[Poorly-differentiated chordoma with INI1 loss: a clinicopathologic study].

To analyze the clinicopathologic characteristics of poorly-differentiated chordoma with INI1 loss in children and to discuss the differential diagnosis. The clinical, radiological, histopathological profiles and molecular pathologic characteristics of two pediatric poorly differentiated chordoma cases with INI1 loss were reviewed. The patients were a girl and a boy. Both lesions involved the slope. Both patients were presented with progressive muscle weakness or neck pain. Radiological examination showed clivus bone destruction and compression of the brain stem and cervical spinal cord. Histologically, the tumor cells lacked typical organization and were associated with inflammatory cells infiltration. On high power field, the tumor cells were ovoid or fusiform with prominent atypia, vacuolated nuclei and prominent nucleoli. By immunohistochemistry, the tumor cells expressed cytokeratin, epithelial membrane antigen, brachyury and were negative for INI1. In both cases, INI1 gene deletion was detected by FISH. Poorly-differentiated chordoma with INI1 loss mainly occurs in children. The morphology is different from classical chordoma.INI1 gene deletion is detectable by FISH. It can be distinguished from atypical teratoid/rhabdoid tumors and other neoplasms by the identification of nuclear brachyury expression. The loss of INI1 expression in poorly-differentiated chordoma might be associated with a poorly-differentiated morphology and an adverse prognosis.