INTRODUCTION

Intraventricular meningiomas are relatively rare and represent 1% to 2% of all meningiomas. The first recorded case of intraventricular meningiomas is probably by Shaw in 1854.¹ He identified an encapsulated fibrous tumor in the trigone of the lateral ventricle. MacDowell performed a left trigonal tumor operation in 1881.² In 1938, Cushing and Eisenhardt first described a case of meningioma located within the third ventricle.³ Since then, there have been multiple reports of cases of intraventricular meningiomas in the literature addressing the potential problems and difficulties encountered in management of these formidable surgical lesions. To date, approximately 600 cases of intraventricular meningiomas have been reported. Of these, approximately 80% are found in the lateral ventricle, 15% in the third ventricle, and 5% in the fourth ventricle.^1–48

We base our analysis on a review of our experience with 50 cases of lateral ventricular meningiomas treated in our Institute from 1990 to 2006. The discussion is focused on lateral ventricular meningiomas, and meningiomas in other ventricles are not considered. In our series, lateral ventricular meningiomas represented 2.1% of the total meningiomas seen during the period. Slow progression of these essentially benign tumors and accommodative capacity of the ventricles make these tumors unique in the sense that the symptoms are subtle and long-standing and they are significantly large at the time of diagnosis. Lateral ventricular meningiomas present a surgical challenge because of the deep location, large size, firm consistency, and the frequently observed intense vascularity. Although meningiomas have been rarely recorded in other sites of the lateral ventricular cavity, most of them are located in the trigone or have an extension toward it. The presence of bulkier choroid plexus may be the reason for higher incidence of tumors in the region of atrium of lateral ventricle. The majority of the lateral ventricular meningiomas are benign in nature and resection often leads to cure from the disease. Malignant meningioma in the lateral ventricle with cerebrospinal fluid (CSF) borne distant metastasis in the brain and spinal cord is also rarely reported.^16,29,45

The exact site of origin of these tumors is unclear, but the various reviews have suggested that these tumors probably arise from the meningeal cells that are transported together with the choroid plexus as the ventricular system invaginates during embryogenesis.^3,22,27 This feature is supported by the fact that the vascular supply of most of these tumors is from the choroidal vessels. Due to the relationship with choroid plexus, some authors prefer to label these meningiomas as “choroidal” meningioma.³⁵

CLINICAL FEATURES

Like most other meningiomas, intraventricular meningiomas also have a female preponderance. Although not observed in our series, some authors have identified a relatively higher incidence of intraventricular meningiomas in children.^8,31,41 Some authors have observed left side predominance,^21,22 while others have noted no significant side preference. These meningiomas are sometime seen as a part of neurofibromatosis 2 (NF2) complex and also in association with multiple meningiomas. The patients may not have any significant neurologic symptoms, even when the tumor has reached a massive size. Owing to the nature of growth pattern, some of these tumors may be detected incidentally. In such cases, considering the slow nature of growth and difficulties that can be encountered during surgery, a conservative observation may be a viable treatment option. High vascularity of the tumors has rarely been associated with intratumoral bleeding and acute onset of symptoms.^34,36,42,46

In general, these patients usually have long-standing dull and generalized headaches as the initial presenting symptom, which increases in intensity as the tumor grows in size. Duration of headache may be as long as 10 to 15 years.³⁸ With tumor growth, the additional symptoms of raised intracranial pressure in the form of vomiting and visual symptoms related to papilledema become prominent. Although not seen in this series, episodic severe headaches simulating symptoms generally related to colloid cysts have been observed in cases with small sized lateral ventricular meningiomas.²¹ Visual field defects are relatively frequent. In our series, 5 of the 14 patients with preoperative visual field defect had almost complete homonymous hemianopia. The exact cause of the visual field defect before surgery is unclear. A vascular steal from the posterior cerebral artery supply zone by the “vascular” tumor could be a probable cause of this symptom. Direct stretching and compression of the optic radiation projection fibers is another possible cause. Considering that the visual field defect improved in eight patients (57%) after surgery, involvement of fibers of optic radiation by pressure could be an important factor. Memory disturbances, neuropsychological deficits and personality changes are relatively late and were seen in 12% cases.¹³ Decrease in scholastic performance due to progressive cognitive changes secondary to chronically raised intracranial pressure is a frequent form of presentation in children. Verbal and visual memory is more frequently affected. The short-term or recent memory is relatively spared.

The incidence of seizure is relatively uncommon in patients with lateral ventricular meningiomas. Focal motor or generalized seizures as presenting symptom have been reported and were seen in three cases (6%). Sensory seizures occurred in five patients (10%). Postoperative seizures are reported in 29% to 70% patients operated by transcortical approaches. In our series, 11 (22%) patients had postoperative seizures. Parietal and temporal lobe signs have been recorded in the literature and were seen in 8% of our cases. Preoperative localizing signs such as hemiparesis, aphasia, agnosia, and alexia are rarely present even in large lateral ventricular meningiomas.¹⁷

INVESTIGATIONS

Magnetic resonance imaging scan (MRI) is an important tool for diagnosing lateral ventricular meningiomas.^39,40 It differentiates intraventricular lesions from the paraventricular tumors. It helps in defining the extent of the tumor, its physical nature, and its vascularity and thereby assists the surgeon in planning the surgical approach. The most common site for the lateral ventricular meningiomas is the trigone of the lateral ventricle and irrespective of its size they are attached to the choroid plexus in the region of the trigone. Asymmetric hydrocephalus with ipsilateral dilatation of the temporal and occipital horns is also common and frequently diagnostic of intraventricular location of the lesion and meningioma. The MRI, in general, shows the lesion as iso- to slightly hypointense on T1-weighted images and iso- to mildly hyperintense on T2-weighted images. There is usually homogeneous enhancement on contrast administration. The advent of MRI has limited the role of angiography in lateral ventricular meningiomas. The MR spectroscopy and blood volume-time intensity maps may assist in the preoperative diagnosis. A high alanine-to-creatinine ratio has been reported as specific MR spectroscopic findings for meningiomas. Functional MRI may be useful in preoperative cortical mapping, so as to identify the sensorimotor and language cortices to plan an optimal surgical approach and select the safest area in which to make a cortical incision.

It is important preoperatively to differentiate these benign intraventricular meningiomas from more frequently encountered malignant tumors in the region and in the ventricle. The differential diagnosis of lateral ventricular meningioma includes choroid plexus papilloma, intraventricular ependymomas, central neurocytomas, and subependymomas.²⁷ Each of these tumors has a characteristic nature of clinical presentation and radiologic features. The presence of a large sized and well-defined lobulated trigone centered tumor in a physically healthy and neurologically stable patient favors a preoperative diagnosis of a meningioma. The duration of the presenting symptoms is also relatively longer in intraventricular meningiomas when compared to other malignant intraventricular tumors. Intense and homogeneous tumor enhancement is more frequent in intraventricular meningiomas. The presence of intratumoral necrotic and cystic changes is relatively uncommon in intraventricular meningiomas and was seen in nine (18%) cases. As in other brain tumors, we observed that longer the duration of clinical symptoms the firmer was the consistency of the tumor. Calcification within the tumor was seen in 14% cases. Moderate to severe tumor surrounding parenchymal edema was seen in 64% of patients. Enlargement of the contralateral ventricle, probably suggestive of the chronic nature of the disease process, was seen in all our cases with medium to large sized tumors. Dilatation of the temporal and occipital horns, probably a result of focal obstruction to the CSF pathway, suggests intraventricular location of the tumor.

Other than the fact that there is no bone related or origin site changes, CT scan shows all typical features of meningiomas.⁴⁹ The tumors are hypodense or slightly hyperdense tumor and have intense contrast enhancement. Calcification may be seen. Dense and large calcifications within the tumor may even be visible on plain skull radiographs.

ANGIOGRAPHY

The blood supply to lateral ventricular meningioma is from both anterior and posterior choroidal arteries. They also can receive supply from lenticulostriate and thalamoperforating vessels. The study may provide useful information on the location of the feeding arteries in relationship to the internal dome of the tumor. The carotid angiogram shows enlargement, tortuosity, and displacement of the anterior choroidal artery. Venous drainage is through the vein of Galen, internal cerebral vein, or the basal vein of Rosenthal. Large veins frequently course over the dome of the tumor before joining the main venous channel. In the venous phase, the internal cerebral veins appear stretched and displaced inferiorly and to the opposite side. The vein of Galen may be elongated and straightened. Vertebral angiogram may show enlargement and anterior displacement of the lateral posterior choroidal artery with a reversal of its curve, and marked anterior convexity.²³

SURGICAL STRATEGY

Surgery on intraventricular meningiomas challenges the surgical skills and philosophical understanding of a neurosurgeon. Surgical experience and thorough knowledge of anatomy are crucial in excising these lesions.^50,51 While a successful surgical resection is compatible with normal life, any error in planning the approach or executing the surgery can lead to disabling neurologic deficits or even death. The anatomy of the trigone, the arterial and venous patterns, and the relationship with visual pathways and hemispheric dominance needs to be evaluated, before attempts toward surgery. When planned, surgery has to be directed toward radical or total tumor resection, as incomplete or partial tumor resection can lead to tumor bleeding related issues. The issues that are relevant while planning surgery for intraventricular meningiomas include assessment of the size of the tumor, its consistency, its vascularity, location of the feeding blood vessels, and the direction of the growth. The basic principles that determine the success of the surgery include early access to the blood supply, minimal retraction of the brain for adequate exposure while removal of large masses, and understanding of the function of the surrounding anatomic structures. An interhemispheric approach and exposure of the medial part of the tumor to control the feeding vessels early in the operation appears to be a reasonable surgical option.^28,52 However, the large sizes of the tumor and the presence of a relatively tense brain leading to difficulty in retraction of the brain led to the employment of transcortical approach in most of our cases. The selection of the cortical incision depends on the site of projection of the tumor and the safest cortical area in the proximity. Exact understanding of the well-described function of the cortical area in question is mandatory while planning the surgical approach, as severe speech and cognitive deficits can mar the surgical outcome. Electrophysiological monitoring and mapping have been identified to be useful in evaluating the best site for cortical incision. Intraoperative tractography of motor and optic tracts using neuronavigation is increasingly being used as a useful technological help. Damage to the visual tracts can be avoided by a three-dimensional understanding of the white matter tracts of the brain by cadaveric study of “fibers” of the brain by fiber dissection techniques. The optic radiation covers the entire lateral aspect of the temporal horn and atrium as it extends to the occipital horn. Anterior, inferior, and posteroinferior routes to the atrium would avoid the optic radiations.

SURGICAL APPROACH

Cushing discussed a temporoparietal approach.³ The middle temporal gyrus approach was described by Olivocrona.⁵³ Cramer was probably the first to use the more popular posterior parieto-occipital incision to approach the meningiomas located in the atrium.¹⁷ Yasargil recommended a parieto-occipital interhemispheric approach for a variety of intraventricular lesions. The incision was in the parasplenial-precuneal area.⁵³ Kempe and Blaylock suggested a posterior transcallosal approach to resect tumors in the ventricular trigone of the dominant hemisphere.³⁰

The middle temporal gyrus approach and posterior parietal and posterior parieto-occipital cortical approaches are the more commonly selected approaches to deal with intraventricular meningiomas located in the region of the trigone. In smaller tumors, a “sulcal” exposure is adopted, limiting the cortical resection to the minimum. In larger tumors, a cortical window was made through resection of a part of gyrus in the “safe” or “silent” area of the brain. The transcortical approaches may result in visual field defects while interhemispheric trans-corpus callosal approaches may be associated with disconnection syndromes.

Transcortical Approach

Depending on the location of the tumor, the direction of its spread, and its minimum distance from the surface, the safest part of the cortex in the vicinity is selected for the approach. The medium and large sized meningiomas within the trigone and body of the lateral ventricle are approached by the posterior parietal-superior parietal lobule or superior parieto-occipital approach. The parieto-occipital approach is along the orientation parallel to the optic radiation over the cerebral convexity and is most suitable to avoid damage to the optic radiation. Moreover, this is often the thinnest region overlying the tumor positioned in the trigone (Figs. 45-1, 45-2, and 45-3). The incision extends from postcentral fissure to the parieto-occipital fissure approximately 3 cm from the falx. The incision lies medial to the majority of the visual fibers and parallel to their projections. The visual field deficits, which remain a significant problem, are attributed to damage caused by manipulation of the tumor at the border of the lateral ventricular ependyma. In our series, five patients operated via this approach had visual field defects. Postoperative hemispheric motor deficits will depend on the extent of cerebral cortical manipulation. It is sometimes surprising to see that even extensive cortical manipulation may lead to no significant cortical dysfunction.

FIGURE 45-1 A, T1-weighted MRI showing the large marginally hypointense lateral ventricular trigone region meningiomas (in a 26-year-old male patient). B, T2-weighted MRI showing the tumor. C, Postoperative scan showing the tumor resection and the direction of surgery.

Figure 45-2 A, T1-weighted MRI showing a large meningioma in the region of the body of the left lateral ventricle (in a 31-year-old female patient). B, T2-weighted scan showing the tumor. C, Contrast enhanced scan showing the tumor extension into the third ventricle. D, Immediate postoperative contrast enhanced scan showing the tumor resection and approach from the right side parasagittal transcallosal route. E, Postoperative axial scan showing the tumor resection.

FIGURE 45-3 A, T1-weighted MRI showing the large trigonal meningiomas (in a 35-year-old female patient). B, T2-weighted MRI showing the tumor. C, Contrast-enhanced scan showing the tumor and its extension. D, Immediate postoperative scan showing the tumor resection and the direction of the surgical approach. Postoperative changes and a blood clot are seen in the region.

The lateral temporal-parietal approach through the angular or supramarginal gyrus provides the shortest distance from the cortical surface to the tumors located in the trigonal region. However, this advantage is often outweighed by frequent postoperative affection of neurologic functions.

Cortical damage of the dominant hemisphere may result in alexia, agraphia, acalculia, and ideomotor apraxia.³⁷ Gerstmann’s syndrome is also believed to result from lesions in this area. Lesions in this region of the nondominant hemisphere may impair memory for visual information, hemineglect, and constructional apraxia. A homonymous visual field deficit is frequently encountered because the visual projection fibers that run parallel to the lateral aspect of the ventricle are transected.

For small and medium sized meningiomas in the trigone and temporal horn, the middle or inferior temporal gyrus approach is used. The temporal lobe incision is in its posterior part centered over the external ear canal. Speech problems such as Wernicke’s and anomic aphasia are reported after excision of meningiomas of the dominant hemisphere. Impaired recognition of emotion as evident in facies or speech is reported in the nondominant middle temporal gyrus approach. The control of feeders of anterior choroidal artery is relatively early, thereby minimizing blood loss during surgery. The posterior choroidal artery feeders may be encountered only after the majority of the tumor is excised. The incision may have to be extended in to the parietal lobe for proper exposure of the meningioma.

SURGICAL TECHNIQUE

Surgery on intraventricular meningiomas has been associated with a range of morbidity and mortality that has been reported to be up to 45%. With the advent of microscope in neurosurgery, the incidence of both morbidity and mortality has reduced. We observed that even a small cortical incision can sometimes suffice as the exposure is constantly widened as the tumor mass is debulked. The surgical strategy was to expose the tumor dome widely, assess its physical nature, and then to perform its radical resection by a piecemeal debulking. This surgical strategy is in variance with other meningiomas where the site of vascular supply and dural attachment is first disconnected and then the tumor bulk is removed. The majority of the tumors were firm and gritty and had moderate to high vascularity. Large veins that frequently course over the dome of the tumor may lead to significant blood loss. As most tumors were exposed from their dome or lateral surface while the major feeding vessels arose from the inferomedial surface, the tumor feeding vessels were exposed at the terminal phase of the operation, and the tumors bled relatively excessively during the process of resection. Considering the location of the feeding vessels and the direction of the surgical exposure, a preoperative feeding vessel embolization appears to be a rational treatment strategy. Embolization of the tumor feeding vessels was not performed in our cases as angiography was performed in only six cases and in these cases, the feeding vessels were thin, multiple, and diffuse in nature. Moreover, the role of feeding vessel embolization has not been convincingly demonstrated in the literature. We preferred a relatively hurried debulking, as it was observed that coagulation at each step to obtain a bloodless operative field was difficult and sometimes resulted in more significant blood loss. Once a large part of the tumor is removed and the operative field is relatively relaxed, an attempt is made to expose the inferomedial surface of the tumor mass to access the feeding vessels. The bleeding continues throughout the operation, but as soon as the principal feeding vessels are coagulated, the situation comes under control. This feature also suggests that a radical resection of the tumor must always be performed in these cases. In one case where a partial tumor resection was performed, the patient developed a postoperative large hematoma. In four cases, there was cerebral swelling during the process of tumor resection. In two of these patients, evacuation of a large clot in the ventricular cavity relaxed the operating field. In the remaining two patients, the cause of the brain swelling could not be identified. Excessive brain retraction or venous compromise of the brain could have led to the brain swelling. In each case, it was realized that a relatively rapid removal of the clot and the tumor was essential to control the bleeding, reduce the brain swelling, and to resect the tumor mass. The thalamostriate and internal cerebral veins are in close proximity to the medial aspect of the tumor and require careful dissection for preservation.

Irrespective of the surgical approach, the goal of the surgery should be complete excision of the meningioma with ability to preserve the neurologic function. During surgery, identifying and maintaining a plane of cleavage between the meningioma and the ependyma, the choroid plexus, and the surrounding white matter should be of paramount importance. Loss of the plane will result in bleeding and injury to vital neural structure. The incidence of neurological deficits is high in such instances. Intraoperative brain swelling after bleeding or excessive brain retraction can also be a difficult problem encountered during surgery. The surgical resection should be piecemeal, and removal of the tumor in large pieces or en mass should be avoided. Such a strategy is useful in cases of convexity meningiomas, but can be quite dangerous in cases with intraventricular meningiomas as the vascular pedicle is located medially. Frequent orientation to the surrounding anatomical structures such as thalamostriate vein, the septum pellucidum, and foramen of Monro prevents unwanted manipulation of important structures. Although there are no specific indications for planning a subtotal resection, incomplete removal may be preferable when the site of attachment invades into the deep structures such as the thalamus or when the anatomy is distorted beyond recognition.

The role of radiosurgery as a primary treatment modality or as a mode of treatment of residual lesion is under evaluation.

In general, the histopathologic features of intraventricular meningiomas are no different from meningiomas elsewhere in the brain.⁸

POSTOPERATIVE MANAGEMENT

Patients with preoperative ventricular enlargement or large tumors are at risk for postoperative subdural hematoma and hygroma formation. Tanaka reported subdural fluid collections in 40% of patients after removal of intraventricular tumors, and symptomatic collections required surgical drainage in 11% of cases.⁵⁴ In our series, although 36% of patients were noted to have subdural hygroma surgical intervention was not needed in any of these patients. The problem of hydrocephalus in intraventricular meningiomas is very closely associated with respect to clinical signs and symptoms and postoperative management. In our opinion, shunting for hydrocephalus should be avoided and may be counterproductive.

Intensive postoperative management is necessary that includes frequent neurologic assessment, as these patients are at risk for intraventricular hemorrhage, subdural hematoma, and hydrocephalus. Imaging studies should be used liberally and any decline in the neurologic function or elevation of intracranial pressure should be investigated and treated aggressively.

The incidence of seizure is relatively uncommon in patients with lateral ventricular meningiomas. However, the postoperative seizures have been reported in 29% to 70% of patients operated by transcortical approaches. In our series, 22% of patients had postoperative seizures, but these could be controlled with drugs. Cortical dysfunction related to adoption of a transcortical approach for intraventricular meningiomas has been frequently reported. The visual field deficits as a result of direct damage of visual pathways during the surgical approach are frequently reported. Four patients in our series developed additional postoperative visual field defects. Considering that two of these patients developed homonymous hemianopia, it appears that occlusion of the major branch of the posterior cerebral artery could have been the cause of field defect. During the average period of follow-up 42 patients (84%) are active and leading normal lives. Four patients (8%) are experiencing neurologic deficits, but are leading normal and independent lives. Four patients died in the postoperative phase. No tumor has recurred after a total tumor resection.

CONCLUSIONS

Lateral ventricular meningiomas are relatively difficult surgical problems, but a successful radical resection is associated with long-term cure from the disease. In all the cases where there was an operative or postoperative major complication, the tumor was large in size.