Intraluminal crystalloids in struma ovarii. Immunohistochemical, DNA flow cytometric, and ultrastructural study. We recently encountered a unique case of follicular variant of papillary carcinoma arising in struma ovarii that contained numerous intrafollicular crystalloids. There was no evidence of capsular or vascular invasion or metastases, though the DNA content of the papillary carcinoma was aneuploid. In contrast, diploid DNA was manifested in the histologically benign thyroid tissue. The nature of the crystalloids and the significance of aneuploid DNA content are discussed. 