Morphological analysis of yolk sac tumor.

Morphological analysis of imprint histology and cytology was performed in 7 patients with yolk sac tumor (YST). As a result, histological figures of YST were classified into 4 patterns. Endodermal sinus pattern was most frequently identified, followed by polyvesicular vitelline pattern. Imprint cytology findings of YST were also classified into 4 patterns. Cuboidal cells were most frequently observed; cells and nuclei were both cuboidal in shape and 25-40 mu and 20-25 mu in diameters, respectively. The chromatic showed fine to coarse granular patterns. The nuclear cytoplasmic (N/C) ratio was 50-70%, and each nucleus contained one to four nucleoli. Next to cuboidal cells, spindle-shaped cells were frequently noticed; 20-40 mu in size with spindle-shaped nuclei 10-20 mu in diameter and fine to coarse granular chromatic pattern. Naked cells and bizarre cells were also noticed. It was postulated that cuboidal cells and spindle-shaped cells were originated from the endodermal sinus pattern and the loose reticular pattern of YST, respectively. When utilized with rapid-frozen specimens, imprint cytology of YST is sufficient for rapid diagnosis during operations.