Canadian Association of Pathologists - Case of the Month, August 2007

Diagnosis:

Metastatic papillary carcinoma of the thyroid.

The smears are highly cellular and consist of sheets of epithelium and papillary structures, some of which have been degloved by the procedure so that bare fibrovascular cores are present. The epithelium shows all of the typical features of papillary carcinoma of the thyroid including dense squamoid cytoplasm, nuclear enlargement crowding and overlapping, powdery chromatin, intranuclear pseudo-inclusions, micronucleoli and linear nuclear ridges ("grooves"). Viscous colloid (so called "bubble gum" colloid) is particularly well seen in the air-dried and giemsa (MGG) stained preparation. Giant cells, another classical feature of papillary carcinoma aspirates, are also present.

It is unusual to see metastatic papillary carcinoma of the thyroid in a high cervical node. In this case the patient had a thyroglossal duct cyst resected four years prior to this presentation, which was found to contain a focus of papillary carcinoma. After thyroidectomy, despite administration of radioiodine x2, serum thyroglobulin remained elevated and a recent CT confirmed the clinical impression of an enlarged level 2 lymph node. The unusual location of the metastatic papillary carcinoma is felt to be due to the atypical location of the primary tumour in a thyroglossal duct cyst.

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