Al-Mefty’s Meningiomas: Medicine & Health Science Books @ Al-Mefty’s Meningiomas Second Edition. Franco DeMonte, MD, FRCSC, FACS Professor of Neurosurgery and Head and Neck Surgery Mary. Al-Mefty O(1). Author information: (1)Department of Neurosurgery, University of Mississippi Medical Center, Jackson. Anterior clinoidal meningiomas are.
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They are second only to clival meningiomas in surgical mortality and morbidity rates, failure of total removal, and high rate of recurrence. Acknowledging that the best chance for cure comes through radical total removal, most authors, both pioneer and modern, have been content with subtotal removal to avoid the devastating sequelae of injury to the encased cerebral vessels; 6, 9, 17, 22, 31, 43, 51, 56 hence, repeated surgery and radiation therapy are frequently required.
However, unless total removal is achieved, detrimental regrowth is expected in the meningipmas of patients. Recent advances in cranial-base and cavernous sinus surgery have facilitated total removal, allowing respectable mortality and morbidity rates for these tumors. According to the classification system of Simpson, 47 the extent of tumor excision was either Grade I complete macroscopic removal of the tumor, with excision of its dural attachment, meftu abnormal bone or Grade II complete macroscopic removal of the tumor and of its visible extensions, with coagulation mningiomas its dural attachment.
Our experience with intraoperative anatomical observation led meninglomas to distinguish three categories of this tumor Groups I, II, and IIIeach with a marked influence on the surgical difficulties, ability to achieve total removal, and outcome.
These groups relate to the presence of interfacing arachnoid membranes between the tumor and the mneingiomas vessels. The presence or absence of this arachnoid membrane depends on the origin of the tumor and its relation to the small intradural carotid artery segment lying outside the carotid cistern.
As the carotid artery emerges from the cavernous sinus inferomedial to the anterior clinoid, it enters the subdural space to be vested in the carotid cistern. This cistern is bordered superiorly by the dura over the anterior clinoid process and the frontal lobe, and inferiorly by the dura covering the superior aspect of the cavernous sinus. The arachnoid does not follow the internal carotid artery into the cavernous sinus space, nor is it attached to the anterior clinoid process.
A 1-or 2-mm segment of naked internal carotid artery lies between the investment of the carotid cistern and the dura of the cavernous sinus. The inferior part of the carotid cistern and the superior part of the interpeduncular cistern are in apposition, creating a single Nefty membrane. If the meningioma’s origin is proximal to the end of the carotid cistern Group Ias is the case with a meningioma originating from the inferior aspect of the anterior clinoid, the tumor will enwrap the carotid artery, directly adhering to the adventitia in the absence of meninngiomas intervening arachnoid membrane Figs.
As the tumor grows, this direct attachment to the vessel wall continues to the carotid bifurcation and along the middle cerebral artery, advancing the arachnoid membrane ahead of it.
This situation makes dissecting the tumor from the carotid artery and the middle cerebral artery branches impossible and explains why some authors describe tumors invading the arterial wall.
Neurology | Al-Mefty’s Meningiomas
Artist’s drawing of a Group I meningioma. The tumor encases the carotid artery and its branches, with direct attachment to the adventitia. The optic nerve maintains an arachnoid plane from the chiasmatic cistern.
A Group I meningioma. Preoperative computerized tomography appearance. During surgery, no arachnoid membrane was found and dissection of the middle cerebral and carotid arteries was impossible. Lateral carotid arteriogram demonstrating narrowing of the carotid and middle cerebral arteries by the encasing tumor. Thus, as the tumor grows, an arachnoid membrane of the carotid cistern and, distally, of the sylvian cistern separates the tumor from the arterial adventitia.
Although the tumor engulfs the vessels, this arachnoid membrane remains intact, making microsurgical dissection feasible despite total encasement of the vessels Figs. This observation correlates with reports in the literature concerning the feasibility of tumor dissection despite total vascular encasement.
A Group II meningioma. Artist’s drawing showing the tumor encasing the carotid artery and its branches. An arachnoid membrane of the carotid cistern separates the tumor from the adventitia, rendering dissection possible.
The optic nerve maintains an arachnoid membrane from the chiasmatic cistern. Retouched operative photograph showing the optic nerve IIthe anterior cerebral artery A 1the middle cerebral artery M 1and part of the internal carotid artery C dissected free from the encasing tumor T. Dissection continues on the proximal carotid artery and into the cavernous sinus.
The dissection is relatively easy, owing to the presence of the arachnoid membrane of the carotid cistern. Computerized tomography scan left and arteriogram, anteroposterior view right. Notice the arterial narrowing by the encasing tumor.
Dissection and tumor removal were facilitated by the presence of an intervening arachnoid membrane. The optic chiasm and the optic nerves in both Group I and Meniingiomas tumors are wrapped in the arachnoid membrane of the chiasmatic cistern, and dissecting them free from the tumor is relatively easy with a microsurgical technique. In patients having undergone meningiojas surgery, the arachnoid membrane may be violated; subsequently, meningimoas dissection plane is lost and the tumor will be in direct contact with the adventitia.
Tumors in Group III originate at the optic foramen, extending into the msfty canal and the tip of the anterior clinoid process. These tumors are usually small. The arachnoid membrane is present between the vessels and tumor but may be absent between the optic nerve and the tumor Figs.
A Group III meningioma. Artist’s drawing showing the tumor originating in the optic foramen. The tumor is small, separated from the carotid by the carotid cistern, but it extends into the optic canal.
Retouched operative photograph showing the carotid cistern intact. The tumor T is small and extends into the optic canal.
meningiomqs Computerized tomography scan of a Group III meningioma arrow. Early in this series, the pterional approach was used in seven patients and subfrontal approach in three.
Sincewe have exclusively used the orbitocranial approach described elsewhere 2, 3 for removal of these tumors. This approach provides the ,efty advantages: Meeningiomas patient is placed supine and a spinal drainage needle is inserted.
The scalp incision is begun 1 cm anterior to the tragus, proceeding in a curvilinear fashion behind the hairline to the level of the superior menigniomas line ap the opposite side. This results in the superficial temporal artery coursing posterior to the incision while the branches of the facial nerve are located anteriorly. Preservation of the superficial temporal artery is important since the artery may be needed for extracranial-intracranial EC-IC anastomosis.
The zygomatic arch is dissected in subperiosteal fashion, sectioned at the most anterior and posterior ends, and displaced downward along with its attachment to the masseter muscle.
This maneuver allows a more basal approach to the floor of the middle fossa, obviating obstruction by the bulky temporal muscle. The temporal muscle is retracted posteriorly and inferiorly, exposing the junction of the zygomatic, sphenoidal, and frontal bones.
Removal of the orbitocranial flap then proceeds as described elsewhere. Drilling is continued to completely remove the sphenoid ridge, unroofing the superior orbital fissure and removing the anterior clinoid extradurally. This maneuver intercepts the arterial feeders coming from branches of the middle meningeal artery.
It also assures removal of the involved bone mrningiomas the insertion and prepares for exposure of the internal carotid upon entry to the cavernous sinus.
The dura mater is opened with a semicircular incision centered on the pterion; an extension from the main incision is directed posteriorly and inferiorly to the floor of the temporal fossa. Opening the dura under the microscope provides a transitional adjustment of the surgeon’s dexterity from bone work to fine microsurgical dissection.
When the dura is opened, brain relaxation is achieved by partial drainage of cerebrospinal fluid CSF through the lumbar catheter. The arachnoid over the sylvian fissure is opened, allowing separation of the temporal and frontal lobes. The arachnoid opening is made and extended on the frontal side to preserve the superficial middle cerebral veins when possible.
The relaxed frontal lobe is held by a self-retaining retractor.
Elevation of the frontal lobe should be minimal — a distance of 1. The olfactory nerve is located and preserved by dissecting it for some distance from the base of keningiomas frontal lobe. Preservation of the olfactory nerve deters excessive frontal lobe retraction, otherwise resulting in avulsion meningiomae the olfactory nerve.
Under the operating microscope, a plane of dissection is established between the tumor and the frontal and temporal lobes. Ultrasonic aspiration is used to debulk large tumors. Caution is used not to carry debulking close to the carotid artery or the middle cerebral artery branches.
Tumor removal around this area is continued using only microsurgical dissection with bipolar coagulation and careful piecemeal removal by microdissection. Once the tumor is debulked, the distal branches of the middle cerebral artery are identified under high magnification and, using microdissection, the tumor capsule is removed from the arterial wall. Despite total encasement of these vessels, a thickened arachnoid membrane separated the tumor from the adventitia in Group II tumors.
Dissection is carried to the bifurcation of the carotid artery, removing the tumor from the anterior cerebral artery. Careful dissection under high magnification is continued to free the ventriculostriate arteries, the perforator of the anterior cerebral artery, and the internal carotid artery branches to the optic apparatus.
Dissection becomes easier along the posterior communicating artery and the anterior choroidal artery, since these two mefry have their own vesting arachnoid membranes. Since the tumor may be supplied by arterial twigs from the cerebral artery, the surgeon first confirms that they are tumor feeders and not hypothalamic perforators or the optic nerve meningiomae supply.
Thus, each arterial branch is dissected and followed to ascertain its course. Particular mefhy is paid to spare the artery of Heubner and the vital branches of the striatum. The Meninggiomas membrane was intact in all of our cases of Group II tumors; consequently, removal of the meningiomad from the interpeduncular fossa and the posteriorly displaced basilar artery was usually easy.
The optic nerves in these tumors are displaced in several different ways. The optic nerve may be pushed inferiorly and medially or elevated by the menijgiomas of the tumor meningiokas between the carotid artery and the optic nerve.
In seven of our cases, the optic nerve was jefty engulfed, but in all cases the optic nerve maintained its arachnoid barrier formed by the wall of the chiasmatic cistern.
When the optic nerve is engulfed, it is easier to begin the dissection from the chiasm and continue forward toward the optic canal. Frequently, the tumor extends a bud into the optic canal, requiring unroofing of the meinngiomas canal and careful dissection of the tumor. The arterial supply to the optic mefyt and chiasm is preserved by the same method of dissection.
Particular attention is paid to preserve the inferior group of arteries, which are the sole blood supply to the decussating fibers in the central chiasm. The pituitary stalk is easily recognized by its distinctive color and vascular network. It is usually displaced backward and to the opposite side. Arachnoidal cleavage is present and careful dissection under the microscope is successful. When the tumor extends into the cavernous sinus, as it did in nine of our cases, proximal and distal control of the carotid artery is necessary.
Early in this series, proximal control was achieved by exploring the internal carotid artery in the neck. More recently, this was accomplished by exposing the intrapetrous segment of the carotid artery. The anterior clinoid is already removed, facilitating exposure of the superior aspect of the cavernous sinus. The tumor is then removed through the superior or lateral wall meefty the cavernous sinus, as reported elsewhere.
After gross tumor removal, the dura around the anterior clinoid is evaporated with the CO 2 laser.