**Core Concept**
Spinal cord edema refers to the swelling of the spinal cord, which can be caused by various conditions including ischemia, trauma, or infection. In the context of magnetic resonance imaging (MRI), spinal cord edema can manifest as increased signal intensity on T2-weighted images, indicating fluid accumulation within the cord.

**Why the Correct Answer is Right**
Spinal cord infarctions, also known as spinal cord strokes, occur when the blood supply to the spinal cord is interrupted, leading to ischemia and subsequent edema. This can result from a variety of causes, including atherosclerosis, vasculitis, or trauma. On MRI, spinal cord infarctions are characterized by hyperintensity on T2-weighted images due to the accumulation of edema fluid within the cord. The increased signal intensity is often seen in the posterior and lateral columns of the cord, which are supplied by the anterior spinal artery. The edema can also lead to cord expansion and compression of the surrounding structures.

**Why Each Wrong Option is Incorrect**
**Option A:** Myelodysplasia refers to congenital anomalies of the spinal cord, such as spina bifida or tethered cord syndrome. While these conditions can cause changes in the spinal cord, they do not typically result in edema.

**Option C:** Myeloschisis is a rare congenital anomaly characterized by a cleft or split in the spinal cord. While it can cause changes in the cord, it is not typically associated with edema.

**Option D:** Cord tumors, such as gliomas or meningiomas, can cause changes in the spinal cord, including edema. However, the edema associated with tumors is typically more heterogeneous and may not be as uniform as that seen in spinal cord infarctions.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that spinal cord infarctions can present with a wide range of symptoms, from mild weakness to complete paralysis. A high index of suspicion is necessary to diagnose spinal cord infarctions, particularly in patients with underlying vascular disease or a history of trauma.

**✓ Correct Answer: B. Spinal cord infarctions**