Poorly Differentiated Chordoma of the Clivus With Loss of SMARCB1 Expression in a Pediatric Patient: A Case Report.

Poorly differentiated chordoma (PDC) is a rare, aggressive subtype of chordoma. A two-year-old girl presented with cervical pain, limb paralysis and respiratory failure. Magnetic resonance imaging and positron emission tomography-computed tomography revealed a tumor compressing the pons at the clivus and osteoblastic metastatic lesions of the left upper arm and right iliac bone. Her tumors shrank substantially after treatment with chemotherapy and proton beam therapy. Our initial diagnosis was an atypical teratoma/rhabdoid tumor, but final diagnosis of PDC was made on the basis of the immunohistochemical expression of brachyury. In addition, the detection of SMARCB1/INI1 mutation confirmed the diagnosis of PDC.