PMC3938068_01
Preoperative chest radiology of lesion. (a) Chest CT image showed a well-defined mass in right anterior mediastinum (white arrow). The tumor was observed to adhere to the wall of great vessel. (b) The contrast enhanced CT scan showed the solid mass with mild heterogeneous enhancement adhered, but not invaded the wall of great vessel.
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F1
Minimal amount of right pleural effusion and pericardial effusion were associated, but neither enlarged lymph node nor remarkable image finding was noted in the lung parenchyma (Figure 1).
Postoperative gross examination of mass. On macroscopical examination, the lesion was gray-red solitary nodular mass without gross necrosis, haemorrhage and calcification. There was no fibrous capsule round the mass.
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F2
The mass was well-circumscribed, but there was no fibrous capsule around the mass and no cystic cavity observed in the mass (Figure 2).
Postoperative photomicrographs of lesion in MEC component. (a) The tumor was composed of nests of epidermoid cells with mucin-producing areas (left side of the figure) and lymphocyte-rich areas (right side of figure). They represented the MEC component and thymoma component, respectively. (b) High magnification showed the mucin-producing cells were surrounded by epidermoid cells in MEC component. (c) Invasive nests of well-differentiated epidermoid cells, mucin-producing and intermediate cells were observed in MEC areas. Bands of fibrous connective tissue were observed in the tumor. (d) The epidermoid cells were observed to be positive for CK5/6, but the mucin-producing cells were CK5/6-negative. (e) MEC component was negative for CD5. (f) The Alcian blue-positive material was seen in lumen of gland structure and the mucin-producing cells within the nest of epidermoid cells. (a, H & E staining with original magnification of 200 x; b-c, H & E staining with original magnification of 400 x; d-e, immunohistochemical staining with original magnification of 400 x; f, Alcian blue staining with original magnification x 400).
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F3
Alcian blue staining revealed mucin in the cytoplasm of the mucin-producing cells (Figure 3).
Postoperative photomicrographs of lesion in thymoma component. (a) The neoplastic cells were large and polygonal with large nuclei and prominent central nucleoli in the lymphocyte-rich background. (b) Some small epidermoid foci resembling abortive Hassall's corpuscles could be observed among the neoplastic epithelial cells, but no mucin-producing cells were found in these epidermoid foci. In these areas, the neoplastic cells were diffusely positive for CK19 (c), but negative for CD5 (d). (a-b, H & E staining with original magnification of 400 x; c-d, immunohistochemical staining with original magnification of 400 x).
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F4
By immunohistochemical staining, the neoplastic cells revealed the positivity for pan-CK (AE1/AE3), CK5/6, CK19 and p63, as well as negativity for CD5 and CD117 (Figure 4).