Contribution of perfusion-weighted magnetic resonance imaging in the differentiation of meningiomas and other extra-axial tumors: case reports and literature review

Meningiomas are the most common primary nonglial neoplasms with typical radiological features. On CT, they usually appear as hyperdense, often calcified lesions; on MRI, they are mostly isointense with cortex on all sequences. Meningiomas enhance strongly after contrast injection and often homogeneously, but areas of necrosis especially in large lesions can also be seen. Though not specific for meningiomas, they very often produce the so-called dural tail sign which is enhancing thickened peritumoral dura [8].

Meningiomas are highly vascular tumors, and in PWI, they appear as hyperperfused lesions with elevated rCBV values. In several DSC examinations, mean rCBV values for all meningiomas were reported to range between 6 and 9 [9, 10] and were lower for meningothelial, fibrous and anaplastic meningiomas (mean rCBV = 5–7) and higher for angiomatous meningiomas (mean rCBV = 11.9) [11]. Also, in all our cases of meningiomas, high perfusion results were demonstrated (rCBV = 7.05 for CPA meningioma, rCBV = 10.4 for intraventricular meningioma) with the most elevated rCBV values found in angiomatous meningioma (rCBV = 18.7).

Apart from characteristic rCBV values, meningiomas usually show typical time-intensity curves with minimal or no return to the baseline level [12]. This phenomenon is due to the absence of the blood–brain barrier in neovessels of these tumors and thus the high rate of extracapillary leakage of contrast material. The typical time-intensity curves were seen in all our cases of meningiomas regardless of their location within falx, in the CPA or intraventricularly (Figs. 1c, 2f and 3f).

Though meningiomas are the most common dural tumors, they need to be differentiated with other meningeal lesions, in particular meningeal metastases, from prostate, lung, kidney or breast cancers [13]. If lesions arise multifocally within meninges, they are highly suggestive of metastases, but if they present as a solitary tumor especially in a patient without previous history of primary malignancy like in our case 2, they can cause severe diagnostic problems. Isolated dural metastases representing less than 1% of intracranial metastases [14] strongly mimic meningiomas, and less than 40 cases of dural metastases interpreted as meningiomas have been previously reported [2, 4, 13, 15]. Kremer et al., evaluating 6 dural metastases and 16 meningiomas, did not find any significant differences between those lesions on conventional MR images [10]. Both dural metastases and meningiomas showed similar appearance on T1- and T2-weighted images, similar hetero- or homogeneous contrast enhancement pattern, and a dural tail sign. Also, in our cases 1 and 2, plain MR images were not sufficient to discriminate both lesions. Though the two lesions looked very similar on conventional MR images, we noticed significant differences between them in PWI—a meningioma showed typical very high (18.7) and a metastasis low (0.4) CBV ratios. Our findings are consistent with the previous reports from perfusion studies of meningiomas and dural metastases. Kremer et al. found that the mean rCBV values of 16 meningiomas (mean rCBV = 8.97, range 4–18) were significantly higher than those of dural metastases of a lung carcinoma (one case: 1.26), lymphoma (one case: 1.29), breast carcinoma (two cases: 1.5, 1.56) and rectal carcinoma (one case: 3.34) [10]. It also has to be stressed that the majority of dural metastases show low perfusion results, but not all of them. Hypervascular lesions such as Merkel carcinoma, kidney carcinoma or melanoma metastases may present elevated rCBV values which make them indistinguishable from meningiomas [10, 16].

High-grade astrocytomas invading the dura mater may also be difficult to distinguish from meningiomas on plain MRI. Moreover, both lesions show high rCBV values in PWI [6, 9]. Cha et al. suggest that in those cases evaluation of the time-intensity curve during the first pass is of special importance and can be helpful in differentiating between these two tumor types. In extra-axial tumors, the curve does not return to baseline, which was also seen in all our cases of meningiomas (Figs. 1c, 2f and 3f), whereas in high-grade gliomas, there is a significant partial return of the curve to the baseline levels [12]. Other dural lesions mimicking meningiomas such as infectious or inflammatory diseases are rare and will not be discussed [2].

Meningiomas located in the CPA account for 10–15% of all lesions in this location and should in particular be differentiated from vestibular schwannomas accounting for 70–80% of all CPA lesions [17, 18]. Other CPA lesions are rare, with the epidermoid cyst being the most frequent (5%) [17]. Most vestibular schwannomas develop from the Schwann cells in the sheath of the inferior vestibular nerve in the IAC. When they grow bigger and give rise to a round or oval component in the CPA cistern, schwannomas can be typically seen as “ice on cone” lesions. On MR images, they show T1-isointensity and T2 high signal intensity, homo- or heterogeneous enhancement and may contain cystic or necrotic components, especially in lesions exceeding 2.5 cm [19]. The differential diagnostic problems can be caused by larger schwannomas without an obvious intracanalicular part and with a dural tail (suggestive of meningioma) or by meningiomas with dural enhancement within IAC (suggestive of schwannoma) like in our case 4. Because MR image is not always conclusive, PWI may be helpful to solve difficult cases. The rCBV values evaluated with DSC MRI are reported to be significantly lower in schwannomas than in meningiomas [9, 20], with the mean rCBV values 3.23 and 8.02, respectively. Even if there is an overlap between rCBV ratios of both entities, the highest reported ratios in schwannomas did not exceed 4.4 while the mean rCBV ratio of typical meningiomas ranges from 6 to 9 [7, 9, 10]. In our cases 3 and 4, perfusion results were similar to those reported in the literature. Though both tumors enhanced strongly after contrast administration, they showed different perfusion results—low rCBV values in schwannoma (Fig. 2b) and high rCBV values in meningioma (Fig. 2e). It is important to remember that the pattern of perfusion within the tumor does not reproduce enhancement characteristics found in the post-contrast MRI, since in conventional MRI contrast enhancement represents areas of disrupted blood–brain barrier rather than tumor vascularity per se [21, 22]. Areas of hyperperfusion in PWI can be identified in both enhancing and nonenhancing tumor regions, and conversely strongly enhancing tumors may show both high or low perfusion results in PWI. This is the case in schwannomas and meningiomas which both strongly enhance in conventional post-contrast MRI studies due to the lack of the blood–brain barrier and significant permeability of tumor vessels for the contrast agent. Their different perfusion pattern reflects the rate of tumor vascularity which is low in schwannomas and high in meningiomas [20].

Our cases 5 and 6 raise a problem of differentiation of intraventricular lesions. Intraventricular tumors represent a diverse group of lesions, some of them infrequent. The most useful indication for the diagnosis are patients’ age and precise intraventricular location. The most common tumors arising from the choroid plexus are choroid plexus papillomas, choroid plexus carcinomas, meningiomas and metastases [23].

Choroid plexus papillomas account for 0.4–0.6% of all intracranial tumors and nearly half of these tumors manifest in the first decade of life [24]. They usually arise in the lateral or the forth ventricle. Choroid plexus papillomas are cauliflower-like masses with prominent lobulations peripherally, calcifications, hemorrhage and cyst formation seen occasionally. They appear as iso- or hyperdense masses on CT and iso- or hypointense structures on T1-weighted and heterogeneous on T2-weighted images. They show strong enhancement on both CT and MR images. Hydrocephalus is very common due to an increase in the CSF production by the tumor [23, 24]. There are no reports in the literature on the results of spectroscopic or perfusion examinations in those tumors. Our study demonstrates low values of rCBV in choroid plexus papilloma (Fig. 3b).

Intraventricular meningioma is a rare tumor, constituting approximately 0.5–2.0% of all intracranial meningiomas, but this tumor is still one of the most common intraventricular neoplasms in the adult population [24, 25]. The majority of them occur after the fourth decade of life though they might be present earlier like in our case 6. Intraventricular meningiomas mostly occupy trigone of the lateral ventricle and are believed to arise from the arachnoidal cap cells trapped within the choroid plexus [24]. Their appearance on conventional imaging studies is similar to that of other meningiomas [24, 25]. MRS of intraventricular meningiomas has also revealed a pattern similar to that of meningiomas outside the ventricular system with decreased amounts of NAA, and increased amounts of lactate, lipids and alanine [25]. To our knowledge, there are no reports on the perfusion appearance of intraventricular meningiomas. Our study proves that the perfusion results in intraventricular meningiomas resemble those of other meningiomas with high rCBV values and the time-intensity curve showing no return to the baseline (Fig. 3e, f).

Cases 5 and 6 show that choroid plexus papilloma and intraventricular meningioma, though appearing similar on conventional MR images, demonstrate different patterns of perfusion: low rCBV values and high rCBV values, respectively. We believe that DSC MRI can be helpful in distinguishing those intraventricular lesions, though further investigations including more cases are required to find the common perfusion patterns especially in choroid plexus papillomas.