Signet ring cell 'mucinous' thyroid adenoma: a follicle cell tumour with abnormal accumulation of thyroglobulin and a peculiar histochemical profile.

This study describes two cases of signet ring cell thyroid adenoma. Signet ring cells contain immunoreactive thyroglobulin and stain positively for mucin by histochemical methods: previous interpretations of these peculiar findings suggested that signet ring celled thyrocytes may show dual endocrine and non-endocrine differentiation. In the present material the histochemical profile of mucinous collections was consistent with a glycoprotein containing 1:2-glycol groups and sialic acid residues. These biochemical features are the same as those of the thyroglobulin molecule although in normal thyroid tissue they can be only partially demonstrated by histochemical methods. It is suggested that the signet ring configuration may be solely due to the intracytoplasmic accumulation of thyroglobulin and that histochemically reactive protein-polysaccharide complexes derived from partial degradation of this glycoprotein may account for the positive mucin staining.