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Aims: Micronodular thymoma with lymphoid stroma (MNT) is an uncommon variant of thymoma, characterized by multiple small nodules consisting of type A thymoma-like cells, which are separated by abundant B lymphocytes. The aim of the study was to elucidate the pathogenesis of the stromal lymphoid hyperplasia, which is currently unclear., Methods and Results: We retrieved six cases of MNT, and immunohistochemically examined the number and distribution of Langerhans cells (LCs) and mature dendritic cells (DCs), and compared them with those in type A and type AB thymomas. Many LCs were present within the small tumour nests, but LCs were rarely seen in the stroma (75.5/HPF versus 6.1/HPF, P < 0.0001). In contrast, mature DCs were present mainly in the surrounding stroma rather than within the tumour nodules (63.5/HPF versus 6.0/HPF, P < 0.0001), forming clusters with mature T lymphocytes adjacent to lymphoid follicles. In large nodules, as well as in type A and type AB thymomas, a few scattered LCs and DCs were identified. All patients were still alive and well., Conclusions: Our results suggest that LCs take up tumour antigens and migrate to the stroma, where they mature and form clusters with T lymphocytes to activate them, resulting in lymphoid follicle formation. The favourable clinical behaviour may be attributable to the immune response induced by LCs., (© 2014 John Wiley & Sons Ltd.)

Objective: Histopathological diagnosis of thymic epithelial tumors according to the current World Health Organization classification is not adequately reproducible; however, most thoracic clinicians are unaware of this. We illustrate this problem in practical settings to raise clinician awareness., Methods: An expert pathologist specialized in thymic pathology and a trained general pathologist independently diagnosed 158 resected thymic epithelial tumors. Assuming that the expert's diagnoses were more accurate, the two pathologists' diagnoses were judged to be concordant when tumor subtypes (thymoma) or categories (thymic carcinoma and neuroendocrine tumor) were in agreement., Results: The concordance rates for different thymoma subtypes were 75 % (3/4), 30 % (11/37), 100 % (17/17), 80 % (39/49), and 53 % (9/17) for types A, AB, B1, B2, and B3, respectively. Discordant cases of type AB thymoma were mainly diagnosed as type B1 or B2 by the general pathologist. Discordant cases of type B2 thymoma were diagnosed as type AB, B1, or B3, and discordant cases of type B3 thymoma were diagnosed as type A, B2, or carcinoma. Discordant cases of thymic carcinoma were diagnosed as type A or B3 thymoma., Conclusion: Investigation of the concordant and discordant cases suggested that reasonable discrepancies can occur because of the noncommittal categorical boundaries inherent in this classification. Thoracic clinicians should consider this potential problem in daily practice.

We present a patient with type B2 thymoma (World Health Organization Thymoma Classification) with the complications of anti-muscle acetylcholine receptor antibody-positive myasthenia gravis and anti-voltage-gated potassium channel antibodies associated with paraneoplastic encephalitis. A timing difference between the onset of these neurological disorders and a dissociation of clinical symptoms was observed during the disease. This report alerts clinicians that long-term follow-up is needed where patients have a residual thymoma and attention should be paid to other concomitant autoimmune disorders., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Type AB thymomas are considered to be nonaggressive tumors, and the great majority are classified as Masaoka stage I or II. This report presents a case with Masaoka stage I and type AB thymoma, which metastasized to the brain 2 years 5 months after removal of the primary tumor. The original mediastinal lesion was adhesive but not invasive to the lung. The patient is now alive with multiple tiny pulmonary metastases 3 years after complete resection of the brain metastasis. Some reports of recurrent thymomas have suggested that the presence of peritumoral adherence to the adjacent structures might be a risk factor for recurrence in patients with such noninvasive thymomas. During the development of fibrosis which thus causes adhesion, the tumor may have an increased chance to metastasize because of the increased vessels and lymphatics.

A 63-year-old woman was referred to our hospital because screening had detected an anterior mediastinal tumor with a right aortic arch. She underwent typical total thymectomy via a median sternotomy but developed left recurrent laryngeal nerve (RLN) palsy postoperatively. The pathology examination revealed that the tumor was a stage I thymoma. This is the first report of a thymoma with a right aortic arch. The left RLN goes around the left ductus arteriosus, which connects the origin of the left subclavian artery to the left pulmonary artery. The RLN was likely to be injured in the neighborhood of the left ductus arteriosus when the tumor and thymus were dissected over the pulmonary artery. During operations for an anterior mediastinal tumor with a right aortic arch, we should be attentive to the location of the tumor, the left ductus arteriosus, and the left RLN.

Thymomas are often associated with various autoimmune disorders. We herein report a middle-aged female patient with thymoma and hypogammaglobulinemia (Good syndrome) who developed symptomatic normocytic anemia. Her computed tomography (CT) scans showed a cervico-mediastinal mass. The findings of a bone marrow biopsy suggested pure red cell aplasia (PRCA), and the serum levels of all immunoglobulins were extremely low. After the resection of the tumor, which was diagnosed to be Masaoka stage II and type AB thymoma, the normocytic anemia dramatically improved, but the hypogammaglobulinemia did not recover.