception to the rule of symmetry

which characterizes all the arterial vessels elsewhere, still I cannot

but regard this exceptional fact of asymmetry as in itself expressing a

question by no means foreign to the interests of the practical.



In the abstract or general survey of all those peculiarities of length

to which the innominate artery, A, Plate 9, is subject, I here lay it

down as a proposition, that they occur as graduated phases of the

bicleavage of this innominate trunk from the level of A, to the aortic

arch, in which latter phasis the aorta gives a separate origin to the

carotid and subclavian vessels of the right side as well as the left. On

the other hand, I observe that the peculiarities to the normal separate

condition of A and B, the carotid and subclavian arteries of Plate 10,

display, in the relationary aggregate, a phasial gradation of A and B

joining into a common trunk union, in which state we then find the aorta

giving origin to a right and left innominate artery. Between these two

forms of development--viz., that where the four vessels spring

separately from the aortic arch, and that where two innominate or

brachio-cephalic arteries arise from the same--may be read all the sum

of variation to which these vessels are liable. It is true that there

are some states of these vessels which cannot be said to be naturally

embraced in the above generalization; but though I doubt not that these

might be encompassed in a higher generalization; still, for all

practical ends, the lesser general rule is all-sufficient.



In many instances, the innominate artery, A, Plate 9, is of such

extraordinary length, that it rises considerably (for an inch, or even

more) above the level of C, the sternal end of the clavicle. In other

cases, the innominate artery bifurcates soon after it leaves the first

part of the aortic arch; and between these extremes as to length, the

vessel varies infinitesimally.



The innominate artery lies closer behind the right sterno-clavicular

junction than the left carotid or subclavian arteries lie in relation to

the left sterno-clavicular articulation; and this difference of depth

between the vessel of the right side and those of the left is mainly

owing to the form and direction of the aortic arch from which they take

origin. The aortic arch ranges, not alone transversely, but also from

before backward, and to the left side of the dorsal spine; and

consequently, as the innominate artery, A, Plate 9, springs from the

first or fore part of the aorta, while the left carotid and subclavian

arteries arise from the second and deeper part of its arch, the vessels

of both sides rising into the neck perpendicularly from the root in the

thorax, will still, in the cervical region, manifest a considerable

difference as to antero-posterior depth. The depth of the left

subclavian artery, B, Plate 10, from cervical surface, is even greater

than that of the left common carotid, A, Plate 10, and this latter, at

its root in the aortic arch, is deeper than the innominate artery. Both

common carotids, A A, Plates 9 and 10, hold nearly the same

antero-posterior depth on either side of the trachea, M, Plate 10, and

D, Plate 9. Although the relative depth of the arterial vessels on both

sides of the trachea is different, still they are covered by an equal

number of identical structures, taking the same order of superposition.



On either side of the episternal cervical pit, which, even in the

undissected body of male or female, infant or adult, is always a

well-marked surgical feature, may be readily recognised the converging

sternal attachments of the sterno-mastoid muscles, L G, Plate 10; and

midway between these symmetrical muscular prominences in the neck, but

holding a deeper level than them, is situated that part of the trachea

which is generally the subject of the operation of tracheotomy. The

relative anatomy of the trachea, M, Plate 10, D, Plate 9, at this

situation requires therefore to be carefully considered. The trachea is

said to incline rather to the right side of the median line; but perhaps

this observation would be more true to nature if it were accompanied by

the remark, that this seeming inclination to the right side is owing to

the fact, that the innominate artery, A, Plate 9, lies obliquely over

its fore part, near the sternum. However this may be, it certainly will

be the safer step in the operation to regard the median position of the

trachea as fixed, than to encroach upon the locality of the carotid

vessels; and to make the incision longitudinally and exactly through the

median line, while the neck is extended backwards, and the chin made to

correspond with the line of incision. And when the operator takes into

consideration the situation of the vessel A, Plate 9, and A, Plate 10,

at this region of the neck, he will at once own to the necessity of

opening the trachea, D, Plate 9, M, Plate 10, at a situation nearer the

larynx than the point marked in the figures. The course taken by the

common carotid arteries is, in respect to the trachea, divergent from

below upwards; and as these vessels will consequently be found to stand

wider apart at the level of K, I, Plate 10, than they do at the level of

M, Plate 10, so the farther upwards from the sternum we choose the point

at which to open the trachea, the less likely are we to endanger the

great arterial vessels.



In addition to the fact, that the carotid arteries at an inch above the

sternum lie nearer the median line than they do higher up in the neck,

it should always be remembered, that the trachea itself is situated much

deeper at the point M, Plate 10, D, Plate 9, than it is opposite the

points F and K of the same figures. The laryngo-tracheal line is, in the

lateral view of the neck, downwards and backwards, and therefore it will

be found always at a considerable depth from cervical surface, as it

passes behind the first bone of the sternum, midway between both

sterno-mastoid muscles.



In the operation of tracheotomy, the cutting instrument divides the

following named structures as they lie beneath the common integument: If

the incision be made directly upon the median line, the muscles F,

sterno-hyoid, and E, sterno-thyroid, Plate 9, are not necessarily

divided, as these structures and their fellows hold a somewhat lateral

position opposite to each other. Beneath these muscles and above them,

thus encasing them, the cervical fascia, f f, Plate 10, is required to

be divided, in order to expose the trachea. Beneath f f the cervical

fascia, will next be felt the rounded bilobed mass of the thyroid body,

lying on the forepart of the trachea; above the thyroid body, the

cricoid and some tracheal cartilaginous rings will be felt; and since

the thyroid body varies much as to bulk in several individuals of the

same and different sexes, as also from a consideration that its

substance is traversed by large arterial and venous vessels, it will be

therefore preferable to open the trachea above it, than through it or

below it.



On the forepart of the tracheal median line, either superficial to, or

deeper than, the cervical fascia, the tracheotomist occasionally meets

with a chain of lymphatic glands or a plexus of veins, which latter,

when divided, will trammel the operation by the copious haemorrhage

which all veins at this region of the neck are prone to supply, owing to

their direct communication with the main venous trunks of the heart; and

not unfrequently the inferior thyroid artery overlies the trachea at the

point D, Plate 9, when this thyroid vessel arises directly from the arch

of the aorta, between the roots of the innominate and left common

carotid, or when it springs from the innominate itself. The inferior

thyroid vein, sometimes single and sometimes double, overlies the

trachea at the point D, Plate 9, when this vein opens into the left

innominate venous trunk, as this latter crosses over the root of the

main arteries springing from the aorta.



Laryngotomy is, anatomically considered, a far less dangerous operation

than tracheotomy, for the above-named reasons; and the former should

always be preferred when particular circumstances do not render the

latter operation absolutely necessary. In addition to the fact, that the

carotid arteries lie farther apart from each other and from the median

place--viz., the crico-thyroid interval, which is the seat of

laryngotomy--than they do lower down on either side of the trachea, it

should also be noticed that the tracheal tube being more moveable than

the larynx, is hence more liable to swerve from the cutting instrument,

and implicate the vessels. Tracheotomy on the infant is a far more

anxious proceeding than the same operation performed on the adult;

because the trachea in the infant's body lies more closely within the

embrace of the carotid arteries, is less in diameter, shorter, and more

mobile than in the adult body.



The episternal or interclavicular region is a locality traversed by so

many vitally important structures gathered together in a very limited

space, that all operations which concern this region require more steady

caution and anatomical knowledge than most surgeons are bold enough to

test their possession of. The reader will (on comparing Plates 9 and 10)

be enabled to take account of those structures which it is necessary to

divide in the operation required for ligaturing the innominate artery,

A, Plate 9, or either of those main arterial vessels (the right common

carotid and subclavian) which spring from it; and he will also observe

that, although the same number and kind of structures overlie the

carotid and subclavian vessels, A B, of the left side, Plate 10, still,

that these vessels themselves, in consequence of their separate

condition, will materially influence the like operation in respect to

them. An aneurism occurring in the first part of the course of the right

subclavian artery, at the locality a, Plate 9, will lie so close to the

origin of the right common carotid as to require a ligature to be passed

around the innominate common trunk, thus cutting off the flow of blood

from both vessels; whereas an aneurism implicating either the left

common carotid at the point A, or the left subclavian artery at the

point B, does not, of course, require that both vessels should be

included in the same ligature. There seems to be, therefore, a greater

probability of effectually treating an aneurism of the left

brachio-cephalic vessels by ligature than attaches to those of the right

side; for if space between collateral branches, and also a lesser

caliber of arterial trunk, be advantages, allowing the ligature to hold

more firmly, then the vessels of the left side of the root of the neck

manifest these advantages more frequently than those of the right, which

spring from a common trunk. Whenever, therefore, the "peculiarity" of a

separate aortic origin of the right carotid and subclavian arteries

occurs, it is to be regarded more as a happy advantage than otherwise.





DESCRIPTION OF PLATES 9 & 10.



PLATE 9.



A. Innominate artery, at its point of bifurcation.



B. Right internal jugular vein, joining the subclavian vein.



C. Sternal end of the right clavicle.



D. Trachea.



E. Right sterno-thyroid muscle, cut.



F. Right sterno-hyoid muscle, cut.



G. Right sterno-mastoid muscle, cut.



a. Right vagus nerve, crossing the subclavian artery.



b. Anterior jugular vein, piercing the cervical fascia to join the

subclavian vein.














PLATE 10.



A. Common carotid artery of left side.



B. Left subclavian artery, having b, the vagus nerve, between it and A.



C. Lower end of left internal jugular vein, joining--



D. Left subclavian vein, which lies anterior to d, the scalenus anticus

muscle.



E. Anterior jugular vein, coursing beneath sterno-mastoid muscle and

over the fascia.



F. Deep cervical fascia, enclosing in its layers f f f, the several

muscles.



G. Left sterno-mastoid muscle, cut across, and separated from g g, its

sternal and clavicular attachments.



H. Left sterno-hyoid muscle, cut.



I. Left sterno-thyroid muscle, cut.



K. Right sterno-hyoid muscle.



L. Right sterno-mastoid muscle.



M. Trachea.



N. Projection of the thyroid cartilage.



O. Place of division of common carotid.



P. Place where the subclavian artery passes beneath the clavicle.



Q. Sternal end of the left clavicle.