Spindle Cell and Mixed Spindle/Lymphocytic Thymomas

Abstract

Forty-three cases of spindle cell thymoma (medullary, WHO type A) and 38 cases of mixed spindle/lymphocytic thymoma (WHO type AB) were studied for their clinicopathologic and immunohistochemical characteristics. Three histologic patterns of spindle cell thymoma were observed: short-spindled (57%), long-spindled (31%), and micronodular (12%). The short-spindled variant was composed of oval to short spindle cells commonly arranged in a hemangiopericytic or microcystic pattern. The long-spindled variant chiefly consisted of fibroblast-like epithelial cells mimicking fibrohistiocytic neoplasms. The micronodular variant was characterized by small nests of short spindle cells dispersed among a lymphoid stroma with frequent germinal centers. All kinds of spindle cell could be admixed with lymphocyte-rich "cortex"-like areas to constitute mixed spindle/lymphocytic thymomas. Immunohistochemically, the epithelial cells in up to 70% of the short-spindled and long-spindled variants of spindle cell thymoma and 90% of mixed spindle/lymphocytic thymomas were positive for CD20, whereas the epithelial cells in all micronodular spindle cell thymomas were negative. All of the spindle cell thymomas and most of the mixed spindle/lymphocytic thymomas in this study were found in stages I and II. Follow up of the patients did not disclose relapse or mortality directly resulting from the tumors. However, the prognosis of stage I and II spindle cell and mixed spindle/lymphocytic thymomas did not significantly differ from those of stage I and II thymomas of other types by a stage-matched survival analysis. Our data showed that spindle cell and mixed spindle/lymphocytic thymomas are distinctive in histologic pattern and immunohistochemical profile. When interpreted within the context of staging, spindle cell and mixed spindle/lymphocytic thymomas presenting in stages I and II most likely behave in an indolent fashion.

Predicting Subtypes of Thymic Epithelial Tumors Using CT: New Perspective based on a Comprehensive Analysis of 216 Patients

“…Histologically, type AB thymoma showed multiple nodules separated by fibrous bands4. The multiple nodules with fibrous septum features on CT imaging are consistent with the macroscopic appearance of a type AB thymoma (Supplementary Fig 2A)26. However, high risk TET subtypes especially thymic carcinoma appear as mainly deep lobulation or spiculate protuberance without tumor septum (Supplementary Fig 2B).…”

“…However, our finding is out of expectation in suggesting that low risk subtype of thymoma (type A and AB) demonstrated a high degree of CT enhancement while high risk ones demonstrated a much lower degree of CT enhancement. Pan et al studied the clinicopathologic characteristics of spindle cell thymoma (medullary, WHO type A) and mixed spindle/lymphocytic thymoma (WHO type AB), and found that the short-spindled pattern of type A thymoma may commonly arrange in a hemangiopericytic or microcystic pattern26, which may explain why a higher degree of CT enhancement exist in low risk subtypes in our study. To the best of our knowledge, this exploration of degree of CT enhancement and stage of TETs has never been investigated before, and focusing on our clinical question itself, this interesting finding implies that degree of CT enhancement can probably predict the classifications of TETs.…”

Dual-energy CT perfusion imaging for differentiating WHO subtypes of thymic epithelial tumors

“…For conventional CECT imaging, the mean CEmax, the only conventional CT quantitative parameter in this study, of Type A and AB were higher than those of the other types. Pan et al 25 found that the short-spindled pattern of Type A and AB may commonly arrange in a haemangiopericytic or microcystic pattern, which may explain why a higher degree of CT enhancement was observed in the above two subtypes in our study. This is consistent with the results of Hu et al 19 , who first reported that the degree of CT enhancement and MNFS could preoperatively help determine the WHO pathological subtypes of TET patients, especially for the low-risk (type A and AB) and high-risk (types B1 B2, B3 and thymic carcinoma) subtypes.…”

Intravoxel incoherent motion diffusion-weighted MR imaging parameters predict pathological classification in thymic epithelial tumors

“…Interestingly, these findings are consistent with the results of a CT contrast enhancement study in which maximal contrast-enhanced ranges (CE max ) were higher in low risk subtypes of thymoma (type A and AB) than in other TETs [ 11 ]. Similarly, this unique perfusion or blood supply feature of TETs may be explained by a study which demonstrated that the short-spindled variant (57% histologic patterns of thymoma type A and AB) was composed of oval to short spindle cells typically arranged in a hemangiopericytic or microcystic pattern [ 28 ]. Those findings, together with our results, indicate that D* might be valuable for accurate prediction of TET type and stage.…”