The best treatment for meningiomas depends on many factors, including how big the tumor is, how fast it is growing, it’s location, and the patient’s general health. Surgery is preferred for tumors that are large, symptomatic, or showed evidence of growth. The selection of the type of surgical approach depends very much on the tumor location.
Meningiomas are classified based on their location in the following categories:
They grow on the brain's surface and may not trigger symptoms until they become large enough to press on the brain, causing seizures and loss of neurological function such as weakness. Surgical access to convexity meningiomas is relatively straightforward as the tumor is located superficially. The preferred surgical approach is a traditional craniotomy just over the tumor location.
They arise from the membrane (cerebral falx) that separates the two sides (hemispheres) of the brain. These can be challenging tumors. They require an interhemispheric approach via craniotomy using the surgical microscope.
They originate from the lining of venous sinuses, most commonly the superior sagittal sinus, which is the major draining venous channel for the brain hemispheres. These lesions have the risk of venous injury and require meticulous microsurgical skills for removal.
They form in the cavities within the brain that produce and distribute the cerebrospinal fluid. These tumors can block the fluid pathways and cause hydrocephalus (excess cerebrospinal fluid with increase pressure within the head). Access is difficult given their deep location, but at Stanford we use a minimally invasive approach with an endoscopic port that causes minimal disruption of normal brain tissue.
Skull base meningiomas
These are the most challenging meningiomas as they arise from the lining at the base of the skull where they are intimately related with critical nerves and vessels. It is extraordinarily important that these tumors are treated by very experienced surgeons with expertise in advanced skull base surgery techniques. There are several subtypes:
Sphenoid wing meningiomas
They originate from the lining that covers the lateral aspect of the sphenoid bone, located just deep to the temple and behind the eye. In the past, these tumors always required a traditional craniotomy, but we have developed and applied minimally invasive techniques using the transorbital approach in conjunction with our oculoplastic surgery team. In this approach a 1.5 cm incision is placed in the crow's feet (wrinkle at the corner of the eye) providing direct access to the tumor with minimal manipulation of normal tissues.
Anterior Clinoid meningiomas
They originate from the lining that covers the medial aspect of the sphenoid bone or anterior clinoid process, and they typically present with progressive visual loss in one eye. For smaller tumor, a minimally invasive transorbital approach is preferred; for larger tumors, it is key to perform a complex skull base operation called microsurgical extradural anterior clinoidectomy for early decompression of the optic canal and carotid artery isolation. This is a very specialized procedure that requires deep understanding of the skull base anatomy and advanced surgical techniques.
Olfactory groove and Planum Sphenoidale meningiomas
They form along the lining of the olfactory groove, where the olfactory nerves run between the base of the brain and the roof of the nasal cavity, or along the flat surface of lining behind the olfactory groove, so called planum sphenoidale. They can cause loss of smell, visual decline, and may grow large enough to create swelling in the brain that induces changes in behavior, judgement, and personality. The surgical approach depends on tumor size and whether olfaction has been compromised by the tumor growth. For small tumors with intact sense of smell, a minimally invasive endoscopic approach along with our oculoplastic surgery team using an incision in the eyebrow is often ideal. For medium size tumors with impaired sense of smell, the endoscopic endonasal approach is our preferred choice, since it provides direct access to the tumor origin without any manipulation of the brain. When sense of smell is intact, we recommend the eyebrow approach or a fronto-orbital approach. For large tumors, we recommend a microsurgical fronto-orbital approach or a modified subfrontal approach that provides excellent access to all tumor surfaces and minimal brain manipulation. These are very demanding cases that require significant expertise.
Tuberculum sellae meningiomas
They originate from the lining located underneath and between the optic nerves, and above the pituitary gland, and they cause progressive visual loss on both eyes. These tumors are traditionally treated using a transcranial route (“from above”). Dr. Fernandez-Miranda has developed key modifications of the endoscopic endonasal approach that allow for direct access to the optic canals where tumor critically compresses the optic nerves. At Stanford, the endoscopic endonasal approach is our preferred option for most tuberculum sellae meningiomas as this approach has shown better visual outcomes and is a less invasive operation.
Cavernous sinus or spheno-cavernous meningiomas
These are among the most complex meningiomas to treat. They originate from the lining of the cavernous sinus, which is a venous cavity that contains the internal carotid artery and several nerves that control the eye muscles. Tumor often involve the carotid artery and cannot be resected without risking injury to the artery and stroke. At Stanford, we tailor each treatment recommendation to the patient symptoms. For asymptomatic cavernous sinus meningiomas, observation is ideal; for those causing compressive symptoms such as retroorbital headaches, facial numbness, double vision or blurry vision, we recommend surgical resection with the goal of symptomatic improvement at the expense of partial tumor resection. The endonasal endoscopic approach is often an excellent alternative to decompress the cavernous sinus and remove the tumor compressing the cranial nerves. In more extensive tumors, an advanced skull base approach, so-called extended middle fossa approach is recommended to maximize tumor removal while preserving neurovascular structures.
They arise from the lining of the petrous and clival bones, which are located deep to the ears and nose, respectively. These tumors sit to the side or in front of the brainstem and are surrounded by multiple cranial nerves that are responsible for relevant functions such as eye movement, face movement and sensation, hearing and balance, swallowing, vocal chords and tongue movement among others. Given their location, surgical removal of petroclival meningiomas is of utmost difficulty. For those located to the side of the brainstem, we use approaches around the ear in conjunction with our expert neuro-otology team, so called, transpetrosal approaches; in recent years, the application of endoscopes has allowed us to use less invasive approaches, so called, keyhole approaches, where a small bony opening is performed behind the ear. For those meningiomas located in front of the brainstem, arguably the most challenging of all meningiomas, Dr. Fernandez-Miranda has developed and pioneered the endoscopic endonasal approach that provides direct access to the tumor without any manipulation of the brain or cranial nerves.
Foramen Magnum meningiomas
They originate from the lining of the foramen magnum, which is the manor outlet of the skull through which the brainstem exits the skull to become the spinal cord. These tumors will compress the lower part of the brainstem or upper part of spinal cord causing neck pain, weakness and numbness in the extremities. For those tumors located behind the brainstem or spinal cord the access is relatively straightforward using a suboccipital approach with an incision that extends to the upper part of the posterior neck. Tumors located lateral to the brainstem or in front of the upper cervical cord are accessed using the microsurgical far lateral approach, which requires significant expertise in microsurgical techniques and skull base surgery. For tumors located in front of the brainstem and not extending below the foramen, Dr. Fernandez-Miranda has described the endoscopic endonasal approach as an ideal alternative to minimize manipulation of vascular and neural structures.
Complete surgical resection is not always possible or recommended; for example, a tumor may encase blood vessels and nerves to the point that complete tumor resection may jeopardize these structures and it will be best to leave tumor behind. The judgement and experience of the surgeon is key to make the best possible decisions, balancing aggressive tumor resection with preservation of function.
Additionally, meningiomas may grow back after surgery, even after complete resection, depending on the grade of the tumor. Meningiomas are classified based on the World Health Organization (WHO) grading system. Most meningiomas are well differentiated, with low proliferative capacity (WHO grade I). Atypical (WHO grade II) and malignant (WHO grade III) tumors are much less common but behave more aggressively.
In these cases, radiation therapy can play a role as an alternative to surgery or as an adjunct to surgery to reduce the risk of the tumor recurring. Radiation therapy can be delivered as either fractionated external beam radiation therapy (EBRT), where the radiation is given in small daily doses over 5-6 weeks, or stereotactic radiosurgery (SRS), where the radiation is given in large doses over a single or limited number of sessions.
Chemotherapeutic, immunotherapeutic, and hormonal agents have been the subject of investigation for malignant and recurrent meningiomas but have not yet been validated and are use only under exceptional circumstances.