Sphenopalatine Ganglion Block

Anatomy and Physiology

The SPG is an extracranial parasympathetic ganglion located within the pterygopalatine fossa. The borders of the pterygopalatine fossa are as follows: (1) anterior border - posterior wall of the maxillary sinus, (2) posterior border - medial pterygoid plate, (3) superior border - sphenoid sinus, (4) medial border - a perpendicular plate of the palatine bone, and (5) lateral border - communicates with the infratemporal fossa. It lies posterior to the middle nasal turbinate and maxillary sinus, forming multiple autonomic, sensory, and motor neural connections.[2]

Sensory Innervation

The maxillary branch of the trigeminal nerve passes through the foramen rotundum, which is located along the superolateral aspect of the pterygopalatine fossa. The SPG is suspended from the maxillary nerve via the pterygopalatine nerves. Sensory fibers arising from the maxillary nerve travel through the SPG, providing sensory innervation to the nasal membranes, soft palate, and parts of the pharynx.[3] 

Autonomic Innervation

Sympathetic innervation through the SPG originates from preganglionic sympathetic fibers in the upper thoracic spine, which course through the sympathetic chain and synapse with postganglionic fibers in the superior cervical sympathetic ganglion. Postganglionic fibers join the carotid nerves, branch off, and travel through the deep petrosal and vidian nerves. These postganglionic fibers course through the SPG to the lacrimal gland, nasal mucosa, and palatine mucosa. Parasympathetic innervation through the SPG originates in the superior salivatory nucleus in the pons. Parasympathetic fibers run in the nervus intermedius, a branch of the facial nerve, through the geniculate ganglion to form the greater petrosal nerve. Parasympathetic fibers synapse in the SPG. Second-order neurons then provide a secretomotor function to the nasal, oral, and pharyngeal mucous membranes, the lacrimal glands, and branches to the meningeal and cerebral blood vessels.[4] The postganglionic sympathetic fibers projecting from the superior cervical ganglion give rise to the deep petrosal nerve. The vidian nerve is formed when the deep petrosal nerve joins the greater petrosal nerve before passing through the pterygoid canal near the fossa's inferomedial portion. The SPG gives off efferent branches to form the superior posterior lateral nasal and pharyngeal nerves. The SPG has direct connections with the greater and lesser palatine nerves. 

Contraindications

Contraindications to SPG block include allergy to any of the medications used, anticoagulation, history of facial trauma, infection, and patient refusal.

Equipment

The pharmacologic agents frequently used for SPG block are local anesthetics (4% cocaine, 2% to 4% lidocaine, or 0.5% bupivacaine), depot steroids, or 6% phenol.[2][5] For the intranasal approach, a cotton tip applicator or catheter is needed. There are 3 approved SPGB devices. There is a void in the literature regarding the efficacy and tolerability of the 2. These catheters are both inserted along the anterior nasal passage and are placed superior to the middle nasal turbinate.[3] They comprise a flexible sheath with an inner, extendible catheter with a curved tip.[3] The Tx360 device is inserted and advanced inferior to the middle nasal turbinate.[3][6][7] The catheter tip is medial, inferior, and posterior to the target mucosa.[8] The opening of the catheter tip is designed to direct anesthetic in a superior, lateral, and anterior direction.[8] A 10 cm curved blunt 20- or 22 gauge needle is preferred for the infra-zygomatic approach. Alternatively, a 22 or 25-gauge 3.5-inch short-bevel needle with the distal tip bent to a 15-degree angle may be used. A C-arm and 0.5 to 1 mL of nonionic, water-soluble contrast are needed. The transoral approach requires a curved dental needle.

Preparation

Preoperatively, it is imperative to note if the patient is on anticoagulant or antiplatelet therapy. Suppose the patient is on anticoagulants or antiplatelet therapy. In that case, it may be necessary to communicate with the patient’s primary care physician or cardiologist to ensure patient safety. Per the primary care physician or cardiologist’s recommendations, agents such as warfarin, heparin, and factor 10a inhibitors should be held. A prothrombin time should be obtained preoperatively in patients on warfarin. A partial thromboplastin time should be obtained preoperatively for heparin use. Blood pressure and heart rate should be checked pre- and post-procedure on the day of the procedure. The patient should be placed in the supine position with the cervical spine extended. The nare(s) should be inspected for potential obstruction causes such as a deviated septum or neoplasm.[3]

Technique or Treatment

SPG block can be performed through transnasal, transoral, or transcutaneous approaches.

Transnasal Topical Approach

1. The patient is placed in the supine position with the cervical spine extended.
2. The measurement of the distance from the opening of the nares to the mandibular notch directly below the zygoma can be used to estimate the depth of needed cotton-tipped applicator advancement.
3. The cotton-tipped applicator is soaked in local anesthetic (viscous lidocaine 4%)
4. The cotton-tipped applicator is advanced into the nares parallel to the zygoma, with the tip angled laterally until it lays on the nasopharyngeal mucosa posterior to the middle nasal turbinate.
5. A second applicator may be placed posteriorly and superior to the initial one.
6. A response is typically seen in 5 to 10 minutes. However, the applicator(s) may be left in position for 30 minutes.

Transnasal Injection Approach

1. The patient is placed in the supine position with the cervical spine extended.
2. A cotton-tipped applicator soaked in local anesthetic is advanced along the superior border of the middle turbinate. It is stopped when the posterior wall of the nasopharynx is reached. Alternatively, a small amount of viscous lidocaine can be instilled into the nare(s), after which the patient inhales briskly to draw the lidocaine toward the posterior nasopharynx.
3. The chosen SPGB device (The SphenoCath, Allevio SPG Nerve Block Catheter, or Tx360 Nasal Injector) is then advanced into the ipsilateral nare.
4. Contrast can be injected under fluoroscopy to visualize needle tip placement.
5. Once the catheter tip is in place, the inner catheter is advanced to administer local anesthetic.
6. The patient should be instructed to remain in the same position for 10 minutes.[5][9][10]

The advantages of the transnasal injection approach are that it is the simplest technique, requires a short procedure time, and has low risk with complications limited to epistaxis and infection. The primary disadvantage of the transnasal injection approach is that it requires the diffusion of local anesthetic across mucous membranes.[2][11]

Transoral Approach

A curved dental needle passes through the greater palatine foramen in the posterior portion of the hard palate. This should be just medial to the gum line opposite the third molar tooth to reach the superior aspect of the pterygopalatine fossa.

An advantage of the transoral approach is that it provides more direct access to the sphenopalatine ganglia. The disadvantages of this approach are that it is a needle-based invasive approach, is technically challenging, and exhibits the greatest complications. It causes most patients discomfort and is unpredictable when ensuring proper anesthetic placement.[11][2]

Infrazygomatic Approach

Fluoroscopy or computed tomography is recommended for patient safety and improved chance of direct delivery of local anesthetic to the SPG.

1. The patient is placed in the supine position.
2. Apply sterile prepping and drape to the appropriate side of the face
3. Obtain a lateral fluoroscopic view of the face using a C-arm by superimposing the mandibular rami on top of one another
4. Anesthetize the skin above the mandibular notch
5. A 10 cm curved blunt 20 or 22-gauge needle is preferred. Alternatively, a 22 or 25-gauge 3.5-inch short-bevel needle with the distal tip bent to a 15-degree angle may be used.
6. Advance the needle in a superior and medial direction toward the pterygopalatine fossa under fluoroscopy.
7. An intermittent anteroposterior (AP) view should be obtained to assess needle depth.
8. Needle tip advancement should terminate immediately adjacent to the ipsilateral nasal wall.
9. To rule out intravascular uptake and intranasal spread, 0.5-1 mL of nonionic, water-soluble contrast should be injected under continuous fluoroscopy.
10. Once proper needle placement is confirmed, 1 to 2 mL of local anesthetics, such as 1 to 2% lidocaine or 0.25% bupivacaine with or without corticosteroids, is injected.

The advantages of the infrazygomatic approach are that it is a needle-based invasive approach and uses fluoroscopy to allow for the direct administration of a local anesthetic to the SPG. A disadvantage of this approach is that computed tomography guidance requires greater radiation exposure to the patient and is more invasive.[11]

Complications

Minor adverse effects of SPG block are typically local and include epistaxis, transient anesthesia, or hypoesthesia of the root of the nose, pharynx, and palate and lacrimation of the ipsilateral eye. Major adverse effects are uncommon but can include infection in the setting of improper aseptic technique and local or retroorbital hematoma.[2][5]

Clinical Significance

The SPG block is used for various headache and facial pain syndromes and has variable efficacy depending on the disease process treated. Significant reduction in pain is meaningful when followed by an increase in functional capacity, reduction in health care use, or reduction in opioid use. If the SPGB works for a short time, it can be followed by radiofrequency neurotomy or SPG stimulation to increase the duration of pain relief. Therefore, it can serve as a diagnostic block and is commonly used for this purpose.[12]

Enhancing Healthcare Team Outcomes

Chronic headache and facial pain syndromes can lead to significant disability, decreased functionality, and an increase in healthcare costs. An interprofessional approach to these patients is most effective and involves management by neurology, psychology, and pain management. Diagnosis and appropriate patient selection for SPG blockade is essential. Neurologists and headache specialists generally fulfill the role of identifying appropriate candidates for the procedure. Additionally, the mental health implications of living with chronic pain must be considered as well. In these patients, psychological screening is appropriate. A referral to a pain psychologist for additional support is prudent when needed. Moreover, nursing providers play an important role during the performance of an SPG block by helping ensure patient comfort and aiding in monitoring for adverse events. The treating provider should properly document adverse events.