Meningioma or meningioma-like mass - from the imaging signs to the diagnosis

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1 Meningioma or meningioma-like mass - from the imaging signs to the diagnosis Poster No.: C-2387 Congress: ECR 2017 Type: Educational Exhibit Authors: E. M. Preda, I. G. Lupescu; Bucharest/RO Keywords: Localisation, Imaging sequences, Diagnostic procedure, MR, CT, Oncology, Neuroradiology brain, Management, Pathology, Multidisciplinary cancer care, Demineralisation-Bone DOI: /ecr2017/C-2387 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 38

2 Learning objectives To synthesize the criteria that can differentiate a meningioma (typical or less typical) from different meningioma-like mass, illustrating by several clinical cases. Background INTRODUCTION Meningiomas represent approximately 15% of all symptomatic and about 33% of all incidental (asymptomatic) intracranial neoplasms. These are the most common nonglial primary tumors of the central nervous system and the most common extraaxial neoplasms, accounting for between 13 and 26 % of all intracranial primary tumours [1,2]. Pathology.There are several histologic variants of meningioma. According to World Health Organization (WHO) classification of brain tumors (2007), meningioma can be benign (WHO grade 1 - accont 70-80% from all meningiomas), ~ but % may be atypical (WHO grade 2,) and 1-3 % may be malignant (WHO grade 3) [3,4]. Through meningioma-like masses (or meningioma mimics) we understand tumors that can display radiologic findings (CT, MRI, angiography) similar to those of meningiomas. This may be encountered during different conditions, including other extraaxial or peripherally located intra-axial lesions, such as neuroma, chordoma, metastases, lymphoma, gliomas, pituitary adenoma, granulomatous disorders. COMMON IMAGING FINDINGS which can be found in mengioma and meningiomalike mass are: extraaxial focal mass, well circumscribed, but rarely carpet like patern, contrast-enhancing lesion, dural attachment, dural tail, most often homogeneous structure with or without contrast, both on CT and MR, but some heterogeneities (calcifications, necrosis, cystic changes or lipomatous components) can be found sometimes in both entities, peritumoral vasogenic edema within the white matter of the brain, bone changes or infiltration. Page 2 of 38

3 IMAGING METHODS Computed tomography (CT) and Magnetic Resonance Imaging (MRI) play important roles in the diagnosis of meningioma and meningioma -like mass. CT is more widely available, proper for rapid screening in urgent settings and can be used when patients have MRI exclusions (such as pacemakers). CT is superior in demonstrating the bone changes and is more sensitive in detecting psammomatous calci#cations. Angiography highlight the vascularization of tumors and play an essential role in presurgical embolization of meningiomas, to reduce blood loss at subsequent surgery. MRI is modality of choice for meningioma and meningioma-like lesions, useful for diagnosis, classification, treatment planning and posttreatment surveillance. In addition to conventional MR imaging techniques (which offer the anatomic information), advanced MRI techniques (diffusion-weighted MR imaging, perfusion-weighted MR imaging and direct imaging of brain metabolites using magnetic resonance spectroscopy) bring physiologic data and information on chemical composition, improving diferential diagnosis between benign and malignant lesions. Findings and procedure details TYPICAL MENINGIOMA has characteristic imaging findings: extraaxial, well defined focal mass, broad-based dural attachment, homogeneous densities (on CT) / intensities (on MR exam), close to those of grey matter, markedly, homogenous enhancement, both on CT and MR, enhacement of the adjacent thickened dura ("dural tail), varying degrees of surrounding vasogenic edema, hyperostosis of the adjacent inner table; and preferential locations: extraaxial mass located over the cerebral convexity, in the parasagittal region, arising from the sphenoid wing, olfactory groove, Page 3 of 38

4 1. TYPICAL imaging features (homogeneous, well-circumscribed, hemispheric, markedly enhancing) can be found in about 85% of meningiomas, both on CT and MRI examinations. CT : lesion, closely abutting the dura, iso- hyperattenuating to gray matter on non-contrast CT and shows homogeneous, strong enhancement after iodinate contrast injection [ Fig. 1 on page 10 ]. But other extraaxial, as well as some superficial intraaxial mass may also exhibit contact with the dural surface and may be well-circumscribed, iso hyperattenuating to gray matter on non-contrast CT, with homogeneous pattern even on NECT or ECT. For example, a round hematoma, superficial located (Fig. 2 on page 11) hyperattenuating on NECT in an hypertensiv patient, as well as hematological neoplasms such as leukemia or secondary involvement of central nervous system in Hodgkin or non - Hodgkin lymphoma may mimics meningioma. MRI: meningiomas are iso- or slightly hypointense to gray matter on T1W images, iso-hyperintense on T2W images and with intense, homogeneous enhancement after intravenous gadolinium injection ( Fig. 3 on page 12 ) An important imaging feature suggestive of an extraaxial location is the presence of a CSF cleft sign ( Fig. 4 on page 13 ), ie a cleft between the tumour and the underlying brain cortex thet may contain CSF or cortical vessels entrapped between the tumour and the underlying cortex. Typically meningiomas not just touch the dura, but have a broad-based dural attachment, also associating the thickening of the dura beyond the edges of the tumor. "Dural tail sign" (DTS), "dural base" or "meningeal sign"( Fig. 5 on page 14 ) are similar terms describing thickening of the dura adjacent to an intracranial mass, often indicating the anchoring point to the dura [5]. Goldsher et al. established in 1990 triple criteria for DTS [6]: presence of at least two consecutive sections through the tumor at the same site in more than one imaging plane; greatest thickness adjacent to the tumor and tapering away from it; enhancement more intense than that of the tumor itself. Page 4 of 38

5 In certain circumstances, the presence of a dural tail may be useful to distinguish meningiomas from other aextraaxial masses, for example, in distinguishing meningioma from schwannoma in the cerebellopontine angle as the latter is not typically associated with a dural tail [7, 8, 9]. ( Fig. 6 on page 15 ) Although common sign for meningiomas, the DTS is not specific as it is also described in some metastases, glial tumours and lymphoma [10, 11] ( Fig. 7 on page 16 ) Edema associated with meningioma is found in more than half of all meningiomas although those are tumors extraaxiale (Fig. 8 on page 17). While peritumoral edema of meningiomas has been proposed to be related to brain invasion, it can occur without brain invasion and is said to predict an increased potential for recurrence. Thought to be vasogenic in origin is probably related to tumor size, histologic subtypes, vascularity, venous stasis, type of arterial supply, sex hormone receptors, secretory activity, inflammation (lymphocytes and macrophage infiltrates), or brain [12, 13, 14, 15]. A peritumoral band ( Fig. 9 on page 18 ) may be seen surrounding the meningioma which represents the border between the tumor and the brain surface, and demonstrates the extraaxial nature of the tumor [16]. Bone changes associated with meningiomas include osteolysis or hyperostosis ( Fig. 10 on page 19 ), with the latter most common, described in 20 % of cases [10] and more common with the en plaque form. The bone changes associated with meningiomas are best depicted and assessed on CT; however, they may be appreciated on MRI. Hyperostosis is most common in tumours arising from the skull base and anterior cranial fossa and the degree of hyperostosis is not proportional to tumour size [17]. 2. However some ATYPICAL/ uncommon imaging features, meaning atypical density/ intensity, including cyst formation, lipomatous transformation, and ring enhancement, exhibit nearly 10-15% of meningiomas [7,18]. Calcifications are frequent in benign meningiomas and best demonstrated on CT. Typically, the presence of calcification within an intracranial mass lesion is an indicator of slow growth or benign nature [19]. Cystic components of meningioma (in cystic meningioma) may exhibit low density nearer to water on CT and typically low signal intensity on T1-weighted and high signal intensity on T2-weighted sequences ( Fig. 11 on page 20 ) as well as heterogeneous Page 5 of 38

6 or peripheral enhancement, as Paek et al. described in a series of 16 histologically proven cases [20]. A lipomatous or lipoblastic meningioma is a rare but, most of the time, benign tumor. Its pathogenesis is still debated: it is usually considered to be part of the metaplastic meningioma (with metaplastic change of meningothelial cells into adipocytes), but several authors recently suggested that fat accumulation inside the tumor was related to metabolic disorders of the meningothelial cells. Fat component may be proved on CT ( Fig. 12 on page 21 ) or MR (resulting in a shortening of the T1 relaxation time and high signal intensity on the T1-weighted sequence) [21]. Haemorrhage is a very rare and unusual presentation of meningiomas, with very few reported cases in the literature and my be subarachnoid, subdural, intracerebral or intratumoural [22]. Ring Enhancement ( Fig. 13 on page 22 ) is an unusual feature that can be seen in both histologically typical meningiomas and in some malignant on aggressive histologic variants, as in due to central non- enhancing zone causes by calcifications, cyst formation, hemorrhage, or necrosis. As mentioned, meningiomas are usually fairly homogeneous masses, with homogeneous enhancement. A convexity meningioma with ring enhancement not to be confused with a necrotic on cystic glioma, a metastasis, or even an abscess ( Fig. 14 on page 23 ). OTHERS USEFUL SINGS: sunburst and spokewheel pattern( Fig. 15 on page 24 ) observed on MRI/DSA (as meningeal vessels that coursing through tumors) - related to meningiomas blood supply; the majority of those are predominantly supplied by, but some tumours also may have significant pial supply to the periphery of the tumour. mother in law sign - an angiograpgic sign of meningioma, in which the tumour contrast blush "comes early, stays late, and is very dense" pneumosinus dilatans(enlargement of the paranasal sinuses) can be a helpful sign to indicate the presence of a anterior skull base meningioma (often missed on non-contrast CT or MR examinations due to their close proximity to bone and low lesion to brain contrast) [23]. Meningiomas located at the skull base, also have the potential to contact and encase vessels, particularly the carotid arteries ( Fig. 16 on page 25 ), sometimes substantial resulting in luminal narrowing, but rarery with cerebrovascular [24, 25]. Dural Page 6 of 38

7 venous sinuses are much more commonly associated with tumoural invasion that may result in partial or complete sinus occlusion (especially superior sagittal sinus). triad of extracranial soft tissue tumour, osteolysis of the skull vault and intracranial extension of the same tumour is considered an indicator of malignancy ( Fig. 17 on page 26 ). 3. PARTICULAR location and types Suprasellar/parasellar - must be differentiated from adenoma (that indent at the diaphragma sellae, giving them a 'snowman' configuration, unlike the spread of meningiomas along the meninges; note the epicentre of the lesion above the sella (Fig. 18 on page 27). Posterior fossa/ cerebellopontine angle - differentiation by schwannoma require followed several elements: calcifications, a "dural tail" and extension pattern of the tumor Intraventricular meningioma are most frequently (80%) seen in the trigone of the lateral ventricles and slightly more frequently on the left, 15% in the third ventricle, 5% in the fourth ventricle ( Fig. 19 on page 28 ). Optic nerve sleath meningioma/ intraorbital meningioma Tentorial meningioma Intraosseous meningioma - most common located in frontoparietal and orbital regions, are more prone to develop malignant changes compared with intracranial meningiomas and the association of osteolysis with a soft-tissue mass, is a strong reason to suspect a malignant meningioma [33] Trauma has been suggested as a risk factor for meningioma formation and may be involved in the formation of intraosseous meningiomas, which can present at the skull base. Meningioma en plaque ( Fig. 20 on page 29 ).represents a carpet or sheet-like lesion that infiltrates the dura and sometimes invades the bone; commonly involve frontoparietal, juxtaorbital, sphenoid wing, diffuse calvarial or rarely spinal region and also more prone to develop malignant change when compared to intracranial meningiomas; due to difficulty in complete resection, the recurrence rate of en plaque meningiomas is higher than the usual counterpart [34]. Page 7 of 38

8 Radiation-induced meningiomas tend to develop over the cerebral convexities rather than at the skull base. Neurofibromatosis type II (NF-2)- should raise suspicion of when found in young patients; almost all familial meningiomas develop within the context of NF-2, and patients with NF-2 are at increased risk for meningiomas as well as vestibular schwannomas (often may be present multiple tumors of both varieties) - Fig. 21 on page 30 ; Meningiomatosis - in the setting of multiple meningiomas, a diagnosis of neurofibromatosis type 2 should be considered ( Fig. 22 on page 31 ); 4. DIFFERENTIAL DIAGNOSIS between benign and atypical or malignant meningiomas > Diffusion tensor imaging (DTI) may aid in the distinction:several studies reporting a decreased apparent diffusion coefficient (ADC) in high-grade tumours [3,11, 36]. Various theories have been proposed to explain the reduced ADC and include a decreased free diffusion of extracellular water and the high nuclear-tocytoplasmic ratio of high-grade tumours, resulting in a reduction in the free translation of intracellular water [3, 36]. Because atypical and malignant meningiomas are more prone to recurrence and an aggressive growth pattern, DTI may provide useful diagnostic information for surgical planning and prognostication. > Isotropic diffusion-weighted imaging (DWI), which measures average magnitude of water motion in apparent diffusion coefficient (ADC), has shown controversial results for differentiating classic from atypical meningiomas[38]. In contrast to isotropic DWI, diffusion tensor imaging (DTI) provides information about magnitude and directionality of water diffusion, and thus may be able to measure the differences in intratumoral diffusion anisotropy as a result of histologic differences between classic and atypical meningiomas. > Magnetic resonance spectroscopy (MRS) is considered to be useful for the diagnosis of meningiomas whose radiological appearance is atypical and it may also play a role in the evaluation of malignant potential [37]. Meningiomas demonstrate increased choline (3.2 ppm) and decreased creatine (3.0 ppm). Alanine has been suggested by various studies to be specific for meningiomas; In cases where alanine levels are absent or ambiguous, glutamine/glutamate (Glx, 3.75 ppm), although not a unique metabolite for meningioma, has been recognised as a potential supplementary metabolite to help detect meningiomas [37]. Lactate has also been shown in some studies to be more frequently observed in non-benign meningiomas, WHO Grade II and III, but is not always a marker of an aggressive meningioma. Page 8 of 38

9 5. DIFFERENTIAL DIAGNOSIS between meningioma - meningioma-like masses Numerous neoplastic and non-neoplastic entities may clinically and radiologically mimic meningiomas: more often haemangiopericytomas, metastases, lymphoma and neurosarcoid. #Haemangiopericytomas are rare, WHO grade II neoplasms with a high local recurrence rate, that do not calcify in contrast to meningiomas, may have a narrow, stalk-like or broad dural attachment and associate rather osteolisis than hyperostosis of the adjacent bone; also may have heterogeneous enhancement prominent internal flow voids. #Dural metastases ( Fig. 23 on page 32 ) (most frequently from breast carcinoma, adenocarcinomas, squamous cell carcinoma of the lung and renal cell carcinoma) may mimic meningiomas; however, they are typically hyperintense in the T2-weighted sequence. The presence of multiple lesions may aid diagnosis. Angiography may be useful for differentiate meningiomas from metastatic dural tumors since an accumulation of contrast agent in the capillary phase may be typical for metastatic disease. Dynamic perfusion MRI provides additional information regarding the vascularity of a tumor that is not available with conventional MRI. Moreover, it maps the cerebral blood volume and calculates the relative cerebral blood volume (rcbv), which is the ratio between the CBV in the tumor and the CBV in the white matter. Studies demonstrate that meningiomas typically have a high rcbv; whereas dural metastatic lesions typically have a low [26, 27]. As well, MR spectroscopy may detect a pattern of lipid and/or lactate signals specific to metastatic tumor), but must be performed prior to embolization. Malignant brain tumors have lower NAA/Cho, NAA/Cho + Cr, NAA/Cr and higher lactate/lipid, lactate/cr tumor ratios when compared to benign brain tumors, unlike meningiomas that have a high alanin/cr ratio [27, 28] - Fig. 24 on page 33. #Secondary CNS lymphoma may spread haematogenously and mimic meningioma (fig.). Lymphoma imaging aspects is: iso-hyperattenuating mass / isointense to hypointense in the T2-weighted sequence and demonstrates intense post-contrast enhancement; lesions may be multiple and also may involve the leptomeninges -Fig. 25 on page 34. #Sarcoidosis involves the CNS in 5 % of cases and may involve the dura but also the leptomeninges, perivascular subarachnoid spaces, cranial nervesand brain parenchyma. Lesions may besolitary and focal, mimicking meningiomas or diffusely infiltrating and are typically hypointense on T1-weighted sequences, hyperintense on T2-weighted sequences and demonstrate homogeneous post-contrast enhancement. The coexistence of pulmonary sarcoid in the majority of cases aids diagnosis [29, 30]. #Melanocytic lesions of the CNS are rare, and lesions involving the dura include both primary melanocytic lesions and metastatic melanoma, and it is Page 9 of 38

10 important to differentiate between primary and metastatic lesions, since the workup and treatment differ [31]. #Neurosarcoidosis has a predilection for the basilar meninges, but any portion of the CNS can be involved Dural involvement may be diffuse or focal and mass-like, and the mass-like involvement of the dura may mimic a meningioma or nerve sheath tumor. Owing to its nonspecific clinical presentation and neuroradiologic imaging characteristics, neurosarcoid is a difficult diagnosis to confirm especially in the absence of systemic disease. Lumbar puncture (for ruling out other neurologic disorders) and chest imaging (to evaluate for pulmonary involvement) may be helpful [32]. IMAGING REPORT- should not forget to include: extraaxial / intraaxial location (CSF cleft sign, the peritumoral band) typical or atypical imaging findings on CT and conventional MR dural relation ("Dural tail sign") bone changes / intracranial / extracranial extension surrounding parenchyma edema / size of tumor / herniation vascularization data: enhacement pattern / angiographic signs (sunburst and spokewheel pattern, mothet in law sign) / dynamic perfusion/ DWI / diffusion tensor imaging (DTI) / MR spectroscopy Particular location or meningioma types Images for this section: Page 10 of 38

11 Fig. 1: Extraaxial well-circumscribed, hemispheric mass, closely abutting the left frontal convexitar dura, isoattenuating to gray matter on non-contrast CT (NECT) and shows homogeneous, strong enhancement after iodinate contrast injection (ECT) Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 11 of 38

12 Fig. 2: Well-circumscribed mass, abutting the falx cerebri dura, hyperattenuating to gray matter on non-contrast CT (NECT) with size and oedema in progression on next day CT, representing an superficial hematoma. Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 12 of 38

13 Fig. 3: Extraaxial well-circumscribed, hemispheric, homogeneous mass, isointense with gray matter on T1W images, also isointense on T2W images and with intense, homogeneous enhancement after intravenous gadolinium injection. - Bucharest/RO Page 13 of 38

14 Fig. 4: CSF cleft sign: CSF cleft between the tumour and the underlying brain cortex: A - conteining cortical vein; B - just CSF. Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 14 of 38

15 Fig. 5: Dural tail sign: meningeal thickening, with strong enhancement, adjacent to the tumor and tapering away from it, present on three consecutive sections through the tumor, on two planes Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 15 of 38

16 Fig. 6: Dural tail sign: meningeal thickening with strong enhancement (arrow) near meningioma (red star) and tapering away from it, distinguishing between meningioma and schwannoma (arrowhead) Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 16 of 38

17 Fig. 7: Dural tail sign: meningeal thickening with strong enhancement (arrow) adjacent to a dural mass representing a dural metastasis encountered in a patient with GIST Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 17 of 38

18 Fig. 8: Varying degrees of vasogenic edema surrounding benigne meningiomas: A without edema, B - with moderate edema Radiology and Medical Imaging Department, Fundeni Clinical Institute, Bucharest, Romania Page 18 of 38

19 Fig. 9: A peritumoral band surrounding the meningioma which represents the border between the tumor and the brain surface, and demonstrates the extraaxial nature of the tumor Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 19 of 38

20 Fig. 10: Bone infiltration accompanying meningiomas: A - a case of benign meningioma accompanied by hyperostosis and B - an anaplastic meningioma with adjacent osteolysis Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 20 of 38

21 Fig. 11: Left frontal Cystic meningioma with prominent cystic components demonstrating low densities on NECT, hyperintensities on T2w image, hypointensities on T1w image and heterogenous enhacement postgadolinium, without edema but with important hyperostosis - Bucharest/RO Page 21 of 38

22 Fig. 12: Small right frontal meningioma with lipomatous components and hyperostozis Radiology and Medical Imaging Department, Fundeni Clinical Institute, Bucharest, Romania Page 22 of 38

23 Fig. 13: Small left parasagittal meningioma, partially calcified, depicting ring enhacement after gadolinium intravenous administration. - Bucharest/RO Page 23 of 38

24 Fig. 14: Left sphenoidal wing meningioma after radiotherapy, showing central necrosis and ring enhancement - Bucharest/RO Page 24 of 38

25 Fig. 15: Right anterior cranial fossa meningioma: Sunburst and Spokewheel sign observed on MRI sequences (a- sagittal T1, b-3d TOF and c- axial T1 after gadolinium injection): as meningeal vessels that coursing through meningioma Radiology and Medical Imaging, Fundeni Clinical Institute, courtesy to I.G.Lupescu Page 25 of 38

26 Fig. 16: Left sphenoidal meningioma that encase left carotid artery, with substantial luminal narrowing Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 26 of 38

27 Fig. 17: Triad of extracranial soft tissue tumour, osteolysis of the skull vault and intracranial extension - an indicator of malignancy - seen in three patients with different malignancies Radiology and Medical Imaging Department, Fundeni Clinical Institute, Bucharest, Romania Page 27 of 38

28 Fig. 18: Sellar meningioma and pituitary adenoma - differential diagnosis - Bucharest/RO Page 28 of 38

29 Fig. 19: Intraventricular meningioma. Radiology and Medical Imaging Department, Fundeni Clinical Institute, courtesy to I.G.Lupescu Page 29 of 38

30 Fig. 20: Left sphenoidal and intraorbitar meningioma "en plaque". - Bucharest/RO Page 30 of 38

31 Fig. 21: Neurofibromatosis type II: association between meningiomas and neurofibromas Ioana Lupescu, et al. Aspecte computer tomografice si IRM particulare in facomatoze.imagistica Medicala, vol 1-2, 2005, pag Page 31 of 38

32 Fig. 22: Meningiomatosis Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 32 of 38

33 Fig. 23: Dural metastase in breast neoplasm Radiology and Medical Imaging Department, Fundeni Clinical Institute, Bucharest, Romania Page 33 of 38

34 Fig. 24: MRS in dural metastases from GIST - Bucharest/RO Page 34 of 38

35 Fig. 25: NonHodgkin lymphoma mimicking paraselar meningioma Radiology and Medical Imaging, Fundeni Clinical Institute, Bucharest, Romania Page 35 of 38

36 Conclusion Understanding the similarities but also the distinct imaging features in an well-known anamnestic, clinical and etiopathogenic context, often allow a differential diagnosis between meningioma and "meningioma-like" process, avoiding unnecessary surgical acts. Personal information Dr. Preda Emi Marinela Prof.Dr.Ioana G.Lupescu Department of Radiology and Medical Imaging Fundeni Clinical Institute, Bucharest, Romania "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania emimpreda@gmail.com References Bondy M, Ligon BL. Epidemiology and etiology of intracranial meningiomas: a review. J Neurooncol 1996;29: Longstreth Jr WT, Dennis LK, McGuire VM, Drangsholt MT, Koepsell TD. Epidemiology of intracranial meningioma. Cancer 1993;72: Toh CH et al, Differentiation between classic and atypical meningiomas with use of diffusion tensor imaging. AJNR Am JNeuroradiol, 2008, oct. 29(9): Perry A. et al, Meningiomas. In: Louis DN, Ohgaki H, Wiestler OD, Cavenee WK, editors. WHO classification of tumours of the central nervous system. th ed. Lyon: IARC; p H. Rokni-Yazdi, H. Sotoudeh, Prevalence of "dural tail sign" in patients with different intracranial pathologies, Eur J Radiol, 60, 2006, pp Goldsher D. et al, Dural "tail" associated with meningiomas on Gd-DTPAenhanced MR images: characteristics, differential diagnostic value, and possible implications for treatment. Radiology 1990; 176: Page 36 of 38

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