The tumor grows in elongated compressed follicles. The cells are columnar in shape, with hyperchromatic nuclei. The tumor bears resemblance to adenomatous polyps in the colon.
Cytologically there is prominent pseudostratification and piling up of cells, and more hyperchromasia than the usual PTC. The classic grooves and inclusions are not always present or seen only focally, but as in this case, other more typical papillary areas were also present.
Here you can better appreciate the elongated nuclei. The cytoplasm is lightly eosinophilic, but may also appear almost clear in some cases. Subnuclear vacuoles are also common, but not so obvious here.
The columnar variant of PTC is extremely rare, accounting for less than 0.5% of papillary carcinomas. It was initially reported in 1986 as an aggressive variant, with frequent metastases and poor prognosis. However, recent studies have found that there are two forms of this variant. Small circumscribed or encapsulated tumors usually arise in younger female patients and are indolent tumors. Larger, locally aggressive and invasive tumors occur in older male patients (Huang).
Histologically, the cells are columnar with pseudostratified hyperchromatic oval nuclei. Subnuclear vacuoles and cytoplasmic clearing are also seen. The cells are commonly arranged in markely elongated follicles arranged in parallel cords (Wenig). Other architectural arrangements include papillary, glandular, cribiform and solid sheets. Usually, a mixture of patterns is seen.
Fletcher thankfully addresses the difference between the columnar cell and tall cell variant of PTC. Columnar cell PTC appears similar to endometrioid or colorectal carcinoma with dark elongated pseudostratified nuclei. Tall cell PTC looks very much like conventional PTC except with an increased height to width ratio (Fletcher).
In a study of 1521 patients with PTC, Ito and colleagues found that the follicular, tall cell and oncocytic variants were most common with incidences of 6.6%, 3.9% and 1.9%. Of these, tall cell variants had significant worse prognosis. Among the rarer variants which account for less than 1% of all cases, columnar cell had the worst prognosis.
Chen JH, Faquin WC, Lloyd RV, Nosé V. Clinicopathological and molecular characterization of nine cases of columnar cell variant of papillary thyroid carcinoma. Mod Pathol. 2011 Feb 25. [Epub ahead of print]
Huang WT, et al. Encapsulated columnar-cell carcinoma of the thyroid: a case report. Kaohsiung J Med Sci. 2005 May;21(5):241-4.
Ito Y, et al. Prevalence and biological behaviour of variants of papillary thyroid carcinoma: experience at a single institute. Pathology. 2008 Oct;40(6):617-22.
Wenig BM, Thompson LD, Adair CF et al. Thyroid papillary carcinoma of columnar cell type: a clinicopathologic study of 16 cases. Cancer. 1998 Feb 15;82(4):740-53.