Cluster headache involves activation of the parasympathetic outflow from the superior salivary nucleus of the facial nerve, predominantly through the sphenopalatine ganglion (SPG).¹ The SPG is a large extracranial structure that has rich autonomic innervation (both sympathetic and parasympathetic), which explains the autonomic features associated with cluster headache. SPG block and radiofrequency ablation (RFA) are indicated in the management of intractable medically-resistant cluster headaches, migraines, and other trigeminal autonomic cephalalgias, and intractable orofacial pain syndromes after exhausting other conservative treatment options (e.g., persistent idiopathic facial pain, “atypical facial pain”).

Sphenopalatine Ganglion Neuroanatomy

The SPG has rich parasympathetic (preganglionic axons and postganglionic cell bodies and axons) and sympathetic (postganglionic axons) components. The parasympathetic preganglionic cell bodies projecting to the SPG originate in the superior salivatory nucleus (SSN) of the facial nerve in the pons.

The efferent fibers of the SSN travel in the nervus intermedius and divide at the geniculate ganglion to become the greater petrosal nerve and chorda tympani nerve. The first-order parasympathetic neurons in the greater petrosal nerve are joined by the postganglionic sympathetic fibers from the deep petrosal nerve, forming the nerve to the pterygoid canal (vidian nerve). The preganglionic parasympathetic neurons then synapse with the second-order parasympathetic neuronal cell bodies located in the SPG.

The postganglionic parasympathetic fibers then run with branches of the maxillary nerve (V2) to reach their targets. Therefore, the only cell bodies located within the SPG are those of the second-order postganglionic parasympathetic neurons, which may explain the clinical observation that patients after RFA of the SPG usually notice improvement of the autonomic parasympathetic symptoms either earlier or even without improvement of the headache pain.

The sympathetic cell bodies projecting to the SPG originate in the upper thoracic spinal cord (T1-T2). The preganglionic sympathetic neurons then synapse in the cervical sympathetic ganglia, mainly the superior cervical ganglion. The postganglionic second-order sympathetic neurons form the carotid sympathetic plexus and reach the pterygoid canal through the deep petrosal nerve, where it joins the first-order parasympathetic neurons in the greater petrosal nerve, forming the nerve to the pterygoid canal (vidian nerve). Postganglionic sympathetic fibers pass through the SPG without synapsing and innervate mainly blood vessels.

Sphenopalatine Ganglion Anatomy

The SPG is located in the pterygopalatine fossa (PPF), which is a small, upside-down pyramidal space 2 cm high and 1 cm wide. The PPF is located behind the posterior wall of the maxillary sinus and is bordered posteriorly by the medial plate of the pterygoid process, superiorly by the sphenoid sinus, and medially by the perpendicular plate of the palatine bone; laterally, it communicates with the infratemporal fossa. Superolaterally lies the foramen rotundum with the exiting maxillary nerve, and inferomedially, there is the vidian nerve (greater petrosal and deep petrosal nerves) within the pterygoid canal. The PPF contains the internal maxillary artery and its branches, the maxillary nerve, and the SPG and its afferent and efferent branches. The SPG is located posterior to the middle turbinate and is a few millimeters deep to the lateral nasal mucosa. It is suspended from the maxillary nerve by the pterygopalatine nerves; inferiorly, it is connected to the greater and lesser palatine nerves; and posteriorly, it is connected to the vidian nerve. Efferent branches of the SPG form the posterior lateral nasal and pharyngeal nerves.^2,³

Approaches to the Sphenopalatine Ganglion

The unique location of the SPG within the PPF, just posterior to the middle turbinate, makes it accessible transnasally as well as with the infrazygomatic approach.

(Reproduced with permission from the Ohio Pain and Headache Institute.)

Coronoid Approach

The needle entry is through the coronoid notch of the mandible. The needle is usually advanced to target the lateral pterygoid plate first and then walked off the bone interiorly to enter the PPF. By that time, the needle usually acquires certain direction, and it is hard to manipulate the needle after it is inside the fossa (Fig. 5-2).

Fig. 5-2 Sphenopalatine ganglion block with the coronoid approach.

(Reproduced with permission from the Ohio Pain and Headache Institute.)

Technique of Sphenopalatine Ganglion Block (Infrazygomatic Approach)

With the patient in the supine position and the head inside the C-arm, a lateral view is obtained and either the C-arm or the head of the patient is rotated until both pterygoid plates are superimposed on each other to better visualize the PPF. The skin entry site overlying the fossa is marked just inferior to the zygomatic arch either anterior to the mandible or through the coronoid notch. A 22-gauge, 3.5-inch blunt needle with a slight bend at the tip is used. The needle is first introduced in the lateral view and advanced medially and superiorly toward the PPF using real-time fluoroscopy. When in a proper direction, an anteroposterior (AP) view is obtained, and the tip of the needle is advanced to be just lateral to the nasal wall (Fig. 5-3). If the lateral pterygoid plate is encountered, the needle should be walked off the bone anteriorly and cephalad to slip into the fossa (the curved tip will help to guide the needle). A total of 0.1 to 0.2 mL of contrast agent is injected under real-time fluoroscopy to rule out intravascular spread because the PPF contains the maxillary artery and its branches (mainly the sphenopalatine artery). After negative aspiration of blood or air (the needle tip is too advanced into the nasal cavity or the maxillary sinus), 1 to 2 mL of 0.5% bupivacaine with or without steroids is injected slowly.

Fig. 5-3 Anteroposterior view showing the needle tip just lateral to the nasal wall. The contrast agent is delineating the pterygopalatine fossa.

(Reproduced with permission from the Ohio Pain and Headache Institute.)

Radiofrequency Ablation Technique

With the patient in the supine position and the head inside the C-arm, a lateral view is obtained and either the C-arm or the head of the patient is rotated until both pterygoid plates are superimposed on each other to better visualize the PPF. The skin entry site overlying the fossa is marked just inferior to the zygomatic arch either anterior to the mandible or through the coronoid notch. A 22-gauge, 10-cm, blunt RFA needle with a 2- or 5-mm active tip with a slight bend at the tip is used (Fig. 5-4). The needle is first introduced in the lateral view and advanced medially and superiorly toward the PPF using real-time fluoroscopy. When in a proper direction, an AP view is obtained, and the tip of the needle is advanced to be just lateral to the nasal wall. If the lateral pterygoid plate is encountered, the needle should be walked off the bone anteriorly and cephalad to slip into the fossa (the curved tip will help to guide the needle). Sensory stimulation is obtained with 50 Hz to look for deep paresthesias behind the root of the nose at less than 0.5 V (Table 5-1). After proper stimulation is achieved and before lesioning, 0.1 to 0.2 mL of contrast agent is injected under real-time fluoroscopy to rule out intravascular spread. Then 0.5 mL of lidocaine 2% is injected, and two radiofrequency lesions are carried out at 80° C for 60 seconds each. After lesioning, 0.5 mL of bupivacaine 0.5% and 5 mg of triamcinolone is injected with the aim of preventing postprocedure neuritis.⁸

Fig. 5-4 Lateral view showing the RFA needle inside the pterygopalatine fossa (PPF). Note that the tip is curved downward to avoid lesioning of the maxillary nerve, which runs at the roof of the PPF.

(Reproduced with permission from the Ohio Pain and Headache Institute.)

Table 5-1 Possible Scenarios of Stimulation before Attempting Radiofrequency Thermocoagulation of the Sphenopalatine Ganglion

Efficacy of Sphenopalatine Ganglion Radiofrequency Ablation

In a retrospective analysis of patients with refractory cluster headache treated by RFA of the SPG, 56 patients with episodic cluster headache and 10 patients with chronic cluster headache were followed over a period of 12 to 70 months.⁵ In the episodic cluster headache group, 60.7% experienced complete pain relief, but only three of 10 patients with chronic cluster headache had the same result. This report showed that RFA of the PPG may improve episodic cluster headache but not chronic cluster headache. Recently, however, Narouze and colleagues⁸ reported a favorable outcome after intractable chronic cluster headache as well. They reported significant improvement in both mean attack intensity and mean attack frequency for up to 18 months in 15 patients. Of these patients, 20% (three of 15) reported no change or increase in the headache intensity or frequency during the first few postprocedure weeks before noticing improvements in their headache pattern. However, 46.7% (seven of 15) of the patients reported a change in the headache pattern with return to the episodic form of cluster headache at a mean follow-up period of 18 months. Three patients remained headache free and off medications for the duration of the follow-up (18 to 24 months).

Two patients reported complete relief of their usual unilateral headache symptoms, and instead they developed episodic cluster headache on the contralateral side.⁸