1.Anesthesia
Intravenous compound general anesthesia can make the patient completely relaxed and ensure the safety of surgery. Vital signs should be as stable as possible during induction of anesthesia.
2.Surgical position
The patient is placed in lateral position with the affected side upward, the upper body is elevated about 15 degrees, and the head is naturally lowered about 15 degrees so that the mastoid process is located at the highest level of the head, and at the same time, it should be 5-10cm above the level of the atrium to keep the pressure of the intracranial venous sinus low, which helps to avoid the rupture of the venous wall when the rock vein is treated by electrocoagulation. The affected shoulder is pulled towards the end of the bed with a shoulder strap to reduce the obstruction of the operative field by the shoulder. However, care must be taken not to overstretch the brachial plexus nerve causing injury.
3.Surgical incision
The affected mastoid notch is used as the upper quarter point of the incision, and an oblique incision of about 4 cm in length is chosen according to the length of the neck and the thickness of the neck muscle. After local infiltration with epinephrine saline (1:200,000), the skin was incised and the skin edge was hemostatic with bipolar electrocoagulation. The occipital muscles are incised with an electric knife up to the skull, and the muscles are peeled and drawn away from the occipital bone. The mastoid process is often connected to the sigmoid sinus by 1-2 ductus foramen posteriorly, and the ductus is electrocoagulated and the bone foramen is closed with bone wax.
4.Bone window
A hole is drilled in the occipital bone at the posterior margin of the mastoid process and enlarged into a 2-2.5 cm diameter oblique oval bone window with the superior end revealing the inferior margin of the transverse sinus, the lateral side revealing the posterior margin of the sigmoid sinus, and the intersection angle of the venous sinus at the angle of entrapment. In patients with large mastoid air spaces, it is often necessary to bite open the mastoid air space to obtain a satisfactory exposure, paying attention to carefully closing the mastoid air space with bone wax to avoid postoperative cerebrospinal fluid leakage. Before biting off the skull, the dura mater should be freed well and the dura mater and venous sinuses should not be injured. The guiding veins should be properly electrocoagulated to stop bleeding when encountered. The edge of the bone window should be closed with bone wax to stop bleeding, and the bleeding of the dura and sinus edge should be avoided by electrocoagulation and cauterization as much as possible, and gelatin sponge and cotton pad can be used to stop bleeding.
5.Dural incision
Make an inverted “T” shaped incision centered on the intersection of the transverse and sigmoid sinuses, and suspend one needle for each of the two dura mater. The edges of the dural incision are covered with wet cotton sheets for protection.
6.Release of cerebrospinal fluid
Under direct microscopic view, the cerebellar hemispheres are gently pulled with a brain press in the direction of the mastoid tip, and the cerebrospinal fluid is slowly released until the arachnoid at the auditory nerve is fully exposed. Displacement of the cerebellum can cause the tiny arteries or veins between the cerebellum and the dura to be pulled off, which must be carefully explored to stop the bleeding.
7. Exposure of the trigeminal or facial nerve
The arachnoid membrane on the surface of the cerebellum is cut at the auditory nerve with microscissors, and the arachnoid membrane around the trigeminal nerve root or facial nerve is gradually exposed along the angle of intersection between the cerebellar curtain and the temporal bone rock and cut above the cerebellum until the entire trigeminal nerve or facial nerve is fully exposed. The arachnoid membrane covering the trigeminal root or facial nerve must be extensively dissected to expose this area. In most cases, the arachnoid membrane is thin, translucent, and easily torn, but in some cases it is very thick. Care must be taken to identify the tiny vessels and nerves beneath it to avoid injury. If there is bleeding in the exposure, the pontine vein between the upper cerebellum and the canopy may be torn, and this area should be explored to control the bleeding before continuing deeper.
8.Processing of supratentorial vein
The superior petrosal vein is a group of veins that drain the lateral cerebellum and pontine brain. It is highly variable and usually converges into one or two short thick trunks that merge into a Y-shape when approaching the dural sinus, penetrate the arachnoid and merge into the superior petrosal sinus. If the superior petrosal vein blocks the exposure of the trigeminal or facial nerve, it may be necessary to free cut the arachnoid membrane around the petrosal vein and then electrocoagulate and cut it. The trigeminal nerve root or facial nerve must be exposed and explored before dissection because the pontocerebral branch of the rock vein often crosses the angle of intersection of the trigeminal or facial nerve root with the pontocerebrum and is the vein that most often forms venous compression of the trigeminal or facial nerve, and dissection of the rock vein first may cause the compressed vein to disappear, leading to false negative findings. In principle, as long as the available space can satisfactorily reveal the trigeminal nerve or facial nerve root, the possibility of cerebellar venous infarction can be reduced by not cutting the rock vein and its branches as much or as little as possible and by preserving the reflux of the rock vein. When cutting the rock vein by electrocoagulation, the power of bipolar electrocoagulation should be low, and the vein should be cut off after repeated electrocoagulation to completely burn the vein, and an extra section of the burned vein should be left at the end of the supratentorial sinus.
9.Treatment of responsible vessels
After dealing with the rock vein, probe along the back of the rock bone under the canopy, anteriorly and medially, entering in front of the facial and auditory nerves, medial or lateral to the rock vein. Care is taken not to disturb the facial and auditory nerves and their surrounding arachnoid membrane during the exploration.
It is important to open the arachnoid widely intraoperatively and to thoroughly examine the site where the trigeminal or facial nerve root enters the pontine brain, as there may be more than one responsible vessel. Extensive opening of the arachnoid anterior to the nerve root is necessary to truly free and loosen the responsible vessel compressing the nerve, so that the Teflon cotton, which pads the vessel, has enough space and does not remain tightly attached to the nerve root to continue mediating the impact of the arterial pulsation or form adhesions with the nerve root, leading to pain recurrence.
10.Closing the incision
After the trigeminal or facial nerve roots are processed and the bleeding is carefully stopped, the operative field is flushed with warm saline containing corticosteroids and vasodilators, and the operative cavity is filled to reduce postoperative intracranial gas accumulation. After the items were counted correctly, a collagen sponge was padded inside the dural incision, the dural incision was tightly sutured, and the outside was bonded with a piece of gum metan white sponge with biogel. The bone debris collected at the time of craniotomy was sterilized and cleaned and backfilled with the bone window, which was shaped and fixed with bioadhesive. The incision is not placed in drainage, and the muscle and subcutaneous are sutured in layers. The skin incision is cemented with bio-quick drying glue.