Figure 1: The cavity left after removal of a giant meningioma from the brain of a patient who died in a “Government Hospital for the Insane” (photo courtesy of the Cushing Brain Tumor Registry at Yale University, circa ~1892).

Figure 2: Relative distribution of the most common intracranial meningiomas is illustrated.

Figure 3: A large olfactory groove meningioma (upper and middle images) with associated edema is evident. Note the displacement of the frontopolar and anterior cerebral arteries on the angiogram. This tumor is best suited for a transcranial approach. If the tumor does not extend significantly beyond the middle of the orbit or lateral to the optic nerves on coronal MR images, an endonasal route is reasonable (lower images).

Figure 4: The details of a bifrontal craniotomy for resection of large tumors with invasion of the nasal sinuses is demonstrated. Note the two different outlines of the craniotomy, the smaller one in hashed lines is more than adequate for giant tumors.

Figure 5: Bony anatomy of the anterior and middle cranial base is reviewed. The orange arrows point the typical origin of olfactory groove meningiomas (image courtesy of AL Rhoton, Jr).

Figure 6: Superior view of the olfactory groove and its anatomic relationships to the surrounding structures is illustrated. Note the change in the horizontal level of dissection along the midline skull base compared with the roof of the orbits. This anatomic relationship should be kept in mind during devascularization of the tumor along the skull base. Anterior and posterior ethmoidal arteries are the main source of intraoperative blood loss and their early control at the base of the tumor can improve the safety and efficiency of the operation (images courtesy of AL Rhoton, Jr).

Figure 7: Tumor location in relation to external and internal landmarks. The head is rotated about 45 degrees. The nondominant hemisphere is the preferred side of approach for this midline tumor.

Figure 8: This is the initial operative view through a right-sided pterional approach. The anterior limb of the Sylvian fissure is widely split. The arachnoid membranes encasing the opticocarotid cisterns are sharply dissected in order to release cerebrospinal fluid for improved brain relaxation. This lateral operative trajectory allows early identification, localization, and protection of important cerebrovascular structures.

Because of the large size of these tumors and the need for early access to the anterior skull base for tumor devascularization, the use of any measure that can help decrease cranial tension, including preoperative steroids, mannitol, lumbar CSF drainage and propofol (Diprivan), is advised to avoid unwanted frontal lobe retraction injury.

Figure 9: I dissect the arachnoid plane between the ipsilateral optic nerve/chiasm/carotid artery and the posterior capsule of the tumor early in the dissection process and place a small cottonoid patty to cover and protect these structures. Great care is taken to work within the arachnoid planes and avoid aggressive manipulation of the nerve. Such early recognition of cerebrovascular structures allows execution of more efficient maneuvers during which I can remove the tumor without always “looking out” for these vital structures. The anterior trajectory of the bifrontal approach places the tumor between the surgeon and the vital cerebrovascular structures, leaving the surgeon less oriented to the exact whereabouts of the optic nerves and carotid arteries.

Figure 10: Next, the base of the tumor is thoroughly devascularized as far as possible to expose the contralateral orbital roof. This maneuver is facilitated by gentle mobilization and rotation of the tumor superiorly and laterally, usually feasible because of the previous measures employed to decrease cerebral tension.

This step is critical for advancing the efficiency of tumor resection and minimizing blood loss, especially in the case of a large vascular tumor. The tumor is shaped like a mushroom and the dural attachment at its base is smaller than its dome. Heat injury to the optic nerves and carotid artery is avoided.

The ethmoidal artery feeders (inset image) along the mid anterior skull base can lead to torrential bleeding because of the avulsion of these vessels during tumor mobilization. I pack Gelfoam powder spheres soaked in thrombin into the bleeding sites within the bone after the skull base has been cleared from the tumor; some pressure and patience often achieves hemostasis. I have even used Bovie cautery to stop bleeding there as these vessels retract into the skull base and their control can be difficult.

Figure 11: The tumor is then debulked using an ultrasonic aspirator, microscissors, and pituitary rongeurs, and shrunken with bipolar cauterization. The olfactory nerves are often too involved with large tumors and are sacrificed. With a small to moderate size tumor, preservation of these nerves is possible through microsurgical techniques. It is ideal to save at least one of these nerves.

Figure 12: Cottonoid patties may be used to create dissection planes between the tumor and the pial membranes. I use microsurgical techniques under high magnification to sharply dissect the arachnoid layers and mobilize the tumor capsule away from the fronto-orbital and other anterior cerebral branching arteries. If the tumor cannot be safely dissected a thin sheet of tumor is left behind.

Figure 13: It is imperative to differentiate tumor-feeding vessels from en passage perforating arteries, especially along the posterior aspect of the tumor capsule. This illustration demonstrates that the A1 segment is adherent to the posterior tumor capsule and the artery of Heubner traveling posteriorly. The inset image shows microdissection of an arterial tumor feeder to ensure its identity (tumor feeder versus en passage) before its sacrifice.

Aggressive indiscriminate coagulation must be avoided along the posterior pole as it can be a significant source of morbidity from this surgery. If an inadvertent perforator avulsion injury occurs, a small piece of cotton is used to plug the bleeding point on the parent artery. Gentle pressure/tamponade and patience is all that is needed to achieve hemostasis. This maneuver will minimize further injury to the parent arterial branch by cauterization. Early devascularization of the tumor, as discussed above, minimizes tumor bleeding and allows microsurgery in clear operative fields.

Figure 14: Once dissection is complete, the tumor and the infiltrated dura are removed. The invaded bone is then drilled away. Preoperative CT scans and navigation can help determine the extent of bony resection. If the air sinuses are encountered, large autograft fat globules plug the defect while a piece of pericranium is used to cover the bony defect. I often remove or drill the crista galli to reach and excise the tumor on its contralateral side.

Figure 15: The anatomy of the base of the tumor is re-emphasized here: Please note the mushroom appearance of the tumor and the anterior ethmoidal arteries. These anatomical relationships will prevent the surgeon from finding the source of bleeding in the tight operative field at the base of the tumor. Bovie electrocautery applied to the base of skull will plug the transosseus feeding arteries whose lumen is often kept open via the bone around them as they defy bipolar coagulation. 

Figure 16: The isolated anatomy of the neurovascular structures in the operative position and intimately involved with the tumor is magnified. The proximal A2 branches are at risk during the dissection and can be significantly adherent to the tumor capsule. 

Figure 17: The top view of the pathology and involved structures demonstrates the location of the hypothalamic perforators that are consistently pushed posteriorly and not encased by the tumor. In addition, the distal A2's are draped and displaced at the superior tumor pole. 

Figure 18: This patient presented with confusion and was found to harbor a large olfactory groove meningioma with associated edema.

Figure 19: The intraoperative findings via a right-sided pterional cranitomy are reviewed. The first photo demonstrates the neurovascular anatomy in relation to the posterior border of the tumor. The lateral subfrontal trajectory allows early identification of the tumor base relative to the optic nerve (ON) and carotid artery (ICA). The tumor is devascularized along its base while protecting the optic nerve and ICA (second row). The base of the tumor is completely disconnected until the contralateral orbital roof and the pial surfaces of contralateral subfrontal region are evident (third row). After the tumor is debulked and removed piecemeal, the anterior cerebral arteries and their associated branching vessels are dissected from the posterior tumor capsule.