An unusual case of a mucin secreting-benign microfollicular adenoma of the thyroid in a 30 year old euthyroid woman is reported. Histologically, the lesion was characterised by follicular cells with the appearance of signet ring cells. Histochemistry showed the mucin content of these cells to consist uniformly of sulphated acid mucins; positive thyroglobulin immunostaining was also shown. The published work on primary mucin secreting tumours of the thyroid gland is reviewed. Dual differentiation is thought to be responsible for combined mucin secretion and hormone production in this type of neoplasm.

Seven cases of cystadenoma of the pancreas were examined in detail histologically and histochemically and two variants were identified: a microcyst type lined by glycogen-rich cuboidal epithelium which also secretes some neutral mucins; and macrocystic type lined exclusively by mucus-secreting columnar cells which secrete predominantly sulphated acidic mucins with some neutral mucins. Electron microscopy of two cases of the microcystic variant showed neoplastic cells with an ultrastructure comparable to that of centroacinar cells of the normal exocrine pancreas.

SUMMARY A patient is reported with chronic abdominal pain, diarrhoea, and associated radiological and endoscopic abnormalities of the sigmoid colon. Light and electron microscopic study of colorectal mucosa showed abnormal collagenous thickening of the subepithelial basement membrane. The authors felt that the clinical and morphological features justified a diagnosis of collagenous colitis. Review of the literature suggested that collagenous colitis was still an unrecognised entity. Lindstrom (1976) recorded the first case of an hitherto undescribed entity for which he suggested the term 'collagenous colitis'. Lindstrom's report concerned a 48 year old woman with chronic watery diarrhoea; a rectal biopsy showed a heavy collagenous deposit in the mucosal basement membrane. To our knowledge, no further description of this singular entity has appeared in the literature.We

suMMARY Forty primary carcinomas of the thyroid of different histological types were reviewed and studied histochemically, with the aim of identifying and assessing "mucin secretion". The patterns of extracellular "pure alcianophilia" and "mixed alcianophilia" were noted in 7-5% and about 50% of these tumours, respectively. A critical review of the pitfalls in methods and interpretation of mucin histochemistry-as performed in previously reported cases of "mucin secreting" or "mucinous" primary thyroid tumours-is presented. The apparent "mucin secretion" described in these unusual neoplasms could be due to histochemical staining of carbohydrate components or breakdown products of thyroglobulin and colloid.Cases of "mucin secreting" or "mucinous" primary carcinomas and adenomas of the thyroid have been increasingly reported in the past decade.' -19 The diagnosis of "mucin secretion" in these unusual thyroid tumours has essentially relied on the apparent positivity of different histochemical methods for mucins. These methods are more conventionally used for the study of epithelial mucins secreted by goblet cells of the gastrointestinal or bronchial tract. The major implication of these reports' -'9 has been that the follicular and parafollicular cells of the thyroidan exclusive endocrine gland, by definition-could also produce "mucins" in primary tumours, in a manner similar to that of epithelial goblet cells in exocrine organs. Does conventional mucin histochemistry applied to thyroid tumours actually identify substances, which could be regarded as being equivalent to gastrointestinal and bronchial mucins, or, alternatively, show up components or breakdown products of thyroglobulin and colloid?2In an effort to clarify further the nature of these so called "mucin secreting" or "mucinous" primary thyroid tumours we carried out a histochemical study on 40 primary carcinomas of the thyroid, using two combined staining methods for mucin identification.Accepted for publication 26 March 1987 Material and methodsThe original haematoxylin and eosin stained slides of 40 primary carcinomas of thyroid were retrieved from our files and reviewed. These 40 cases were classified according to current histological nomenclatures20 21 and included 22 papillary, nine follicular, five anaplastic, and four medullary carcinomas. All the material had been fixed in formol saline (pH 7). The paraffin blocks of these 40 cases were recut and numerous additional sections stained by two combined histochemical methods for mucins: 1 Alcian blue (pH 2.5) and periodic acid Schiff after diastase digestion (AB/PAS), which distinguishes between acidic mucins stained blue by AB and neutral mucins stained magenta by PAS (mixtures of acidic and neutral mucins produce a purple colour). 2 High iron diamine and alcian blue pH 2-5 (HID/AB), which differentiates sulphomucins stained brownish black by HID and sialomucins stained blue byAB.These two combined histochemical methods were performed in batches, with adequate positive and negative controls, and st...

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