Purpose <p>This anatomical study aimed to define relative level-specific safe areas and critical vascular zones for left-sided ventral approaches to the thoracic and lumbar spine.</p> Methods <p>Thirty-two formalin-fixed cadavers (16 females, 16 males; mean age 85 years) were included. Lumbar and thoracic segmental arteries and veins between T5 and L3 were identified and their localization documented in detail by dividing each vertebral body into cranial, middle, and caudal thirds, as well as anterior and posterior halves. Adjacent intervertebral discs were included. Vessel courses, variations, and the relation to the hemiazygos vein and the artery of Adamkiewicz were systematically recorded.</p> Results <p>No vertebral region was consistently free of vessels. Arterial distribution differed between thoracic and lumbar levels, with T12 demonstrating a transitional pattern between these regions. In the thoracic spine, the cranial third of the vertebral body and the caudal half of adjacent discs showed the lowest arterial density (&lt; 15%), representing regions of comparatively low vascular density. Venous variability was higher in anterior than in posterior vertebral halves. At T12 and in the lumbar spine, the lowest arterial density occurred at the disc level. Critical vascular zones included the caudal third of T5–T11 and the middle third of T12 and below. The artery of Adamkiewicz was macroscopically identified in 16% of the cases.</p> Conclusion <p>Segmental vascular anatomy is highly variable. Level-specific mapping of arteries and veins enables the identification of relative safe areas and critical vascular zones to improve safety during anterior and lateral thoracolumbar approaches.</p>