What does it mean on MRI Heterogeneous increased T2 signal intensity seen at the C7 level of the cervical cord is likely artifactual as corresponding signal abnormality not confirmed on sagittal T2?

It means that initially the radiologist saw a lesion at the spinal cord (at the last cervical vertebrae - C7), but when he looked to confirm it from another plane, it was not there so he concluded that it was an artifact. MRI artifacts are shadows, lesions, lines that appear on images but they don't have anatomical correspondence. Most of the are cause by blood flow, spinal fluid flow, patient movement, hardware problems, and many other reasons.