The sphenopalatine ganglion (SPG) is a large extracranial structure that has rich sympathetic and parasympathetic autonomic innervations, which explains the autonomic features associated with cluster headache. Cluster headache involves activation of the parasympathetic outflow from the superior salivary nucleus of the facial nerve, predominantly through the SPG.1
SPG block and radiofrequency ablation (RFA) are indicated in the management of intractable medically resistant cluster headaches, migraine, and other trigeminal autonomic cephalalgias.
Intractable orofacial pain syndromes (eg, 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 radiofrequency ablation (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 the 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 pterygopalatine fossa 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, medially by the perpendicular plate of the palatine bone, and 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 (Table 18-1).