Far-lateral approach to intradural lesions of the foramen magnum without resection of the occipital condyle

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Object. The goal of this study was to determine whether drilling out the occipital condyle facilitates surgery via the far-lateral approach by comparing data from 10 clinical cases with that from studies of eight cadaver heads.

Methods. During the last 6 years at Louisiana State University Health Sciences Center—Shreveport, 10 patients underwent surgery via the far-lateral approach to the foramen magnum. Six of these patients harbored anterior foramen magnum meningiomas, one patient a dermoid cyst, two patients vertebral artery (VA) aneurysms, and an additional patient suffered from rheumatoid disease of the craniocervical junction. The surgical approach consisted of retromastoid craniectomy and C-1 laminectomy.

The seven tumors and the pannus of rheumatoid disease were completely excised, and the two aneurysms were clipped without drilling the occipital condyle. In one patient a chronic subdural hematoma was found 3 months after surgery, but no patient displayed any complication associated with surgery. It is significant that in no patient was a cerebrospinal fluid leak present. All patients experienced improved neurological function postoperatively.

To compare surgical visibility, eight cadaveric specimens (16 sides) were studied, including delineation of the VA and its segments around the craniocervical junction. Increase in visibility as a function of fractional removal of the occipital condyle was quantified by measuring the degrees of visibility gained by removing one third and one half of the occipital condyle. Removal of one third of the occipital condyle produced a mean increase of 15.9° visibility, and removal of one half produced a mean increase of 19.9°.

Conclusions. On the basis of their findings the authors conclude that removal of the occipital condyle is not necessary for the safe and complete resection of anterior intradural foramen magnum tumors.

Article Information

Address reprint requests to: Anil Nanda, M.D., Louisiana State University Health Sciences Center, Department of Neurosurgery, P.O. Box 33932, 1501 Kings Highway, Shreveport, Louisiana 71130–3932. email: ananda@lsuhsc.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Photograph obtained during cadaveric study. After reflecting the skin flap, the sternocleidomastoid muscle is reflected anteriorly after it is detached from the superior nuchal line and the mastoid process. This exposes the splenius capitis muscle (note the direction of the fibers). The spinal accessory nerve is seen emerging from the two heads of the sternocleidomastoid. The posterior belly of the digastric muscle is exposed. The internal jugular vein (IJV) is located deep with respect to the sternocleidomastoid muscle and courses deep with respect to the digastric muscle. The occipital artery crosses the internal jugular vein, which extends deep in relation to the digastric muscle. m = muscle.

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    Photograph obtained during cadaver study showing the boundary and content of the suboccipital triangle. It cannot be overemphasized that, although the most important content of the suboccipital triangle is the VA, fat and areolar tissue form the bulk content of the triangle. The rectus capitis posterior minor muscle is medial to the rectus capitis posterior major muscle and usually is not seen in this approach. The superolateral boundary is formed by the superior oblique muscle and the inferolateral boundary is formed by the inferior oblique muscle.

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    A panoramic view of the suboccipital region after the muscles of the triangle have been removed. The VA emerges from the foramen transversarium of the axis or C-2 and runs superiorly and laterally. Here it is crossed by the dorsal root of the C-2 nerve. The artery then enters into the foramen transversarium of the atlas. Note the proximity of the VA to the internal jugular vein. The VA enters the suboccipital triangle, runs on the lateral mass of the atlas, and curves anteriorly and laterally to enter the intradural compartment.

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    After a lateral suboccipital craniotomy that included the rim of foramen magnum was performed, the posterior arch of the atlas is removed. The posterior rim of the transverse foramen of the atlas is removed to free the VA. The VA is mobilized medially and inferiorly to make space to drill the occipital condyle.

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    Photograph showing the measurement of the longest axis of the occipital condyle (OC) after transposition of the VA. Lines (partially covered by the measuring tape) divide the condyle into three equal parts.

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    Illustration showing degrees of visibility gained by drilling one third or one half of the occipital condyle.

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    Photograph showing the technique of dural opening after the occipital condyle has been drilled. A cuff of the dura mater is kept around the VA for later closure.

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    Photographs showing the comprehensive intradural view in which the lower cranial nerves (CNs) are seen. Upper and Center: The gap between the root of the glossopharyngeal nerve (CN IX) and the rootlets of the vagus nerve (CN X) is appreciable. The flocculus of the cerebellum and the choroid plexus of the fourth ventricle are easily seen (center). The PICA passes between the rootlets of the vagus nerve (center). Here the loop of the anterior inferior cerebellar artery (AICA) is quite low. The entry of the glossopharyngeal, vagus, and accessory nerves into the jugular foramen is clearly seen as well as the entry of the hypoglossal nerve (CN XII) into the hypoglossal canal. Looking superiorly, the trigeminal nerve (CN V) and the acousticofacial bundle (AFB) can also be seen. Lower: The petrosal vein is seen draining into the superior petrosal sinus.

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    Case 6. Left: Sagittal T1-weighted MR image revealing a homogeneously enhancing tumor located anterior to the foramen magnum. Right: Postoperative sagittal T1-weighted MR image demonstrating no enhancement indicative of residual tumor.

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    Left: Axial T1-weighted MR image revealing a homogeneously enhancing tumor located anterior to the foramen magnum. Right: Contrast-enhanced T1-weighted MR image obtained at the 1-year follow-up examination confirming that there is no residual tumor.

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