HYPOTHYKOIDISM 387 



upon postmortem examination but not upon histological studies. Micro- 

 scopic examination of the gland has, however, been demonstrated to be 

 insufficient to establish the entire absence of thyroid tissue as rests of the 

 'same have been discovered among the anterior cervical tissues embedded in 

 fat or at the base of the tongue. 



True thyroaplasia is rare. E. Thomas, in his excellent critical survey 

 of this condition, has collected eleven cases in which serial microscopic 

 sections demonstrated the absence of the thyroid. (Langhans, Kocher, 

 Muratow, Maresch, Peucker, Aschoff, Erdheim, Dieterle, MacCallum 

 and Fabyan, Schilder.) The majority were females. All showed high 

 grade cretinism, none becoming sexually developed. All died early, none 

 reaching maturity. Thomas emphasized the condition of dystopic hypo- 

 plasia of the thyroid, in which the thyroid gland is absent but its function 

 at least in small degree is maintained by tiny rests of thyroid tissue at the 

 root of the tongue. Five cases were collected (Marchand, Schilder, 

 Lezowa, Roussey, Clunet). Instances confidently reported in the literature 

 as thyroaplasia reaching adult life probably belong to this dystopic hypo- 

 plastic type. The aberrant thyroid tissue in other cases may be function- 

 ally of considerable importance, especially when the thyroid gland in the 

 neck is rudimentary. Thus several writers have observed myxedema to 

 appear after the removal of the tongue tumors. Ungerman and Schilder 

 described individuals showing thyroid tissue only at the base of the tongue. 

 In a number of such instances, small cysts which correspond to the peri- 

 brachial bodies have been found in the cervical tissues. These collections 

 of cells do not form thyroid tissue. 



The systemic effects of thyroaplasia are identical with those of severe 

 cretinism. 



The Thyroid Gland in Hypothyroidism. The thyroid gland may 

 show hyperplastic processes,, i. e., goiter or hyperplasia. According to the 

 views developed in the discussion of the pathogenesis of goiter all hyper- 

 plasia of the thyroid are to be regarded as due to thyroid insuffi- 

 ciency. The goiters of sporadic hypothyroidism may be simple and small, 

 and when larger they often exhibit cystic and other retrogressive changes. 

 They differ in no essential feature from those of endemic goiter, under 

 which heading this topic will be accordingly treated in detail. 



More important in the sporadic expression of hypothyroidism are 

 atrophic changes in the thyroid gland. In the case of children developing 

 cretinism after a preliminary period of normality, for example about the 

 seventh year, the question may be raised as to whether or not complete 

 atrophy of the gland has occurred. This has indeed been found to have 

 taken place in a number of cases. According to the findings of the English 

 Myxedema Commission, Ponfick and Abrikosoff, the pathological process 

 involved is a very chronic connective tissue overgrowth: the alveoli 

 show reduction in size and number of the cells, and round cell 



