Figure 2.

Intra-operative photographs of the medulla spinalis and the spinal cord. A. Intra-operatively, the floor of the fourth ventricle was covered with small cystic lesions (fourth ventricle, cervical medulla on top). B. Intra-operative photograph showing thickening and discoloration of the arachnoid around the spinal cord (image of part proximal of C1). C. Intra-operatively, the cyst wall covered all cranial nerves and arteries lateral to the brain stem, inhibiting normal flow of cerebrospinal fluid (accessory nerve and arteries lateral to the brain stem).