Microvascular Decompression: Salient Surgical Principles and Technical Nuances

The overall goal of this procedure is to safely decompress the offending vessel from the trigeminal nerve. This is accomplished by first positioning the patient correctly. The second step of the procedure is to make the right skin incision.

The third step of the procedure is to drill off the bone and incise the dura in the standard fashion. The final step of the procedure is exposure of the superior portion of the CP angle, decompression of the nerve and closure. Ultimately, an excellent outcome can result in terms of pain relief with minimal surgical morbidity by using microvascular decompression.

Today we're gonna show you how we perform a microvascular decompression of the trigeminal nerve in order to treat trigeminal neuralgia. The main advantage of this surgery is in order to treat the main cause of trigeminal neuralgia, which typically involves compression of the nerve by a blood vessel. This procedure has a significant advantage over other procedures such as radiofrequency, lesioning, balloon compression, or radiosurgery in the fact that the nerve is restored to a more healthier environment.

The cause of the compression is usually identified and treated and the outcomes are excellent. Patients who undergo the surgery typically experience immediate pain relief post-op, and that occurs in about 80 to 90%of patients by 10 years later. Typically, we expect to see 60 to 70 of those patients remain pain-free.

After the patient is brought into the operating room, anesthesia is induced. Both local and general anesthesia are used. Once anesthetized, place the patient in pins while on the operating room table.

Move the patient to the lateral park bench position with the side of the desired microvascular decompression facing up. Next pad the patient's pressure points and place an axillary roll. Tape the patient's chest and hips securely to the table to allow later rotation of the table.

If necessary, tape down the patient's shoulder for purposes of visualization. Rotate the head approximately 10 to 15 degrees away from the affected side head rotation. Should not exceed 30 degrees.

Then flex the next slightly so that the planned surgical trajectory is now almost orthogonal to the floor, and the vertex is tilted slightly down. Ensure that there is no pathologic compression of venous drainage from the head. Specifically, there should be room for at least two finger breaths between the mandible and upper thorax.

Next, secure the head with three point head fixation. The next step is to hook up the electrophysiologic leads to monitor the brainstem auditory evoked response and facial nerve activity.Perfect.Cut. Prior to prepping and draping, assess the external landmarks.

It is helpful to draw the inion inal line with an indelible marker. This dotted line represents the superficial representation of the location of the transverse sinus. Next, draw a dotted line overlying the course of the digastric groove.

The portion of this line inferior to the inal line represents a superficial representation of the location of the sigmoid sinus. Draw a curva linear incision approximately two finger breaths behind the pin for the length of the ear with the incision location defined. Prep and drape the patient using a scalpel, deepen the incision.

Then using a scalpel and monopolar cautery dissect down to the bone. Next place self retaining retractors in the opening. To begin the C Craniectomy picture the superficial representation of the junction of the transverse and sigmoid sinuses.

Begin drilling to expose the transverse sigmoid junction. The next step is to perform a three centimeter C craniectomy using the M eight drill. Once the transverse and sigmoid sinuses have been exposed, extraorally wax the bone edges thoroughly.

It is important to drill far enough laterally to allow proper dural reflection and visualization. When the mastoid air cells are encountered, wax them vigorously. Next, open the dura in a stellate fashion.

Take the dural incision as close as possible to the transverse sigmoid junction. Then tack up the dural leaves using four zero neural on. At this point, a corridor directly adjacent to the junction of the tentorium and petras temporal bone should be visible after the dura has been reflected and sutured.

Place a Layla retractor with telfa underlying the retractor. Now elevate the cerebellum and gently retract it medially. Using suction and bipolar electrocautery, allow the CSF to egress this results in gentle relaxation of the cerebellum.

With the cerebellum now having fallen away from the petro tentorial junction, advance the retractor with further gentle elevation of the cerebellum. As the corner is turned and the cerebellum pontine angle is exposed, visualize the seven eight nerve complex. During this exposure, pay vigilant attention to the brainstem, auditory evoked responses and the facial nerve monitoring To guard against retraction injury, visualize the trigeminal nerve superior and medially to the seven eight nerve complex.

The next step is to use micro scissors to open the arachnoid around the trigeminal nerve. Inspect the trigeminal nerve beginning at the site of brainstem exit and proceeding laterally looking for the cause of the trigeminal neuralgia. The cause of the neuralgia in this case is a rastro ventral loop of the superior cerebellar artery, which is the most common vessel found in trigeminal neuralgia.

After the causative vessel is identified, dissect and free it. Next mobilize the vessel loop away from the trigeminal nerve. Then place a small piece of Teflon underneath the vessel to elevate it off the trigeminal nerve following decompression.

Reexamine the trigeminal nerve on all sides to be certain that no additional compressing vessels are present. To begin the closure process, irrigate the wound with saline and remove all retractors. Close the dura using a running 4.0 neural.

On next place a piece of gel foam over the dural incision. Use methyl methacrylate to fill in the cranial defect. Use a small KLS plate to secure the methyl methacrylate prosthetic to the skull.

Next, copiously, irrigate the wound with bacitracin irrigation. Then use two oh vicryls to close the muscle in multiple layers. Use three zero vicryls in the gala and dermis.

Use a running four zero Monocryl to close the skin finish by covering the wound with bacitracin ointment. 59 patients underwent microvascular decompression by two of the authors at Vanderbilt University Medical Center between July, 2006 and July, 2009. Of these 93%of the patients experienced significant improvement or full resolution of facial pain at follow-up ranging from six weeks to two years.

In addition, these authors found that when the cranial defect is filled, the incidence of cerebral spinal fluid leakage dropped significantly. As a result, bone flap or methyl methacrylate flap replacement of c craniectomy defect is now standard protocol for closure of these procedures. So while performing this procedure, it's very important for the surgeon to understand the anatomy of the trigeminal nerve and how the vessel that's compressing the trigeminal nerve will impact it.

Usually the superior cerebellar artery is the most common artery involved in compression of the nerve, and this is from the superior part of the nerve. Sometimes the anterior inferior cerebellar artery can compress the nerve from below. Typically with superior cerebellar artery compression, we see facial pain in the region of the second and third division.

If on a rare situation, the trigeminal nerve is compressed from below, usually from the anterior inferior cerebellar artery, pain syndromes tend to occur in the midsection upper part of the nerve. It's important at the end of the surgery as the patient awakes to verify the following neurological functions remain intact, that the patient's able to follow commands in all four extremities, that the patient's corneal reflexes are intact, and that facial movement is symmetric. Hearing preservation is usually verified later on as the patient awakens more and can be tested for this.