Introduction

Meningiomas arising from the choroid plexus of either ventricle are rare but challenging lesions and represent ~1 to 2% of all meningiomas.1–4 In a recent review of 400 intraventricular meningiomas by Criscuolo and Symon,1 the majority of the tumors arose within the lateral ventricles (80%), followed by those arising from the third (15%) and fourth (5%) ventricle, respectively. This stratification correlates well with the amount of choroidal plexus tissue within these ventricles. Among meningiomas within the lateral ventricles, the trigone is by far the most common location, with more than 80% of tumors arising at this site.1–4 In contrast, intraventricular meningiomas were almost never found within the anterior horn, and those tumors arising from the temporal horn were relatively uncommon lesions. Interestingly, analysis of the culled literature on intraventricular meningiomas1 disclosed a distinct preponderance of left-sided lesions (59%). Whereas in the adult population intraventricular meningiomas represent 1 to 2% of all meningiomas, in the pediatric population as many as 9.4% of all meningiomas are located within the ventricular system.5,6

Intraventricular meningiomas can grow to considerable sizes before becoming clinically symptomatic. In patients reaching medical attention, symptoms may be intermittent and initially often nondescript and nonlocalizing. Patients may also present with symptoms of acute intracranial hypertension.

Since the first successful resection of an intraventricular meningioma by Cushing in 1916, surgical treatment has been particularly challenging due to the deep location of the tumor. Transcallosal or transcortical routes are mandatory for sufficient resection.7 Despite the fact that meningiomas in general respond well to radiosurgical treatment,8,9 in view of that modality’s size limits, its radiotoxicity, and higher recurrence rates,10 the treatment of choice for intraventricular meningiomas still remains surgery.

History

The first description of an intraventricular meningioma was given by Shaw in 1854 in an autopsy case. Cushing was the first to successfully remove an intraventricular meningioma, in 1916. In the classical monograph by Cushing and Eisenhardt,7 the three intraventricular meningiomas reported represented 1% of their total experience. Walter Dandy, another great neurosurgical pioneer, also published three intraventricular meningiomas in his monograph.11

In the following decades, several case reports and case series have been published.1–3,6,12–14 Delandsheer was the first to summarize the entity of intraventricular meningiomas by publishing 175 cases.2 Given that even today in high-volume centers the frequency of intraventricular meningiomas rarely exceeds one case per year, institutional series rarely report more than 20 cases. The largest recent series have been published by Guidetti et al in 1991,3 Criscuolo and Symon in 1986,1 Fornari in 1982,15 McDermott in 2003,6 Nakamura in 2002,4 Bertalanffy et al in 2006,16 and Liu 2009.3

At the Neurosurgical Department of the Medical University of Vienna, a total of 20 meningiomas arising from the lateral and fourth ventricles were described between 1980 and 200616 (i.e., during a period with sufficient computed tomography [CT] and magnetic resonance imaging [MRI]). Another three cases, managed before the availability of CT imaging, have been described earlier at our institution.15 All larger series of intraventricular meningiomas, including ours, suffer from the relatively small patient number treated over a long time period, making robust assessments of surgical outcomes difficult and thus preventing intergroup comparisons of surgical strategies and approaches. A common problem, however, remains since Cushing´s time: how to avoid damage to the visual pathway while preserving the interconnectivity of the dominant temporoparietal cortex in intraventricular meningiomas.

Clinical Presentation

According to recent reports, the majority of intraventricular meningiomas are larger than 2.5 cm upon admission.4,16 In the recent Hannover series,4 81% of all intraventricular meningiomas considered were larger than 3 cm in diameter. In our series, the average tumor size was 5 cm, with the largest lesions reaching 8 cm; only two tumors with a mean size of 2.5 cm were found incidentally. To date, only Kim et al10 have published on the radiosurgical treatment of small intraventricular meningiomas. With the widespread use of CT and MRI, however, it is foreseeable that the number of incidentally discovered small intraventricular meningiomas will increase and that the management of small asymptomatic lesions by either surgery or radio-surgery will become an important issue in the near future. Tumor size is—together with tumor location and the presence of hydrocephalus—an important determinant of the patient’s clinical presentation.

In general, the clinical presentation of patients with symptomatic intraventricular meningiomas does not differ significantly from those harboring other intraventricular tumors. Usually the most common symptom is headache. Two thirds of our patients had a history of headache, frequently intermittent in nature, and reaching back several years in some. Ultimately, headache was present in nearly all of our patients upon admission. The most common symptoms of patients presenting with intraventricular meningiomas are summarized in Table 32.1 .

Focal neurological deficits, including hemiparesis or visual pathway defects, were present in 15 to 78% of the cases reported.1–4,12,16–18 In larger tumors and lesions at strategic sites within the ventricular system, blockage of the cerebrospinal fluid (CSF) pathways can lead to signs of intracranial hypertension. Initially, these symptoms may be intermittent. However, in one third of cases, symptoms of permanently elevated intracranial pressure, including nausea and vomiting, were the leading signs bringing patients to medical attention. In most severe cases, patients may arrive comatose and require acute external ventricular drainage as a life-saving measure.

Gait disturbance is common in most series. Together with cognitive deterioration, urinary incontinence, and visual disturbance, these symptoms are usually due to chronic hydrocephalus and are not considered local neurological signs. Occlusive hydrocephalus or partial obstruction of the temporal horn may be present in all cases.4

Visual symptoms are more commonly observed in larger intraventricular meningiomas and were present in one third of all patients.3 The mechanism underlying visual disturbances can be either intracranial hypertension or damage of the optic radiation. In cases of acute occlusive hydrocephalus, intracranial hypertension is not necessarily associated with papilledema. Either or both visual field defects and papilledema were found in 85% of Guidetti et al’s cases, with bilateral papilledema being present in 60% of cases.3 Visual field defects were detectable in 15 to 67% of all cases upon admission ( Table 32.1 ).

The incidence of seizures is surprisingly high, ranging between 7 and 30% in the literature. According to Guidetti et al,3 seizures were most frequently generalized in nature, although focal epilepsy and complex partial seizures of temporal origin were also reported ( Table 32.1 ).

Only large tumors arising from the lateral ventricle of the dominant hemisphere will result in symptoms of aphasia, alexia, or acalculia.4,16

In contradistinction to tumors arising from the third ventricle, endocrinological disturbances are not typical signs of lesions within the lateral ventricles.

Neuropsychological abnormalities are commonly encountered but only infrequently reported. Modern diagnostic evaluation should include psychometric tests to reveal impairment of verbal and intellectual functions. The mechanism underlying impairment of memory functions is either direct compression of eloquent parenchyma in rare cases of temporal tumor location or, more frequently, blockage of CSF pathways with subsequent entrapment of the temporal horn.

Diagnostic Procedures

Plain skull radiograms can demonstrate calcifications in both normal choroid plexus and calcified intraventricular meningiomas.18,19 Nevertheless, the first correct diagnosis of an intraventricular meningioma was made by Dandy in 1918, according to Criscuolo and Symon,1,11 after ventriculography. Pneumencephalography, one of the first diagnostic procedures in neurosurgery, is mentioned only for the purpose of historical completeness.

Ten years later, angiography using direct carotid artery puncture allowed the direct visualization of contrast-enhancing intracranial tumors. Meningiomas were usually easily detectable because of their characteristic shape and staining. Intraventricular meningiomas were typically identified as global masses with sharp margins projecting to the lateral ventricle. Their arterial supply is derived exclusively from the choroidal arteries. Tumor blood supply can be drawn from either the anterior or posterior choroidal arteries exclusively, or from both arteries in conjunction3,4,12,20,21 ( Fig. 32.1A ). The angio-graphic tumor blush indicates the extent of tumor blood supply and gives sufficient information about the vascularity of the tumor. Moreover, detailed angiographic assessment can disclose the exact site where the feeding arteries enter the tumor, which is usually at the anterior or anteroinferior tumor margin. This information is crucial for the planning of surgical strategies, especially in highly vascularized tumors. In selected cases, the reason to perform diagnostic angiography preoperatively is to derive this crucial anatomical information and to decide the most suitable surgical approach in view of these data. Additionally, the venous phase provides information about the possible enlargement and displacement of internal cerebral veins and shows the drainage pattern to the vein of Galen. Although the hemodynamic information derived from angiography is precise and helpful, noninvasive imaging technologies have obviated the need for catheter angiography in the majority of these cases.

Theoretically speaking, preoperative embolization would be helpful in these highly vascularized tumors with their significantly enlarged choroidal arteries. The advantage of preoperative embolization would be most pronounced in parietal approaches because feeding artery control is obtained later than in other (i.e., temporal) approaches (to be discussed). Nevertheless, embolization was never performed in our series. Whereas superselective endovascular approaches to choroidal arteriovenous malformations for the purpose of glue embolization are usually possible using flow-directed microcatheter systems, this technique is not applicable in preoperative tumor embolization. In the latter cases, microcatheters of considerably larger diameter, allowing superselective polyvinyl alcohol (PVA) particle embolization, are required. These microcatheter approaches are usually more traumatic and may result in mechanical vasospasm, intimal damage, and infarction in this delicate vascular area. On the other hand, embolization followed by gamma knife radiosurgery has been reported as a possible alternative treatment for intraventricular meningiomas.22

Electroencephalography (EEG) does not usually have a role in the preoperative assessment of asymptomatic intraventricular meningiomas. In cases of documented seizure activity, EEG is the routine procedure to assess the efficacy of anticonvulsive treatment. In general, the rate of intraventricular meningiomas presenting with pre-operative seizures ranges between 7 and 35% in the current literature ( Table 32.1 ). In marked contrast, the rate of postoperative epilepsy after transcortical approaches ranges from 29 to 70% and in transcallosal approaches 0 to 10%.1–3,12,16–18,23

CT gives the correct diagnosis of an intraventricular meningioma in the majority of cases. Additionally, the presence of hydrocephalus, possible intratumoral calcifications and hemorrhages, as well as the extent of peritumoral edema, are precisely outlined. The CT-derived information is usually accurate enough for emergency treatment (e.g., external ventricular drainage or third ventriculostomy).24

On noncontrast CT scans, the majority of intraventricular meningiomas usually appear as hypodense or isodense lesions. Because tumoral calcifications are encountered in roughly 50 to 90% of cases, CT is appropriate for their detection.4,16,18

After contrast administration, meningiomas usually show homogeneous and strong enhancement. Whereas choroid plexus papillomas often have lobulated surfaces, the shape of intraventricular meningiomas is rather smooth and globular. However, in three of the 16 cases reported by Nakamura et al,4 the tumor shape was also described as lobulated.

Ventricular enlargement, either generalized or partial in nature, is a common finding on CT. The mechanism underlying partial ventricular enlargement is usually entrapment of the temporal and posterior horns. In the series of Nakamura et al,4 all ventricular meningiomas located in the trigone presented with enlargement of temporal and posterior horns. Ventricular hemorrhage is a rare but potentially fatal complication of intraventricular meningiomas.25

CT angiography and MR angiography are standard diagnostic procedures for intraventricular meningiomas and provide crucial information about the arterial tumor supply, the vascularity of the tumor itself, the displacement of larger vessels, and the venous drainage pattern. When compared with standard catheter angiography, CT and MR angiography are noninvasive procedures that can be easily exported to, and processed in, modern neuro-navigation systems.

There is no doubt that, in patients harboring intraventricular meningiomas, MRI is by far the most important imaging tool for the detection, surgical planning, and postoperative surveillance ( Table 32.2 ). T1-weighted images with and without contrast as well as thin-slice T2 images are part of the basic workup used for standard neuronavigation. As in all cases of deep-seated tumors, a surface rendering of the convexity of the brain is created to plan the craniotomy, to exactly localize the site of corticotomy, and to define the trajectory to the target.

A more sophisticated MRI-based technique, specifically DTI tractography, has become an integral part of the radiological workup and is a prerequisite for accurate planning of the surgical approach to intraventricular meningiomas.26–28 The main focus in these studies is on the course of the optic radiation and its relationship to the tumor. This preoperative morphological assessment is of paramount importance for the choice of the most suitable, atraumatic surgical approach ( Fig. 32.1B ). There is abundant literature describing the course of the optic radiation anatomically,29,30 surgically,26,30–33 and radiologically.33–36 Still, one of the most impressive descriptions of fiber dissections was provided by Klingler in 1956.37

Additionally, functional MRI, MRI spectroscopy, and MR angiography are among the modern MRI-based technologies used for treatment planning. Functional MRI with motor and sensory tasks provides additional information to direct the appropriate surgical approach and to avoid parenchymal damage. MR spectroscopy38 may be helpful in the differential diagnosis of intraventricular meningiomas and allows the differentiation between meningiomas and other intraventricular lesions (e.g., gliomas and neurocytomas). MR angiography is also able to detect the exact location of large bridging veins potentially obstructing the surgical approach and can demonstrate the displacement of important intraventricular veins.

In the majority of neurosurgical centers, neuronavigational devices are used in patients with deep-seated tumors. Some publications have outlined the usefulness of this procedure in the safe removal of intraventricular meningiomas.39 We have integrated structural MRI (T1 postcontrast, T2), DTI imaging of important white matter tracts, and functional data into a three-dimensional (3-D) model. This information is of paramount importance for planning the exact surgical approach. Unfortunately, the accuracy of all these neuronavigational systems decreases over time with ongoing surgery and with the amount of CSF aspiration, which is a significant issue in all ventricular tumors.

Intraoperative MRI allows the surgeon to update the navigational information and can show the completeness of tumor resection if required.27,40,41 Especially in cases of intraventricular meningiomas, intraoperative MRI has the potential to delineate the course of the fiber tracts of the optic radiation intraoperatively and repetitively.

Differential Diagnosis of Intraventricular Tumors

The differential diagnosis of intraventricular tumors includes meningiomas, choroid plexus papilloma, glial tumors, ependymomas, neurocytomas, and rare pathologies (e.g., epidermoid, plexus cysts, or tuberous sclerosis) ( Table 32.3 14,42). Most pathologies are easily diagnosed on grounds of their distinct location or characteristic appearance on CT and MRI. However, it is very difficult and sometimes impossible to distinguish intraventricular meningiomas from choroid plexus papillomas. Both pathologies are globoid lesions arising from the choroidal plexus and both exhibit a strong and homogeneous contrast enhancement. When compared with intraventricular meningiomas, choroid plexus papillomas are reported to have a lobulated rather than a smooth surface and exhibit an even more robust contrast enhancement. As previously mentioned, these distinctions are sometimes arbitrary in nature, and Nakamura et al4 recently reported on three of 16 intraventricular meningiomas in their series presenting with a markedly lobulated surface reminiscent of plexus papilloma. When compared with choroid plexus papillomas, which occur more frequently in the pediatric population and arise more frequently within the third and fourth ventricles, intraventricular meningiomas have a preponderance for the trigone of the lateral ventricle.1,14,42–44