The aneurysmal bone cyst (ABC) is a fast-growing tumor of undefined neoplastic nature. It is occasionally an aggressive benign lesion whose treatment of choice is a complete resection, even though the risk of profuse transoperative bleeding exists. We present a female patient with thoracic spine deformity, with progressive paresthesias and muscle weakness of lower extremities that evolved to paralysis of both lower extremities and sphincter incontinence. Based on radiographic films, lytic lesions were identified at T7 to T9 vertebrae as well as medullary space invasion. In electrophysiologic tests, a complete somatosensorial pathway block was reported. Prior to resection of the neoplastic lesion and thoracolumbar stabilization, an incisional biopsy was performed. There was no postoperative medullary functional improvement. Morphological findings corresponded to an aneurysmal bone cyst at T8. This lesion is mainly located in the long bones and less frequently of the spine, where instability and medullary compression may occur. It is possible to confuse this neoplasia with other lesions. Hence, definite diagnosis with biopsy is necessary for determining an adequate therapeutic plan to eradicate recurrence risk or associated neurologic sequelae, as well as to gain proper stability at the involved vertebral segments.