Interactive · Patient Education
Understand Your Lumbar MRI
Your MRI report is written for doctors. This page is written for you — click any numbered point on the scan to learn what that structure is and why it matters.
Educational images and labels — not a diagnosis, and not your scan. Bring your actual MRI to your visit and Dr. Hobbs will walk through it with you.
How to read the view
Axial = looking down
A cross-section slice, as if looking down through your body from above. Great for seeing the canal, nerves, and disc at one level.
Sagittal = from the side
A side view showing the whole lumbar spine at once — disc heights, alignment, and the spinal canal top to bottom.
Bright means water
On these T2 images, fluid glows white. Healthy discs look brighter; worn discs turn dark. The fluid around your nerves is the bright stripe.
Want yours explained, image by image?
Walking patients through their own MRI is part of every consultation.
Anatomy guide
Every labeled structure, explained
Use the viewer above to explore the images, or read the complete explanations below.
Axial MRI — Level L4–L5
A view looking straight down through a slice of the lower spine.
- Intervertebral Disc
- The cushion between two vertebrae, made of a soft jelly-like center and a tough outer ring. When the center pushes out through the ring, it is called a herniated disc — a very common cause of sciatica. Herniated disc.
- Back Wall of the Disc
- The annulus fibrosus is the tough outer wall of the disc. The back portion sits right against the nerves, which is why most disc herniations happen here and so often press on a nerve root. Herniated disc.
- Spinal Fluid & Nerves
- The thecal sac is a fluid-filled sleeve protecting the bundle of nerves (the cauda equina) that runs down your spinal canal. It glows bright white on this MRI. When the canal narrows and squeezes this sac, it causes many symptoms of spinal stenosis. Spinal stenosis.
- Exiting Nerve Roots
- These are the nerves branching off and leaving the spine through small side openings (foramina) on their way to your legs. Pinching of an exiting nerve root is a classic cause of sciatica — pain, numbness, or weakness down the leg. Sciatica.
- Facet Joints
- The small paired joints at the back of each spinal segment that let you bend and twist. Like any joint, they can develop arthritis — a common source of back pain, and when they enlarge they can help narrow the spinal canal. Degenerative changes.
- Ligamentum Flavum
- A ligament lining the back of the spinal canal. As it thickens with age, it takes up space inside the canal and squeezes the nerves — one of the main causes of spinal stenosis. Spinal stenosis.
- Paraspinal Muscles
- The strong muscles running alongside your spine that support your posture and movement. Protecting these muscles is a key goal of minimally invasive surgery, which works between them instead of cutting through them. Minimally invasive surgery.
Sagittal MRI — Lumbosacral Spine
A side view of the spine, from L1 down through the sacrum.
- Vertebral Bodies (L1–L5)
- The stacked blocks of bone that form the spinal column and carry most of your weight. They are labeled L1 through L5 from top to bottom. When one slips forward over another, it is called spondylolisthesis.
- Intervertebral Discs
- The cushions between the vertebral bodies. From the side you can see their height and whether any are worn or bulging. On this T2 MRI, healthy discs hold water and look brighter; degenerated discs look dark. Degenerative disc disease.
- Sacrum (S1)
- The triangular bone just below L5 that joins the spine to the pelvis. The lowest disc, L5–S1, is one of the most common sites of a herniated disc and sciatica. Sciatica.
- Coccyx
- The tailbone — the small fused segments at the very bottom of the spine, below the sacrum.
- Conus Medullaris
- The tapered lower end of the spinal cord itself, usually finishing around the L1–L2 level. Below this point, the spinal canal carries a bundle of nerve roots rather than the cord.
- Cauda Equina
- Latin for “horse’s tail.” Below the spinal cord, the nerve roots fan out and float in spinal fluid on their way to the legs, bladder, and bowel. Sudden compression here (cauda equina syndrome) is a rare emergency — seek care or call 911 for new severe weakness or loss of bladder or bowel control. Spinal stenosis.
- Thecal Sac
- The fluid-filled sac (dural sac) that surrounds and protects the cauda equina nerves. It looks bright on this T2 MRI. Narrowing that pinches this sac is what produces many spinal stenosis symptoms. Spinal stenosis.
- Ligamentum Flavum
- A ligament between the laminae at the back of the spinal canal (highlighted green). When it thickens with age it bulges inward and squeezes the nerves — a leading cause of spinal stenosis. Spinal stenosis.
- Anterior Longitudinal Ligament
- A strong ligament (highlighted blue) running down the front of the vertebral bodies. It stabilizes the spine and limits backward bending.
- Posterior Longitudinal Ligament
- A ligament (highlighted orange) running along the back of the vertebral bodies, just in front of the spinal canal. It helps hold the discs in place. Herniated disc.
Your next step
Discuss your spine care with Dr. Hobbs
Jonathan G. Hobbs, M.D. is a board-certified neurosurgeon at Lakeshore Bone & Joint Institute. For questions about understand your lumbar mri, call the office to arrange an individual evaluation and discuss which options may be appropriate.
Consultation offices: Crown Point, Chesterton. Your symptoms, examination, imaging, and prior treatment help guide the discussion.