**Core Concept**
Spinal cord tumors can be primary or metastatic, and their investigation requires a combination of imaging and clinical evaluation. The first investigation of choice should ideally provide a detailed anatomical assessment of the spinal cord and surrounding structures.

**Why the Correct Answer is Right**
The first investigation of choice for spinal cord tumors is MRI (Magnetic Resonance Imaging) due to its high sensitivity and specificity in detecting spinal cord lesions. MRI provides excellent soft tissue contrast, allowing for the differentiation of various types of tumors, such as gliomas, meningiomas, and metastatic lesions. Additionally, MRI can assess the spinal cord's anatomy, including its size, signal intensity, and any associated cord compression or syrinx formation.

**Why Each Wrong Option is Incorrect**
**Option A:** CT (Computed Tomography) scans may be useful in detecting bony lesions or calcifications but lack the soft tissue contrast necessary for evaluating spinal cord tumors.
**Option B:** Plain X-rays are generally not useful for detecting spinal cord tumors, as they cannot provide sufficient detail of the soft tissues.
**Option C:** Myelography involves injecting a contrast agent into the spinal canal and taking X-rays, which can be useful in detecting cord compression or blockage but does not provide detailed anatomical information.

**Clinical Pearl / High-Yield Fact**
MRI is the investigation of choice for spinal cord tumors due to its non-invasive nature, lack of ionizing radiation, and excellent soft tissue contrast, allowing for accurate diagnosis and preoperative planning.

**Correct Answer: C. Myelography.**