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median plane for fear of wounding the superior laryngeal vessels and nerve which pierce the thin lateral portions of the thyreo-hyoid membrane.
The wound in suicidal cut-throat is generally at this level. The more important structure which are usually divided are: more or less of the left sterno-mastoid muscle, the superi thyreoid vessels, the thyreo-hyoid membrane, the base of the epiglottis, and, less frequently, the carotid vessels, the internal jugular vein, and the superior laryngeal nerve. When the wound is above the hyoid bone, the lingual and external maxillary vessels and the muscles of the tongue are the more important structures injured.
At the level of the middle of the anterior border of the thyreoid cartilage is the rima glottidis.
In the operation of thyreotomy care is taken to divide the thyreoid cartilage exactly in the median plane so as to avoid injuring the vocal folds.
A little more than an inch below the prominentia laryngea is the anterior arch of the cricoid cartilage, which may be readily felt, and, when the neck is extended. often seen; it lies a little below a point midway between the lower margin of the chin and the superior border of the sternum. Above the cricoid is the crico-thyreoid ligament; in the operation of laryngotomy only the middle portion of the ligament is divided, in order to avoid injury to the crico-thyreoid muscles. The small crico-thyreoid branch of the superior thyreoid artery lies close to the inferior border of the thyreoid cartilage. Below the cricoid cartilage is the trachea, which recedes as it descends, so that it lies 1 in. from the surface at the level of the superior border of the sternum. The isthmus of the thyreoid gland lies in front of the second, third, and fourth rings of the trachea (Fig. 1087); not infrequently, however, it reaches up to the cricoid. Immediately in front of the trachea, below the isthmus of the thyreoid, is the pretracheal fat, containing one or two lymph glands and the inferior thyreoid veins, each represented by one or more branches which converge as they descend. The pretracheal lymph glands receive afferent vessels from the larynx and thyreoid gland, while their efferent vessels open into the inferio: deep cervical glands. In the adult the innominate artery crosses the front of the trachea at the level of the superior border of the sternum; in the child, however it not infrequently crosses half an inch higher, a relation which must be remembered in performing the operation of low tracheotomy.
In the operation of high tracheotomy the upper three rings of the trachea are divided. The incision, which should be median, divides the integuments, the tributaries of the anterior jugular veins, the general envelope of deep cervical fascia, and, after passing between the depressor muscles of the hyoid bone, the pretracheal fascia, which descends from the cricoid to enclose the isthmus of the thyreoid gland. By dividing this fascia transversely below the cricoid, the isthmus may be pulled downwards and the upper rings of the trachea exposed. In some cases it is necessary either to divide the isthmus or to extend the incision upwards through the cricoid cartilage. In opening the trachea, the edge of the knife should be directed upwards so as to avoid injuring the vessels at the upper border of the isthmus. The anterior jugular veins are in danger of being wounded if the skin incision is not strictly median. In low tracheotomy the trachea below the isthmus is opened; it is a more troublesome operation, on account of the depth of the trachea and the presence in front of it of the large inferior thyreoid veins and of the transverse anterior jugular vein. In children the difficulty is increased by the higher position of the innominate artery and left innominate vein, by the presence of the thymus gland, and by the shortness of the neck.
Thyreoid Gland. The thyreoid gland, which is moulded on and adherent to the anterior aspects and the sides of the upper part of the trachea and to the lower and posterior portions of the lamina of the thyreoid cartilage, is covered by the infrahyoid muscles and overlapped by the sterno-mastoid. The posterior borders of its lobes come in contact with the oesophagus and lower part of the pharynx, while posteriorly they partially overlap the carotid sheath.
The thyreoid gland, like the prostate, possesses, in addition to its own proper capsule, an outer capsule or sheath derived from the cervical fascia. The capsule proper, like that of the liver, is inseparably connected with the gland. The sheath. on the other hand, is formed by the middle (pretracheal) layer of deep cervical fascia, which splits to enclose the thyreoid. Between the true capsule and the
sheath is a loose cellular interval which is crossed by branches of the thyreoid arteries and veins on their way to and from the gland. The arteries traverse the space directly, while many of the veins (accessory thyreoid veins of Kocher) ramify for some distance on the surface of the capsule before they pierce the sheath.
In excising one of the lobes, the surgeon reaches the gland through the median plane in the interval between the infra-hyoid muscles. If, in order to obtain more room, it is found necessary to divide the depressor muscles on one or both sides, this should be done towards their upper attachments, as their nerves of supply, derived from the ansa hypoglossi, enter the muscles nearer their lower attachments. By freely dividing the middle layer of cervical fascia where it forms the anterior portion of the sheath of the thyreoid, the gland can be brought out of the wound and so mobilised that the main vessels may be brought into view and ligatured.
The superior thyreoid vessels, on each side, are brought into view by freeing and drawing forwards the superior pole of the corresponding lobe. As the inferior thyreoid artery, on each side, arches medially behind the carotid artery it lies in the cellular interval between the carotid sheath and the pretracheal fascia. Immediately after piercing the posterior part of the sheath of the gland the vessel divides into two or more branches which pierce the capsule to enter the gland
FIG. 1088.-A DIAGRAM OF THE RELATIONS OF THE CERVICAL FASCIA TO THE THYREOID GLAND. Blue deep cervical fascia (sterno-mastoid layer). Redouter capsule of thyreoid gland (pretracheal layer of cervical fascia). Yellow = capsule proper of the thyreoid gland.
substance. The recurrent nerve, which also lies between the posterior part of the sheath and the postero-medial aspect of the corresponding lobe, ascends, either posterior to the inferior thyreoid artery or between its main divisions.
The parathyreoids can generally be distinguished from the thyreoid tissue itself, and from the lymph glands, by their grayish-yellow colour as well as by their smooth and shining surfaces. The superior parathyreoid is found on each side. usually, one at the posterior border of the corresponding lobes, about opposite the cricoid cartilage. It is in close relation to the pharyngo-oesophageal junction, from which it is separated by the posterior part of the sheath of the thyreoid gland. The inferior parathyreoid gland, on each side, is supplied by a small vessel from one of the branches of the inferior thyreoid artery; it occupies the same cellular interval at the posterior aspect of the inferior pole of the gland, a little lateral to the inferior thyreoid artery and the recurrent nerve. It is this close relationship of the recurrent nerves and the inferior parathyreoid glands to the posterior aspect of the lobes of the thyreoid gland which has induced surgeons, in excising one of the lobes, to make the resection intracapsular at the posterior aspect of the gland, the posterior part of the capsule along with a layer of thyreoid substance being left behind, attached to the trachea. In this way injury to the recurrent nerve and inferior parathyreoid gland is avoided, as the branches of the inferior thyreoid artery are ligatured after they have pierced the capsule. De Quervain, on the other hand, prefers to ligature the main trunk of the inferior thyreoid
artery before it pierces the sheath, that is to say, as it lies in the cellular tissue between the carotid sheath and the prevertebral fascia. In order to reach the vessel in that situation the surgeon should keep outside the sheath of the thyreoidill gland, between it and the carotid sheath which is retracted laterally along with the infra-hyoid muscles. When the inferior thyreoid artery has been ligatured the posterior branch of the superior thyreoid artery furnishes a sufficient blood-supply to the inferior parathyreoid gland.
Triangles of the Neck-The lateral aspect of the neck is divided into an anterior and a posterior triangle by the sterno-mastoid muscle; the former is further subdivided into digastric, carotid, and muscular triangles by the digastric and omo-hyoid muscles. The posterior triangle is subdivided into occipital and subclavian portions by the posterior belly of the omo-hyoid.
The sterno-mastoid muscle forms one of the most important superficial land
marks of the neck. The anterior border of the muscle, the more distinct of the two, may be felt along its whole extent. Between the prominent sternal origin and the broad ribbon-like clavicular origin is a slight triangular depression which overlies the inferior part of the internal jugular vein.
By dividing the cervical fascia along the anterior and posterior borders of the muscle the surgeon is able to displace the muscle backwards and forwards so as to obtain free access to the structures deep to it. If the posterior fibres of the muscle are divided at their clavicular and mastoid attachments the muscle can be still more freely mobilised. In dividing the fascia along its posterior border the cutaneous branches of the cervical plexus are generally divided, but care is taken not to injure the accessory nerve. Should it be found necessary to remove the upper third or more of the muscle, the divided end is stitched to the levator scapula or to the scalenus medius, according to the amount resected. In dividing the muscle completely across at the lower part of the neck, as is done, for example, in congenital wry-neck, the close relation of the anterior and external jugular veins to its corresponding borders must be kept in mind. After division of the muscle,
the lower part of the anterior belly of the omo-hyoid is seen, lying upon that part of the carotid sheath which overlies the internal jugular vein.
Digastric Triangle. This triangle is subdivided into an anterior or submaxillary portion and a posterior or parotid portion by a process of the deep cervical fascia, known as the stylo-mandibular ligament. In the anterior portion is the submaxillary gland, which is overlapped by the posterior half of the inferior border of the mandible and reaches down to the great cornu of the hyoid bone. The anterior facial vein passes downwards and backwards, superficial to the gland, while the external maxillary artery, embedded in its deep surface, arches upwards under cover of the angle of the mandible, where it approaches the palatine tonsil, being separated from it, however, by the superior constrictor of the pharynx. The lingual artery may be ligatured in the digastric triangle, where it lies behind the hyoglossus a little above the great cornu of the hyoid bone; the superficial guides to the vessel are the inferior border of the submaxillary gland, and the hypoglossal nerve and its vena comitans, which lie upon the hyoglossus, the latter being recognised by the vertical direction of its fibres. The floor of the digastric triangle is formed, from before backwards, by the mylo-hyoid, hyoglossus, and superior constrictor of the pharynx. The lymph glands of this space receive their lymph from the face, lips, teeth and gums, tongue, and floor of the mouth; hence the frequency with which they become the seat of abscess formation and malignant enlargement. To palpate them the surgeon stands behind the patient and thrusts the fingers well upwards under cover of the mandible, the patient's chin being a little depressed so as to relax the cervical fascia.
Carotid Triangle. The central landmark of this triangle is the great cornu of the hyoid bone, the tip of which, when the fascia is relaxed, may be readily felt, immediately in front of the anterior border of the sterno-mastoid, at a point corresponding to the centre of a line drawn from the tip of the mastoid process to the prominentia laryngea. The deep cervical fascia holds the superior part of the sterno-mastoid forwards towards the angle of the mandible, so that, with the fascia undivided, the anterior border of the sterno-mastoid overlaps the internal jugular vein and the bifurcation of the common carotid artery.
The course of the carotid vessels is indicated, upon the surface, by a line extending from the superior end of the sterno-clavicular articulation to a point midway between the angle of the mandible and the tip of the mastoid process; a point upon this line, at the level of the superior border of the thyreoid cartilage, overlies the bifurcation of the common carotid. The anterior belly of the omo-hyoid crosses the common carotid at the level of the cricoid cartilage. The pulsations of the carotid vessels may be felt in the hollow between the larynx and the anterior border of the sterno-mastoid. In the carotid triangle the external carotid lies medial and anterior to the internal carotid. The seat of election for ligation of the external carotid is between its superior thyreoid and lingual branches, a finger's-breadth below the tip of the great cornu of the hyoid bone; the difficulty in the operation is due to the plexus of veins (formed by the common facial, lingual, and superior thyreoid veins) which overlies the artery. The lingual and external maxillary arteries frequently arise from a common trunk which must not be mistaken for the external carotid. The superior thyreoid artery arises opposite the upper cornu of the thyreoid cartilage, which may be distinctly felt 1 in. below the tip of the great cornu of the hyoid bone. The vessel and its companion vein are common sources of hæmorrhage in cut-throat. The guide to the lingual artery, in the carotid triangle, is the tip of the great cornu of the hyoid bone, above which it forms an arch, crossed by the hypoglossal nerve. The vessel enters the digastric triangle by passing forward medial to the tendons of the stylo-hyoid and digastric muscles. When ligature of the artery is called for, it is usually necessary to secure the vessel as it lies in the carotid triangle so that the ligature may be applied on the proximal side of its dorsalis linguæ branch.
From a surgical point of view the internal jugular vein is the most important structure in the anterior triangle. In the carotid division of the triangle it overlaps the carotid vessels, and its sheath lies close beneath the general envelope of deep cervical fascia from which it is separated by a loose cellular interval. About
the level of the hyoid bone it receives the large common facial vein, while at an inferior level it receives the superior and middle thyreoid veins which are often greatly enlarged in goitres.
By the term deep cervical glands is included a broad chain of lymph glands which is closely related to the internal jugular vein, and which stretches from the transverse process of the atlas to the root of the neck. The chain is in reality made up of subsidiary glandular groups, each of which receives its lymph vessels from fairly well-defined areas. In the first place, the chain may be divided into an upper and a lower portion, the former situated above the bifurcation of the common carotid artery, the latter below it. Each of these divisions is again subdivided into a medial and a lateral chain.
Of the four groups, the superior medial is the most important, as it is there that disease first manifests itself in the vast majority of cases. The reason for this predilection is the fact that this group of glands, in addition to receiving efferent lymph vessels from the glands of the circular chain, receives also lymph vessels directly from the nasal part of the pharynx, including the palatine and pharyngeal tonsils. These latter structures are now known to provide the chief portals of entrance through which the tubercle bacilli reach the efferent lymph vessels. Wood, of Philadelphia, has succeeded in tracing the lymph vessels from the palatine tonsils directly into one of the glands of this group, namely, that situated a little below the angle of the mandible, under cover of the anterior border of the sternomastoid immediately below the posterior belly of the digastric. The relations of the deep surface of this gland are important. It lies upon the anterior surface of the internal jugular, in the angle between it and the common facial vein. It plays such an important rôle in tuberculous adenitis that it is now termed by surgeons the tonsillar lymph gland. In the great majority of cases it is the first gland in the neck to show signs of tuberculous enlargement. When the superior medial deep cervical glands become enlarged they form a swelling which projects from beneath the sterno-mastoid forwards into the carotid division of the anterior triangle. The mass soon becomes adherent to the general envelope of deep cervical fascia, and, if the disease is allowed to run its course, the latter becomes perforated, with the result that a subcutaneous tuberculous abscess soon develops. The glands are also liable to become adherent to the digastric muscle, and to the stylo-mandibular ligament, which separates them from the submaxillary lymph glands. The most important adhesions, however, from the surgeon's point of view, are to the common facial and internal jugular veins.
The superior lateral group of deep cervical glands lies postero-lateral to the internal jugular upon the origins of the splenius and the levator scapulæ muscles. They are smaller in size than the medial group, but when enlarged they may form a swelling which projects across the posterior triangle as far as the trapezius. They are embedded in a quantity of fibro-fatty tissue which supports the accessory nerve and the cervical plexus. Wood has shown that the lymph vessels from the pharyngeal tonsil, after piercing the posterior wall of the pharynx, pass downwards and laterally behind the sheath of the great vessels to enter the glands situated deeply, just below the tip of the mastoid process.
The inferior medial group forms a somewhat narrow chain, which is continued down the anterior aspect of the internal jugular as far as its junction with the subclavian. Above the bifurcation of the common carotid artery this chain is continuous with the superior medial jugular group, while, below, it comes into relation with the superior mediastinal glands.
The inferior lateral group of deep cervical glands is continuous above with the superior lateral group. Like the superior lateral group, they lie altogether behind the internal jugular vein, upon the levator scapula, the scalenus medius, and the brachial plexus. The most inferior glands of the group, viz., the supraclavicular, are subdivided into a superficial and a deep cluster by the omo-hyoid muscle and the middle layer of deep cervical fascia. They receive their afferent vessels from the subclavicular group of axillary glands.
The hypoglossal nerve is deeply placed in the carotid triangle, being overlapped by the internal jugular vein and the inferior border of the posterior belly of the