Microvascular Decompression (MVD) of the Trigeminal Nerve

Preoperative Preparation

• MRI brain with FIESTA/CISS sequences + MRA to identify neurovascular conflict
• Audiometric baseline (hearing and brainstem auditory evoked potentials - BAEPs)
• Informed consent including risks of CSF leak, hearing loss, facial numbness, cerebellar injury, stroke, and death (~1%)
• General anesthesia; IV antibiotics

Step 1 - Patient Positioning

• Patient is placed in the lateral decubitus (park-bench) position with the symptomatic side up, or in the semi-sitting position (some centres)
• The head is fixed in a 3-pin Mayfield skull clamp attached to the operating table
• The head is flexed slightly forward and tilted away from the surgeon to open the retrosigmoid corridor
• Intraoperative neuromonitoring is set up: BAEPs (to protect hearing/CN VIII) and facial nerve EMG

Step 2 - Skin Incision and Exposure

• A 3-4 cm curved vertical incision is made ~2 cm posterior and inferior to the mastoid process (behind the ear)
• The skin, subcutaneous tissue, and posterior cervical muscles (sternocleidomastoid, splenius capitis) are incised and retracted
• The occipital bone is exposed; the mastoid emissary vein is identified and controlled with bone wax if encountered

Step 3 - Retrosigmoid Craniectomy / Craniotomy

• A ~2.5 x 2.5 cm bur-hole or craniotomy is made in the occipital bone just medial to the sigmoid sinus and below the transverse sinus
• The junction of the sigmoid and transverse sinuses (the "sinodural angle") is the critical landmark
• The bone flap is elevated (or a craniectomy is performed) with a high-speed drill and Kerrison rongeurs
• The dura mater is exposed overlying the posterior fossa cerebellum

Step 4 - Dural Opening

• The dura is opened in a cruciate or C-shaped fashion, taking care not to injure the underlying sigmoid sinus
• The dural flaps are tacked back with sutures
• CSF is gently released from the cisterna magna by arachnoid opening inferiorly, which relaxes the cerebellum and avoids the need for forceful retraction

Step 5 - Microsurgical Approach to the Cerebellopontine Angle (CPA)

• Under the operating microscope, the cerebellum is gently retracted superiorly and medially using a self-retaining retractor or dynamic retraction
• The cerebellopontine cistern is entered; the arachnoid is incised sharply
• The surgeon navigates along the petrosal surface of the cerebellum toward the brainstem
• CN VII and CN VIII (facial and vestibulocochlear nerves) are identified first as they exit the IAC and serve as anatomical landmarks
• The trigeminal nerve (CN V) is located superiorly, running horizontally toward Meckel's cave

Step 6 - Arachnoid Dissection and Nerve Exposure

• Thickened arachnoid adhesions around CN V are carefully dissected using fine microsurgical scissors and bipolar forceps
• The root entry zone (REZ) of CN V at the pons is fully exposed - this is the critical zone where demyelination occurs due to vascular pulsation

Step 7 - Identification of the Offending Vessel

• The surgeon carefully inspects the entire circumference of the trigeminal nerve REZ, including the ventral, dorsal, and inferior aspects (an endoscope may be used to look around the nerve)
• The offending vessel is identified (most commonly the SCA looping inferiorly and compressing the superior aspect of CN V at the REZ)
• The vessel may be adherent, indenting, or distorting the nerve
• All neurovascular contacts must be documented; some cases involve multiple offending vessels

Step 8 - Decompression (The Key Step)

A. Transposition (preferred for arteries)

• The offending artery is mobilized away from the nerve using a dissector
• A small pledget of shredded Teflon felt (PTFE) is interposed between the vessel and the nerve root as a permanent cushion, preventing re-contact
• The sponge must be sized appropriately - not too large (can cause new compression)
• Some surgeons use the "sling" technique: the vessel is transposed and fixed to the dura with a suture (5-0 prolene), keeping it away from the nerve permanently without any foreign material touching the nerve

B. Coagulation and division (for veins)

• Offending veins (e.g., superior petrosal vein tributaries) are bipolar coagulated and divided since they cannot be safely transposed

Step 9 - Verification of Decompression

• The decompression is inspected under the microscope (and optionally with a 30-degree angled endoscope) to confirm no residual vascular contact
• The nerve should lie free without any pulsating vessel touching it
• BAEPs are monitored throughout to detect any cochlear/brainstem ischemia

Step 10 - Closure

• The microsurgical field is irrigated copiously with warm saline
• Meticulous hemostasis is achieved
• The dura is closed watertight with 4-0 sutures (a dural patch/fascia graft may be used if needed)
• The craniectomy defect is filled with cranioplasty material (titanium mesh, PMMA cement, or the bone flap is replaced)
• Muscles and fascia are closed in layers
• Skin is closed with interrupted sutures or staples
• A subgaleal drain may be placed

Postoperative Care

• Patient is monitored in ICU/step-down for 24 hours
• Head of bed elevated 30 degrees
• Watch for: CSF leak, hearing loss, facial weakness (CN VII), cerebellar edema, hematoma
• Hospital stay: typically 2-4 days
• Return to normal activity: 4-6 weeks

Outcomes

• Initial pain relief: >90% of patients after successful MVD
• Long-term cure: ~70-80% at 10 years (among the best of all TN procedures)
• The procedure preserves trigeminal sensation (unlike rhizotomy/ablative procedures)
• Recurrence is lower than Gamma Knife or radiofrequency ablation, per the Mayfield Clinic MVD overview and the NIH/PMC surgical TN review

Key Complications to Know