Microvascular decompression surgery for trigeminal neuralgia and hemifacial spasm: Naunces of the technique based on experiences with 100 patients and review of the literature
Section snippets
Diagnosis
The character of the pain in trigeminal neuralgia is typically unilateral, episodic, severe, stabbing, shock-like, or lancinating and exacerbated by cutaneous stimuli such as tactile pressure, chewing, brushing, breeze of air, or shaving [7]. The tentative desirable response to neuropathic pain medications such as Carbamazepine or Gabapentin often supports the diagnosis of typical trigeminal neuralgia and is potentially a predictor of a good response to MVD surgery. The character of the pain
Imaging
All patients who are planning to undergo an MVD operation should have a brain magnetic resonance imaging (MRI) or computed tomography (CT) scan to exclude a structural pathology such as a meningioma, acoustic neuroma, or an epidermoid tumor. Epidermoid tumors may present with hemifacial spasm, due to facial nerve irritation, as their only dominant presenting symptom and should be excluded [8]. Even if a high resolution MRI does not identify an offending vascular loop, the consideration for a
Operating room set-up and patient positioning
We place the patient in a lateral decubitus (lateral) position. The surgical technician who hands the instruments to the surgeon stands on one side of the patient and the surgeon either stands (during the craniotomy) or sits (during microsurgical portion of the operation) on the other side across from the technician (Fig. 1A); this position of the surgeon relative to the technician allows an easy transfer of surgical instruments between them.
The lateral position has several advantages over the
The incision
We have recently employed a modified reverse “U” incision—originally described year ago by Walter Dandy—and have enjoyed its advantages over the more commonly used linear incision (Fig. 1E). The Dandy incision typically avoids the neurovascular bundle (occipital nerve and artery) that is usually injured by the linear incision and potentially decreases the risk of postoperative occipital neuralgia. The Dandy incision also obviates the need for deep muscle dissection caudal to the floor of the
The craniotomy or craniectomy
Craniotomy (or craniectomy) is bounded superiorly by the transverse sinus and laterally by the sigmoid sinus. In older patients, the suboccipital dura and the edges of the sinuses may be especially adherent to the inner cortex of the bone, and craniectomy may be beneficial to avoid the risk of dural sinus injury. Placement of the initial burr hole at the junction of the transverse and sigmoid junction would facilitate the later steps in the craniotomy. We have referred to this burr hole as the
Technical pearls for a thorough microvascular decompression for trigeminal neuralgia
It is important to remember that the presumed site of neurovascular conflict is typically at the root entry zone of the nerve as it enters the brainstem and usually not along the nerve in the CP angle cisterns, although the central myelin may extend distally along the nerve. Detailed, patient, and careful inspection (360°) of the space around the root entry zone and the nerve in the CP cisterns is important. Generous opening of the arachnoid layers in the region around the nerve and gentle
The intradural portion of the MVD operation for patients with hemifacial spasm
For patients with hemifacial spasm, the dural closure is depicted in Fig. 6A. For patients with trigeminal neuralgia, the junction of the tentorium and petrous apex is identified and the cottonoid is advanced parallel to this junction (groove) and toward the petrous side. For the patients with hemifacial spasm, the petrous bone (as it turns slightly to join the floor of the posterior fossa) is identified, and the cottonoid is advanced over the rubber dam toward the lower cranial nerves (Fig. 6B
Technical pearls for a thorough microvascular decompression for hemifacial spasm
It is important to remember that the presumed site of neurovascular conflict is at the root exit zone of the nerve as it enters the brainstem, and not along the nerve in the CP angle cisterns. Detailed and careful inspection of the space around the root exit zone is important. Gentle handling of the surrounding neurovascular structures allows safe and thorough inspection. Arterial compression by an offending vessel along the shoulder of the root exit zone has rarely been reported [12].
Closure
Before closure of the dura, the CP angle is well irrigated with saline solution to assure that there is no bleeding, to clear the field, and, importantly, to make sure the implanted Teflon pieces are not becoming mobile and displaced because of the flow of the fluid and CSF. The dura is then approximated primarily. We do not perform a “watertight” dural closure and have had a very low rate of CSF leakage through the incision or the nose. Mastoid air cells are rewaxed thoroughly and the bone
Postoperative care
Patients are watched overnight in the Intensive Care Unit and then transferred to the floor. We do not routinely perform a head CT postoperatively. Dexamethasone taper for 1 week is administered prophylactically against aseptic meningitis. Nausea and pain are controlled through appropriated medications. Preoperative pain medications for trigeminal neuralgia are weaned off starting 1 week after surgery if the patient remains pain free.
The effect of surgery may be delayed especially for the
Final thoughts
As mentioned previously, MVD surgery is an effective and gratifying surgery, both for the patient and the surgeon. The surgeon should take advantage of microsurgical techniques in performing the operation. In the presence of alternative methods of therapy, including percutaneous procedures that carry relatively minimal risk, MVD operations should be performed with low risk to the patient. There is a learning curve involved with this operation and the surgeon should remain always critical of
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