The first question to ask is where exactly is the tumor located within the spinal canal. The broad categories are: intramedullary, intradural-extramedullary, and extradural. An intramedullary mass will be centered within the substance of the spinal cord itself, which has been described as the claw sign. An intradural-extramedullary mass will form a meniscus with the cord and push it away. An extradural mass will be outside the thecal sac. Vertebral body or clear epidural involvement suggests an extradural location. In cases where the distinction is difficult, assess the cord above and below the mass.
Once that determination has been made, the chart below can help generate a differential by focusing on both the imaging characteristics and clinical context:
The chart is not comprehensive, but it does list the most common primary masses to be found within those locations within the spine. As always, metastases are a consideration in any of these locations. Making the distinction can be challenging at times, especially when the mass is large and distorts normal structures.