Ultrasound grading of thyroid nodules suggests a grade 4b, indicating a 5% to 50% chance of malignancy. In other words, most thyroid nodules with a grade 4b classification are benign disease, while a small percentage are malignant. Ultrasound imaging of thyroid nodules is divided into grades 1-5 based on whether the nodules have clear borders, rich blood supply, and whether they are accompanied by calcification or have a longitudinal to transverse diameter ratio of more than 1. Generally speaking, grade 4 is divided into grades 4a, 4b, and 4c. -Therefore, most grade 4b thyroid nodules are benign nodules.