CPT code 64405 describes the clinical procedure wherein a physician or other qualified healthcare professional administers an injection consisting of an anesthetic agent, a corticosteroid, or a combination of both into the region of the greater occipital nerve. The greater occipital nerve is a major peripheral nerve arising from the posterior primary ramus of the second cervical nerve, commonly referred to as C2. It provides vital sensory innervation to the posterior scalp, extending upwards to the vertex of the skull. This specific injection procedure is primarily performed to diagnose and manage acute or chronic conditions such as occipital neuralgia, tension-type headaches, cervicogenic headaches, and certain refractory types of migraines that have not responded adequately to conservative medical management. The injection serves a crucial dual purpose in clinical practice. Diagnostically, it helps confirm that the greater occipital nerve is indeed the primary source of the patient's pain, particularly if immediate subjective relief is achieved following the administration of the local anesthetic. Therapeutically, it aims to provide prolonged pain relief and reduce regional inflammation through the sustained anti-inflammatory action of the injected corticosteroid alongside the temporary nerve-blocking effect of the anesthetic. During the execution of the procedure, the patient is typically positioned either sitting up or lying prone, depending on the provider's preference and patient comfort. The physician carefully palpates the occipital artery and the superior nuchal line to identify the precise injection landmark, which is usually located approximately one-third of the anatomical distance from the external occipital protuberance to the mastoid process. After thoroughly preparing the overlying skin with an appropriate antiseptic solution, a needle is precisely inserted into the targeted subcutaneous area, and the medicinal mixture is carefully infiltrated around the nerve structure. The healthcare provider must exercise meticulous anatomical caution to avoid injecting the medication directly into the adjacent occipital artery or vein, which could lead to systemic toxicity. Following the completion of the injection, firm localized pressure is applied to the site to achieve hemostasis, and the patient is closely observed for a brief period to monitor for any immediate adverse reactions or complications, such as localized bleeding, hematoma formation, or allergic reactions. This highly effective, minimally invasive technique remains an essential and widely utilized therapeutic tool within the comprehensive interventional pain management algorithm for debilitating and refractory head and neck pain.