27 April 2016 - Case of the Week #386

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Case of the Week #386

Clinical history:
A 44 year old woman with a 5 year history of diffuse multinodular goiter presented with an enlarging thyroid gland. Following FNA, a thyroidectomy was performed.


Micro images:


Additional images:



What is your diagnosis?































Diagnosis:
Warthin tumor-like variant of papillary thyroid carcinoma


Discussion:
Papillary thyroid carcinoma (PTC) is the most common type of thyroid malignancy, accounting for about 80% of thyroid cancers. Females are affected more than males, and the mean age at initial diagnosis is about 40 years (Rosai and Ackerman's Surgical Pathology, 2011). According to the current classification of thyroid tumors by the World Health Organization (WHO), the major morphologic variants of papillary carcinoma are follicular, macrofollicular, oncocytic, clear cell, tall cell, columnar cell, diffuse sclerosing and solid (Pathology and Genetics of Tumours of Endocrine Organs (IARC WHO Classification of Tumours), 2004). In 1995, Apel et al described 13 cases of a new variant of PTC, naming it Warthin-like papillary carcinoma, due to its resemblance to the salivary gland tumor (Am J Surg Pathol 1995;19:810). These tumors are generally categorized as variations of the oncocytic variant of PTC. The epidemiological features are believed to be similar to those of classical papillary thyroid carcinoma (Am J Surg Pathol 1995;19:810).

Histopathology shows a circumscribed tumor with papillary architecture (Arch Pathol Lab Med 2000;124:1192). The papillary formations are lined by cells with oncocytic cytoplasm and nuclear features of classical PTC (ground glass nuclei, nuclear pseudoinclusions, nuclear grooves). There is a brisk lymphoplasmacytic infiltrate within the papillary stalks (Arch Pathol Lab Med 2000;124:1192). As there is a well known association of Warthin-like papillary carcinoma with Hashimoto thyroiditis, extensive lymphocytic infiltration of the gland and associated with germinal center formation may be seen in the adjacent thyroid tissue (Rosai and Ackerman's Surgical Pathology, 2011).

The histologic differential diagnosis includes both the oncocytic / Hurthle cell and tall cell variants of PTC. This is an important distinction as the tall cell variant demonstrates more aggressive biological behavior (Turk Patoloji Derg 2013;29:150). While papillary Hurthle cell carcinoma shows similar architecture, oncocytic cytoplasm and nuclear features, it lacks the lympoplasmacytic infiltrate and the association with thyroiditis. The tall cell variant shares similar features; however, tumor cells characteristically demonstrate a height that is more than three times their width (Rosai and Ackerman's Surgical Pathology, 2011).

The long-term prognosis of the Warthin-like variant is excellent, similar to that of classical papillary thyroid carcinoma (Case Rep Endocrinol 2015;2015:251898, Turk Patoloji Derg 2013;29:150). In the series by Apel et al, all arose in a background of thyroiditis and behaved indolently. In a larger series of 17 cases by Baloch and LiVolsi, all were confined to the thyroid gland, and none revealed vascular invasion or invasive growth into the surrounding thyroid. Three cases showed regional lymph node metastases (Arch Pathol Lab Med 2000;124:1192).

Defining the variant of PTC in the pathology report, including this Warthin-like variant, has important clinical implications, as their progression, recurrence, aggressiveness and prognosis differ (Case Rep Endocrinol 2015;2015:251898).


Discussion by Dr. Jennifer R. Kaley, University of Arkansas for Medical Sciences (USA).