Anatomy

The SPG is the largest extracranial parasympathetic ganglion in the body making it a complex routing center with connections to the trigeminal, facial, and sympathetic systems. It is comprised of somatosensory, sympathetic, and parasympathetic fibers and receives sensory, motor and sympathetic input. Only preganglionic parasympathetic fibers synapse in the ganglion hence its labeling as parasympathetic. Sensory and sympathetic fibers pass through the ganglion but never synapse. The sympathetic component of the SPG comes from post-ganglionic sympathetic fibers originating in the superior cervical sympathetic ganglion. These fibers form the deep petrosal nerve and join the parasympathetic fibers in the Vidian nerve before passing through the SPG. These nerves terminate in the lacrimal gland and nasal palatine mucosa. The parasympathetic portion of the SPG begins in the superior salivatory nucleus. This is the nervus intermedius which is part of the facial nerve. The facial nerve forms the greater petrosal nerve which finally enters the SPG as the Vidian nerve. The parasympathetic fibers provide secretomotor function to various mucous membranes including the nose, mouth, lacrimal gland, and pharynx. The SPG is a small triangular-shaped mass near the sphenopalatine foramen. It is located posterior to the middle turbinate and maxillary sinus, inferior to the sphenoid sinus, anterior to the medial pterygoid plate and lateral to the palatine bone. It resides in the pterygopalatine fossa that is formed from the aforementioned bony anatomy. The pterygomaxillary fissure is the entrance to the pterygopalatine fossa (Figure 16.1). The foramen rotundum is located superolateral and the pterygoid canal inferomedial in the posterior aspect of the pterygopalatine fossa. The SPG is situated 2–7 mm lateral to the lateral nasal mucosa. The sensory root comes from two pterygopalatine branches of the maxillary nerve that pass through the SPG and form the greater and lesser palatine nerves. The sensory distribution is to the nose, throat, and sinuses. The motor fibers are derived from the nervus intermedius through the greater superficial petrosal nerve and synapse with neurons distributed with deep branches of the trigeminal nerve.

Knowing the vasculature of the pterygopalatine fossa (PPF) is of great importance as hematoma formation from any puncture of the maxillary artery is a possibility with this procedure. The maxillary artery is the terminal branch of the external carotid artery and, in the PPF, it splits into multiple branches which include the sphenopalatine artery, descending palatine artery, infraorbital artery, and posterior superior alveolar artery. There is a large venous plexus overlying the PPF and this can be a source of bleeding along with the maxillary artery [3–7].

Intranasal Topical Application

This approach is a very simple technique that causes little pain or tissue trauma and is tolerated well by the patient. It can be safely executed in the office setting. Local anesthetic (2% lidocaine, 0.25% bupivacaine, or 4% cocaine) is applied to the nasopharyngeal mucosa posterior to the middle turbinate usually with a cotton tip applicator. The close proximity of the ganglion to this area allows for absorption of local anesthetic from the nare. Intranasal catheters and cotton applicators are used to increase patient comfort. Pretreatment of the nare with a vasoconstrictor such as phenylephrine can be performed to decrease the risk of bleeding. Although diffusion of local anesthetic to the SPG can be unpredictable, this route should be trialed first before subjecting the patient to more invasive approaches [8]. Estimation of the depth of insertion can be done by measuring the distance from the nare opening to the mandibular notch. The applicator can be marked with this distance so you do not go too deep in the nare. After soaking the applicator with local anesthetic for several minutes, the applicator is advanced in a line parallel to the zygoma while being angled laterally. A second applicator may be inserted if room permits. The applicator is usually left in situ for 30 to 45 minutes with signs of a successful procedure being ipsilateral tearing, conjunctival injection, and nasal congestion [9]. If there is no pain relief with this procedure, it is possible the applicator is placed too shallow or too deep with the local anesthetic not reaching the SPG [7], or the SPG is not involved in pain transmission. If the intranasal block does not provide relief, these authors would proceed with the infrazygomatic technique.

Greater Palatine Foramen Approach

This approach was commonly deployed by dentists where injection was through the greater palatine foramen with a curved dental needle. The needle was passed through the posterior portion of the hard palate just medial to the gum line at a location opposite the third molar. This will reach the superior aspect of the PGF near the maxillary nerve. This a very painful procedure for the patient and frequently results in hematoma formation because of the proximity to the maxillary artery. This technique can result in inadvertent injury to the infraorbital or orbital nerves [8].

Infrazygomatic Arch Approach

For this approach, fluoroscopic guidance is used to guide direct placement of local anesthetic into the superior portion of the PPF. It has been performed blindly in the past but fluoroscopic guidance is now recommended. This technique takes out reliance on spread across mucous membrane and bone to take effect. This approach is the most often used for neurolytic procedures including radiofrequency (RF) thermocoagulation [8]. Monitoring of vital signs with ASA standard monitors is recommended and sedation may be necessary. A lateral fluoroscopic image is obtained and the mandibular notch is identified. The right and left PPFs are aligned and the skin is anesthetized (Figure 16.2

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