Microvascular decompression of cranial nerves: lessons learned after 4400 operations

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Object. Microvascular decompression has become an accepted surgical technique for the treatment of trigeminal neuralgia, hemifacial spasm, glossopharyngeal neuralgia, and other cranial nerve rhizopathies. The senior author (P.J.J.) began performing this procedure in 1969 and has performed more than 4400 operations. The purpose of this article is to review some of the nuances of the technical aspects of this procedure.

Methods. A review of 4415 operations shows that numerous modifications to the technique of microvascular decompression have occurred during the last 29 years. Of the 2420 operations performed for trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia before 1990, cerebellar injury occurred in 21 cases (0.87%), hearing loss in 48 (1.98%), and cerebrospinal fluid (CSF) leakage in 59 cases (2.44%). Of the 1995 operations performed since 1990, cerebellar injuries declined to nine cases (0.45%), hearing loss to 16 (0.8%), and CSF leakage to 37 (1.85% p < 0.01, test for equality of distributions). The authors describe slight variations made to maximize surgical exposure and minimize potential complications in each of the six principal steps of this operation. These modifications have led to decreasing complication rates in recent years.

Conclusions. Using the techniques described in this report, microvascular decompression is an extremely safe and effective treatment for many cranial nerve rhizopathies.

Article Information

Address reprint requests to: Peter J. Jannetta, M.D., Department of Neurological Surgery, University of Pittsburgh Medical Center, 200 Lothrop Street, Suite B-400 PUH, Pittsburgh, Pennsylvania 15213.

© AANS, except where prohibited by US copyright law.

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Figures

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    Upper: Drawing showing the patient's head placed at the foot of the operating table to allow more leg room for the surgeon during the microsurgical portion of the procedure. The head is secured with three-point fixation and the patient is turned in the lateral decubitus position. The head is rotated slightly away from the affected side and flexed to approximately two finger breadths from the sternum. Lower: Drawings showing how the angle of the vertex is tailored depending on the cranial nerve approach. For trigeminal or cochlear nerve approaches, the vertex of the head is kept parallel to the floor to keep the seventh—eighth nerve complex at a more inferior position with respect to the trigeminal nerve. For a seventh or lower cranial nerve approach, the vertex is dropped 15° toward the floor to rotate and expose the proximal aspect of the seventh nerve and to rotate the vestibulocochlear complex more cephalad.

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    Upper: Drawing depicting how the intersection of the digastric groove and the iniomeatal line defines the junction of the transverse and sigmoid sinuses. With a “mind's eye” view of optimal burr hole placement and craniectomy, an incision is drawn centered over the planned craniectomy. Lower: Drawings showing different surgical incisions based on the size of the patient's neck. Short and thick—necked patients require a more posteriorly (medially) directed incision. This angled incision positions the thicker neck musculature more posteriorly (medially) and out of the operative field. This small adjustment is critical in allowing freer movement of the surgeon's hands and instruments while performing the microsurgery.

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    Drawing depicting how bone exposure should demonstrate the junction of the transverse and sigmoid sinuses. Surgical exposure can then be tailored according to the cranial nerve approach desired.

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    Drawing showing how, in the event of inadvertent petrosal vein avulsion, bleeding can be controlled by gentle pressure and packing of the tentorial side using Surgicel covered with a cottonoid. The retractor can be used for placing gentle pressure on the cottonoid and Surgicel while the surgeon looks for the free end of the avulsed vein.

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    Diagram showing that the dorsal root entry zone of the trigeminal nerve can be variable in length and may extend to a more distal portion of the nerve.

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    Drawing of the most common vessel found causing typical trigeminal neuralgia, a rostroventral superior cerebellar artery loop, which compresses the trigeminal nerve either at the brainstem or distally.

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    Diagrams depicting how dissection and mobilization of the arterial loop depend on the anatomy of compression. This figure demonstrates the microsurgical movements that are performed when a typical superior cerebellar artery loop is found compressing the trigeminal nerve. The concepts of Teflon felt placement and proximal-to-distal sweeping movements of the felt along the nerve apply for lower cranial nerve decompressions as well. A: Before the vessel can be moved, the arachnoid must be sharply dissected over the entire length of the loop proximally and distally. B: After the vessel is freed, the vascular loop is lifted off the brainstem at the rostral aspect of the nerve and a medium-sized cigar-shaped piece of Teflon felt is placed between the vessel and the nerve. It is very important to position the distal portion of the felt with the tips of the forceps. The Teflon felt should not be pushed into position by holding its proximal portion. C: After the Teflon felt is placed under the loop, the pledget is gently pushed in a proximal-to-distal fashion along the nerve toward Meckel's cave. This movement elevates the arterial loop and causes it to begin to rotate outward from the ventral surface of the nerve. D: A second Teflon felt, approximately the same size, is placed where the first felt was originally positioned. Using the same proximal-to-distal sweeping motion, the felt should be advanced over the length of the nerve toward Meckel's cave. E: As the Teflon pledgets are advanced, the vascular loop progressively rotates from the ventral aspect of the nerve to the dorsal side. F: A third Teflon pledget is placed where the first felt was originally positioned and, again, a proximal-to-distal sweeping movement along the trigeminal nerve flips the vascular loop to the dorsal aspect of the nerve. G: After the vascular loop is flipped to the dorsal surface of the nerve, pledgets are placed between the vessel and the nerve.

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