I have a tiny hypoechoic nodule in isthmus measuring 8.5-5.9mm .is it a colloid nodule ?

Do not know: You need to discuss the possibilities with your doctor. Please review the radiologist's ultrasound report as well. Given its size, it may be something to follow up on, since biopsy may be difficult (if even necessary depending on us appearance).

Follow your doctors: Advice , yes it could be a colloid nodule, most likely your doctor will observe , or later if size increases may do fna ( fine needle aspiration biopsy ) to make sure it not malignant