Micronodular thymoma with lymphoid stroma diagnosed 10 years after the first operation: a case report
Micronodular thymoma with lymphoid stroma is a rare subtype of thymoma. Here we report a case of micronodular thymoma with lymphoid stroma that was completely resected after incomplete resection 10 years earlier.
A 70-year-old Japanese woman who had undergone resection for a thymic cyst 10 years earlier was found to have a solid nodule with a multilocular lesion at the site of the previous operation. We suspected that the tumor was a malignant tumor and performed trans-sternal radical thymectomy and diagnosed the lesion as micronodular thymoma with lymphoid stroma pathologically. When we reassessed the thymic cyst that had been resected 10 years earlier, a few lesions of micronodular thymoma with lymphoid stroma were found in the cyst wall. Based on these findings, we concluded that only the cystic component of micronodular thymoma with lymphoid stroma had been removed, and that the residual lesion grew locally over the next 10 years before being completely resected by reoperation.
We experienced an unusual case of micronodular thymoma with lymphoid stroma, which is a rare subtype of thymoma. Greater care should be taken to exclude a thymoma with a cystic lesion, even if a thymic cyst is strongly suspected on computed tomography and magnetic resonance imaging.
KeywordsMicronodular thymoma with lymphoid stroma Thymic cyst Incomplete resection Local recurrence
Micronodular thymoma with lymphoid stroma
Magnetic resonance imaging
Micronodular thymoma with lymphoid stroma (MNT) is a rare subtype of thymoma . Only a few cases of MNT have been reported, especially concerning the long-term prognosis. MNT is a slow-growing neoplasm and no cases of recurrence after operation, distant metastasis, or cancer death with this entity have been reported. Therefore, additional treatment is thought to be unnecessary after complete resection. Here we report a case of MNT that was incompletely resected 10 years earlier and was completely resected after it began to regrow. To the best of our knowledge, this is the first report of a case of local recurrence of MNT. Furthermore, the tumor was misdiagnosed as a thymic cyst at the previous operation 10 years earlier, so it is necessary to consider a thymoma with cystic lesion even if thymic cyst is highly suspected.
The residual lesion was completely removed with the thymus, and there was no recurrence at 2 years after the operation.
This is a case of MNT that had been misdiagnosed as a thymic cyst at a previous operation 10 years earlier and was completely resected after local recurrence. To the best of our knowledge, this is the first report of recurrence, and no previous reports of MNT have included a follow-up exceeding 10 years.
First reported in 1999 , MNT is a rare subtype of thymoma, accounting for almost 1% of cases . The median age of patients is 64, and most are over 40 years of age. MNT is more common in men than women and the male-to-female ratio is 1.3 . Paraneoplastic syndrome is not more frequently associated with MNT than with other types of thymoma. For example, 5% of patients with MNT develop myasthenia gravis, while 9% of them develop other autoimmune diseases (for example, pure red cell aplasia). Most patients are asymptomatic, and half have cystic lesions on imaging [1, 3]. In histology, MNT is defined as having short spindle-shaped and oval-shaped epithelial cells that form small nodules, with many lymphocytes and lymphoid follicles around the nodules . Of note, the lymphocytes and lymphoid follicles are not malignant but are instead thought to be attracted by the immunologic reaction against the nodules .
MNT grows slowly, and approximately 95% of cases are pathological stage I or II. There have been no reports of recurrence after operation, distant metastasis, or cancer death due to MNT, so no additional treatment is thought to be necessary after complete resection [1, 5, 6]. In the present case, we diagnosed the cyst resected at the previous operation as only part of the MNT and the remaining lesion continued to grow during the 10-year period after the incomplete resection. The reason for this diagnosis was that the tumor resected during the present operation had linear connective tissue which consisted of scar tissue from the previous operation and the cyst was also found to consist of MNT after a reassessment of the findings. We were able to completely resect the tumor after 10 years because MNT is a low-grade malignancy that regrew only locally.
Regarding the difference between thymic cysts and a cystic lesion of MNT, Suster and Moran reported that a thymic cyst has a layer of epithelial cells that line the wall, while such a layer is absent in the cystic lesions of MNT . However, their findings remain controversial because other experts do not support Suster and Moran’s conclusion . The present case did have a layer of epithelial cells lining the wall, so the presence or absence of this layer cannot be used for the differentiation between thymic cysts and MNT. A careful assessment of the presence of a malignant component in the wall of a cyst is important for avoiding a misdiagnosis.
This case report describes a case of MNT that regrew after incomplete resection 10 years earlier, and is the first case report to describe recurrence of MNT. MNT is a rare subtype of thymoma, and we could completely resect the tumor at reoperation because it is of low-grade malignancy and is a slow-growing tumor. In some cases, it is difficult to distinguish thymoma with a cystic lesion from a thymic cyst, as in the present patient. However, it is important to assess the presence of a malignant component in the wall of a cyst in order to avoid a misdiagnosis.
The authors would like to acknowledge the help of Hisashi Tateyama MD, PhD in confirming the diagnoses.
This work has not received any funding.
Availability of data and materials
Data sharing is not applicable to this article as no datasets were generated or analyzed in this study.
YK drafted the manuscript. MT and HY performed the operation. All authors decided on the treatment plan and participated in the patient’s management. HO diagnosed this case pathologically. HN and MT corrected the manuscript. All authors read and approved the final manuscript.
Ethics approval and consent to participate
This study was approved by the ethics committee of our institution (authorization number 18-17).
Consent for publication
Written informed consent was obtained from the patient for the publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
The authors declare that they have no competing interests.
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- 1.Tateyama H, Girard N, Marx A, Marchevsky AM, Ströbel P, Marom EM, Detterbeck F, Mukai K. Micronodular thymoma with lymphoid stroma. In: Travis WD, Brambilla E, Nicholson AG, editors. WHO classification of Tumours of the Lung, Pleura, Thymus and Heart. Lyon: World Health Organization; 2015. p. 205–6.Google Scholar
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