Malignant thymoma is classified into two groups as type Ⅰ and Ⅱaccording to the clinical features and histologic characteristics. The type I malignant thymoma is called as invasive thymoma and this group of thymoma can invade to mediastinum,
lung
and
cervical lymph node. The type Ⅱmalignant thymoma is known as thymic carcinoma and categorized into true malignant tumor which can metastasize to distant organs. However, new disease entity "well differentiated thymic carcinoma" was established
by
some
authors bases on the histologic features. We have recently experienced a case of invasive thymoma which metastasized to supraclavicular lymph node. The histologic findings of this case showed the same features of well differentiated thymic
carcinoma
described previously. We report this case with emphasis to pathological examination and immunohistologic characteristics.
A 46-year-old male patient admitted because of recurrent and combined pneumonia. Norcardia, pseudomonas, acinetobacter, and Staphylococcus aureus were found in the pleural effusion and sputum. The pneumonic consolidation was found in both lung
field and
empyema was noted in the left lung field. Multiple lymph nodes were palpable in the left supraclavicular areas. Biopsy was done with the clinical impression of malignancy. Two lymph nodes were excised, measuring 1.0cm and 0.8cm respectively.
Microscopically the lymph node was replaced with lobulated mass composed of epithelial cells and lymphocytes. The epithelial cells were round to ovoid and had small round eosinophilic and prominent nucleoli. Perivascular palisading and
perivascular
spaces, which was described as organoid differentiation of well differentiated thymic carcinoma, were frequently found. The epithelial components were positive to CAM 5.2(anti-cytokeratin antibody). The lymphocytes were positive to JL1 and
CD45RO,
and
negative to CD45RB and L26(CD20, pan-B). In conclusion, the tumor showed features of thymoma histologically and immunohistochemically. Later, it was proved that the patient had experienced thymectomy due to myasthenia gravis six years ago. The
pathological features of the excised thymoma were same as metastatic supraclavicular mass.
We conclude that careful examination to search for capsular invasion is needed in thymoma to rule out invasive thymoma. Additionally, anti-JL1 monoclonal antibody is useful for the diagnosis of the thymoma, since it is expressed only in the
immature
cortical thymocytes.
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