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Table 1: Key points for the differential diagnosis of cell-dense and matrix-rich types according to the ultrastructures of chordomas^{^a}
Cell-Dense Type Matrix-Rich Type
Tumor cell content in a low-power field (×3000) Densely arranged Seldom or none
Extracellular matrix content Relatively sparse Abundant
Complex of rough endoplasmic reticulum and the mitochondria Rich Relatively seldom
Nuclei and chromatin Abnormal nuclei with condensed, deeply staining heterochromatin Regularly shaped nuclei, mainly with loosely arranged euchromatin
Cell junctions Desmosomes are obvious Few desmosomes
Collagen fibrils Type III collagen fibrils can be found Seldom
Exocytosis Easily found Seldom
↵a Reprinted with permission from Bai et al¹³ and Elsevier.

	Cell-Dense Type	Matrix-Rich Type
Tumor cell content in a low-power field (×3000)	Densely arranged	Seldom or none
Extracellular matrix content	Relatively sparse	Abundant
Complex of rough endoplasmic reticulum and the mitochondria	Rich	Relatively seldom
Nuclei and chromatin	Abnormal nuclei with condensed, deeply staining heterochromatin	Regularly shaped nuclei, mainly with loosely arranged euchromatin
Cell junctions	Desmosomes are obvious	Few desmosomes
Collagen fibrils	Type III collagen fibrils can be found	Seldom
Exocytosis	Easily found	Seldom