Skull base neoplasms consisting of cells with vacuolated cytoplasm have the important list of differential diagnosis - chordoma (destroying bone), microcystic meningioma and chordoid meningioma (dura-based), chordoid chondrosarcoma (destroying bone), chordoid glioma (of the third ventricle and hypothalamus) and, of course, metastasis (adenocarcinoma of gastrointestinal origin and clear cell carcinoma of renal or ovarian origin).

The presence of broad bands of collagenous stroma between lobules of neoplastic cells is against the possibility of microcystic meningioma and chordoid meningioma. Chordoma's physalliferous cells often engulfed red blood cells when pre-surgical hemorrhage has taken place. At least some cells seen in chordoid glioma have plump eosinophilic cytoplasm. Inflammation can be seen in chordoma and chordoid glioma. Chordoid chondrosarcoma can sometimes be very difficult to differentiate from chordoma. When not certain, mucicarmine stain, PAS stain and immunohistochemistry would hold your hand in signing out your final diagnosis. Chordoma would be strongly positive for AE1 and negative for mucicarmine and PAS (unlike metastatic adenocarcinoma and clear cell carcinoma). Meningioma is positive for EMA but negative for AE1. Chordoid glioma is positive for GFAP and EMA. Chordoid chondrosarcoma is positive for S100 but negative for others. I favor chordoma in this case based on the photos given.

 chordoma(脊索瘤)

DDX:1.microcystic meningioma（微囊性脑膜瘤），鞍区可发生脑膜瘤。

2.metastatic adenocarcinoma（转移性腺癌），尤其是印戒细胞癌。

3.myxopapillary ependymoma（粘液乳头型室管膜瘤），该瘤发生区此少见，主要在骶尾部终丝。