LEFT THYROID LOBE (135 GRAMS): POORLY DIFFERENTIATED "INSULAR" THYROID CARCINOMA (8 CM.) WITH EXTENSIVE VASCULAR INVASION AND FOCAL EXTENSION INTO PERITHYROIDAL SOFT TISSUE.
Note: This is a recently recognized and aggressive type of thyroid carcinoma. For further details, see Am J Surg. Pathol. 8: 655-668, 1984.
The term "insular" refers to a growth pattern comprised of tightly packed islands or nests. This can sometimes be confused with a similar pattern, zellballen , often seen in neuroendocrine tumors. One important difference between the insular and zellballen patterns is that zellballen are surrounded by S100-positive sustentacular cells , while the insular growth pattern lacks such cells.
Medullary carcinoma of the thyroid is often in the differential when considering an insular carcinoma of the thyroid. In this case however, the negativity of the Congo Red stain argues against medullary carcinoma, and the negativity of the calcitonin immunoperoxidase stain virtually rules it out.
Insular carcinoma of the thyroid is felt to be a particularly aggressive tumor.
Killeen RM Barnes L Watson CG Marsh WL Chase DW Schuller DE, Poorly differentiated ('insular') thyroid carcinoma. Report of two cases and review of the literature, Arch Otolaryngol Head Neck Surg, 116:1082-6, 1990 Sep
Papotti M Botto Micca F Favero A Palestini N Bussolati G, Poorly differentiated thyroid carcinomas with primordial cell component. A group of aggressive lesions sharing insular, trabecular, and solid patterns, American Journal of Surgical Pathology, 17:291-301, 1993 Mar