Both Rathke’s cleft cyst and craniopharyngioma are considered to arise from the remnants of Rathke’s diverticulum despite the quite different histological characteristics. These two lesions may consist of a disease spectrum extending from Rathke’s cleft cyst to craniopharyngioma. However, in spite of increasing evidence of these intermediate histologies, very few cases of the actual transformation from Rathke’s cleft cyst to craniopharyngioma have been reported in the same patient. A 47-year-old man suffered from recurrent visual dysfunction. Aspiration and partial cystectomy was performed to a suprasellar massive cystic lesion. The histological diagnosis was Rathke’s cleft cyst with a small component of squamous metaplasia. Seven months later, the cyst was re-expanded. The cyst wall was irregularly thickened. Re-operation was performed, and the thickened anterior wall was widely removed. Postoperative histological examination showed multiplication of stratified squamous epithelia forming a papillary arrangement. Ki-67 staining showed positive cells randomly distributed not only in the basal layer but also in various epithelial layers, with a labeling index of more than 20 %. The histological diagnosis was squamous papillary type of craniopharyngioma with high potential of proliferation. Subsequent immunohistochemical examinations showed positive reaction to cytokeratin 8 only in the initial epithelium and negative in the latter epithelium. The present case was thought as an actual evidence of the proposed link between Rathke’s cleft cyst and craniopharyngioma. Cytokeratin 8 could be the important examination to differentiate Rathke’s cleft cyst from craniopharyngioma.
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