I. Introduction
The origin of microvascular decompression (MVD) began with clinical studies on the surgical treatment of trigeminal neuralgia (TN). Decades of research have shown that compression of the cerebelloponline angle (CPA) by vessels responsible for different rootentr/exit zoons (REZ) can lead to a syndrome known as neurovascular compression (NVC). syndrome.
MVD has become the surgical treatment of choice for patients with primary TN, glossopharyngeal neuralgia (GN) who can tolerate craniotomy. The combination of MVD with CPA partial rhiZotomy (PR) to maximize surgical efficiency and minimize complications is a major effort of functional neurosurgeons.
II. Diagnosis of primary TN
1. Clinical manifestations of primary TN: Primary TN is mainly manifested by recurrent paroxysmal severe pain in the trigeminal nerve distribution area. Most of the pain is unilateral, and occasionally bilateral onset is seen as tearing, electric shock, stabbing, cutting or burning pain, which may be accompanied by lacrimation, salivation, runny eyes or facial convulsions.
Trigger points or trigger points exist, mostly located in the upper and lower lips, nose, nasolabial folds, gums, cheeks, and corners of the mouth, and can be triggered by actions such as chewing, eating, drinking, wind, cold, brushing teeth, washing face, and speaking. Some patients may have intermittent periods ranging from a few weeks to a few years, and the imaging of TN and its significance are detailed in the Expert Consensus on Microvascular Decompression for Facial Myasthenia in China (2014).
2. Secondary TN: TN secondary to CPA tumor is difficult to differentiate from typical primary TN in terms of symptoms and signs, and the diagnosis depends on CT and MRI. when TN is associated with other cranial nerve disorders, the possibility of CPA tumor increases significantly. In this article, we focus on the surgical treatment of primary TN.
3. Differential diagnosis of primary TN: The multi-causal nature of TN leads to difficulties in its diagnosis and differential diagnosis. Primary TN needs to be differentiated from other painful diseases of the head and face. For example, GN, intermediate neuralgia, pterygopalatine neuralgia, atypical facial pain, cluster headache, postherpetic pain, odontogenic pain, etc. The typical clinical features of primary TN that can be differentiated include: (1) a clear range of pain; (2) seizures; (3) the presence of remission periods; (4) the presence of triggering factors and trigger points; and (5) the effectiveness of carbamazepine at the beginning.
Diagnosis of primary GN
1. Clinical manifestations of primary GN: GN is less common. Episodes of pain are limited to the root of the tongue, tonsil area, pharynx, mandibular angle, mastoid area, and external auditory canal area on one side, and can be triggered by swallowing, chewing, talking, coughing, and yawning, and can be accompanied by cardiogenic syncope, arrhythmia, and hypotension in a few patients. Carbamazepine is mostly effective.
2. Differential diagnosis of primary GN: stem overgrowth, occupying lesion of CPA, malignant tumor (such as nasopharyngeal carcinoma) invading the skull base are common secondary causes, therefore, preoperative frontal and lateral plain radiographs of the stem and CT or MRI should be routinely examined.
Indications and contraindications for surgery
1. Indications for surgery: Not all primary TN and GN require surgical treatment, and carbamazepine will remain the most effective and commonly used drug for symptomatic treatment of TN and GN for a long period of time in the future.
Toxic side effects of carbamazepine should be noted, including drowsiness, dizziness, gastrointestinal reactions, ataxia, liver damage, decreased white blood cells, and severe allergic reactions (e.g., exfoliative dermatitis). The toxic side effects of the drug make it intolerable for a significant proportion of patients to seek alternative treatments.
Clinical indications for MVD should be both avoided and clarified: for patients who can tolerate craniotomy, MVD is the surgical treatment of choice, superior to other means such as gamma knife or radiofrequency.
Indications for surgery for TN and GN include.
(1) Primary TN, GN, excluding secondary lesions;
(2) Severe symptoms that affect the patient’s daily life;
(3) Poor results of conservative treatment or serious side effects;
(4) The patient has the requirement of active surgical treatment.
2. Contraindications to surgery.
(1) The same as other contraindications to general anesthesia craniotomy, such as the presence of serious systemic diseases and poor control, etc;
(2) Insufficient understanding of the efficacy of surgery and possible complications and inadequate preparation.
V. Surgical techniques
1. Management strategy of supraclavicular vein.
(1) The principle of handling the supraclavicular vein in CPA exploration: the subclavian vein branches located at the skull base can be cut off after direct electrocoagulation if they obstruct the surgical approach, while the supraclavian vein branches near the cerebellar curtain should not be cut off as far as possible to avoid serious consequences such as venous infarction or even hemorrhage. In TN MVD surgery, if the supratentorial vein obstructs the surgical access, it is not possible to penetrate from the gap between the trigeminal nerve root and the cerebellar curtain without disconnecting the vein, the access can be made from above the auditory nerve.
(2) Electrocoagulation and hemostasis of the supratentorial vein: When the branch of the supratentorial vein is short, thick and free, it is sometimes futile and dangerous to try to reveal the REZ between the trigeminal nerve root and the cerebellar curtain by dissecting the arachnoid membrane or through the superior auditory nerve approach, because strong pulling on the cerebellar hemisphere can tear the trunk of the supratentorial vein from the supratentorial sinus and cause unexpected hemorrhage.
The vein should be repeatedly cauterized with less power close to its cerebellar side when electrocoagulated, and the thicker branches of the genus sometimes need to be cut completely in fractions. The arachnoid membrane around the vein should be cut free as much as possible before electrocoagulation to avoid contraction of the arachnoid membrane due to electrocautery, which may pull the vein and cause tearing and bleeding at the supratentorial sinus. Occasionally, the vein may rupture and bleed during traction or electrocoagulation, which often takes the operator by surprise, and patient compression to stop the bleeding after aspiration of the field is the only treatment.
(3) Circumstances in which it is not recommended to cut the supraclavicular vein: extreme caution should be exercised in the following cases: (i) the supraclavicular vein to be cut mainly drains venous blood from the brainstem;
(2) The supraclavicular branch to be cut is closer in color to the arterial appearance than the other branches, i.e., the veins are arterialized, and it is estimated that the blood flow in the branch is more rapid, and the cut may cause acute congruent flow disorder; (3) There are few supraclavicular branches within the visual field, and the proposed branch is abnormally large, and it is expected that it will be difficult to compensate for the other branches after the cut.
In the above three cases, even if the supraclavicular vein cannot be fully exposed without treatment, or even if the supraclavicular vein is the responsible vessel, it is not recommended to cut it by electrocoagulation, and trigeminal sensory root PR is feasible to ensure the therapeutic effect.
2, vascular decompression techniques.
(1) TN pain decompression technique: The main responsible vessels in TN MVD surgery are the superior cerebellar artery and its branches, the anterior inferior cerebellar artery and its branches, the branch of the supratentorial vein, and the basilar artery in that order. Veins alone or involved in compression are often seen in TN, but rarely in other cerebral neurological disorders. Since arachnoid thickening adhesion itself may be an important pathogenic factor of TN, the sensory roots of the trigeminal nerve should be fully dissected from the brainstem to the bursa of Meyer, so that they can be completely released in the axial position, and then vascular decompression should be performed. Teflon cotton or polyester spacers (polyethylene terephthalate) are used for decompression.
(2) GN decompression technique: The main responsible vessels in the GN MVD procedure are the posterior inferior cerebellar artery and its branches, the anterior inferior cerebellar artery and its branches, the vertebral artery, and the branches of the inferior rock vein, in that order.
A number of factors determine that the responsible artery cannot be satisfactorily nudged during REZ decompression of the glossopharyngeal nerve and vagus nerve.
(i) The hyohypopharyngeal and vagus nerve roots are anatomically located adjacent to the skull base, and the REZ cannot be fully exposed because of the small local operating space; in some cases with severe skull base depression and small volume of the posterior cranial fossa, the REZ cannot even be exposed at all;
(2) The responsible vessels are mostly the tortuous and sclerotic posterior inferior cerebellar artery trunk and vertebral artery, and there are more arterial penetrations;
(iii) The responsible vessels are mostly hidden in the posterior lateral sulcus of the medulla oblongata;
④The posterior group of cerebral nerves is more slender and closely arranged, and more susceptible to injury. When it is impossible to accurately distinguish CN or TN even by calling for spraying dicaine, the MVD surgical towel may be the only wise choice to explore the trigeminal nerve root and the linguopharyngeal and vagus nerve roots at the same time.
Trigeminal sensory root PR: If no responsible vessels are found in TN MVD, trigeminal sensory root PR can be performed. it is important to distinguish typical from atypical TN, the efficiency of MVD for atypical TN is much lower than that of typical TN, and trigeminal sensory root PR is often required.
In cases of ineffective or recurrent TN, PR should be the main surgical option for secondary surgery, and to ensure efficacy, only MVD should be considered when the following conditions coexist.
(1) Younger patients;
(2) The adhesions are not found to be significant during the secondary exploration;
(3) clear arterial vascular compression is present;
(4) Satisfactory vascular decompression. Therefore, the indications for PR can be relaxed when choosing the procedure to avoid the dilemma in case of ineffective surgery or recurrence.
4, linguopharyngeal nerve root dissection and vagus nerve root PR: linguopharyngeal nerve root dissection and vagus nerve root PR, MVD and the combination of the two are effective methods of treating CN, and the choice of the surgical procedure should be based on the intraoperative investigation.
(1) MVD should be performed if there is a clear responsible vessel compressing the REZ;
(2) PR if no responsible vessel is compressing the REZ;
(3) MVD+PR if the responsible vessel is not clearly compressed or if there is clear vascular compression but satisfactory decompression cannot be achieved for various reasons.
In atypical GN, the pain may involve the anterior and posterior external ear, mastoid area, and the skin of the pharynx below the anterior angle of the mandible, and the upper l to 3 filaments of the vagus nerve may need to be cut during surgery.
Evaluation of efficacy
1. Criteria for evaluating the efficacy after TN surgery.
(1) Cure: complete disappearance of symptoms;
(2) Significant remission: symptoms basically disappear, occasional attacks but no drug treatment is required;
(3) Partial remission: symptom reduction, but still need drug control;
(4) Ineffective: no change or worsening of symptoms. Both of the above (1) and (2) are considered effective.
2. Evaluation time of TN postoperative efficacy: delayed cure of TN and MVD can be seen occasionally, but generally not more than 3 months.
3, TN postoperative ineffective or relapse treatment: patients with ineffective or relapse can be considered for secondary MVD, PR, radiofrequency destruction, balloon compression or stereotactic radiosurgery according to the specific conditions of the first surgery and the current physical condition of the patient.
4, GN postoperative efficacy evaluation criteria: good efficacy: complete disappearance of pain or greater than 95% relief without medication; fair efficacy: greater than 50% pain relief with or without medication; poor efficacy: no pain relief.
5. Time for evaluation of efficacy after GN surgery: delayed cure after CN MVD surgery is rare, so the evaluation of efficacy can be performed immediately after surgery.
6.Management of ineffective or recurrent patients after GN surgery: Patients with ineffective or recurrent patients can be considered for secondary MVD, and it is recommended to perform PR of the superior root of the linguopharyngeal nerve root (and) vagus nerve root while releasing adhesions and vascular decompression.