Skeletal metastases are 25 times more common than primary bone tumors. Spinal metastases are common because they tend to develop in hematopoietic active bone marrow, which is predominantly located in the adult spine. Most spinal metastases are found in the thoracic and lumbar regions. They are frequently disseminated via the blood-hematogenous spread. Both venous dissemination and arterial dissemination may occur. Batson's plexus of valveless veins, a major source of spinal metastases, connects with venous plexuses inside the spinal canal. Pressure difference in these veins directs tumor cells from the pelvis (prostate) into the lumbar or thoracic vertebral bodies. The tumors may also get to the spine by direct dissemination or through the lymphatic system. They frequently invade the vertebral bodies or the pedicles. Metastases can also grow along nervous tissue and thus enter the epidural space inside the spinal canal. The most common sources of vertebral metastases are the breast, /ungs, thyroid, Sidney, and prostate. An easy way to remember these organs is by bringing to mind the "classical" NY sandwich: bacon, /ettuce, and tomatoes with a kosher fickle.
As the metastatic lesions grow, they destroy the vertebral body, penetrate through cortical bone, invade the spinal canal, and compromise the neural elements. Cord compression and neurological deficits may also occur when vertebral bodies collapse due to compromised structural integrity.
X-rays are the less sensitive diagnostic tool for spinal metastases detection. Vertebral bodies can loose upwards of 50% of their density before it becomes detectable in plain films. The vertebral bodies may appear heterogeneous or motley on plain films. This appearance is not specific and can be found in osteoporosis as well. The vertebral bodies' shape, texture, and cortices should be critically observed. Special attention should be paid to the posterior vertebral body wall. The presence of a lytic (darker) or blastic (whiter) vertebral body may give away the presence of metastases. In some patients with metastatic prostate cancer the vertebral bodies may seem completely white (Figures 11-1A and 11-1B). The pedicles should be critically inspected. They are
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