Micronodular thymoma with lymphoid stroma: report of two cases and particular association with thymic lymphoid hyperplasia in one case

Thymic epithelial tumours: histopathological classification and differential diagnosis

The epithelial and lymphoid compartments of the thymus can give rise to a wide variety of tumours, including thymomas, thymic carcinomas, lymphoreticular proliferations, germ cell tumours, and sarcomas. While some of these have close similarity to their counterparts in other organs, both in terms of histology and immunohistochemistry, as well as molecular features, others are unique to the thymus. The epithelial tumours, which can develop in the thymus, will be discussed in this review, with a particular emphasis on resolving differential diagnosis by means of morphology, immunohistochemical profiles, and molecular diagnostics.

Micronodular thymic tumor with lymphoid stroma: A case report and review of the literature

BACKGROUND

Micronodular thymic tumors with lymphoid stroma include micronodular thymoma with lymphoid stroma (MNT) and micronodular thymic carcinoma with lymphoid hyperplasia (MNC), whose micromorphological features are lymphoid stromal hyperplasia and nodular arrangement of tumor epithelial cells. This type of tumor is rare; therefore, the corresponding clinical guidelines, histopathological diagnostic criteria, prognostic factors, and therapeutic regimens have not been established.

CASE SUMMARY

This study covers a novel presentation of MNC in a patient and summarizes the clinicopathological characteristics of this type of tumor by using pooled-analysis methods. Morphologically, this tumor type is a series of benign to malignant pedigrees. We establish the following criteria for the classification of micronodular thymic tumors with lymphoid stroma: (1) Tumor cells with moderate-to-severe dysplasia; (2) Tumor cell mitotic figures > 2/10 high-power fields; (3) Appearance of neoplastic necrosis; (4) No terminal deoxynucleotidyl transferase-positive immature T lymphocytes within the tumor; (5) Tumor cells with a Ki-67 index ≥ 10%; and (6) Tumor cells express CD5. Cases that fall into the borders of two categories in terms of morphology are attributed to atypical MNT. It is proposed that the diagnosis of MNT should be established on the diagnostic criteria mentioned above.

CONCLUSION

Our diagnostic algorithm can effectively distinguish malignant tumors from benign tumors and provides a potent basis for predicting a prognosis, which offers a practical reference for oncologists and pathologists.

Micronodular thymoma with lymphoid stroma: Two cases, one in a multilocular thymic cyst, and literature review

Micronodular thymoma with lymphoid stroma (MTWLS) is a rare type of thymoma that shows a similar pattern but varied morphology and immunophenotype of tumor cells. Because of the extremely limited number of cases reported, the pathology and biology of MTWLS are equivocal. Herein, we report two cases located in the anterior mediastinum: Case 1: a 58‐year‐old woman with a cystic mass measuring 5 × 3.0 × 2.5 cm in Mosaoka stage I; and Case 2: a 50‐year‐old man with a solid mass measuring 2.5 × 2.5 × 2.0 cm in stage IIb. Both patients were treated by thymectomy and are alive without recurrence or metastasis 15 and 17 months after surgery, respectively. Regardless of the spectrum of pathology and stage of MTWLS, this unique type of thymoma has a homogeneously favorable prognosis.

Ectopic micronodular thymoma with lymphoid stroma in the cervical region: a rare case associated with Langerhans cells proliferation

Micronodular thymoma (MNT) with lymphoid stroma is a rare thymic epithelial neoplasm with the characteristics of multiple nodules separated by abundant lymphoid stroma. MNTs mainly arise in the anterior mediastinum and thymus, while ectopic MNTs are extremely rarely seen. Here, we report an ectopic MNT that occurred in the neck of a 62-year-old woman. There were also scattered eosinophilic granulocytes and S100⁺/CD1a⁺ Langerhans cells within the tumor. This case provides a better understanding of such rare, poorly understood cases.

Micronodular thymic neoplasms: case series and literature review with emphasis on the spectrum of differentiation

We report nine cases of micronodular thymoma with lymphoid B-cell hyperplasia and one case of micronodular thymic carcinoma with lymphoid hyperplasia from our institution. For a better understanding of these rare tumors, clinical records, and histological features of these cases were reviewed, with detailed review of additional 64 literature cases of micronodular thymic neoplasms. The joint analysis identified 64 cases of micronodular thymoma with lymphoid B-cell hyperplasia and 9 cases of micronodular thymic carcinoma with lymphoid hyperplasia. Both groups revealed slight male predilection, with male:female ratio of 1.3:1 and 5:4, and occurred at >40 years of age, with a mean of 64 (41-83) and 62 (42-78) years, respectively. Myasthenia gravis was noted in 3/64 (5%) and 1/9 (11%) patients, respectively. Other systemic, disimmune, or hematologic disorders were noted in 6/64 (9%) and 1/9 (11%) patients, respectively. Components of conventional thymoma were reported in 11/64 (17%) micronodular thymomas with lymphoid B-cell hyperplasia, with transitional morphology between the two components in most of them. Cellular morphology was predominantly spindle in micronodular thymoma with lymphoid B-cell hyperplasia when specified (30/43), and epithelioid in micronodular thymic carcinoma with lymphoid hyperplasia (6/9), and cytological atypia was more encountered in the latter. Dedifferentiation/transformation from micronodular thymoma with lymphoid B-cell hyperplasia to micronodular thymic carcinoma with lymphoid hyperplasia seems to occur in a small subset of cases. Three cases of micronodular thymomas with lymphoid B-cell hyperplasia were described with co-existent low-grade B-cell lymphomas. Follow-up data were available for 30 micronodular thymomas with lymphoid B-cell hyperplasia and 6 micronodular thymic carcinomas with lymphoid hyperplasia, with a mean of 47 (0.2-180) months and 23 (3-39) months, respectively. Patients were alive without disease, except for five micronodular thymoma with lymphoid B-cell hyperplasia patients (dead from unrelated causes), and one micronodular thymic carcinoma with lymphoid hyperplasia patient (dead of disease).

Micronodular thymoma with lymphoid stroma in a multilocular thymic cyst: a case study

Herein, we report a case of micronodular thymoma with lymphoid stroma in a previously healthy 73-year-old male. Thymectomy was performed. The solid and macrocystic masses were encapsulated with focal invasion. The solid portion consisted of nodules of bland-looking spindle or round epithelial cells in lymphoid stroma containing prominent germinal centers. The epithelial cells had moderate amount of cytoplasm and occasional mucin production. The cystic portion was lined with cuboidal epithelium. According to World Health Organization (WHO) classification, the mass was diagnosed as a micronodular thymoma with lymphoid stroma accompanied by a pre-existing multilocular thymic cyst. Micronodular thymoma with lymphoid stroma, a possible variant of type A thymoma, is an extremely rare tumor. This so-called "unusual" variant may imply the schematic weakness of the current WHO classification that cannot cover all morphologic types. Further study is recommended for clarification of this variant and its incorporation into the current classification.

Micronodular thymic carcinoma with lymphoid hyperplasia: a clinicopathological and immunohistochemical study of five cases

Five cases of an unusual variant of thymic carcinoma are described, which represent the counterpart of the so-called micronodular thymoma with lymphoid hyperplasia. The patients were three men and two women aged 42-78 years (mean 64 years). Three patients were asymptomatic and the tumors were found incidentally on chest radiographs performed for unrelated reasons. Two patients complained of dyspnea, chest pain and shortness of breath prompting further investigations. The tumors ranged in size from 3.2 to 10.0 cm and were described as infiltrative masses often invading adjacent structures. Prominent cystic changes were not identified. Histologically, the neoplasms were composed of epithelial tumor cells arranged in a micronodular growth pattern set in a stroma showing florid lymphoid hyperplasia. Contrary to micronodular thymoma, the epithelial cell component of the present cases showed unequivocal signs of malignancy characterized by cytological atypia and increased mitotic activity. Immunohistochemical studies showed the lymphoid component to be of mixed B- and T-cell lineage. None of the patients had a history of myasthenia gravis or other autoimmune disorder. Follow-up revealed that 4 patients were alive and well 3-26 months after diagnosis while 1 patient was dead of disease 21 months after diagnosis. The tumors in this series represent a distinct subtype of thymic carcinoma histologically strongly resembling micronodular thymoma with lymphoid hyperplasia. Awareness of this type of thymic carcinoma is important in order not to dismiss this tumor for a neoplasm of lower-grade malignancy.