A disproportionate accumulation of fibrous tissue is not a causal factor in human goitre growth.

Histological preparations from human nodular goitres reveal the presence of variable and sometimes considerable amounts of acellular material separating the individual follicles. Part of this interstitial tissue consists histologically of fibrous strands. However, quantitative data on the fibrous tissue content of goitres are scarce. In the present study the proportion of fibrous tissue in normal human thyroids and human goitres was determined biochemically by measuring their content of collagen, the predominant component of fibrous tissue. Total collagen content increased in parallel to thyroid weight. The relative collagen content, however, decreased slightly but significantly with increasing thyroid weight. The collagen/DNA ratio (= fibrous tissue/cell number ratio) was not higher in goitres than in normal human thyroids. These results indicate that in goitre growth, there is no disproportionate accumulation of fibrous tissue accompanying the multiplication of thyroid follicular cells. They are in line with the earlier findings that despite histological heterogeneity, the main component of nodular goitres is newly generated follicles.