Studying the gross and neuroanatomy of the trigeminal nerve is an essential task prior to neural blockade. The trigeminal nerve has both sensory and motor fibers. Visceral efferent fibers contribute to innervate some muscles of mastication and facial expression. Through its somatic afferent fibers, the trigeminal nerve transmits nociception, light touch, and temperature sensation from the skin of the face, teeth, anterior two thirds of the tongue, the nose, and oral cavity mucosa. Figure 11.1 shows the three branches of the trigeminal nerve (ophthalmic, maxillary, and mandibular).

The gasserian ganglion, also known as the trigeminal ganglion or the semilunar ganglion, sits in an invagination of the dura mater of the posterior cranial fossa, known as Meckel’s cave (Fig. 11.1). Injection of local anesthetic in Meckel’s cave, which contains cerebrospinal fluid, can potentially lead to total spinal anesthesia or spread to other cranial nerves. Its three sensory divisions, the ophthalmic (V1), maxillary (V2), and mandibular (V3), divide and exit anteriorly as shown in Fig. 11.1. The mandibular branch exiting through the foramen ovale has clinical applications as the reader will see in this chapter.

Blockade of the gasserian ganglion has been applied as surgical anesthetic for procedures of the head and neck in very limited instances. More commonly, it is used as a treatment for trigeminal neuralgia after failure of conservative therapy and also for cancer pain involving the face. Trigeminal ganglion neurolysis has been effective when oral therapy fails. The palliation of cancer-related pain arising from direct nerve involvement or surgical trauma has successfully been accomplished through blockade of the trigeminal ganglion or its divisions. Neurolysis of the trigeminal ganglion relieves cluster headaches refractory to oral therapy [8–12] and intractable atypical facial pain [13, 14].

To decrease the chances of adverse events, the use of radiological guidance such as computed tomography [15], fluoroscopy [16], or ultrasonography [17] along with a blunt-tipped curved needle is highly recommended. The blockade of the trigeminal ganglion has been performed without radiological guidance in the past but is not advisable. Those measures not only increase patient’s safety but also improve the access to the main anatomical landmark, the foramen ovale.

The patient is placed in a supine position with the head slightly extended. Facial skin is sterilely prepped. It is recommended that conscious sedation be administered for patient comfort with blood pressure, pulse oximetry, and electrocardiogram monitoring. Fluoroscopic x-ray guidance is used. The skin entry site is usually located approximately 2–3 cm lateral to the commissural labialis (the corner of the mouth) in a mid-pupillary line. Localization of the foramen ovale is critical to the success of this block. The anteroposterior fluoroscopic view usually shows the petrous ridge through the orbit, and 1 cm medially, it also shows a dip in the petrous ridge. Rotation of the C-arm head obliquely away from the nose approximately 20–30° and approximately 30–35° in the caudo-cranial direction will bring the foramen into view just medial to the mandible and at the top of the petrous “pyramid.” Lidocaine 1 % is applied to the skin and subcutaneous tissue over the shadow of the foramen ovale. For a diagnostic local anesthetic block, a 22-g B-bevel needle, 8–10 long, is used (for radiofrequency lesioning, an RFA 10-cm needle with a 2–5-mm active RFA tip is used). The needle is advanced through the entry point toward the foramen ovale, rotating the needle tip as needed to keep it on course initially downward and laterally, then medially aiming for the foramen ovale. To prevent intraoral entry, placement of one finger in the mouth could be done. When bone is encountered, the needle could be walked posteriorly along the skull into the foramen. A lateral view should be obtained, revealing the needle through the foramen ovale in a trajectory superior and toward the medial aspect of the external auditory meatus. A mandibular nerve paresthesia is commonly elicited. It is mandatory to test negative aspiration of cerebrospinal fluid (CSF) confirming that the needle did not penetrate the dura matter. The needle position is confirmed with injection of nonionic water-soluble contrast and negative aspiration of blood and CSF. For diagnostic local anesthetic blockade, small increments of local anesthetic (lidocaine 2 %, bupivacaine 0.5 %, or ropivacaine 0.5 %) are injected for a total of 1 ml. Monitoring the patient is essential to confirm that local anesthetic did not reach the CSF, putting the patient at risk of inadvertent spinal anesthetic and potential respiratory arrest. Figure 11.2 illustrates the trajectory of the needle in correct placement for the gasserian block.

The ophthalmic branch (V1) of the trigeminal branch is a purely sensory branch [36]. It enters the orbit via the superior orbital fissure. In turn, it divides into three branches, the frontal, nasociliary, and lacrimal nerves. The latter two provide innervations to nasal structures and the lacrimal gland, respectively. The supraorbital and the supratrochlear are terminal branches of the frontal nerve: They exit the orbit anteriorly and provide innervations to upper eyelid, forehead, and anterior scalp. As illustrated in the next paragraph, they are clinically most significant of the V1 branches.

The maxillary branch (V2) is also a pure sensory branch [37]. It exits the middle cranial fossa into the pterygopalatine fossa in a horizontal fashion through the foramen rotundum. Then, it passes through the inferior orbital fissure to the orbit before exiting to the face via the infraorbital foramen. That passage through the four facial compartments lead to the division of the many branches of V2 to four regional groups of branches. Understanding the exit of V2 from the middle cranial fossa to the face simplifies the understanding of its innervations of facial structures (Fig. 11.1). Table 11.2 summarizes the four groups and the facial areas they innervate.

The mandibular nerve is formed by the joining of the large sensory mandibular division of the trigeminal nerve and a small motor nerve root. They both cross the foramen ovale leaving the middle cranial fossa and forming the mandibular nerve [37]. This combined trunk then divides into a small anterior and larger posterior trunk (Fig. 11.1). Prior to this division, it gives off the nervus spinosus, innervating the dura matter and mucosal lining of the mastoid sinus, and the internal pterygoid, innervating the internal pterygoid and sending branches to the otic ganglion.

From the anterior trunk comes the buccinator nerve to innervate the skin and mucous membrane overlying the buccinator muscle. The anterior trunk also gives off three motor branches: the masseteric, deep temporal nerves, and the external pterygoid nerve. They provide motor innervations to the masseter muscle, temporalis muscle, and external pterygoid muscle, respectively.

The posterior trunk contains mostly sensory fibers. The following branches come off the posterior trunk: The auriculotemporal nerve provides sensory innervations to the following structures – the tympanic membrane, the lining of the acoustic meatus, the posterior temporomandibular joint, the parotid gland, the skin overlying the temporal region, and the skin anterior to the tragus and helix. The lingual nerve innervates the dorsum and lateral aspects of the anterior 2/3 of the tongue, the lateral mucous membrane, and the sublingual gland. The inferior alveolar nerve innervates the lower teeth and the mandible. Its terminal branch, the mental nerve, innervates the chin and the skin and mucous membrane of the lower lip.

The most commonly blocked branches of V1 are the supraorbital and supratrochlear branches. To block the supraorbital nerve, the patient is placed in a supine position. The landmark for this block, the supraorbital foramen, is palpated along the upper border of the orbit. After skin prepping, with precautions not to spill any disinfecting solution in the eye, a 25-gauge, 1.5-in.-long needle is introduced into the skin through the identified supraorbital foramen in a perpendicular plane to the skin. Some paresthesia is usually elicited; then, 3–4 ml of local anesthetic solution (lidocaine 1–2 %, bupivacaine 0.5 %, or ropivacaine 0.2 %) is injected in a fanlike fashion. Radiofrequency lesioning for the supraorbital nerve as a treatment for postherpetic neuralgia has been described. The technique for radiofrequency lesioning is similar to the local anesthetic block with the exception of using a RFA needle and confirmation of positive sensory response at 2-Hz stimulation in the somatic nerve distribution. To achieve a blockade of the supratrochlear branch of the ophthalmic division, simply direct the needle medially at the level of the supraorbital foramen and repeat similar steps as described above.

The preferred approach for blockade of the maxillary (V2) and the mandibular (V3) branches of the trigeminal nerve is through the mandibular notch, also known as the coronoid notch. These blocks could be done without radiologic guidance. However, fluoroscopic guidance is highly recommended. Patient is placed in supine position, and the x-ray C arm is placed in a lateral view. The patient is asked to open and close his/her mouth few times if possible to facilitate palpation of the mandibular notch which could be marked. After skin sterilization, the skin is anesthetized with lidocaine 1 %. A 22-g B-bevel needle, 8–10 cm long is used (for radiofrequency lesioning, an RFA needle, 10 cm long, with a 2–5-mm active RFA tip is used). The needle is introduced under fluoroscopic guidance at the site already marked and advanced in a horizontal plane. Fluoroscopic guidance is used to direct the needle tip through the infratemporal fossa (Fig. 11.3). A small-angulation cephalad and slightly posterior will allow the needle to be in proximity to the lateral nasal mucosa taking extreme care not to pierce through it. The end point of the advancement of the needle is the lateral pterygoid plate. If the maxillary nerve is the final target, a slight superior and posterior angulation will elicit paresthesia into this nerve distribution (nose ridge, upper lip, gum, and face). If the mandibular nerve is targeted, a slight caudad and anterior angulation usually elicits paresthesia in its somatic distribution (lower mandible, lower lip, lower jaw, and tongue). If radiofrequency lesioning is planned, sensory testing at 50 Hz should be achieved preferably below 0.6 V in the nerve distribution prior to any treatment. Negative aspiration of blood and CSF should be demonstrated prior to any treatment. Figure 11.4 shows the advancement and final position of the needle. Figure 11.5 shows RF needle in position.