**Core Concept**
The subarachnoid space is the region between the arachnoid mater and the pia mater, two of the three meningeal layers surrounding the brain and spinal cord. This space contains cerebrospinal fluid (CSF) and is the site for various diagnostic and therapeutic interventions, including myelography.

**Why the Correct Answer is Right**
Myelography is a radiographic technique used to visualize the spinal cord and nerve roots. The procedure involves injecting a water-soluble contrast agent into the subarachnoid space, where it spreads along the spinal cord and nerve roots, allowing for detailed imaging of these structures. This is particularly useful for diagnosing conditions such as herniated discs, spinal stenosis, and nerve compression syndromes. The contrast agent used in myelography is typically a non-ionic iodinated compound that is well-tolerated and does not cause significant irritation to the subarachnoid space.

**Why Each Wrong Option is Incorrect**
**Option A:** The subdural space is the region between the dura mater and the arachnoid mater, and it is not typically used for myelography due to the risk of bleeding and the potential for the contrast agent to be absorbed into the bloodstream.
**Option B:** The epidural space is the region between the dura mater and the vertebral column, and while it is sometimes used for diagnostic and therapeutic interventions, it is not the preferred site for myelography.
**Option D:** The extradural space is another term for the epidural space, and as mentioned earlier, it is not the preferred site for myelography.

**Clinical Pearl / High-Yield Fact**
It is essential to note that myelography is typically performed under fluoroscopic guidance, and the patient is usually positioned in a prone or lateral decubitus position to allow for optimal visualization of the spinal cord and nerve roots.

**Correct Answer:**
✓ Correct Answer: C. Subarachnoid