Meningiomas arise from the meningothelial cells of the arachnoid membranes, which are attached to the inner layer of the dura mater. This close relationship between the meningioma and the dura mater can be demonstrated on MR imaging. Normal dura mater is a non-neuronal connective tissue and appears as a hypointense thin layer adjacent to the hypointense inner table of bone on T1- and T2-WI (Fig. 14-1). After contrast injection, dura and the dural reflections of falx cerebri, tentorium, and cavernous sinus enhance as a thin discontinuous layer (Fig. 14-2).² The demonstration of the dura mater and the adjacent meningioma on MRI supplies information about the extra-axial location and the origin of meningioma. In this respect, MRI is advantageous over computed tomography (CT) imaging, in which bone and enhanced dura both appear as hyperdense structures and cannot be distinguished from each other. The sensitivity of MRI is two to three times higher than that of CT for imaging dural and meningeal pathologies.³ Dural attachment of a meningioma is usually broad and the angle between the tumor and the dura is an obtuse one, indicating the extra-axial location of the meningioma (Figs. 14-2 and 14-3). Rarely the dural attachment may be narrow and a pedunculated meningioma can be demonstrated, more so in cases with large subarachnoid spaces where the peduncle becomes more conspicuous.

FIGURE 14-1 On contrast-enhanced (CE) T1-WI, the dura mater appears as a hypointense line compared to the brightly enhancing meningioma as demonstrated in a cavernous sinus meningioma (A) and a petroclival meningioma (B).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-2 Meningiomas show a broad based attachment to the underlying dura, which is seen as a thin enhancing line adjacent to the tumor, along the brain surface and dural duplications like the tentorium. (Images in A and B are coronal; C is sagittal CE T1-WI.)

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-3 Meningiomas present an obtuse angle between the tumor and the underling dura mater which reflects their broad dural base and extra-axial localization. (Image in A is an axial and B and C are sagittal CE T1-WI.)

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

Pathologic enhancement of the dura mater and the adjacent inner table of bone, known as pachymeningeal enhancement, may be due to abnormally increased capillary permeability, increased blood volume, edema, tumor invasion of the dura mater, or as a result of surgery.² The local pachymeningeal enhancement adjacent to a meningioma which tapers smoothly away from the tumor is designated as a dural “tail” (Fig. 14-4). The dural “tail,” which is depicted radiologically only on MRI, is reported in 52% to 72% of meningiomas. Nevertheless, it is nonspecific, and has also been associated with lymphomas, sarcoidosis, schwannomas, metastatic tumors, syphilitic gumma, and hemangiopericytomas.⁴^–¹⁰ A dural “tail” may also be demonstrated, without contrast injection, on MR FLAIR sequences. Both meningiomas and the dural “tail” are demonstrated on FLAIR sequences, yet the dural “tail” usually has higher signal intensity than the tumor.¹¹

FIGURE 14-4 Meningiomas classically present a dural “tail” and this is observed in various localizations in the brain. CE T1-W images of sphenoid wing (A), foramen magnum (B), convexity (C, D, E), sphenopetroclival (F), and petroclival (G) meningiomas in this figure all have an enhancing prominent dural tail.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

MRI FINDINGS SUPPORTING EXTRA-AXIAL LOCALIZATION OF MENINGIOMAS

The extra-axial localization of a mass is an important diagnostic finding, albeit it is not always simple to appreciate this finding, more so when a dural relation cannot be detected (Fig. 14-5). A cerebrospinal fluid (CSF) interface between a mass and the brain surface is another finding supporting the extra-axial localization (Fig. 14-6). Occasionally the subarachnoid space around a meningioma may enlarge and acquire the form of a cyst. Another finding reflecting the extra-axial localization of a meningioma is the “buckling” or compression and displacement of adjacent brain cortex and the white matter (Fig. 14-7).

FIGURE 14-5 Demonstration of the dural relation can aid in the anatomic classification of the meningioma. Although the exact origin of the meningioma cannot be distinguished on axial contrast enhanced T1-WI (A), the demonstration of a dural tail near its dural attachment on the hyperostotic anterior clinoid process on coronal images (arrow in B) clearly indicate that this is a clinoidal meningioma.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-6 The cerebrospinal fluid ring surrounding meningiomas indicates their extra-axial localization. The clinoidal (A) and convexity (B, C, D) meningiomas demonstrated in this figure all present a CSF rim that appears hyperintense on T2-WI (A, B), hypointense on T1-WI (C), and FLAIR images (D).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-7 Buckling of the surrounding cortex is another indication of extra-axial localization. This is well demonstrated on three convexity meningiomas. Please note the peritumoral edema as demonstrated by the hyperintensity in the FLAİR image (A), the peritumoral CSF cleft as demonstrated on T1-WI of a convexity meningioma (arrow in B), and another conveity meningioma (arrows in C and D).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

BORDER AND CONTOUR OF MENINGIOMAS

The borders and contours of meningiomas are usually regular and the margins are sharp as a result of the extra-axial location of the tumor which is surrounded by a CSF ring (Fig. 14-8). Despite the extra-axial location, meningiomas may indent into the adjacent brain cortex and so exhibit irregular margins. A meningioma that has multiple lobulated outgrowths on its contour is designated as “mushrooming” meningioma (Fig. 14-9).

FIGURE 14-8 Meningiomas are extra-axial tumors, and therefore are demarcated from the surrounding brain tissue usually with clear, sharp, and regular margins, as demonstrated in this T2-WI of a parasagittal meningioma.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-9 Irregular margins with nodular outgrowths, which is known as “mushrooming,” may be observed in meningiomas as demonstrated in these CE T1-WI of a giant sphenoid wing (A, B, C) and a tuberculum sella meningioma (D).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

CONTRAST ENHANCEMENT OF MENINGIOMAS ON MRI

MRI contrast agents are gadolinium chelates that shorten the T1 relaxation times in certain tissues to increase signal intensity on T1-WI and produce contrast enhancement that improves the sensitivity of MRI for residual, recurrent, and multiple meningiomas.¹² On early MR studies, some small meningiomas with signal intensities close to that of the brain cortex on T1- and T2-WI were not recognized if contrast medium was not used.¹ Routine use of contrast media is necessary to increase the sensitivity for meningioma detection. Meningiomas that are homogeneous on T1-WI and T2-WI enhance in general intensely and in a uniform manner (Fig. 14-10). Calcified, cystic, necrotic, and hemorrhagic meningiomas enhance less intensely, and more heterogeneously (Fig. 14-11). No correlation was established between contrast enhancement and the histopathologic features of meningiomas.¹³ Contrast media are among strong radiodiagnostic tools; however, caution is recommended in patients with poor kidney functions, as cases of nephrogenic systemic fibrosis have been related to some ingredients of MR contrast agents.

FIGURE 14-10 In general, meningiomas enhance homogeneously and intensely after contrast medium injection on T1-WI, as seen in the case of a petroclival meningioma. Note that the dural tail also enhances brightly (arrow).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-11 Intratumoral calcification and vasculature may cause heterogeneous enhancement in meningiomas. CE T1-WI of the olfactory groove meningioma demonstrated in A and B revealed a heterogenous signal inside the tumor due to both calcification and prominent intratumoral vasculature. The MRI signal was also heterogeneous in this giant sphenoid wing meningioma due to intratumoral vessels (C, D). Also microcystic-syncytial meningiomas may enhance heterogeneously as demonstrated in E and F.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

EDEMA RELATED TO MENINGIOMAS ON MRI

Despite their extra-axial location, meningiomas can cause mild to extensive vasogenic white-mater edema in up to 75% of cases.¹⁴ Calcified meningiomas exhibit less vasogenic edema.¹⁵ Many factors were associated with the development of edema. These include shape of meningioma, mechanical injury to the adjacent brain tissue, compression of nearby vasculature, angiogenic factors, large surface area of the tumor, invasive pattern of brain–tumor interface and hyperintensity of meningioma on T2-WI.¹⁴^–¹⁶ Nevertheless, the exact cause of edema is still unknown. Newer techniques such as diffusion tensor imaging may provide additional information. Vasogenic edema in the white matter presents in the form of “finger edema” and is hypointense on T1-WI, and of hyperintense and of homogeneous signal intensity on FLAIR and T2-WI (Fig. 14-12). Small and isointense meningiomas amid edema can be depicted only after contrast medium administration.

FIGURE 14-12 A large proportion of meningiomas present with peritumoral edema of varying degrees. Peritumoral edema can be detected by various MR sequences. Vasogenic edema around a meningioma may best be detected on a FLAIR sequence as a hyperintense signal as demonstrated in A. Edema is seen as homogeneous hyperintensity on T2-WI (B). The size of the edema does not correlate with the size of the tumor as seen on T1-WI (C), where a relatively small clinoidal meningoma has produced marked edema and swelling of the uncus.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

MR SIGNAL INTENSITY CHARACTERISTICS OF MENINGIOMAS

Signal intensity characteristics of meningiomas have been studied extensively and correlated with the histologic subtypes of meningiomas. According to Elster and colleagues, in 62% of meningiomas, the signal was isointense with cortical gray matter, and in the remaining 38% hypointense to gray matter intensity on T1-WI so that no correlation could be established concerning the histologic type on T1-WI (Fig. 14-13).¹⁷ On proton density (PD) and T2-WI meningiomas are isointense in 50% and mildly hyperintense to cortex in 40% of cases (Fig. 14-14).¹⁸ Signal intensity of meningiomas on T2-WI could be correlated to histologic subtypes in 75% of cases, so that varied MR findings may be explained on a histologic basis.¹⁷ Fibroblastic meningiomas with a dense collagenous matrix produce hypointense signal on T2-WI (Fig. 14-15). Transitional meningiomas with abundant psammoma bodies have relatively low signal intensity on T2-WI (Fig. 14-16). Syncytial meningiomas with microcystic elements exhibit high signal intensity on T2-WI (see Fig. 14-11E, F).¹³ Angioblastic meningiomas with high cellularity and dilated blood vessels show hyperdense signal with a mottled appearance on T2-WI (Fig. 14-17).¹³

FIGURE 14-13 On T1-WI, meningiomas generally exhibit an isointense (A) or less commonly hypointense signal compared to the cortical gray mater (B).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-14 On T2-WI, meningiomas exhibit an isointense (A) or mildly hyperintense signal (B) compared to the cortical gray mater.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-15 T2-WI demonstrates the hypointense signal of a fibroblastic meningioma on T2-WI (A) with heterogeneous enhancement on CE T1-WI (B).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-16 Psammomatous meningiomas may show iso- to hyperintense heterogeneous signal on T2-WI (A, B) and homogeneous contrast enhancement on CE T1-WI (C). In the presence of heavy calcifications psammomatous meningiomas may demonstrate a hypointense signal on T2-WI (D) and heterogeneous contrast enhancement on CE T1-WI (E, F).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-17 Angioblastic meningiomas may have a rich intratumoral vascular network, seen as signal void linear (A) or serpentine (B, C) structures on all T2-WI.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

Central necrosis in meningioma, which is encountered quite often (14% in the series of Russel and colleagues),¹⁹ will appear as a heterogenous hyperintense signal on T2-WI, whereas cysts show a homogeneous hyperintense signal on the same images (Fig. 14-18). Signal intensities of atypical and malignant meningiomas are not significantly different from those of benign meningiomas.¹³ Clear-cell meningioma is recently defined as World Health Organization (WHO) grade II subtype, with high spinal prevalence and recurrence rates. If a meningioma is accompanied with extensive leptomeningeal enhancement, a clear-cell meningioma should be suspected and followed up for aggressive behavior.²⁰ Fifteen anaplastic rhabdoid meningiomas studied by Kim and colleagues²¹ displayed cystic changes in 38%, extensive edema in 75%, hyperostosis in 50%, and bone destruction in 25% of cases. The authors concluded that the aforementioned radiologic features do not seem to be useful in distinguishing rhabdoid meningiomas from other high-grade tumors or even from benign meningiomas.²⁰

FIGURE 14-18 Necrosis is not uncommon in meningiomas and is seen as hyperintense signal on T2-WI (A) and as nonenhancing hypointense irregular areas on CE images (B, C).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

UNUSUAL FINDINGS OF MENINGIOMAS ON MRI

Meningiomas may manifest unusual radiologic features in 15% of cases that may complicate or mislead the diagnosis. Hemorrhage associated with meningiomas is a well known finding;²¹ however, blood products display variable signal intensities on MRI and a definitive diagnosis is not simple. Intratumoral hemorrhage is usually accompanied by tumor necrosis and the two findings cannot be differentiated on T1- and T2-WI in the acute phase of the bleeding, except on 3T. Chronic blood products are hypointense whereas necrosis is hyperintense on T2-WI. Inratumoral microhemorrhage can be depicted on T2-weighted gradient-echo (GE) images as punctate hypointense structures. Unusual presentations of meningiomas related with a subdural, a subarachnoid, or intracerebral hemorrhage are possible; however, the presence of extratumoral hemorrhage may be diagnostically misleading, especially if contrast medium is not used to highlight the meningioma adjacent to a subdural or subarachnoid hemorrhage. Subarachnoid hemorrhage is detected as hyperintensities in the sulci on FLAIR images. A review of the literature disclosed 33 cases of ipsilateral subdural hematomas associated with meningiomas.²²

Fat storage in meningioma cells or lipomatous transformation has been described and such cases are called “lipoblastic” meningioma that appear hyperintense on T1-WI and mildly hypointense on T2-WI.²¹

Most meningiomas have a broad dural base; rarely a meningioma may have a thin attachment to the dura mater, which is known as “pedunculated meningioma” (Fig. 14-19). Meningiomas without any detectable dural attachment may also be observed, and this finding is more common in the pediatric population.

FIGURE 14-19 Although most meningiomas have a broad dural base, rarely a meningioma may exhibit a narrow dural attachment denoted as a “pedunculated meningioma.”

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

A few cases of meningiomas have been described in the literature as having both intra- and extracranial components, and possessing different MR signal characteristics (Fig. 14-20). In a jugular foramen meningioma the parapharyngeal component displayed lower signal intensity and less enhancement, which may be related to the histologic composition and its collagen content. The increased collagen content has been explained as being the result of fibroblast migration into the extracranial component of the meningioma.²³

FIGURE 14-20 Meningiomas with intra- and extracranial components may show different signal intensity in each part (small and large arrows). A, A cavernous sinus meningioma with a sphenoidal sinus component that is less enhancing on CE T1-WI. CE T1-WI (B, C) show a tuberculum sella meningioma with an ethmoidal sinus component that is relatively hypointense.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

Cystic meningiomas are not uncommon, and their detailed radiologic description will assist in surgical planning. Three types of intratumoral cysts have been described in meningiomas. True intratumoral cysts have homogeneous hyperintense signal on T2-WI and show an enhancing cyst wall. These cases warrant differential diagnosis from schwannomas and even cystic astrocytomas (Fig. 14-21). The second type may arise due to tumoral degeneration or necrosis, which produces cystic cavities with irregular walls, and heterogeneous content of hyperintensity on T2-WI (Fig. 14-22). The third and most common type are meningiomas with extratumoral cysts. In this variant the cyst may be a true arachnoid cyst or a cerebrospinal fluid loculation due to arachnoid adhesions (Fig. 14-23).²⁴ FLAIR sequences may be used to differentiate between water-like cystic lesions and CSF, which is especially useful to study extratumoral cystic components of meningiomas.²⁵

FIGURE 14-21 Cystic meningiomas are uncommon, as demonstrated on the T1-WI of this convexity meningioma (A is a nonenhanced; B and C are contrast enhanced images). Enhancing cyst walls are diagnostic for intratumoral cysts (B, C).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-22 CE T1-WI (A, B, C) convexity meningiomas show peripherally located hypointense cysts with heterogeneous content and irregular contour which reflects necrosis rather than a true cyst.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-23 Extratumoral cysts may be seen around meningiomas, which may be due to CSF loculations or arachnoid cysts as demonstrated on CE T1-WI (A, B).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

Multiple meningiomas are reported in 9% of cases.²⁶ Although multiple meningiomas are known to be associated with neurofibromatosis type II, most patients do not harbor other features of this disease. Multiplanar imaging with contrast injection is mandatory to rule out possible additional small meningiomas (Fig. 14-24).¹ In general, meningiomas may arise at any site where meningothelial cells are found, such as in arachnoid associated with cranial nerves, spinal and intraventricular locations. Surgical decision is also a function of the anatomic location of the tumor, so that knowledge of the typical and unusual locations where meningiomas arise is essential. Intracranial meningioma locations are, according to descending order of frequency, as follows: convexity, parasagittal, sphenoid, fronto-basal, posterior fossa, cerebellopontine angle, petroclival, clivus, intraventricular, and orbital (Fig. 14-25). However, 1% of meningiomas are extradural and ectopic so that they may be encountered in the diploe, the skin of the skull, the paranasal sinuses, the parapharyngeal space, and even the mediastinum.²⁷

FIGURE 14-24 In approximately one tenth of cases, meningiomas may be multiple. CE T1-WI in (A) demonstrates the presence of two independent parasagittal meningiomas. B, CE T1-WI demonstrating the presence of a convexity and a tentorial meningioma. C, CE T1-WI. demonstrating the coexistence of a sphenoid wing and a clinoidal meningioma.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-25 On CE-T1-WI, falcotentorial (A, B), paranasal sinus (C), and jugular foramen meningiomas (D) are some examples of uncommon localizations.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

MRI CHARACTERISTICS OF CALCIFICATION AND BONE CHANGES ASSOCIATED WITH MENINGIOMAS

The ability to detect calcification within meningioma on MR images is variable. A mild or moderate degree of calcification is usually not discernible on MRI on T1- and T2-WI, although heavily calcified meningiomas exhibit hypointense signal on T2-WI (Fig. 14-26). Psammoma bodies appear isointense on T1- and T2-WI. Intratumoral vasculature is also demonstrated as punctate or linear hypointensities or as “signal void” structures on conventional MR images. If the vessel is not demonstrated in its typical morphology, a signal void structure may reflect calcification, blood, or vasculature on routine sequences. Recently GRE T2* and SWI sequences have gained wide acceptance to detect subtle calcifications.

FIGURE 14-26 The ability of MRI to detect calcification is variable. Heavy calcifications may be seen as hypointense on T2-WI (A, B). C, Corresponding CT image of B. Further, a calcified meningioma may show heterogeneous enhancement as in D and E. F, Corresponding lateral radiograph of E.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

Bone changes occur in approximately 25% to 48% of all meningiomas.²⁸^–³⁰ These changes may take the form of hyperostosis, osteolysis, and bone rarefaction which can exist independently or in combination with each other. The radiologic gold standard is high-resolution CT to demonstrate and diagnose these bony changes associated with meningiomas. Nevertheless all bone should be evaluated on standard MR images. On T1- and T2-WI the normal inner and outer tables of the skull are displayed as a hypointense layer without structure, and the diploe is seen as hyperintense on T1-WI due to its fat content. Hyperostosis is seen usually as widening of the layer of hypointense signal, and sometimes MR reveals inhomogeneous areas of increased signal intensity in the bone on conventional sequences (Fig. 14-27). However, because the cortical and trabecular detail cannot be well discerned on MRI, osteolysis or rarefication of bone cannot be easily appreciated. Bone invasion by meningioma can be diagnosed on MRI if increased signal is seen in the involved bone or if on fat suppressed-contrast enhanced studies, enhancement of bone is displayed (Figs. 14-28 and 14-29).

FIGURE 14-27 Bone changes may be seen as hyperostosis, osteolysis, or a combination of the two. In hyperostosis, bone is usually thickened and the signal intensity is variable. A, B, The same tuberculum sella meningioma that has thickening of the underlying bone with hyperintense signal on CE T1-WI, reflecting hyperostosis. Similarly, in the convexity meningioma (C, D, E), CE T1-WI (C) and T2-WI (D) show thickening of all bone layers with decrease in diploic fat signal. On CE T1-WI (E) bone enhancement is not detected. These findings indicate hyperostosis.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-28 The severity of bone changes ranges from very subtle to marked. In some cases this change is very subtle as on the CE T1-WI (A, B) where the fat signal in the clivus is diminished and hypointense signal belonging to the bone periosteum and dura is lost, reflecting bone invasion of the petroclival meningioma. The CE T1-WI of the convexity meningioma (C) reveals marked hyperostosis with a focal area of bone invasion. Evident bone invasion is demonstrated by contrast enhancement of bone near the meningioma as seen on CE T1-WI (D).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-29 Hyperostosis and osteolysis can coexist in meningiomas. Coronal CE T1-WI shows a convexity meningioma with extension into the superior sagittal sinus and thickening of the bone reflecting hyperostosis (A). However, a CE T1-WI sagittal image of the same patient shows speculated enhancement at the tumor–bone border reflecting bone invasion (B) which was also confirmed by CT as osteolysis (C).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

MRI OF VASCULATURE ADJACENT TO A MENINGIOMA

Conventional MRI has the ability to display arteries as signal void structures on T1- and T2-WI. Major arteries adjacent to meningiomas can be scrutinized for displacement, encasement, or stenosis without angiography (Fig. 14-30). In cases where the meningioma is located near a venous sinus, on conventional images blood flow in the sinus may not be appreciated if the flow is low. Such cases should be studied by MR venography to depict a narrowing or occlusion of the sinus by meningioma (Figs. 14-31, 14-32, and 14-33).

FIGURE 14-30 MRI displays arteries as signal void structures on CE T1-WI. Arteries may be encased, as in (A) demonstrating a cavernous sinus meningioma. B, A sphenopetroclival meningioma encasing both internal carotid arteries and the basilar artery. C, A cavernous sinus meningioma narrowing the lumen of the left ICA. Irregularities of the vessel wall are indicative of meningioma invasion as demonstrated in this foramen magnum meningioma (D).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-31 A venous sinus may be compressed by a nearby meningioma. This finding can sometimes be shown on CE-MRI as demonstrated on the T1-WI images of this petroclival meningioma (A, B).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-32 Meningiomas can invade and obliterate flow in venous-sinuses, which is best demonstrated on MR venography. (A is a CE T1-WI, and B is a venography) show obliteration of the venous confluens by a torcular meningioma. C, D, The parasagittal meningioma has invaded the superior sagittal sinus on CE T1-WI and compromised flow on MR venography (E). The parasagittal meningioma as seen on axial and coronal T1-WI (F, G) shows incomplete obstruction of the superior sagittal sinus on MR venography (H).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

FIGURE 14-33 Patency of venous sinuses can readily be demonstrated with MR venography. The parasagittal meningioma demonstrated on the axial T2-WI (A), the coronal CE T1-WI (B), and the sagittal noncontrast T1-WI (C). Patency of the superior sagittal sinus was demonstrated on MR venography (D, E).

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

RADIOLOGIC DIFFERENTIAL DIAGNOSIS OF MENINGIOMAS

Variable neoplastic and infectious mass lesions come into consideration for the differential diagnosis of meningiomas (Fig. 14-34). Radiologically hemangiopericytomas strongly resemble meningiomas, because they are dural-based and have a falx predilection. They may also exhibit the same MR signal characteristics as meningiomas; they may show intratumoral hemorrhage, a mushrooming configuration, rich vasculature, and bony erosion. A definite diagnosis may necessitate angiographic investigation.¹⁰ Schwannomas are the second most frequent extra-axial tumors that come into differential consideration. Cystic and hemorrhagic schwannomas are common, but calcification and hyperostosis are not features of this tumor. A dural tail may accompany schwannomas if they abut the dura. Schwannomas are usually hypointense on T1-WI and hyperintense on T2-WI, whereas meningiomas are more often isointense to cortex. Granulomatous diseases such as sarcoidosis, tuberculosis, plasma cell granulomas, and Erdheim Chester, Rosai-Dorfman disease may exhibit dural based mass lesions and mimic meningiomas. Ganglioglioma or pleomorphic xanthoastrocytoma (PXA) if located near the tentorium may mimic a cystic meningioma. Meningeal metastases, plasmacytomas, lymphoma, and leukemic infiltrations may all resemble meningioma, apart from being usually multiple lesions. Vascular lesions adjacent to the tentorium such as cavernous angiomas may also be mistaken for meningiomas. Intraventricular meningiomas may be mimicked by choroid plexus papillomas, but are not associated with hydrocephalus like papillomas. Meningiomas that invaginate the brain may be mistaken for an intra-axial tumor, more so if the meningioma harbors atypical features. In such challenging cases one needs to remember that neoplastic tissue is rich in water and is hyperintense on T2-WI; yet meningiomas are commonly isointense to brain cortex. In difficult cases, differential diagnosis of meningiomas necessitates the application of advanced MR techniques that are presented in a separate chapter.

FIGURE 14-34 The appearance of meningiomas on MRI is very variable and therefore there is a large number of differential diagnoses. Hemangiopericytomas imitate all MRI findings of meningiomas. CE T1-WI in (A) shows an intraventricular hemangiopericytoma and the CE T1-WI in (B) shows a cystic tentorial hemangiopericytoma. Schwannomas may be difficult to differentiate from intraventricular meningiomas on CE-MRI. CE T1-WI in (C) shows a schwannoma that extends into the internal acoustic canal. Note the coexisting convexity meningioma, which is very common in cases with NF-2. Axial CE T1-WI shown in (D) demonstrates marked enhancement of a choroid plexus papilloma and associated hydrocephalus. Except for hydrocephalus, this tumor mimics radiologic findings of a meningioma. Meningiomas may mimic MRI characteristics of dural based metastases as demonstrated on the CE T1-WI in E and F. Coronal (G) and sagittal (H) CE T1-WI show a cavernous angioma attached to the tentorium, displaying findings similar to those of an intraventricular meningioma.

(Courtesy of Canan Erzan, MD, Marmara University School of Medicine, Istanbul, Turkey.)

MRI OF RESIDUAL AND RECURRENT MENINGIOMAS

A long-term recurrence-free survival can be obtained in meningioma patients after gross total surgical resection of the tumor involving dura and bone. This, however, is seldom possible and a large proportion meningiomas do recur after surgical resection. The recurrence rate for meningiomas is variable; for benign meningiomas it is 7% to 20%, for atypical meningiomas 29% to 40%, and for malignant meningiomas 50% to 78%.²¹ The degree of surgical removal is one of the major determinants of recurrence and important in shaping a postsurgical treatment strategy. Routine contrast-enhanced (CE) MRI sequences are very sensitive in detection of residual tumor. In our experience, early postoperative MRI, performed within the first 48 hours after surgery, has been very effective in objectively determining the degree of residuals in most neuro-oncologic surgeries.³¹^–³³ The tissue resolution of MRI is very high for complex localizations such as the cavernous sinus, where MRI is far superior to CT in demonstrating the presence of residual tumor. On early postoperative imaging, anatomic distortion and the presence of CSF mixed with blood may obscure a small residual tumor so that contrast enhancement is necessary to highlight a tumor (Fig. 14-35).