組織型の異なる同時多中心性胸腺腫

Synchronous Multicentric Thymoma

胸腺腫は胸腺上皮由来の腫瘍で，腫瘍細胞の形態と随伴する未熟Tリンパ球の多寡によりA，AB，B1，B2，B3型胸腺腫およびそれ以外のまれな組織型に分類される1）．通常は孤発性であり，同時性や異時性を含め，多中心性に発生することは比較的まれである．また，その組織型が完全に異なっていたという報告例は少なく，上皮型とリンパ球型が同時かつ多中心性に発生したという本邦報告例はない．われわれは，A型とB2型が同時かつ多中心性に発生したと考えられた胸腺腫の手術例を経験したので報告する．

A 76-year-old man was referred to our hospital because of an abnormal shadow on chest X-ray. His physical exams and laboratory data were not notable. Chest computed tomography （CT） showed 2 nodular lesions with clear margin in anterior mediastinum. The nodule at the left inferior pole of the thymus was 9 cm in diameter, and another one at the right inferior pole was 3.5 cm in diameter. We performed thymo-thymectomy by median sternotomy. Histological study revealed that the left tumor was type B2 thymoma and the other one was type A thymoma. Both were completely encapsulated without invasion, which means stage Ⅰ by Masaoka’s classification. The patient has showed no evidence of recurrence for 11 years following the surgery. This is the 1st case in Japan that reported synchronous multicentric thymoma with apparently different histology of type A and B2.