A 15-yr-old man had a chief complaint of a palpable neck mass for 4 months. He had no family or past medical history. The patient first recognized the neck mass 4 months before, and it rapidly increased in size during the latter 2 months. All laboratory tests, including thyroid function tests, were unremarkable. The neck computed tomography revealed a relatively well-demarcated solid mass at the superior and lateral portion of the left thyroid gland (), suggesting that this lesion may be either a primary thyroid mass with exophytic growth or a soft tissue tumor pushing the thyroid, in particular, a neurogenic tumor. The fine needle aspiration cytology disclosed moderate cellularity with a predominance of bipolar spindle-shaped cells having oval- to spindle-shaped nuclei and finely granular chromatin without nucleoli. The plump spindle cells in the clusters were arranged in a fascicular or streaming pattern with a mild degree of pleomorphism. The cytoplasm of the spindle and oval cells was moderate and pale eosinophilic. These cytologic findings were initially regarded as a benign follicular lesion and could not lead to a definitive diagnosis ().
The neck computed tomography reveals a well-demarcated solid mass at the superior and lateral aspect of the left thyroid gland, suggesting either a primary thyroid mass or soft tissue tumor.
Fig. 2 The fine needle aspiration cytology shows several cell clusters, which are composed of spindle-shaped (A) or epithelioid cells (B). The nuclei are round to oval and spindle-shaped and show finely granular chromatin with a moderate amount of pale eosinophilic (more ...)
The patient subsequently underwent total thyroidectomy and left cervical lymph node dissection. The mass was encapsulated and covered by the same capsule as the thyroid, measuring 6×5×5 cm in dimensions. The cut surface showed a well-demarcated, lobulated and grayish tan solid mass with rubbery consistency ().
A capsule covers the mass and the thyroid gland, and the cut surface of the mass shows a well-demarcated, lobulated and tan-colored solid mass with rubbery consistency.
Microscopically, the tumor was separated from the thyroid parenchyme by a thick fibrous capsule and showed a biphasic growth pattern, which was an admixture of spindle and epithelial cell components in almost equal proportions (). The spindle cell component consisted of fascicles of atypical fibroblast-like spindle cells, and the epithelial component was composed of solid nests of plump epithelioid cells with well-formed glandular structures (). The periphery of the tumor showed focal calcification and more densely packed spindle cells without an epithelial component (). Focal areas of hemangiopericytic pattern were also present (). The glandular structures were lined by round or cuboidal cells with round to oval nuclei and abundant eosinophilic cytoplasm. Some glandular lumens are filled with pale basophilic materials, which were periodic acid schiff and alcian blue positive. The intervening spindle cells were slightly plump and had elongated, vesicular nuclei with a scant amount of eosinophilic cytoplasm. On average, 15 mitotic figures were seen per 10 high-power fields both in epithelial and spindle cells.
Fig. 4 Microscopically, the tumor shows a biphasic growth pattern (A). The spindle cell component consists of fascicles of atypical fibroblast-like cells, and the epithelial component is composed of solid nests of epithelioid cells with well-formed glandular (more ...)
On immunohistochemical staining, the glandular elements were diffusely and strongly stained with cytokeratin, whereas the spindle cells were diffusely stained with vimentin and focally with epithelial membrane antigen (). The tumor cells were diffusely positive for CD99. Stains for muscle specific actin, smooth muscle actin, S-100, carcinoembryonic antigen, synaptophysin, chromogranin, thyroglobulin, and thyroid transcription factor-1 (TTF-1) were all negative in the tumor cells.
On immunohistochemistry, the epithelial cells are diffusely and strongly stained with cytokeratin (A), whereas the spindle cells are diffusely stained with vimentin (B).
On ultrastructural examination, the tumor was composed of solid nests of epithelial cells and fascicles of spindle cells, which were partially covered by basal lamina. The epithelial cells had desmosome-like cell junctions, whereas the spindle cells had no cell junctions. No tonofilaments, granules, microvilli, or other specific organelles were found ().
On ultrastructural examination, the tumor is composed of solid nests of epithelial cells and fascicles of spindle cells, which are separated by basal lamina (A, arrows). The epithelial cells have desmosome-like cell junctions (B, arrowhead).
The SYT-SSX fusion gene transcript was identified in the paraffin-embedded tumor tissue using the reverse transcriptase-polymerase chain reaction method ().
Fig. 7 The SYT-SSX fusion gene transcript was detected (arrow) in paraffin-embedded tumor tissue using the reverse transcriptase-polymerase chain reaction method. (Lane M, 100-bp ladder DNA marker; lane P, positive control; lane N, negative control; lane S, (more ...)