The clinical findings in five intradural and two extradural arachnoid cysts were discussed. All patients of intradural arachnoid cyst were female, and their lesions were located at the upper or mid thoracic level. Three patients showed sensory disturbance and five showed motor weakness of the lower extremities. MRI and CTM showed enlargement of the subarachnoid space and displacement of the spinal cord. One patient had syringomyelia, two had cervical disc disease, and two had spinal cord herniation at the thoracic level. During the operation, the cyst walls were removed in all patients. Simaltaneously, herniated spinal cords were replaced intradurally. Later, cervical anterior fusion was performed in one patient, but another patient was follow-up without recourse to an operation. Syringomyelia disappeared without any direct treatment. The patients showed good recovery after operation, but the patients of extradural arachnoid cyst showed weakness and sensory disturbance of the lower extremities. Their dural defects were located at the thoracic level. MRI and CTM showed large cysts and bone erosion. After removal of the cyst wall and closure of the dural defect, each patient made a good recovery. Although MRI and CTM were helpful both for diagnosis and operation, 3D MR myelography would have been helpful to show the three dimentional relationship of the cyst and the subarachnoid space, as well as the pathogenesis of the arachnoid cyst and/or spinal cord herniation.
