[Pathology] Atlas of Thymic Epithelial Neoplasms (part 4), Thymic Epithelial Neoplasms, Atlas of Mediastinal Pathology
Fig. 2.30 Trabecular growth pattern in spindle-cell thymoma shows
elongated strands of cells that are several layers thick separated by
vascular stroma simulating a neuroendocrine neoplasm. The tumor cells in
this case were p63 positive and negative for neuroendocrine markers
Fig. 2.31 Ribbon-like growth pattern in spindle-cell thymoma shows a
lobulated growth surrounded by connective tissue that contains
serpiginous cords of tumor cells; the pattern can be highly reminiscent of a
neuroendocrine neoplasm such as thymic carcinoid
Fig. 2.32 Higher magnification from ribbon-like growth pattern in
spindle-cell thymoma shows spindle to oval cells with hyperchromatic
nuclei aligned in parallel arrays forming serpiginous cords of cells
Fig. 2.33 Spindle-cell thymoma showing prominent basaloid peripheral
palisading of nuclei similar to that observed in large cell neuroendocrine
carcinomas of the lung. The nuclear morphology, however, is
bland and does not show the stippling of chromatin or prominent
nucleoli of large cell neuroendocrine carcinoma
Fig. 2.34 Spindle-cell thymoma showing a subtle “tzellballen” pattern
composed of small nests of cells separated by fibrovascular stroma. Such
cases need to be distinguished from mediastinal paragangliomas,
welldifferentiated neuroendocrine carcinoma, and metastatic melanoma
Fig. 2.35 Another histologic appearance in spindle-cell thymoma that
can be confused with metastases of melanoma or primary neuroendocrine carcinoma
is characterized by large clusters of spindle cells displaying a prominent nesting pattern
Fig. 2.36 Spindle-cell thymoma with pseudosarcomatous stroma (the
so-called “metaplastic” thymoma) is an unusual variant characterized
by anastomosing strands and islands of cohesive epithelioid cells separated
by a highly cellular spindle-cell stroma simulating a biphasic
malignant neoplasm (i.e., carcinosarcoma)
Fig. 2.37 Spindle-cell thymoma with pseudosarcomatous stroma
shows a discrete island composed of oval to polygonal epithelioid cells
with minimal cytologic atypia surrounded by a cellular spindle-cell
stroma. The epithelial cells test positive for cytokeratins, p63, and
PAX8; the stromal spindle cells are positive for vimentin and may also
display focal weak actin and EMA positivity
Fig. 2.38 Higher magnification of epithelial cell island in spindle-cell
thymoma with pseudosarcomatous stroma shows cells with oval nuclei
and abundant eosinophilic cytoplasm; note that the cells are devoid of
mitotic activity
Fig. 2.39 Focal areas in spindle-cell thymoma with pseudosarcomatous
stroma may display squamoid features and degenerative atypia;
these features should not be confused with evidence of malignancy or
the development of thymic carcinoma
To be continue: [Pathology] Atlas of Thymic Epithelial Neoplasms (part 5)
Suggested Reading
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