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Meningiomas are common tumors of the central nervous system that account for approximately 15% of all intracranial tumors and are the most common extra-axial neoplasm. Most meningiomas are benign, although atypical and malignant meningiomas also exist. Typical imaging characteristics include a well-circumscribed, homogeneously enhancing, extra-axial mass on both computed tomography and magnetic resonance imaging. The presence of an associated cyst is an uncommon imaging feature that may make it difficult to distinguish the tumor from a primary intra-axial glial neoplasm. The presence of peritumoral edema can also be a misleading finding. We present a case of a woman who presented with a history of multiple recent falls, decreased energy, and increased somnolence and was found to have a “cystic meningioma.” Typical imaging characteristics, histologic subtypes, treatment, and prognosis are also discussed.
A 62-year-old woman presented for evaluation of a head injury related to a fall. She had a recent history of multiple falls, decreased energy, and increased somnolence and had undergone a hysterectomy and bilateral oophorectomy 2 months prior to presentation for severe menorrhagia secondary to uterine fibroids and adenomyosis. Computed tomography (CT) of the head without intravenous contrast demonstrated pronounced vasogenic edema throughout the right frontal lobe with an underlying mass and associated mass effect with subfalcine herniation (Figure (Figure11). Magnetic resonance imaging (MRI) of the brain without and with gadolinium intravenous contrast was subsequently performed (Figure (Figure22).
A right frontotemporal craniotomy was performed under general anesthesia. At the time of surgery, a mass adherent to the dura, but superficial to the right frontal lobe (Figure (Figure33), was completely resected. The pathologic specimen was submitted for microscopic and immunohistochemical analysis (Figure (Figure44).
The patient tolerated the procedure well and was discharged on postoperative day 4 without any neurological deficits or other complication.
DIAGNOSIS: Transitional meningioma (World Health Organization [WHO] 2007 Grade 1).
Meningiomas are common tumors of the central nervous system that account for approximately 15% of all intracranial tumors and are the most common extra-axial neoplasm (i.e., neoplasm that does not arise from the brain or spinal cord) (1). The WHO classifies meningiomas into many different subtypes based on histological parameters. Of these subtypes, transitional, fibroblastic, and meningothelial are the most common.
Histologically, transitional meningiomas are characterized by whorl formation with closely wrapped cells (Figure (Figure4).4). The intervening cells contain fibroglial fibrils and are typically spindle shaped. Degeneration and calcification of the whorls may result in the formation of psammoma bodies. Fibroblastic meningiomas are characterized by narrow spindle cells with abundant reticulum and collagen fibers between individual cells. Meningothelial meningiomas contain polygonal cells arranged in lobules with sparse interlobular trabeculae.
Most meningiomas are benign neoplasms with a WHO grade 1 classification. Approximately 8% of meningiomas are considered “atypical” (WHO grade 2) and tend to have a higher incidence of recurrence (2). The presence of necrosis, excessive mitotic activity, and evidence of brain invasion are histologic features that result in an “atypical” classification (3). Anaplastic meningiomas (WHO grade 3) account for <1% all meningiomas and have a much shorter mean survival time, with a 5-year-survival rate of approximately 64%, compared with 95% for atypical meningiomas (2). “Benign” metastasizing meningiomas have also been reported, but are rare (4).
The etiology of meningiomas is not entirely known, although these tumors are occasionally seen at locations of prior trauma or radiation. Genetic alterations, including inherited mutations of NF-2 in the setting of neurofibromatosis type 2 and loss of chromosome 22q in sporadic cases, are associated with a higher incidence (5). Patients with neurofibromatosis type 2 may have multiple meningiomas and also have an increased incidence of other central nervous system tumors, including schwannomas and ependymomas.
Meningiomas generally have the characteristic imaging appearance of a well-circumscribed, solid, homogeneously enhancing extra-axial mass on both CT and MRI. Adjacent osseous changes, most commonly hyperostosis, may also be seen (Figure (Figure55). The term “cystic meningioma” has been used to describe meningiomas with intratumoral or peritumoral cysts (1, 6). The presence of an associated cyst is an uncommon imaging feature that may make it difficult to distinguish the tumor from an intra-axial primary glial neoplasm. The presence of peritumoral edema, as in the case presented, can also be a misleading finding. The exact cause of cyst formation is not entirely known, although many mechanisms have been proposed. These include cystic degeneration of the tumor, secretion of fluid from tumor cells, or loculated cerebrospinal fluid from scar tissue within or adjacent to the tumor (1). Imaging features that are more suggestive of an atypical or malignant subtype include heterogeneous enhancement and a narrow base of attachment to the dura with a larger cap invaginating into the brain, or “mushroom” shape (1).
Prognosis and treatment options depend on a variety of factors, including histological subtype, location of the tumor, age of the patient, and associated comorbidities. Small meningiomas in asymptomatic patients can be followed with serial imaging studies, preferably MRI, to assess for interval growth. Most benign tumors, depending on location and accessibility, can undergo total resection with a very low recurrence rate of approximately 6% (3). Transarterial embolization is occasionally utilized prior to surgical resection given the highly vascular nature of some of these tumors. The classic conventional angiographic appearance of meningiomas is early arterial enhancement that persists into the venous phase (Figure (Figure66), also referred to as the “mother-in-law” pattern; i.e., the contrast enhancement “comes early and stays late.” Radiation therapy may be used without surgery when the tumor cannot be resected, either because of high-risk tumor location with close proximity to critical structures or in poor surgical candidates, to control tumor growth and improve symptoms. In cases of malignant meningiomas, adjuvant therapy with radiation or a combination of radiation and chemotherapy, in addition to resection, may increase median survival by up to 3 years (3).