Hello and welcome to HCM, The bones of the spine - which are called vertebrae and their processes create a spinal canal - which is like a tube going down from the lower part of the head all the way down to the back of the pelvis. Inside of the spinal canal there runs a spinal cord which is a structure made of nervous tissue. A disc is a small structure between your vertebral bodies - like a cushion. Sometimes a disc can slip out of its usual place - due to injury or for other reasons. This is also called disc herniation or disc protrusion. A herniated disc presses on the spinal cord inside of the spinal canal. Because the size of the canal is now smaller due to the protruding disc inside the spinal canal - this is what is called the canal compromise . Myelomalacia means that your spinal cord - the nervous tissue is damaged - the location of the damage at c4/5 means that it is in your cervical spine at the level between 4th and 5th cervical vertebrea - which is your neck area. You probably saw the neurosurgeon because you were having some symptoms in your arms like tingling /numbness or even weakness - perhaps dropping objects from your hands. Myelomalacia is a serious medical condition and you should contact your surgeon as soon as possible. Hope I answered your question. Regards and best of health.