Biopsy of the spine may be needed when a suspicious lesion appears on X-ray, CT scan, or MRI. Although these imaging studies help identify the location, shape, and effect of lesions on the surrounding soft tissues, only by removing the pathologic tissue can a positive identification be made.
The most common lesions of the vertebrae are infections and tumors. Tumors can be primary (first developed at that site) or metastasized (spread from a tumor somewhere else in the body). Sometimes what look like lesions are really artifacts from the imaging. This means a shadow or distortion gives the impression of a true lesion.
There are other possible explanations for your situation. Sometimes the biopsy needle misses the lesion or fails to collect enough of the pathologic tissue to show up in the lab analysis. And there can be false negatives. This means the test came back negative when there really was something there.
And finally, it’s entirely possible that whatever was there has resolved. If that’s the case, then your symptoms should also slowly disappear. However, if there has been no change (improvement) in your weakness or you have developed other symptoms, a follow-up appointment is needed as soon as possible.
Your concern is justified and should be explained. Don’t hesitate to contact your physician and ask some questions. No one likes the idea of a second biopsy, but it may be necessary.