Meningiomas are the most common benign intracranial tumor. Accounting for over one third of all intracranial neoplasms,^[1,2] they have been found in as many as 2.3% of patients at autopsy.^[3] As the utilization of computed tomography (CT) scanning and magnetic resonance imaging (MRI) has increased, so has the detection of asymptomatic meningiomas, and it is now estimated that as many as 2 in 5 meningiomas produce no symptoms.^[4] This contrast-enhanced head computed tomography (CT) scan demonstrates a homogenously enhancing mass within the anterior skull base of a 77-year-old woman. The patient presented with loss of smell and progressive personality changes, including a loss of inhibition and decreased interest in her normally busy social life. An uncomplicated craniotomy achieved a gross-total resection; pathology revealed the lesion to be a World Health Organization (WHO) grade I meningioma.^[5]

Image courtesy of Anand Rughani, MD.

For patients with the presenting symptoms of a meningioma, a head CT scan often serves as the initial imaging test, but an MRI scan of the brain with and without contrast is necessary to aid in the diagnosis.^[6] In many cases, the radiologic appearance of a meningioma is compelling enough to enable an almost certain diagnosis. A noncontrast head CT scan (left) was performed on a 55-year-old woman who presented with a new-onset seizure in the absence of other symptoms. The image shows some subtle right parietal edema, hinting at an underlying lesion. An axial, T1-weighted MRI scan (right) reveals a homogenously enhancing, dural-based lesion, the classic appearance of a meningioma.

Images courtesy of Anand Rughani, MD.

While many meningiomas are found incidentally, the majority of them are identified through clinical symptoms. Meningiomas arise from the arachnoid membrane, which envelopes the entire neuraxis.^[7,8] The lesions can therefore occur throughout the nervous system, although most of them are seen intracranially. Indeed, 90% of meningiomas are supratentorial, with the remainder occurring in the posterior fossa or spine. There are several classic locations (although they are found only rarely within the ventricular system), and the presentation can vary according to the specific site. This T1-weighted MRI scan with contrast shows a pineal region meningioma. A clear dural attachment to the tentorium can be appreciated.

Image courtesy of Jeffrey Florman, MD.

Although spinal meningiomas can occur at all levels of the spine, about 80% are found in the thoracic region.^[9,10] These often present with symptoms and signs of myelopathy, such as progressive gait and sensory disturbances, with evidence of an upper motor neuron lesion on examination. The differential diagnosis for such tumors should always include schwannomas, neurofibromas, and metastases. The sagittal, contrast-enhanced, T1-weighted MRI sequences seen here were obtained in three separate patients. From left to right, they demonstrate meningiomas at C7-T1, T5-6, and T10-11. Imaging features can help to distinguish a meningioma from a schwannoma; schwannomas are very rarely posterior to the spinal cord and are often seen expanding the neural foramen. Meningiomas are more likely to demonstrate a clear dural attachment.^[11]

Images courtesy of Jeffrey Florman, MD, and Anand Rughani, MD.

Meningiomas that occur at the craniocervical junction (as seen on these sagittal [left] and axial [right] MRI scans) are termed foramen magnum meningiomas.^[12] The classic presentation of foramen magnum tumors involves sensory changes followed by weakness that begins in the ipsilateral arm and then progresses to the ipsilateral leg, which is in turn followed by progression to the contralateral leg and then to the contralateral arm. On examination, patients can have preserved tactile sensation, with loss of pain and temperature sensation contralateral to the lesion. Loss of position and vibratory sensation is often greater in the upper extremities than in the lower ones.

Images courtesy of Anand Rughani, MD.

This intra-operative photograph demonstrates the meningioma seen in the prior MRI scan at the cervicomedullary junction. The dashed white line indicates the tumor, the blue arrow points to the dura, and the green arrow demonstrates nerve rootlets of the spinal accessory nerve (cranial nerve XI). The orange arrow is directed towards the upper aspect of the cervical spinal cord. A gross-total resection was achieved with excellent recovery. Pathology revealed the tumor to be a WHO grade I meningioma.

Image courtesy of Jeffrey Florman, MD.

The differential diagnosis for meningioma often should include hemangiopericytoma and metastasis.^[13] This sagittal, gadolinium-enhanced, T1-weighted MRI scan shows a hemangiopericytoma that mimics an olfactory groove meningioma. Hemangiopericytomas were previously known as angioblastic meningiomas but are now considered to be a type of sarcoma, with no relationship to meningiomas. Rarer than meningiomas by a factor of approximately 40, they are often found along the dura, similar to meningiomas. However, they frequently lack the calcification that develops in some meningiomas, and they are not associated with the hyperostosis of adjacent bone that often occurs with meningiomas. Moreover, hemangiopericytomas are frequently much more vascular than meningiomas. (Imaging can demonstrate rich vascularity in these lesions.)

Despite such differences, there are no definitive radiologic tools that can distinguish meningiomas from hemangiopericytomas. Typically, both types of lesions are quite similar in appearance, and only pathology can establish the diagnosis of hemangiopericytoma. Unlike meningiomas, though, hemangiopericytomas are seen to metastasize in about 30% of cases. In addition, the local recurrence rate, up to 80%, is much higher than that for meningiomas.

Image courtesy of Jeffrey Florman, MD.

Metastatic disease, seen here, represents another common meningioma mimic. These axial (left) and coronal (right), contrast-enhanced, T1-weighted MRI scans show a dural-based, enhancing tumor. The enhancement pattern is slightly more heterogeneous than that demonstrated in most meningiomas, and there is some irregularity of the margins, suggesting brain invasion. At the time of surgery, the underlying pial membranes and cortex were found to have been invaded by tumor, which turned out to be a metastatic anal cancer.

Images courtesy of Anand Rughani, MD.

Most meningiomas are relatively slow growing, with benign behavior. The WHO classifies meningiomas into three grades.^[5] WHO grade I meningiomas have a relatively low risk of recurrence, while higher-grade types are associated with an increased likelihood of recurrence and aggressive behavior. Among the WHO grade II meningiomas are the chordoid,^[14] clear cell,^[15] and atypical lesions,^[16,17,18] while WHO grade III meningiomas include papillary, rhabdoid, and anaplastic tumors. WHO grade I meningiomas are the most common; there are at least nine subtypes within this grade, with the most common being meningothelial, fibrous, and transitional meningiomas. The three-dimensional, reconstructed CT scan seen here, from a 61-year-old female who presented with an enlarging mass on her scalp, demonstrates a left frontal meningioma with bone invasion. Its radiologic appearance is more suggestive of an aggressive subtype.

Image courtesy of Jeffrey Florman, MD.

This plain anteroposterior radiograph, performed in the patient seen in the previous slide, demonstrates left frontal lucency where the meningioma has invaded the bone. (A skull film is rarely chosen as an initial diagnostic test; the resulting differential diagnosis can be quite broad and include tumors of bone.)

Image courtesy of Jeffrey Florman, MD.

This intraoperative photograph, from the same patient seen in the previous two slides, demonstrates the bone invasion by the meningioma, as visible through the skull. The scalp has been reflected anteriorly. No bone has been removed yet.

Image courtesy of Jeffrey Florman, MD.

This craniotomy photo, from the same patient seen in the previous three slides, shows a wide dural margin surrounding the meningioma. The extent of resection correlates with the likelihood of tumor recurrence. A wide resection of dura and involved bone yields the highest chance of cure, while incomplete resection is associated with higher recurrence rates. The goal of surgery, therefore, is aggressive resection of the tumor along with a substantial margin of dura. Treatment of meningioma typically consists of surgery alone, but radiation therapy can be used in cases of surgically inaccessible, residual, or recurrent tumors, as well as in patients with an unacceptably high surgical risk.^[19] The recurrence rate in meningioma is 7-25% for low-grade tumors, increasing to 29-52% for atypical lesions.^[1]

Image courtesy of Jeffrey Florman, MD.

Radiation-induced meningiomas, which typically arise from low-dose radiation to the scalp for tinea capitis or high-dose radiation for cancers of the blood or head and neck, tend to be higher-grade, multifocal lesions. A latency period of decades exists between radiation delivery and tumor appearance. The patient pictured in this MRI scan is a 38-year-old female who presented 32 years after having craniospinal radiation for acute lymphoblastic leukemia. The single axial image shows two of three meningiomas. The larger lesion is attached to the falx cerebri, the dural structure that divides the left and right cerebral hemispheres, and the smaller tumor is along the convexity of the right frontal lobe. Parafalcine and convexity meningiomas combined represent almost half of all meningiomas.^[20,21]

Image courtesy of Anand Rughani, MD.

The second-most-common intracranial location for meningiomas is the sphenoid ridge.^[22] These lesions can be divided into medial, middle, and lateral sphenoid wing meningiomas. Those of the medial sphenoid wing can involve the optic nerve and carotid artery. The axial (left) and sagittal (right), T1-weighted MRI sequences seen here show a left sphenoid wing meningioma in a 68-year-old male who presented with progressive visual loss in the left eye.

Images courtesy of Anand Rughani, MD.

The olfactory groove is the third-most-common intracranial location for meningiomas. The typical presentation of an olfactory groove meningioma (seen here on a sagittal MRI scan) includes loss of smell (anosmia), followed by visual loss, and frontal lobe dysfunction, which can be typified by personality changes, loss of interest and motivation (abulia), and decreased inhibition.

Image courtesy of Jeffrey Florman, MD.

Meningiomas of the cerebellopontine angle account for 5-10% of all meningiomas. These lesions must be distinguished from vestibular schwannomas and metastases; imaging characteristics can reliably aid in the differentiation.^[23] This contrast-enhanced, T1-weighted MRI scan demonstrates a classic vestibular schwannoma. Exhibiting an "ice cream cone" appearance, it has a cylindrical shape that extends into the internal auditory canal (orange arrow). Schwannomas lack the dural thickening seen adjacent to a meningioma. The brainstem (green arrow) is quite distorted by the tumor, resulting in compression of the fourth ventricle (blue arrow) and causing hydrocephalus in this patient. This individual presented with severe gait ataxia related to brainstem and cerebellar dysfunction.

Image courtesy of Anand Rughani, MD.

This MRI scan shows an enhancing, dural-based tumor that is slightly posterior to the internal auditory canal. The fact that the tumor does not extend into the canal is the most compelling indication that it is not a vestibular schwannoma; the most likely diagnosis is a meningioma. In contrast to the prior image, this one shows much less local mass effect, although that is not necessarily a distinguishing feature between meningiomas and vestibular schwannomas.

Image courtesy of Jeffrey Florman, MD.

Another common location for meningiomas in the skull base is the sellar region.^[24] Meningiomas at this site should be differentiated from other typical sellar tumors, especially pituitary adenomas. The sagittal MRI scan (right) reveals that the base of the tumor is arising from the tuberculum sellae, an important feature that distinguishes this lesion as a meningioma. On the coronal (left) and sagittal images, the orange arrow points to the tumor, which is seen to be displacing the optic chiasm (green arrow) upward and encasing the carotid arteries. The flow voids of the internal carotid arteries are marked with the blue arrows.

Another factor identifying this tumor as a meningioma rather than a pituitary adenoma is the fact that the pituitary gland (yellow arrow on the sagittal image) can be seen as distinct from the tumor. Although traditional surgical approaches for treating meningiomas and pituitary adenomas have often involved craniotomy, these lesions can now be approached through an endoscopic endonasal route, which serves to minimize brain retraction.

Images courtesy of Jeffrey Florman, MD.

The pituitary gland (yellow arrow) can be seen clearly on this postoperative MRI scan (same patient as in slide 18), the tumor having undergone gross-total resection.

View video of convexity meningioma surgery here.

View video of meningioma resection in the tuberculum sellae here.

Image courtesy of Jeffrey Florman, MD.