Besides usual complications observed during a surgery performed in a sitting position, exceptional ones, sometimes even more serious, have been also described. These involve quadriplegia developed due to the cervical spinal cord malacia. In patients with spondylotic changes causing the spinal canal stenosis, a simple protracted compression of the cervical spinal cord at the head hyperflexion may be considered to cause the rise of a spinal lesion. In young patients without degenerative changes of the cervical spine and with the free spinal canal the cause of myelomalacia has been unknown. Therefore, it is very difficult to prevent the development of this complication. A combination of mechanical, vascular and circulatory effects shares in the rise of a spinal damage. The monitoring of somatosensory and motor evoked potentials is of essential meaning in the prevention of a spinal affection developed during the per-operative positioning of a patient. The authors have documented these problems by means of three very similar casereports. A transversal lesion of the cervical spinal cord in C6 segment developed in all the three cases after a surgery of the posterior cranial fossa performed in a sitting position. A clear cause has not been determined. The report has analyzed and discussed possible hypotheses concerning this complication rise.

        Key words: operating complication, cervical flexion myelopathy, sitting position, posterior fossa surgery