<prompt> Most sensitive investigation for preoperative localization of abnormal parathyroid glands isNeck ultrasound99mTc labelled Sestamibi isotope scanCT scanMRI  <response>: Neck ultrasound locates glands in approximately 75 of cases. 99mTc labelled Sestamibi isotope scans identify approximately 80 of abnormal parathyroid glands.CT MRI is not indicated prior to first-time neck exploration. 