Lymphatic involvement in vertebral and disc pathology.

STUDY DESIGN: Analysis of lymphatic vessels in childhood and adult normal and pathological vertebral bone and intervertebral disc tissue. OBJECTIVE: To determine whether lymphatic vessels are present in spinal vertebrae and intervertebral discs in normal children and adults (4-30 years) as well as in pathological lesions of the spine. SUMMARY OF BACKGROUND DATA: There is uncertainty regarding the presence or absence of lymphatic vessels in normal intervertebral discs and the role of lymphatics in the pathobiology of disc degeneration and infective, neoplastic, and other spinal pathology. METHODS: The presence of the specific lymphatic endothelial cell markers, podoplanin, and LYVE-1 was determined immuno-histochemically in normal cervical, thoracic, and lumbar disc and vertebral tissues of adults and children, as well as in a wide range of spinal disorders. RESULTS: Lymphatics were not found in intact normal intervertebral discs or within spinal vertebrae of children or adults. Lymphatics were present in the outer periosteum and paraspinal ligaments and surrounding connective tissue. Lymphatic vessels were seen in infected and displaced degenerate disc tissue. Lymphatic vessels in vertebral bone were seen only when neoplastic and non-neoplastic lesions of the spine were associated with vertebral destruction and the lesion extending through the bone cortex into surrounding connective tissue. CONCLUSION: Lymphatics are not found in intact normal spinal vertebrae or the intervertebral discs of children or adults. Lymphatics in vertebral bone are found in pathological lesions of the spine when these have extended beyond the normal anatomical confines of the vertebra or intervertebral disc; this most likely occurs by ingrowth of lymphatics from surrounding connective tissues. These findings strongly suggest that metastatic tumor spread to the spine does not occur by lymphatics and that lymph node involvement of primary malignant spinal tumors occurs only after extraosseous spread.