The sphenopalatine ganglion (SPG) is associated with the trigeminal nerve, the major nerve involved in headache (HA) disorders (see Figure 1).1 The mechanism behind migraines is not fully understood, but it’s thought that blocking the SPG may help relieve migraine pain.1,2
The SPG is the main source of cranial and facial parasympathetic innervation. The autonomic nerves of the SPG supply the lacrimal glands, which produce tears, as well as the sinuses, which can produce the nasal discharge or congestion associated with some migraines.2-4
SPG’s Role in Headaches
When a headache occurs, meninges inflammation activates pain receptors. These receptors send pain impulses through the trigeminal nerve, which then sends a signal to the brain that is perceived as pain. In cluster and migraine HA, pain signals pass through the SPG, connecting with autonomic nerves, which produce eye tearing or nasal discharge. This is called the trigeminal autonomic reflex.3,4
During a migraine, parasympathetic outflow from the SPG causes vasodilation of cranial blood vessels. This dilation allows for inflammatory mediators to activate meningeal nociceptors, which are responsible for the migraine pain. It’s theorized that a patient who experiences parasympathetic symptoms during migraines (eg, nausea, emesis, sweating, lacrimation, etc.) may benefit from SPG blocking because the SPG propagates these parasympathetic signals.3,4
A prospective, randomized and double-blinded placebo-controlled study published in JAMA in 1996 showed potential benefit for using intranasal lidocaine when compared with saline alone.5 The study included a total of 81 patients with a chief complaint of headache who fulfilled criteria for International Headache Society. The primary outcome measure found at least a 50 percent reduction of headache within 15 minutes of treatment. Fifty-five percent of patients had at least a 50 percent reduction of headache compared with 21 percent of patients in the control group, and nausea and photophobia were significantly reduced. Rescue medication for headache relief was needed in 28 percent of patients in the lidocaine group versus 71 percent of patients in the control group. Of those patients who showed initial improvement, only 42 percent relapsed versus 83 percent in the control group.
How to Perform an SPG Nerve Block
The SPG can be locally accessed by several approaches, but for the purposes of quick and easy access in the ED setting, the transnasal approach is best.3 The materials needed include:
- Cotton-tip applicator, 10 cm long
- Anesthetic of your choice:
- Lidocaine 1%, 2%, or 4% (onset 15 minutes, duration of action 30 minutes to 2 hours)6
- Bupivacaine 0.25% or 0.5% (onset 10–20 minutes, duration of action 2–4 hours)6
- 5 mL syringe and large bore needle to draw up the anesthetic
- Plastic pill cup or any small container that can hold the anesthetic with enough depth to fully submerge the cotton-tip applicator
- Atomizer (optional).
- Have the patient lie in a supine position with the head tilted up in a sniffing position.
- Make sure the patient is on a cardiac monitor. Even though you are using less than the toxic dose, you are administering anesthetic over a highly vascular area.
- Anesthetize the nasal passage entry by one of two ways (optional):
- Inject 0.5 mL of 2% viscous lidocaine into each nostril with the open end of a 3 mL syringe (without needle). Have the patient sniff to draw the anesthetic posteriorly.
- Use an atomizer to draw up 1 mL of 1% lidocaine per naris and aerosolize into each naris. Remember, you can administer a maximum of 1 mL per naris.
- Soak one or two cotton-tip applicators in the anesthetic of your choice. If you are pre-anesthetizing the nasal passage, we recommend using only 1% or 2% lidocaine to soak the applicators, the goal being to remain well below the toxic dose.
- Advance one cotton-tip applicator along the superior border of the middle turbinate of each nostril until the tip contacts the mucosa overlying the SPG (see Figure 2).
- Leave the applicators in for 10 minutes or until the patient feels relief, then gently remove the applicators.3,7
Make sure you inform patients of the possible side effects so they know what to expect, including:
- Bitter taste from the anesthetic
- Local trauma causing epistaxis
- Numbness in the posterior pharynx4
SPG nerve blocks are a quick and non-invasive way to treat primary headaches that do not require IV placement. Such blocks may be a good option for patients who feature difficult IV access.3