Size. If it's small and centrally located, you might not feel it. Ultrasound is the best way to "pick up" or detect these small nodules.
Size and Location. For a nodule to be palpable (able to be felt on a neck exam), three conditions must be met. 1. The nodule must be large enough to cause a bulge (1 CM or 0.4 inch). 2. The nodule must be in a location on the thyroid (front surface) that can be felt. 3. The person examining the neck must know where to feel, and what they are feeling for. If your doctor can feel it, he can help you feel it.
Nodules. Small nodules are usually not felt. Small nodules are common, and often never diagnosed. In patients with thick, muscular or obese necks, nodules can, in fact, be fairly big without notice.