Tarsal tunnel

What it means

The tarsal tunnel is a narrow channel on the inside of the ankle, just below and behind the bony bump you can feel there (the medial malleolus). It is formed on one side by ankle bones and on the other by a tough band of connective tissue called the flexor retinaculum, which stretches over the top like a roof. Passing through this tunnel are the posterior tibial nerve, an artery and vein, and several tendons that help move the foot and toes. It is the ankle's equivalent of the wrist's carpal tunnel, and it exists mainly to keep these structures bundled together and protected as they curve around the ankle into the sole of the foot.

Why it appears on a CT or MRI report

The tarsal tunnel is normal anatomy, so it is usually named simply as a landmark when a radiologist is describing what runs through it or what sits nearby. MRI is the best way to evaluate this region because it shows nerves, tendons, and soft tissue in detail that CT and X-ray cannot. A report may mention the tarsal tunnel when noting swelling of the posterior tibial nerve, a cyst or mass narrowing the space, tendon inflammation, varicose veins within the tunnel, or thickening of the flexor retinaculum. It can also appear in a normal report simply to confirm the area was checked and looks unremarkable.

What it usually means

On its own, a mention of the tarsal tunnel is not a diagnosis — it is a location. What matters is whether anything is compressing or irritating the nerve as it passes through. When something does narrow the space, such as a small cyst, swollen tendon sheath, bony spur, or generalized swelling from flat feet or an old ankle injury, the posterior tibial nerve can become squeezed, a condition called tarsal tunnel syndrome. This can cause burning, tingling, numbness, or shooting pain on the inside of the ankle and sole of the foot, sometimes worse with standing or walking. Many cases are mild and respond well to conservative measures such as rest, supportive footwear or orthotics, and anti-inflammatory treatment, while a smaller number benefit from an injection or surgery to relieve pressure on the nerve.

When to follow up

If you have burning, tingling, numbness, or pain on the inner ankle or in the sole of the foot, especially if it worsens with activity or at night, mention this to your doctor so they can examine the area and correlate it with the imaging. They may also recommend a nerve conduction study to measure how well the posterior tibial nerve is functioning. Sudden, severe weakness, significant loss of sensation, or foot symptoms following a recent injury deserve prompt medical attention.

A plain-language way to picture it

Think of the tarsal tunnel as a short tunnel under a bridge, with a bundle of cables (the nerve, blood vessels, and tendons) running through it. As long as the tunnel stays roomy, everything passes through freely. But if something inside the tunnel swells or a growth crowds the space, the cables get pinched against the tunnel wall — and the nerve, being the most sensitive cable in the bundle, is usually the first to complain, sending tingling or burning signals down into the foot.