What is an Anterior impression on the thecal sac?

An anterior impression on the thecal sac is a radiographic finding seen on magnetic resonance imaging (MRI) of the spine. It refers to an indentation or concavity on the front surface of the dural sac, which contains the spinal cord and nerve roots. This impression is usually caused by the presence of a disc protrusion or herniation from an intervertebral disc, which is a cushion-like structure located between the vertebrae. The disc material may bulge out and press against the thecal sac, creating an anterior impression. This can lead to compression of the spinal cord or nerve roots, causing symptoms such as back pain, radiating pain, numbness, and weakness in the affected area. The presence of an anterior impression on the thecal sac is an important diagnostic finding and can help guide treatment decisions for conditions such as disc herniations and spinal stenosis.