LOCAL SPREAD OF METASTATIC VERTEBRAL TUMORS - A HISTOLOGIC-STUDY

Study Design. Nineteen solitary metastatic vertebral tumors obtained b y total en bloc spondylectomy were analyzed histologically. Objectives . To determine the mechanisms of local spread of vertebral tumors and identify barrier tissues to tumor progression in the vertebra. Summary of Background Date. Histologic studies of specimens resected at amput ation or an bloc excision have determined the pattern of local spread of bone and soft tissue tumors in the extremities and identified barri er tissues to tumor spread. However, a similar assessment of vertebral malignancies is difficult. The development of total en bloc spondylec tomy for primary vertebral malignancy and solitary metastases has allo wed the collection of tissue samples sufficient to analyze the pattern of local spread of tumors, using the concept of compartment and barri er. Methods. Histologic sections of all vertebral elements were prepar ed from specimens collected after en bloc spondylectomy. Serial 5-mm s ections in the sagittal plane were also prepared and examined. Results . Analysis of tumor location showed that metastatic tumors reached the vertebral column by invading the bone marrow of the dorsal region of the vertebral body. The anterior longitudinal ligament, posterior long itudinal ligament, periosteum abutting the spinal canal, ligamentum fl avum, periosteum of the lamina and spinous process, interspinous ligam ent, supraspinous ligament, cartilaginous endplate and the anulus fibr osus served as barriers to tumor progression. The posterior longitudin al ligament was the weakest barrier tissue and was gradually destroyed by the tumor at the point of perforating vessels. Even after destruct ion of the barrier tissue, tumor cells were covered with a thin, fibro us reactive membrane. Two pathways allowed tumor spread to the adjacen t vertebrae: 1) from the edge of the vertebral body to the adjacent ve rtebral body beneath the longitudinal ligament, and 2) through the par avertebral muscles to the neighboring lamina. Conclusions. Each verteb ra can be represented by a compartment surrounded by several barriers. The most common path for tumor spread is through the posterior longit udinal ligament to the epidural space.