Malformations of the Neck.—Various congenital deformities result from interference with the developmental processes which take place in and around the fore-gut. These malformations are associated chiefly with imperfect development of the visceral or branchial arches and clefts, or of the hypoblastic diverticula from which the thyreoid and thymus glands are formed.
The term cervical auricles is applied to small outgrowths, composed of skin, connective tissue, and yellow elastic cartilage, found usually along the anterior border of the sterno-mastoid. These appendages are usually unilateral, and are derived from the second visceral arch. Sometimes they are situated near the orifice of a lateral fistula. When, on account of their size, or their situation on an exposed part of the neck, they give rise to disfigurement, they should be removed.
Thyreo-glossal Cysts and Fistulæ.—The thyreo-glossal cyst is developed in relation to the thyreo-glossal tract of His, which in early embryonic life extends from the foramen cæcum at the base of the tongue to the isthmus of the thyreoid. Those that form in the upper part of the tract, in relation to the base of the tongue, have already been described ([p. 538]). Those arising from the lower part form a swelling in the middle line of the neck, usually above, but sometimes below the hyoid bone. They have to be diagnosed from other forms of cyst occurring in the middle line of the neck—sebaceous and dermoid cysts—and when giving rise to disfigurement they should be excised.
Such a cyst may rupture on the surface, usually as a result of superadded infection, and give rise to a thyreo-glossal or median fistula of the neck. As a rule the external opening of the fistula is above the hyoid bone, only the upper part of the duct having remained pervious. When the whole length of the duct has persisted, the fistula extends from the skin to the foramen cæcum, passing usually in front of, but sometimes through the substance of, the hyoid bone. Occasionally the fistula only extends as high as the hyoid.
Fig. 268.—Congenital Branchial Cyst in a woman æt. 33.
(Microscopically the cyst was lined with squamous epithelium and the wall contained rudimentary salivary-gland tissue.)
The part of the tract near the tongue is lined by squamous epithelium; the lower part by columnar epithelium, which, below the level of the hyoid, is usually ciliated. Lymphoid tissue and mucous glands are found in its wall.
The treatment consists in excising the duct and the connections, and it is usually necessary to resect the central portion of the hyoid bone to ensure complete removal.
The lateral fistula of the neck—formerly described as a branchial fistula—according to Weglowski, usually takes origin from the remains of the hypoblastic diverticulum, which arises from the pharyngeal part of the third visceral cleft and extends downwards to form the thymus gland. The internal opening is situated in the lateral wall of the pharynx in the region of the posterior palatine arch close to the tonsil, and the fistula passes out above the hypoglossal nerve, and runs downwards and laterally between the carotids and along the medial border of the sterno-mastoid muscle. When the fistula is complete, the external opening is situated a short distance above the sterno-clavicular joint. As the lower part of the thymus canal most often persists, an incomplete external fistula is the form most frequently met with. It is lined with ciliated columnar epithelium.