Thecal Sac: Definition

The thecal sac, also known as the dural sac, is a structure within the spinal canal that contains the spinal cord, nerve roots, and cerebrospinal fluid (CSF). It is a protective covering that surrounds and encloses the spinal cord and the roots of the spinal nerves.

The thecal sac is formed by the dura mater, which is the tough, fibrous membrane. The dura mater forms a sac-like structure that extends from the base of the skull down to the sacrum, the triangular bone at the base of the spine.

Within the thecal sac, the spinal cord runs through the vertebral canal, protected by the bony vertebral column and surrounded by CSF. The spinal nerves, which branch off from the spinal cord, also travel through the thecal sac before exiting the spinal column through small openings called intervertebral foramina.

The thecal sac acts as a barrier and provides cushioning and protection for the delicate spinal cord and nerves. It helps to maintain the normal pressure and fluid balance around the spinal cord and facilitates the circulation of CSF, which nourishes and protects the nervous tissue.

Pathologies such as herniated discs, spinal stenosis, or tumors can potentially compress the thecal sac, causing symptoms such as neck or back pain, numbness, or weakness in the limbs. In such cases, medical intervention may be necessary to relieve the pressure on the spinal cord and nerves.

Learn more about thecal sac compression here

About the Author

Dave Harrison, MD

Dr. Harrison is a board certified Emergency Physician with a part time appointment at San Francisco General Medical Center and is an Assistant Clinical Professor-Volunteer at the UCSF School of Medicine. Dr. Harrison attended medical school at Tufts University and completed his Emergency Medicine residency at the University of Southern California. Dr. Harrison manages the editorial process for