Trigeminal Nerve Block Technique
- Author: Anusha Cherian, MBBS, MD, DNB; Chief Editor: Meda Raghavendra (Raghu), MD more...
Neurolytic agents provide a longer duration of pain relief, typically lasting for a few months. They achieve this by causing destruction of nerve fibers and wallerian degeneration of axonal fibers and Schwann cells. The neurons regenerate in 3-5 months. Often, it might take 1-2 weeks before complete pain relief is experienced.
The neurolytic agents used in trigeminal nerve block include the following:
Glycerol (100%) – This agent is typically used for treating trigeminal neuralgia; it is a mild neurolytic agent, but it can also cause perineural damage
Alcohol (50-70%) – Currently, this agent is rarely used because of its high rate of complications; it can seep into surrounding tissues and cause necrosis and cellular injury, and it can also cause vasospasm
Phenol (4-10%) – This agent is also commonly used; it can cause warmth and numbness on injection, and it can cause convulsions and cardiovascular collapse if inadvertently injected intravascularly
Techniques for Trigeminal Nerve Block
Trigeminal nerve block can be accomplished either via the classic approach (guided by the anatomic landmarks) or with the help of imaging (guided by fluoroscopy or computed tomography [CT]).
The patient is placed in a supine position with the head in a neutral position and the eyes staring straight ahead. The key anatomic landmark—a point 2-3 cm lateral to the angle of the mouth on the side to be blocked—is marked.
The skin over the cheek on the involved site is prepared with iodophor or povidone-iodine and draped. A skin wheal is raised with a local anesthetic. A 22-gauge 10-cm long spinal needle is inserted here and advanced upward toward the mandibular condyle (see the images below). This plane should be in line with the pupil as the patient’s eyes stare ahead, and the trajectory should be cephalad toward the external auditory meatus.
At a depth of 4-6 cm, the greater wing of the sphenoid at the base of the skull is contacted. The needle is withdrawn and redirected more posteriorly so as to enter the foramen ovale. It is then advanced 1-1.5 cm. Paresthesia at the mandible is elicited, followed by paresthesia in the maxilla and orbit.
The foramen ovale is identified by using the C-arm image intensifier. The patient’s head is placed in the reverse occipitomental position (chin up and neck extended), turned 30° to the opposite side. The x-ray beam is directed with a 30° caudal angulation. A small focal point and a small field size are recommended. The foramen ovale can be imaged here; in some cases, this proves quite difficult.
The 22-gauge spinal needle is advanced to reach the foramen ovale in much the same fashion as in the classical approach (see above). Lateral screening is done to check the depth of insertion. As the needle enters the trigeminal cistern, cerebrospinal fluid (CSF) is aspirated. The needle is then gradually withdrawn until CSF is no longer aspirated.
Contrast is injected to visualize the filling of the cistern and to confirm that the needle has not entered a vessel. Next, 0.3 mL of bupivacaine 0.25% is injected, and the patient’s response to this is assessed. Longer-lasting blockade with alcohol or glycerol can be planned later, after the response to the local anesthetic has been evaluated.
When a hyperbaric solution is used, the patient must be seated in an upright position to help the drug settle in the inferolateral position of the cistern through the action of gravity. The patient is left in this position for at least 1 hour.
Trigeminal nerve block may also be performed under ultrasound guidance. The advantage of using ultrasonography is that vascular structures, particularly the maxillary artery, can be visualized throughout its course in the infratemporal and the pterygopalatine fossa and inadvertent intravascular injection of the agent used to block the nerve may be prevented. It also prevents exposure to radiation as occurs during x-ray imaging. A recent article published a case series on 15 consecutive adult patients with uncontrolled facial pain due to various causes. Trigeminal nerve block was performed under ultrasound guidance in these patients. The authors confirmed this technique to be feasible, safe, and effective. Five ml of local anesthetic placed below the lateral pterygoid muscle in the pterygopalatine fossa results in immediate sensory block in the distribution of trigeminal nerve in most patients.
Hematoma of the face and subsclera is a common complication of this technique; the pterygopalatine space is highly vascular and is close to the middle meningeal artery. Direct intravascular injection of the drug into the carotid artery may occur. Total spinal anesthesia may develop. CSF is frequently encountered on withdrawal of the syringe in the trigeminal cistern. Injection of local anesthetic in this area can cause cardiac and respiratory arrest as the drug spreads on the ventral surface of the brainstem.
For these reasons, trigeminal nerve block must be performed only by experienced personnel. Maximal caution must be exercised, and resuscitative equipment must be kept ready. Performing the block under imaging guidance can prevent these complications to a large extent.
With an intravascular injection, drug toxicity can manifest as cardiovascular or central nervous system effects. Pain, masticatory weakness, neurolysis, or persistent paresthesia may occur. Facial numbness may be profound. Abolition of corneal reflexes can produce exposure keratitis and dryness of eyes.
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