**Core Concept**
The question tests the knowledge of the anatomical classification of spinal tumors, specifically their relationship with the dura mater and the spinal cord. Intradural extramedullary tumors arise from the meninges or the spinal nerves, while intramedullary tumors originate from the spinal cord itself.

**Why the Correct Answer is Right**
Intradural extramedullary tumors are the most common type of primary spinal tumor. These tumors arise from the meninges or the spinal nerves and are located within the dural sac but outside the spinal cord. Examples of intradural extramedullary tumors include meningiomas, nerve sheath tumors (schwannomas and neurofibromas), and arachnoid cysts. The correct classification is crucial for surgical planning and approach.

**Why Each Wrong Option is Incorrect**
**Option A:** Intramedullary extradural tumors do not exist as a distinct category, as intramedullary tumors are by definition located within the spinal cord, and extradural spaces are outside the dura mater.

**Option B:** While intramedullary tumors are a significant type of primary spinal tumor, they are less common than intradural extramedullary tumors.

**Option D:** Intra-axially only is not a valid classification for spinal tumors, as the term "intra-axial" typically refers to intracranial pathology.

**Clinical Pearl / High-Yield Fact**
Meningiomas, a type of intradural extramedullary tumor, are the most common primary spinal tumor in adults, accounting for approximately 25% of all spinal tumors. They are often slow-growing and can cause symptoms due to compression of the spinal cord or nerves.

**✓ Correct Answer: C. Intradural; Extramedullary**