http://www.nationalpainfoundation.org/dis_cond/TN/TN_Anatomy.swf
The trigeminal nerve has three branches. In general these branches correspond to the upper, middle, and lower portions of the face.
The first (upper) branch includes the eye, eyebrow, and forehead. The second (middle) branch corresponds to the upper lip, upper teeth, upper gum, cheek, lower eyelid, and side of the nose. The third (lower) branch involves the lower lip, lower teeth, lower gum, and one side of the tongue. It also includes a narrow area that extends from the lower jaw in front of the ear to the side of the head.
The ophthalmic nerve (V1) enters the middle cranial fossa through the superior orbital fissure and courses within the lateral wall of the cavernous sinus (part of the venous system that returns blood from the brain to systemic circulation - dissected away in the illustration) on its way to the trigeminal ganglion. The maxillary nerve (V2) enters the middle cranial fossa through foramen rotundum and may or may not pass through the cavernous sinus en route to the trigeminal ganglion. The mandibular nerve (V3) enters the middle cranial fossa through foramen ovale, coursing directly into the trigeminal ganglion. The trigeminal ganglion (a.k.a. semilunar ganglion in reference to its sometimes "half moon" shape) lies in a depression known as the trigeminal cave (or Meckel's cave). The trigeminal nerve exits the trigeminal ganglion and courses "backward" to enter the mid-lateral aspect of the pons (a division of the brainstem - shown in faded yellow).
Branchial motor nerves exit the mid-lateral aspect of the pons, course within the trigeminal nerve, pass through the trigeminal ganglion, and exit the middle cranial fossa within the mandibular nerve through foramen ovale. Branchial motor nerves can not be distinguished from sensory nerves on gross dissection and are therefore described as "within" the trigeminal and mandibular nerves. Therefore, these grossly named nerves carry bi-directional signals. Branchial motor nerves convey outgoing information while the majority of nerves contained in the mandibular nerve and in the main trunk of the trigeminal nerve proximal to the trigeminal ganglion convey incoming sensory information.
Visceral motor nerves are not a true component of the trigeminal nerve, but are important "hitchhikers" along its branches. These hitchhiking fibers originate centrally as part of other cranial nerves and travel along sensory branches of the trigeminal nerve en route to glands within the head and neck. Again, this creates trigeminal nerve branches that carry bi-directional signals.
The trigeminal nerve is commonly referred to as "the great sensory nerve of the head and neck". Its three major branches, for which it is named, and multiple smaller branches carry information about light touch, temperature, pain, and proprioception (position sense) from the face and scalp to the brainstem. Sensory fibers originate in the skin, course toward the trigeminal ganglion (joining with other fibers to form larger branches along the way), pass through the trigeminal ganglion, and travel within the trigeminal nerve to the sensory nucleus of the trigeminal nerve located in the brainstem. The vast majority of sensory nerve cell bodies are located within the trigeminal ganglion, hence its massive size. The exception is a small subset of primary sensory nerves whose cell bodies are located in the brainstem that carry proprioceptive information from the muscles of mastication. It is important to note that the trigeminal nerve has multiple nuclei with complicated structures within the brainstem. I refer generally to sensory and motor nuclei for the sake of simplicity. Neuroanatomy texts provide a deeper understanding.
The trigeminal nerve is divided into the ophthalmic nerve (V1), maxillary nerve (V2), and mandibular nerve (V3), each of which will be discussed individually below.
OPHTHALMIC NERVE (V1)
Branches of the ophthalmic nerve (V1) convey sensory information from the skin of the forehead, upper eyelids, and lateral aspects of the nose. It is formed by the union of the frontal nerve, nasociliary nerve, and lacrimal nerve.
The frontal nerve arises from the supraorbital nerve and supratrochlear nerve. The supraorbital nerve courses from the forehead through the supraorbital notch (foramen) to join the supratrochlear nerve. The supratrochlear nerve carries information from the medial forehead, medial portion of the upper eyelid, and bridge of the nose.
The nasocilary nerve arises from the infratrochlear nerve, anterior ethmoidal nerve, and posterior ethmoidal nerve. The infratrochlear nerve carries information from the medial eyelid and lateral aspect of the nose. The external branches of the anterior ethmoidal nerve convey sensation from the apex of the nose and ala (nostril). The anterior ethmoidal nerve also carries information from the ethmoidal air cells along with the posterior ethmoidal nerve.
The lacrimal nerve conveys sensation from the lateral portion of the upper eyelid and conjuctiva. In addition, post-ganglionic visceral motor fibers (see visceral motor component of the trigeminal nerve below) hitchhike along the lacrimal nerve en route to the lacrimal gland.
MAXILLARY NERVE (V2)
Branches of the maxillary nerve (V2) convey sensory information from the lower eyelids, zygomae, and upper lip. It is formed by the union of the zygomatic nerve and infraorbital nerve.
The glossopharyngeal nerve (cranial nerve IX) also contributes an important trigeminal hitchhiker - the lesser petrosal nerve. The lesser petrosal nerve has a complicated intracranial course, eventually exiting the skull through or near the foramen ovale. It carries pre-ganglionic fibers to the otic ganglion. After synapse, post-ganglionic fibers exit the ganglion, hitchhiking along the auriculotemporal nerve to innervate the parotid gland.
The zygomatic nerve arises from the zygomaticofacial nerve and zygomaticotemporal nerve. The zygomaticofacial nerve courses from the lateral cheek through the zygomaticofacial foramen to join the zygomaticotemporal nerve. The zygomaticotemporal nerve carries information from the lateral cheek posterior to the zygomatic process.
The infraorbital nerve conveys sensory information from the lateral aspect of the nose, lower eyelid, medial cheek, and upper lip as it courses through the infraorbital foramen. It is then joined by superior alveolar branches from the upper teeth which play an important role in transmitting dental pain.
MANDIBULAR NERVE (V3)
Branches of the mandibular nerve (V3) convey sensory information from the lateral scalp, skin anterior to the ears, lower cheeks, lower lips, and anterior aspect of the mandible. It is formed by the union of the buccal nerve, lingual nerve, inferior alveolar nerve, and auriculotemporal nerve.
The buccal nerve carries information from the lower cheek, gums, and mucous membranes of the mouth.
The lingual nerve conveys sensation from the anterior two-thirds of the tongue. In addition, pre-ganglionic visceral motor fibers (see visceral motor component of the trigeminal nerve below) hitchhike along the lingual nerve en route to the sublingual gland and submandibular gland.
The inferior alveolar nerve arises from the mental nerve and inferior alveolar plexus. The mental nerve courses from the chin and lower lip through the mental foramen to join the inferior alveolar plexus. The inferior alveolar plexus carries primarily painful sensation from the lower teeth and plays an important role in dental anesthesia.
The auriculotemporal nerve carries information from the lateral scalp (via superficial temporal branches) as well as from skin anterior to the ear and jaw (auricular and articular branches). In addition, post-ganglionic visceral motor fibers (see visceral motor component of the trigeminal nerve below) hitchhike along the auriculotemporal nerve en route to the parotid gland. Interestingly, the auriculotemporal nerve splits around the middle meningeal artery just before it merges with other major branches of V3.
BRANCHIAL MOTOR COMPONENT OF THE TRIGEMINAL NERVE -
The term "branchial" refers to structures embryologically derived from the branchial arches. The branchial motor component of the trigeminal nerve consists of lower motor neurons whose cell bodies are located in the motor nucleus of the trigeminal nerve in the brainstem. These nerves exit the mid-lateral aspect of the pons, course within the trigeminal nerve, pass through the trigeminal ganglion, and within the mandibular nerve before branching. The muscles innervated by the branchial motor component can be remembered as "the muscles of mastication (chewing) plus two tensors." That is, the temporalis, masseter, medial and lateral pterygoids, tensor veli palatini, and tensor tympani.
VISCERAL MOTOR COMPONENT OF THE TRIGEMINAL NERVE -
The term "visceral" refers to viscera, including smooth muscle and glands. Visceral motor neurons include both sympathetic and parasympathetic neurons. Only parasympathetics are shown in the illustration for simplicity, but sympathetic neurons are implied. In the head and neck, visceral motor neurons innervate the multiple glands involved in lacrimation and salivation. These include the lacrimal gland, parotid gland, sublingual gland, submandibular gland, and minor salivary glands of the palate and mouth. As noted above, visceral motor nerves are not a true component of the trigeminal nerve, but "hitchhike" along its branches. They originate centrally from other cranial nerves and travel along sensory branches of the trigeminal nerve en route to glands. Visceral motor nerves can be subdivided into pre-ganglionic ("before the ganglion") and post-ganglionic ("after the ganglion") fibers. Pre-ganglionic fibers travel from cranial nerve nuclei in the brainstem (where their cell bodies are located) to peripheral ganglia in the head and neck. These include the pterygopalatine ganglion, otic ganglion, and submandibular ganglion. Within these ganglia, pre-ganglionic fibers synapse with post-ganglionic fibers (whose cell bodies make up the bulk of the ganglia), which in turn travel to innervate glands. Post-ganglionic fibers are labeled as "parasympathetics to…" in the illustration.
The facial nerve (cranial nerve VII) gives rise to two important trigeminal hitchhikers - the Vidian nerve and the chorda tympani nerve. The Vidian nerve (a.k.a. nerve of the pterygoid canal) emerges from the pterygoid canal (not labeled) carrying pre-ganglionic fibers to the pterygopalatine ganglion. After synapse, post-ganglionic fibers exit the ganglion and hitchhike along trigeminal nerve branches en route to the lacrimal gland and minor salivary glands of the palate and mouth. The chorda tympani exits the skull through the petrotympanic fissure (not labeled) and courses extracranially to join the lingual nerve. It carries pre-ganglionic fibers to the submandibular ganglion which "hangs" from the lingual nerve. After synapse, post-ganglionic fibers exit the ganglion to innervate the submandibular gland and sublingual gland. The intracranial course of the facial nerve (cranial nerve VII) prior to the emergence of the Vidian and chorda tympani nerves is complex and non-essential for understanding basic trigeminal nerve anatomy.
TRIGEMINAL NEURALGIA
A 55 year old white male presents complaining of severe pain involving his lips, gums, and cheeks. He describes the pain as sharp and stabbing, and rates it a 10 out of 10 on the pain scale. It is intermittent, with individual episodes lasting only seconds, but occurring throughout the day and night. He reports that these episodes started approximately two weeks ago. He notes that the episodes are sometimes triggered by chewing and says he has been eating less for fear of the pain. He has not noticed any facial weakness or numbness.
DISCUSSION: Trigeminal neuralgia, a.k.a. "tic douloureux" for the wince or "tic" it causes in response to pain, is a condition characterized by sudden, recurrent episodes of excruciating facial pain typically lasting only seconds. Though brief, these episodes often occur in rapid succession throughout the day and night causing patients significant distress. Trigeminal neuralgia usually occurs in patients over 50, with symptoms lasting for several weeks at a time. Intermittent remission and relapse may occur over many years. Pain can occur along any branch of the trigeminal nerve, though V1 (the ophthalmic nerve) is rarely involved. Stimulation of "trigger zones" such as the corner of the mouth, side of the nose, oral mucosa, etc. characteristically precipitate painful episodes. Patients may alter the way they chew, wash their face, shave, etc. to avoid these triggers. Trigeminal neuralgia is not associated with facial numbness or weakness and the majority of cases are of unknown etiology.
If you have trigeminal neuralgia, even mild stimulation of your face — such as from brushing your teeth or putting on makeup — may trigger a jolt of excruciating pain.
You may initially experience short, mild attacks, but trigeminal neuralgia can progress, causing longer, more frequent bouts of searing pain. Trigeminal neuralgia affects women more often than men, and it's more likely to occur in people who are older than 50.
Because of the variety of treatment options available, having trigeminal neuralgia doesn't necessarily mean you're doomed to a life of pain. Doctors usually can effectively manage trigeminal neuralgia with medications, injections or surgery.
Trigeminal neuralgia symptoms may include one or more of these patterns:
Occasional twinges of mild pain
Episodes of severe, shooting or jabbing pain that may feel like an electric shock
Spontaneous attacks of pain or attacks triggered by things such as touching the face, chewing, speaking and brushing teeth
Bouts of pain lasting from a few seconds to several seconds
Episodes of several attacks lasting days, weeks, months or longer —some people have periods when they experience no pain
Pain in areas supplied by the trigeminal nerve (nerve branches), including the cheek, jaw, teeth, gums, lips, or less often the eye and forehead
Pain affecting one side of your face at a time
Pain focused in one spot or spread in a wider pattern
Attacks becoming more frequent and intense over time
Causes
By Mayo Clinic staff
In trigeminal neuralgia, also called tic douloureux, the trigeminal nerve's function is disrupted. Usually, the problem is contact between a normal blood vessel — in this case, an artery or a vein — and the trigeminal nerve, at the base of your brain. This contact puts pressure on the nerve and causes it to malfunction.
Trigeminal neuralgia can occur as a result of aging, or it can be related to multiple sclerosis or a similar disorder that damages the myelin sheath protecting certain nerves. Less commonly, trigeminal neuralgia can be caused by a tumor compressing the trigeminal nerve. In other cases, a cause can't be found.
Triggers
A variety of triggers may set off the pain of trigeminal neuralgia, including:
Shaving
Stroking your face
Eating
Drinking
Brushing your teeth
Talking
Putting on makeup
Encountering a breeze
Smiling
Surgical Management
Prior to considering surgery, all trigeminal neuralgia patients should have a MRI, with close attention being paid to the posterior fossa. Imaging is performed to rule out other causes of compression of the trigeminal nerve such as mass lesions, large ectatic vessels, or other vascular malformations.
The surgical options for trigeminal neuralgia include peripheral nerve blocks or ablation, gasserian ganglion and retrogasserian ablative (needle) procedures, craniotomy followed by microvascular decompression (MVD), and stereotactic radiosurgery (Gamma Knife®).
Percutaneous transovale needle techniques include radiofrequency trigeminal electrocoagulation, glycerol rhizotomy, and balloon microcompression. Microvascular decompression (MVD) is often preferred for younger patients with typical trigeminal neuralgia. High initial success rates (>90%) have led to the widespread use of this procedure. This procedure provides treatment of the cause of trigeminal neuralgia in many patients. Percutaneous techniques are advocated for elderly patients, patients with multiple sclerosis, patients with recurrent pain after MVD, and patients with impaired hearing on the other side, however some authors recommend needle techniques as first surgical treatment for many patients. It is generally agreed that MVD provides the longest duration of pain relief while preserving facial sensation. In experienced hands, MVD can be performed with low morbidity and mortality. Most authors offer MVD to young patients with trigeminal neuralgia.
Trigeminal Neuralgia Radiosurgery
Radiosurgery is performed by delivering a high dose of ionizing radiation in a single treatment session using multiple beams precisely focused at the target inside the brain. Several reports have documented the efficacy of Gamma Knife®‚ stereotactic radiosurgery for trigeminal neuralgia . Because radiosurgery is the least invasive procedure for trigeminal neuralgia, it is a good treatment option for patients with co-morbidities, high-risk medical illness, or pain refractory to prior surgical procedures.
Between 1992 and 2007, a more than 750 radiosurgical procedures for TN were performed at the University of Pittsburgh Medical Center. Our report summarizes the long-term outcome in 220 patients who had undergone Gamma Knife® radiosurgery for idiopathic, longstanding pain refractory to medical therapy. One hundred and thirty-five patients (61.4%) had prior surgeries including microvascular decompression, glycerol rhizotomy, radiofrequency rhizotomy, balloon compression, peripheral neurectomy, or ethanol injections. Eighty-six patients (39.1%) had one, 39 (17.7%) had two, and ten (4.5%) had three or more prior operations. For the other 85 patients, radiosurgery was the first surgical procedure. A maximum dose of 70 to 80 Gy was used.
The outcome of pain relief was categorized into four results (excellent, good, fair, and poor). Complete pain relief without the use of any analgesic medication was defined as an excellent outcome. Complete pain relief with still requiring some medication was defined as a good outcome. Partial pain relief (>50% relief) was defined as a fair outcome. No or less than 50% pain relief was defined as a poor outcome. Most patients responded to radiosurgery within six months (median, two months). At the initial follow-up within six months after radiosurgery, complete pain relief without medication (excellent) was obtained in 105 patients (47.7%), and excellent and good outcomes were obtained in 139 patients (63.2%). Greater than 50% pain relief (excellent, good, and fair) was obtained in 181 patients (82.3%).
Complications after Radiosurgery
The main complication after radiosurgery for trigeminal neuralgia was new facial sensory symptoms caused by partial trigeminal nerve injury. Seventeen patients (7.7%) in our series developed increased facial paresthesia and/or facial numbness that lasted longer than 6 months.
Repeat Radiosurgery
Trigeminal neuralgia patients who experience recurrent pain during the long-term follow-up despite initial pain relief after radiosurgery can be treated with second radiosurgery procedure. The target is placed anterior to the first target so that the radiosurgical volumes at second procedure overlaps with the first one by 50%. We advocate less radiation dose (50 to 60 Gy) for second procedure, because we believe that a higher combined dose would lead to a higher risk of new facial sensory symptoms.
Indications for Radiosurgery
The lack of mortality and the low risk of facial sensory disturbance, even after a repeat procedure, argue for the use of primary or secondary radiosurgery in this setting. Repeat radiosurgery remains an acceptable treatment option for trigeminal neuralgia patients who have failed other therapeutic alternatives.
No comments:
Post a Comment