Microscopic thymoma: A report of four cases with review of literature

Context: Thymectomy is an effective therapy for patients with myasthenia gravis, and the lesions usually identified are lymphoid hyperplasia and thymomas. Nodular epithelial proliferations, termed as microscopic thymoma, are rare. Aims: Our aim was to assess the incidence and clinicopathological features of microscopic thymomas. Setting and Design: Retrospective analyses. Materials and Methods: Thymectomies performed in 105 patients with myasthenia gravis were reviewed, and patients with microscopic thymomas were studied with respect to their clinicopathological features. These were compared with those in other reports in literature. Results: Four thymuses showed features of microscopic thymomas, an incidence of 3.8%. There were 2 males and 2 females, all myasthenic; the mean age was 31 years. The resected thymic tissues were seen as soft, capsulated adipose tissue. They showed variable degrees of involution or were atrophic. All had multifocal proliferation of ovoid-to-polygonal cells with tongue-like insinuations into the fat. After thymectomy, there was improvement in the symptoms. Eight patients reported in literature had similar clinicopathological features. Conclusions: Thorough examination of the thymectomies is required to increase the detection of these lesions for assessment of their incidence, causes, pathogenesis and functional significance