Fig. 279.—Section of Goitre shown in [Fig. 278], to illustrate compression of Trachea.
When the secreting elements increase out of proportion to the stroma, numerous rounded or irregular spaces filled with a thick yellow colloid material are formed in the substance of the goitre—colloid goitre. The majority of these spaces are not larger than a pea, but one or more may enlarge and form cysts of considerable size—cystic goitre. These varieties, especially the cystic form, attain greater dimensions than any other form of goitre.
When the fibrous stroma is greatly in excess—fibrous goitre—the swelling is smaller, firmer, and shows a greater tendency to contract and compress the trachea. If the sclerosis is extreme and the secretory tissue undergoes atrophy, myxœdema may result.
In some cases the hyperplasia affects chiefly the blood vessels of the thyreoid—vascular goitre. The capillaries, veins, and arteries are increased in size and number; the swelling pulsates and increases in size when the patient makes any muscular effort. Hæmorrhagic cysts may also develop in the substance of these goitres.
Effects on the Trachea.—The trachea may be displaced laterally when the enlargement of the gland affects one lobe more than the other; or it may be compressed and narrowed from side to side—the scabbard trachea—when both lobes are about equally affected and the enlargement extends posteriorly so as almost to surround the air-passage ([Figs. 278], [279]). The third effect is that of softening of the cartilaginous rings of the trachea so that the air-tube, instead of having a considerable degree of elastic resiliency, is soft and flaccid and readily yields to pressure. Under these conditions an alteration in the attitude of the patient, from the erect or sitting to the recumbent position, would appear to be sufficient to permit of a compression of the trachea.
Further changes in the trachea consist in catarrh and engorgement of the blood vessels of its mucous membrane, attended with an abundant secretion of mucus, which, if it accumulates behind a narrowed segment of the trachea, may still further encroach on the lumen.
Pressure on other Structures.—The recurrent nerve may be pressed upon intermittently causing spasms and choking, or continuously causing abductor paralysis and hoarseness.
The gullet is rarely compressed; if marked difficulty in swallowing develops, some additional factor should be suspected, notably carcinoma at the junction of the pharynx with the œsophagus. The carotid arteries are displaced laterally beneath the sterno-mastoids without detriment; the superficial veins—anterior and external jugular—are greatly distended in those cases in which the goitre grows downwards behind the sternum.
Clinical Features.—The symptoms vary widely in different cases, and their severity is not proportionate to the size of the goitre. The disfigurement produced by the swelling is often the only cause of complaint. In some cases the symptoms are due to the pressure of the enlarged thyreoid on surrounding structures. In others toxic effects, in the form of cardiac, nervous, muscular, and general metabolic disturbances, predominate, and are due to absorption of excessive or abnormal thyreoid secretion. This thyreoid toxæmia varies in degree; in the milder cases it merely amounts to a nervousness or excitability that may unfit the patient for occupation; it reaches its maximum in the condition of hyperthyreoidism characteristic of exophthalmic goitre or Graves' disease ([p. 614]).