[Two cases of posterior spinal artery syndrome (PSAS)].

We have reported two patients with posterior spinal artery syndrome. Both of them had sudden onset back pain, paraparesis, loss of deep sensation and bladder-bowel disturbances. MRI disclosed spinal cord lesions positioned at its posterior part including the posterior column or posterior horn at thoracic levels. Spinal artery syndrome is a rare disorder, especially the posterior spinal artery syndrome (PSAS). In our department, only ten patients had spinal artery syndrome out of 2,064 patients admitted to our hospital these 20 years. All the other 8 patients had anterior spinal artery syndrome. It supports the notion that PSAS is rare. The detection rate of PSAS may increase after the routine use of spinal MRI in clinical practice. Our two patients had bilateral, symmetric symptoms. These symmetric signs and symptoms are usually seen in PSAS. The bilateral posterior spinal arteries connect with each other through many complex anastomoses. Moderate blood flow insufficiency may produce no clinical symptoms because of compensation by these anastomoses. When symptoms appear, these anastomoses do not compensate blood flow deficit and may produce bilateral symptoms.