1794 HUMAN ANATOMY. 



PRACTICAL CONSIDERATIONS : THE THYROID BODY 



Congenital absence of the thyroid body, or its atrophy with loss of function, 

 occurring at any time before puberty, is apt to be followed by the interference with nu- 

 trition and with normal mental and physical development that produces the condition 

 known as cretinism. Similar atrophic changes occurring later in life cause myxce- 

 dema^ and the same condition — also known as cachexia strumipriva — may be brought 

 about by the complete excision of the gland. Calcification of the gland may take 

 place in old age. The isthmus may be congenitally absent and two separate lobes be 

 present, representing the originally distinct embryonic lateral anlages of the organ. 



Accessory thyroids may undergo hypertrophy and form large masses occupying 

 the pleural or the mediastinal cavity (Osier-Packard) ; or they may develop at the 

 base of the tongue, — lingual goitre ; or, on account of their embryonic relation to 

 the thyro-glossal duct (which passes behind the hyoid bone), they may be found in 

 the median line of the neck below or behind the hyoid, and may be mistaken for 

 growths of a different character (page 554). 



The thyroid gland may be temporarily enlarged in women during menstruation. 



Hypertrophy of the thyroid gland (goitre) may be {a) parenchymatous when 

 it results from a general hyperplasia of the gland-tissue ; (^b) vascular, due to a 

 great increase in the size and number of the blood-vessels ; (r) cystic, characterized by 

 the formation of walled-oi? cavities within the already enlarged gland ; (t/) fibrinous, 

 the connective-tissue elements being in excess ; {e) exophthalmic (Graves's disease), 

 in which the thyroid enlargement is associated with exophthalmos and functional 

 derangement of the vascular system ; {/') adeyiomatous, the hypertrophy affecting 

 one or more lobules or the isthmus. This last form appears as a one-sided or asym- 

 metrical swelling, is common, and is often classified with tumors of the thyroid, 

 rarer forms of which are the cancerous and sarcomatous. It may be noted that the 

 gland is relatively larger in females, and that the right lobe is larger than the left. 

 This has been thought to explain the greater frequency of goitre on the right side, 

 and in women. 



Inflammation of the thyroid is rare, and usually occurs during typhoid or other 

 infections, although it is favored by previous thyroid disease or overgrowth. The 

 tumefaction which it produces may cause acutely many of the symptoms brought on 

 more slowly by the chronic forms of enlargement. These symptoms, so far as they 

 have any anatomical bearing, are : (i) The swelling rises and falls with the larynx 

 during deglutition. This is due to the attachment of the thyroid gland to the cricoid 

 cartilage by the upward prolongations of its capsule known as the suspensory liga- 

 ments and to the subjacent larynx and trachea by connective tissue. (2) Dyspnoea. 

 The gland is covered and its growth anteriorly resisted by the sterno-hyoid and 

 sterno-thyroid muscles (Fig. 545), and, to a less degree, by the omo-hyoid and the 

 anterior border of the sterno-mastoid. Its forward progress is also resisted by the 

 pretracheal layer of the cervical fascia. Its close relation to the trachea, therefore, 

 renders the latter subject to direct pressure, especially in the firmer forms of bilateral 

 enlargement, or in those adenomata which begin in the isthmus or lie between the 

 trachea and the sternum. In the unilateral forms the trachea may be displaced to 

 one side. (3) Headache, vertigo, cyanosis, and epistaxis. The relation of the 

 outer border of the thyroid to the carotid sheath explains the disturbance of the cir- 

 culation in the carotid and internal jugular (either through direct pressure or by 

 deflection of the vessels outward ) and accounts for these phenomena. (4) Dys- 

 phagia is relatively rare, but may occur as the result of pressure upon the upper 

 end of the gullet or the lower portion of the pharynx. It is more common in left- 

 sided goitres, owing to the curvation of the oesophagus towards the left. As a great 

 rarity the isthmus of the gland is found between the trachea and oesophagus (Burns). 



(5) Dysphonia, or aphonia, due to pressure upon the recurrent laryngeal nerves. 



(6) Pulsation or bruit. These may be apparent, and caused by the close relation of 

 the enlargement to the common carotid artery, or — much more rarely — real, and 

 due to the relatively enormous blood-supply of the vascular form of goitre, the thyroid 

 with its four constant arteries and occasional fifth one (the thyroidea ima, — 10 per 



