The route of metastatic vertebral tumors extending to the adjacent vertebral body: a histological study.

Background: Each vertebra can be regarded as a compartment surrounded by several anatomically characterized barriers. However, in some cases tumors extend beyond these barriers. The route of vertical extension to the adjacent vertebrae is unclear. The extent of vertical extension of a metastatic spinal tumor is important in making the preoperative decision regarding the cranio-caudal surgical margin. The objective of this study was to investigate the route of vertical extension of metastatic vertebral tumors.

Methods: We examined 20 en bloc resected metastatic vertebral bodies in which the tumors had extended outside the vertebral body. Five to eight sagittal sections including the pedicle, and the lateral and central parts of the PLL were prepared from each resected specimen. The sections were stained with hematoxylin and eosin, and elastica van Gieson. Histological examination focused on the routes of the vertical extension of the tumor at each barrier tissue and the degree of tumor extension along each route.

Results: Vertical extension of the tumor was observed at the ALL in 6 cases, at the central part of the PLL in 14 cases, at the lateral part of the PLL in 20 cases, at the cartilaginous endplate in 3 cases, and at the periosteum on the lateral side of vertebral body in 7 cases. The tumor had extended the farthest at the lateral part of the PLL in 18 cases, at the lateral side of the vertebral body in 1 case, and through the disc in 1 case.

Conclusions: Metastatic vertebral tumors most commonly extend vertically at the lateral part of the PLL. The lateral part of the PLL is raised by the tumor, which extends between the PLL and the posterior aspect of the disc.