Local Spread of Metastatic Vertebral Tumors

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Abstract
Nineteen solitary metastatic vertebral tumors obtained by total en bloc spondylectomy were analyzed histologically. To determine the mechanisms of local spread of vertebral tumors and identify barrier tissues to tumor progression in the vertebra. Histologic studies of specimens resected at amputation or en bloc excision have determined the pattern of local spread of bone and soft tissue tumors in the extremities and identified barrier tissues to tumor spread. However, a similar assessment of vertebral malignancies is difficult. The development of total en bloc spondylectomy for primary vertebral malignancy and solitary metastases has allowed the collection of tissue samples sufficient to analyze the pattern of local spread of tumors, using the concept of compartment and barrier. Histologic sections of all vertebral elements were prepared from specimens collected after en bloc spondylectomy. Serial 5-mm sections in the sagittal plane were also prepared and examined. 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 longitudinal ligament, periosteum abutting the spinal canal, ligamentum flavum, periosteum of the lamina and spinous process, interspinous ligament, supraspinous ligament, cartilaginous endplate and the anulus fibrosus served as barriers to tumor progression. The posterior longitudinal ligament was the weakest barrier tissue and was gradually destroyed by the tumor at the point of perforating vessels. Even after destruction of the barrier tissue, tumor cells were covered with a thin, fibrous reactive membrane. Two pathways allowed tumor spread to the adjacent vertebrae: 1) from the edge of the vertebral body to the adjacent vertebral body beneath the longitudinal ligament, and 2) through the paravertebral muscles to the neighboring lamina. Each vertebra can be represented by a compartment surrounded by several barriers. The most common path for tumor spread is through the posterior longitudinal ligament to the epidural space.