Demonstration of fibrils in the hyaline globules of yolk sac tumor with parietal differentiation in fine-needle aspiration smears.

Hyaline globules of the yolk sac tumor (YST) have been described as homogeneous pink intracellular globules and intercellular basement membrane material [Akhtar et al.: Diagn Cytopathol 1990:6:184-192]. In Diff-Quik-stained air-dried smears of a lung fine-needle aspiration (FNA) of YST metastatic from anterior mediastinum, short curvilinear nonbranching fibrils are demonstrated in the metachromatic hyaline substance. The fibril-containing hyaline substance, which presents as intracellular globules as well as extracellular matrix deposits, is a diagnostic clue for YST with parietal differentiation [Ulbright et al.: Am J Surg Pathol 1986; 10:151-164]. The fibrils are not observed in the translucent homogeneous golden yellow hyaline substance in the Papanicolaou preparation. The fibrils are speculated to be the core protein of proteoglycans. To the best of the author's knowledge, this is the first demonstration of fibrils in the hyaline substance of YST with parietal differentiation.