Thymic hyperplasia is frequently observed in Graves' disease. However, detectable massive enlargement of the thymus is rare, and the mechanism of its formation has remained elusive. This case showed dynamic changes in thymic hyperplasia on serial computed tomography images consistent with changes in serum thyrotropin receptor (TSH-R) antibodies and thyroid hormone levels. Furthermore, the patient's thymic tissues underwent immunohistochemical staining for TSH-R, which demonstrated the presence of thymic TSH-R. The correlation between serum TSH-R antibody levels and thymic hyperplasia sizes and the presence of TSH-R in her thymus suggest that TSH-R antibodies could have a pathogenic role in thymic hyperplasia.
Adult ; Female ; Graves Disease/*complications/surgery/therapy ; Humans ; Male ; Receptors, Thyrotropin/blood ; Thymus Gland/diagnostic imaging ; Thymus Hyperplasia/*diagnostic imaging/etiology/immunology ; Thyroid Hormones ; Thyroidectomy ; Thyrotropin/blood ; Tomography, X-Ray Computed ; Young Adult

OBJECTIVETo study the clinicopathologic features, immunophenotypes and differential diagnosis of thyroid carcinoma showing thymus-like differentiation (CASTLE).

METHODSThe clinical and pathologic features of 8 cases of CASTLE were reviewed. Immunohistochemical study was performed using a panel of antibodies. In-situ hybridization for Epstein-Barr virus-encoded RNA (EBER) was also carried out.

RESULTSThere were altogether 4 males and 4 females. The age of the patients ranged from 25 to 57 years (mean = 48.8 years). All of them presented with painless mass at the anterior neck. Two patients also complained of hoarseness of voice. On CT scan, the tumor had a low density with contrast enhancement. Seven cases were located in the mid to lower pole and the remaining one in the upper pole of thyroid gland. Four cases were relatively circumscribed. The other 4 cases showed evidence of extrathyroidal invasion. Grossly, the tumor had a nodular or lobulated appearance and was gray-white in color, with a mean diameter of 4.3 cm. Microscopically, the tumor was infiltrative and consisted of islands, nests or lobules of epithelial cells separated by thick fibrous septa. The fibrous stroma showed various degree of lymphoplasmacytic infiltration, resulting in a prominent lymphoepithelioma-like pattern in 3 cases. Two cases showed squamoid differentiation, mimicking thymic Hassall corpuscles. Immunohistochemically, the tumor was consistently positive for cytokeratins, CD5, bcl-2, p63 and CD117. CEA was variably expressed. The staining for thyroglobin and TTF1 was negative. There was no labeling for EBER in all the cases. Two patients experienced local recurrence at 22 months and 12 years after surgery, respectively. They were treated with re-resection. All patients remained well on follow up. The duration of follow up ranged from 4 to 55 months.

CONCLUSIONSCASTLE is a low-grade thyroid carcinoma with the morphologic features and immunophenotypes overlapping with those of thymic carcinoma. Awareness of this rare entity is important to both the pathologists and clinicians.

Adenoma ; metabolism ; pathology ; surgery ; Adult ; CD5 Antigens ; metabolism ; Carcinoma ; diagnostic imaging ; metabolism ; pathology ; surgery ; Cell Differentiation ; Disease-Free Survival ; Female ; Follow-Up Studies ; Humans ; Keratins ; metabolism ; Male ; Middle Aged ; Neoplasm Recurrence, Local ; Proto-Oncogene Proteins c-bcl-2 ; metabolism ; Reoperation ; Thymus Gland ; pathology ; Thymus Neoplasms ; pathology ; Thyroid Neoplasms ; diagnostic imaging ; metabolism ; pathology ; surgery ; Tomography, X-Ray Computed