Question: How should I code a left GON block? Washington Subscriber Answer: Use 64405 (Injection, anesthetic agent; greater occipital nerve) and modifier LT (Left) to report the unilateral greater occipital nerve (GON) block. Neurologists often use occipital nerve blocks for patients with 723.8 (Occipital neuralgia). This condition produces an aching, burning, or throbbing pain, or a tingling or numbness, along the back of the head. The GON originates from the C2 spinal nerve and provides sensory innervation to the back of the scalp extending to the top of the head. Your neurologist will typically inject the GON just above the base of the skull for occipital or cervicogenic headaches or neck pain. Tip: Your neurologist should clearly indicate the injection location in his documentation. In fact, some providers include in their documentation a small illustration that can be marked with the various injection sites. You can then ensure that you're choosing the correct nerve block code each time.