VULNERABILITY OF GREAT MEDULLARY ARTERY

Study Design. The present study describes anatomic observations on gre at medullary artery and intercostal artery pertinent to thoracolumbar spinal surgery. Objectives. This study reveals the vulnerable course o f the great medullary artery and its relationship to the lateral or po sterolateral approach to thoracic spine. Summary of Background Data. T here are no previous anatomic data on the length of the great medullar y artery, its intradural course, its relationship with the anterior sp inal artery, and the distance between two adjacent intercostal arterie s. Methods. The location of the intercostal arteries was defined, and the distance between two adjacent arteries was measured at a point on the lateral surface of the vertebra midway between its anteroposterior diameter. The intradural length of the great medullary artery and the angle it formed with the anterior spinal artery at the point of anast omosis were also measured. Results. The mean intradural length of the great medullary artery was 3.6 cm (range, 1.7-8.1 cm), and it passed o ver 1-3 disc spaces before joining the anterior spinal artery at a mea n angle of 20.1 degrees (range, 12-28 degrees). The average distance b etween two adjacent intercostal arteries from T6 to L2 was 3.6 cm (ran ge, 2.8-4.0 cm), which provides a safe window through which a herniate d thoracic disc may be approached if surgery is indicated. Conclusions . The acute angle between the great medullary artery and anterior spin al artery indicates that these two arteries are in close proximity for considerable length and are liable to be compressed together with the intervening vascular collaterals by a space-occupying lesion, such as disc herniation or a fractured fragment. The longer the intradural co urse of the great medullary artery, the more vulnerable it is to compr ession by disc herniation or fracture. The intercostal and lumbar arte ries are located at the midportion of the lateral aspect of the verteb ral bodies rather than at the level of intervertebral discs. Discectom y or decompression of the anterior thoracic canal may be accomplished through a lateral or posterolateral extracavitary approach between two intercostal or lumbar arteries.