Meningioma
These are the most common primary intracranial tumor, comprising 14.3-19% of primary intracranial neoplasms. They are defined as slow-growing, well-circumscribed, benign lesions with pathologically distinct “psamomma bodies,” or calcifications. Meningiomas arise from arachnoid cap cells and thus can arise from any structure in the CNS that is covered by arachnoid mater, a meningeal layer surrounding the brain and spinal cord beneath the skull and vertebrae. The peak incidence occurs at 45 years of age and is more common in females, with a male: female ratio of 1:1.8. Women are even more likely than men to have spinal meningiomas, with reported incidence 3.37 times more likely in women1. Only 1.5% of meningiomas occur in childhood and adolescence. Of those lesions, 19-24% are associated with neurofibromatosis type 1 (NF1). Meningiomas are most commonly located in the parasagittal space (20.8%), followed by convexity (over the surface of the brain – 15.2%), within the tuberculum sellae (12.8%), and the sphenoidal ridge (11.9%).
Histopathology is used to guide WHO grading, which has 3 levels. Meningothelial, psammomatous, and microcystic meningiomas – amongst others – are the lowest grade, WHO I. These have low risk of recurrence following gross total resection and aggressive growth. Chordoid, clear cell, and atypical meningiomas are WHO grade II. Papillary, rhabdoid, and anaplastic lesions are malignant, WHO grade III. These have the highest risk of recurrence and aggressive growth. Brain invasion by meningiomas independently should not be used to associate with malignancy, but there is higher risk of recurrence. Metastases overall are extremely rare.
Symptoms are associated with tumor location, but many meningiomas remain asymptomatic for years, even throughout a patient’s entire life. A common presenting symptom is seizure due to irritation of the cerebral cortex with supratentorial meningiomas.
Asymptomatic meningiomas found incidentally on imaging are recommended to be followed up with imaging in 3 months to rule out aggressive growth and on a 6-month follow-up and if still stable, on a 1-year follow up and if still stable, then with annual imaging every 2-3 years.
The first-line treatment for symptomatic meningiomas is surgical resection. If patients are not surgical candidates or the tumor is inaccessible, malignant, or recurrent, radiation therapy may be considered. Radiation therapy may also be used as an adjunct for partially resected lesions. Note that there are reports converting a grade I benign meningioma to a higher grade more aggressive tumor. Therefore, it is our opinion that if an asymptomatic meningioma continues to grow and is surgically resectable, or if it causes symptoms, it should be resected as the first-line therapy.
As these tumors tend to be bloody, preoperative embolization and autologous blood donation are essential for uncomplicated surgical removal.
The Simpson grading system is used to evaluate the extent of resection, with grade I being macroscopically gross total resection with removal of dural attachment and abnormal bone, and grade V being simple decompression with or without biopsy, without tumor removal. Degree of tumor resection is the most significant factor associated with recurrence. Recurrence after total removal occurs in 11-15% of cases but 29% with partial removal2. Convexity meningiomas may recur more rapidly than skull base meningiomas, and thus Simpson grade I resection is recommended3.
Convexity Meningioma
One of the most common locations of meningiomas (12.8%). Recurrence depends on grade, with 1.5% five-year recurrence for benign lesions and 44% for malignant/atypical meningiomas1.
Olfactory Groove Meningioma
Account for 9.8% of meningiomas. Remain asymptomatic until lesion has grown significantly in size. May cause Foster Kennedy Syndrome, which has a triad of symptoms: anosmia, ipsilateral optic atrophy (due to compromise of the nerve), and contralateral papilledema (due to compromise of the venous flow). Can also be associated with mental status changes and urinary incontinence due to frontal lobe mass effect. Lesions located posteriorly within the olfactory groove may cause visual impairment due to compression of the optic chiasm and/or optic nerves. Very large lesions may cause seizures or short-term memory loss due to compression of the fornix. Lesions > 3 cm in size are difficult to resect completely and have higher morbidity and mortality. Surgical resection entails gross total resection. For smaller tumors than 4 cm, it can be done through frontotemporal craniotomy but for tumors larger than 4 cm, it needs extrnsive skull base approach through a bicoronal craniotomy and naso-orbital osteotomy through the frontal sinus, in order to access the olfactory groove and resect the origin of the tumor in order to avoid recurrence1.
References
- Kshettry VR, Hsieh JK, Ostrom QT, Kruchko C, Benzel EC, Barnholtz-Sloan JS. (2015). Descriptive epidemiology of spinal meningiomas in the United States. Spine. 40(15): E886-E889.
- Yamashita J, Handa H, Iwaki K, et al. (1980). Recurrence of intracranial meningiomas, with special reference to radiotherapy. Surg Neurol. 14: 33-40.
- Hasseleid BF, Meling TR, Ronning P, Scheie D, Helseth E. (2012). Surgery for convexity meningioma: Simpson Grade I resection as the goal. Journal of Neurosurgery. 117(6): 999-1006.
- Morokoff AP, Zauberman J, Black PM. (2008). Surgery for convexity meningiomas. Neurosurgery. 63(3): 427-434.
- Mortazavi MM, Mantovani A, Da Silva HB, and Sekhar LN F (2015). Olfactory groove and planum sphenoidale, and tuberculum sellae meningiomas In Sekhar LN, Fessler RG (second edition), Atlas of Neurosurgical Techniques. Brain. (pp. 227-237) New York, NY: Thieme Publishers.