Clinical presentation: A 46 year old male patient experienced several months of dull headache. Immediately prior to presenting to his local doctor, the patient reported tingling and some numbness along the right side of his body. Neurological examination was normal, with the exception of reduced sensation mainly involving the right arm.

Diagnostic workup: A brain CT scan without contrast showed a mass located in the left hemisphere, along the midline. There was some brain swelling or edema associated with the mass. There was no evidence of overlying skull involvement (i.e., no hyperostosis) on the CT bone windows. A brain MRI with and without contrast showed the large mass to have features consistent with a meningioma (relatively uniform contrast enhancement and a thickened "dural tail"). The mass was left parafalcine and was associated with mild surrounding brain edema. A magnetic resonance venogram (MRV) was ordered to determine whether or not the superior sagittal sinus was "open" or "patent". Fortunately, the sinus was open, however the tumor clearly abutted this critical venous structure.

Treatment paradigm: Surgery was offered to the patient owing to the large size of the lesion, its symptomatic presentation, and the eventual direct risk the tumor would confer to the patency of the superior sagittal sinus. It was discussed that should there be a surgical remnant, the patient could be followed with periodic ("serial") imaging (in this case MRI with contrast), and any evidence of recurrent or progressive tumor could be treated with repeat surgery or with focused SRS (see above). The goal of the operation was gross-total resection of the tumor. It was explained to the patient that should there be evidence of brain adherence (stickiness) or some degree of brain invasion by the tumor (less likely, but certainly possible with higher grades of meningioma), this would increase the risk of a postoperative seizure, a risk that would be reduced by the temporary use of an anti-seizure medication (anticonvulsant) during the postoperative convalescence period.

Operative procedure/operative approach: A stereotactic left parietal craniotomy was carried out. Intraoperative image guidance utilized the immediate preoperative contrast MRI multiplanar images. This allowed a more accurately located and optimally measured craniotomy to be carried out. There was evidence of "focal" brain invasion (i.e., "subpial" tumor pentration into the brain cortex in a small area along one of the tumor-brain surfaces), but for the most part the tumor was noninvasive. It could be readily peeled off the vicinity of the superior sagittal sinus. Its origin was determined to be from the dural surface over the paramidline parietal lobe, and not from the falx itself, and this parietal dura along with all the visible tumor were resected uneventfully. A duraplasty was carried out, and the original bone flap immediately restored at the conclusion of the operation. There was no evidence of bone involvement (i.e., no hyperostosis or invasion).

Technical nuances and potential surgical pitfalls: A generous stereotactic craniotomy (creating a bone window that allows for a 1 cm margin around the tumor's margins) should be carried out with careful protection of the sinus during opening. Identification and utilization of the arachnoid plane present between the brain-tumor interface is important. This plane may not be present in certain areas of brain invasion (if any) but nodular tumor may still be seen and felt in such instances. Meticulous dissection off the superior sagittal sinus is required should the tumor abut this structure. A neurosurgeon should always be prepared for sinus violation and blood transfusion in tumors involving or abutting venous sinues. Surgically resistant tumor that adheres to the sinus is best left in situ in order to preserve this venous structure; a focal remnant in this location can readily be treated with postoperative SRS. Another important consideration here is complete removal of any involved dura (in order to achieve a Simpson grade I resection, thereby reducing the risk of tumor recurrence). If this is not possible, bipolar cauterization of any dural remnant is recommended when and where safe to do so. An appropriate biosynthetic duraplasty should also be carried out to restore normal anatomical layers in this setting.

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Background: An intraosseous meningioma is one that grows within a bone. Presumably, in this location meningiomas originate from arachnoid cap cell rests (islands) found in or along vascular channels coursing through the skull (such as diploic or emissary veins or nutrient arteries). Frequently the location for an intraosseous meningioma is in the sphenoorbital region (junction of the sphenoid bone's greater wing - "the temple" region - and the bone constituting the orbital cavity - "eye socket"). In this location, proptosis (bulging of the eye on the side of the tumor) with or without visual compromise (e.g., impaired vision, impaired eye movements, chemical or vascular irritation of the eye) is a common presentation.

Clinical presentation: This 62 year old female presented with slowly progressive bulging of the right eye, along with eye congestion (chemosis and scleral injection) but no frank loss of vision (visual acuity) or impairment of eyeball mobility (ocular motility). Physical examination was remarkable for nontender protrusion (proptosis) of the right eye and sclerial injection/chemosis. Extraocular muscle function and visual acuity were normal. There was no tenderness to the right sphenotemporal region, but there was a mild fullness here compared with the left side.

Diagnostic workup: CT head scan with and without contrast showed a mass whose epicenter was the right greater wing of the sphenoid bone. The mass appeared to encroach upon the right orbital contents. There was proptosis noted on the scan. Bone windows and contrast enhancement suggested a right-sided intraoosseous meningioma. A small protrusion of this tumor (focal exophytic component) was noted deep to the right temporal muscle. A brain MRI with and without contrast was obtained which confirmed the CT findings. There was no obvious invasion of the intraorbital contents. Also noted on this study was the close proximity of the inner (medial) aspect of the tumour to the right internal carotid bifurcation.

Treatment paradigm: Surgery was the appropriate recommendation for this symptomatic tumor, particularly in order to prevent the anticipated tumor-related compromise of the patient's right eye function. A combined procedure ("multidisciplinary approach") with a craniofacial plastic surgeon, ophthalmic surgeon and neurosurgeon was planned in order to optimize the safety and efficacy of the procedure.

Operative procedure/operative approach: A right orbitozygomatic craniotomy was carried out, with gross total resection of the tumor. Stereotactic CT bone-window image-guidance was used intraoperatively as this gave excellent real-time information about the location of sphenoorbital drilling in order to avoid drill-encroachment upon the orbital contents and critical neurovascular structures especially near the medial part of the tumor (around the lesser wing of the sphenoid). No separate dural involvement was found. A cranioplasty was carried out at the end of the procedure for both cosmetic and structural reasons.

Technical nuances and potential surgical pitfalls: Stereotactic CT bone-window image guidance and a multidisciplinary approach has been found to be very useful for intraosseous sphenoorbital meningiomas to enhance the safety of the procedure. Particular care should be taken when drilling along the superolateral orbital cavity bone (vicinity of the lateral rectus muscle; includes prevention of possible high-speed drill-syphon effect), and along the medial aspect of the greater wing of sphenoid as one approaches the lesser wing/orbital apex (optic canal and arterial structures of the carotid bifurcation). Further, postoperative CSF leak can occur from a small durotomy in the region of the superior orbital fissure/frontotemporal dural confluence. Any dural involvement by tumor (e.g., nodular or en-plaque) should be managed with dural excision and duraplasty.

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Background: Meningiomas can occur anywhere in the central nervous system, including in the vicinity of the brainstem. In this location, they can cause significant disability from compression of the brainstem structures resulting in, for example, a variety of cranial nerve palsies (cranial neuropathy), and weakness affecting one or more limbs (including "cruciate paralysis"). Double vision (diplopia), swallowing (dysphagia) and speaking (dysphonia) difficulties, disturbances of facial function (facial paresis), impaired hearing and balance, and limb weakness and spasticity have all been reported in the setting of different brainstem region tumors such as meningiomas. Interestingly, it doesn't take a large-size tumor in this location (the infratentorial space or posterior fossa) to cause significant neurological impairment, mainly because the brainstem region is relatively unaccommodating owing to its restricted dimensions to begin with compared with the space over the brain's convexities (supratentorial space). Finally, it should be noted that hydrocephalus and raised intracranial pressure can result, albeit uncommonly, from brainstem region tumors that obstruct the flow of cerebrospinal fluid anywhere from the cerebral aqueduct (of Sylvius) in the midbrain, down to the bottom part (obex) of the fourth ventricle. Similarly, cerebrospinal fluid build-up in the spinal cord (syringomyelia or syrinx formation) can occur secondary to a compressive brainstem region tumor. Meningiomas and other tumors occuring at the junction of the lower brainstem and upper cervical spinal cord are referred to as craniocervical junction tumors.

Clinical presentation: A 48 year old female presented with slowly progressive loss of muscle bulk (atrophy or wasting) involving the right side of her tongue, and some "clumsiness" of speech and swallowing (i.e., mild dysarthria and dysphagia). Physical examination was normal except for right hemitongue atrophy and deviation consistent with a right hypoglossal nerve (12th cranial nerve) palsy.

Diagnostic workup: A brain MRI was carried out, with and without contrast. This revealed a contrast-enhancing mass with a "dural tail" in the region of the lower brainstem (medulla) on the right side. The mass was located in the vicinity of the right 12th cranial nerve, and explained the patient's symptoms and signs. A CT angiogram (CTA) was subsequently ordered just to confirm that this mass was not an unusual presentation of a brain aneurysm or other vascular abnormality. The CTA suggested this was a solid tumor.

Treatment paradigm: Owing to the age of the patient, and the symptomatic nature of the mass, the patient was recommended for treatment as opposed to "observation". Surgery was favored over stereotactic radiosurgery owing to the surgical accessibility of the mass, the potential for avoidance of brainstem radiation in a relatively young person, and to confirm the diagnosis of meningioma versus some other possibility such as a dural-based metastasis (i.e., a tumor that has spread from another region; click here to go to the metastasis section; or a Schwannoma; click here to go to the Schwannoma section). It was explained to the patient that any residual or recurrent tumor could be treated with repeat surgery or with SRS if needed.

Operative procedure/operative approach: A right far lateral craniotomy using a modified "park bench position" was carried out. There was no need for mobilization of the vertebral artery or for occipital condyle drilling in this case. Stereotactic MRI image-guidance was used, as was lower cranial nerve monitoring (electrodes were placed for cranial nerves 11 and 12; an endotracheal tube with electrophysiological recording capacity was used to monotor cranial nerves 9 and 10). In addition, somatosensory- and motor-evoked potential monitoring (SSEP, MEP) was carried out. Immediate preoperative lumbar drain placement was not required owing to early and direct access to the cisterna magna. The far lateral approach in the park bench position allowed excellent visualization and access to the structures of the craniocervical junction, with a 45 degree trajectory across the right anterolateral medulla. The lesion was identified as a meningioma, and a Simpson Grade 2 resection was carried out. Not all of the dural origin could be removed and therefore this origin was bipolar coagulated following gross-total resection of the tumor itself. Fortunately, the 12th cranial nerve was effaced and displaced by the mass, but was not itself incorporated into the tumor. A watertight dural closure was obtained, bolstered by fibrin glue (Tisseel) and local muscle; lumbar drain placement was not necessary here. The original bone-flap was restored.

Technical nuances and potential surgical pitfalls: Meticulous patient positioning and padding for this approach cannot be overstated. The potential for disorientation from the midline can be minimized using intraoperative MRI image-guidance, and following the usual anatomical midline landmarks which should be visualized intraoperatively - i.e., inion, midline external occipital keel and the C1-posterior arch's midline tubercle (all of which may still appear "shifted" or rotated in the modified park bench position). Particular caution must also be paid to the vertebral artery during the exposure - the surrounding venous plexus and yellow-brown fat are good clues to its proximity. CSF leak is a potential complication of posterior fossa surgery, and its incidence can be reduced by measures mentioned above. Lower brainstem cranial nerve monitoring as indicated above is advised for tumors in this location. Motor-evoked potential monitoring is recommended for brainstem surgery, but requires excellent neuroanesthesia experience and coordination.

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