microvascular_decompression_for_hemifacial_spasm

Microvascular decompression for hemifacial spasm

see also Hemifacial spasm treatment.


Many ablative procedures are effective for hemifacial spasm (HFS) (including sectioning of divisions of the facial nerve), however, this leaves the patient with some degree of facial paresis. The current procedure of choice for HFS is microvascular decompression (MVD) wherein the offending vessel is physically moved off of the nerve, and a sponge (e.g. Ivalon®, polyvinyl formyl alcohol foam) is interposed as a cushion. Other cushions may not prove to be as satisfactory (muscle may disappear, and Teflon felt may thin 1)).

Most often, the offending vessel approaches the nerve at a right angle, and causes grooving in the nerve. Compression must occur at the root exit zone; decompression of vessels impinging distal to this area is usually ineffective.

Intra-operative brainstem auditory evoked potentials (BAER), 2) or more applicable, direct VIII nerve monitoring 3) may help prevent hearing loss during MVD for 7th or 8th nerve dysfunction. Furthermore, monitoring for the disappearance of the (delayed) synkinetic response may aid in determining when adequate decompression has been achieved (generally reserved for teaching institutions) 4).

The facial nerve should not be manipulated, and one should avoid dissection around the VII and VIII nerves near the IAC 5). Vessels must be preserved, especially the cochlear artery and small perforators. Place gentle medial traction on the cerebellum (<1 cm is recommended 6) ), and incise the arachnoid membrane between the flocculus and the eighth nerve (to avoid tension on nerves that could cause post-op deficit). The IX nerve may be followed medially from the jugular foramen to locate the origin of the VII nerve (the origin of VII is 4 mm cephalad and 2 mm anterior to that of the IX nerve 7)).


Redo MVD remains a feasible treatment option for HFS patients who have failed to benefit from prior MVD, but is associated with higher risks of cranial nerve and vascular injuries 8).

Three-dimensional reconstructions were found to provide much clearer characterization of this area than traditional preoperative imaging. Therefore, Teton et al., suggest that use of these reconstructions in the preoperative setting has the potential to help identify appropriate surgical candidates, guide preoperative planning, and thus improve outcome in patients with HFS 9).

The classic surgical position for microvascular decompression (MVD) is lateral decubitus position with the head rotated 10 degrees away from the affected side.

Ko et al. measured the angles of the posterior fossa, specifically focusing on the surgical corridors used in MVD surgery for hemifacial spasm (HFS), to identify the proper surgical position.

The following parameters were assessed on preoperative magnetic resonance images (MRI): petrous angle (PA), sigmoid angle (SA), sigmoid diameter (SD), and root exit zone-sigmoid sinus edge angle (REZ-SEA).

The mean PA was 59.7 ± 5.6 degrees, SA was 16.8 ± 8.6 degrees, SD was 13.4 ± 3.5 mm, and the mean REZ-SEA was 59.6 ± 5.8 degrees. The difference between the maximum SA to avoid cerebellar hemisphere injury and the minimum REZ-SEA required to verify the facial nerve REZ is assumed to be the usable range of angles for the operative microscope; the average midpoint of this range was 38.2 ± 6.4 degrees.

Turning the patient's head 10 degrees away from the affected side was generally appropriate for performing MVD surgery because it provided a mean microscope angle of 48 degrees. However, some patients had corner values for the sigmoid angle, REZ-SEA, and sigmoid sinus diameter. Rotating a patient's head based on precise calculations from preoperative MRI helps to achieve successful surgery 10).

“5–5-5” incision (5mm medial, extending 5cm up to 5cm down), used for approach to seventh/ eighth nerve complex:

A video demonstrates the surgical steps of a MVD at left facial REZ in a 41-year-old man who presented with typical hemifacial spasm on the left side due to VIIth nerve REZ compression by PICA. A classical retromastoid and infrafloccular approach was performed to avoid stretching of the VIIIth nerve and access the VIIth nerve ventro-caudally. The next step is insertion-along the brainstem, VII-VIIIth nerves REZ, and flocculus-of a plaque made of Teflon felt (Edward-type) which is semi-rigid, and by principle does not exert direct compression on the facial REZ, thus avoiding compression and/or transmission of pulsations on the VIIth nerve. The patient's postoperative period was uneventful and clinical outcome good 11)


1)
Rhoton AL. Comment on Payner T D and Tew J M: Recurrence of Hemifacial Spasm After Microvascular Decompression. Neurosurgery. 1996; 38
2)
Friedman WA, Kaplan BJ, Gravenstein D, et al. Int raoperative Brain-Stem Auditory Evoked Potentials During Posterior Fossa Microvascular Decompression. J Neurosurg. 1985; 62:552–557
3)
Moller AR, Jannetta PJ. Monitoring Auditory Functions During Cranial Nerve Microvascular Decompression Operations by Direct Recording from the Eighth Nerve. J Neurosurg. 1983; 59:493–499
4)
Moller AR, Jannetta PJ. Microvascular Decompression in Hemifacial Spasm: Intraoperative Electrophysiological Observations. Neurosurgery. 1985; 16:612–618
5) , 6)
Fukushima T, Carter LP, Spetzler RF, Hamilton MG. In: Microvascular Decompression for Hemifacial Spasm: Results in 2890 Cases. Neurovascular Surgery. New York: McGraw-Hill; 1995:1133–1145
7)
Rhoton AL. Microsurgical Anatomy of the Brainstem Surface Facing an Acoustic Neuroma. Surg Neurol. 1986; 25:326–339
8)
Lee S, Park SK, Lee JA, Joo BE, Park K. Missed Culprits in Failed Microvascular Decompression Surgery for Hemifacial Spasm and Expenses for Redo Surgery. World Neurosurg. 2019 May 31. pii: S1878-8750(19)31508-6. doi: 10.1016/j.wneu.2019.05.231. [Epub ahead of print] PubMed PMID: 31158550.
9)
Teton ZE, Blatt D, Holste K, Raslan AM, Burchiel KJ. Utilization of 3D imaging reconstructions and assessment of symptom-free survival after microvascular decompression of the facial nerve in hemifacial spasm. J Neurosurg. 2019 Jul 12:1-8. doi: 10.3171/2019.4.JNS183207. [Epub ahead of print] PubMed PMID: 31299649.
10)
Ko HC, Lee SH, Shin HS. Proper Head Rotation when Performing Microvascular Decompression for Hemifacial Spasm: An Orthometric Consideration Based on Preoperative MRI. J Neurol Surg A Cent Eur Neurosurg. 2022 Feb 15. doi: 10.1055/s-0041-1725950. Epub ahead of print. PMID: 35170003.
11)
Sindou M, Esqueda-Liquidano M, Brinzeu A. Microvascular Decompression for Hemifacial Spasm. Neurosurgery. 2014 Sep 24. [Epub ahead of print] PubMed PMID: 25255262.
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