Encapsulated columnar-cell neoplasms of the thyroid. A report of four cases suggesting a favorable prognosis.

Four encapsulated thyroid neoplasms with columnar-cell features were studied. The patients were a 29-year-old man and three women aged 42, 60, and 83 years. The tumors measured from 1.2 to 8.0 cm in maximum dimension. All were completely surrounded by a thick capsule; three demonstrated invasion into the capsule (but no farther), whereas one (from the 60-year-old woman) did not. In addition to columnar-cell areas, all the neoplasms had areas with follicular and solid growth, in varying proportions. Although the growth pattern in the columnar-cell zones was usually papillary, nuclear characteristics of papillary carcinoma were not present in these areas or elsewhere. Follow-up on the four patients was 112, 51, 112, and 29 months, respectively, and none had any evidence of recurrence or metastasis. The findings suggest that encapsulated columnar-cell thyroid tumors have a much more favorable prognosis than those that are unencapsulated and invasive into adjacent thyroid or extrathyroid tissue.