The Anterior Transcallosal Interhemispheric Approach

This approach provides excellent exposure of the frontal horns and bodies of the lateral cavities and even gives access to the anterior part of the third ventricle. The standard position of the patient is supine with elevation and flexion of the head. The incision is made behind the hairline, usually in a bicoronal fashion. For the craniotomy, two bur holes are drilled on the contralateral side close to the sagittal sinus. Preoperative imaging studies with MR or CT venography and intraoperative neuronavigation are recommended for planning placement of the bur holes to avoid damage not only to the sinus but also to irregular bridging veins.⁴⁶ In general, a craniotomy diameter of 4 to 5 cm is sufficient for tumor removal; however, it may be necessary to vary the size of the craniotomy based on the extent of the tumor and the depth at which it has to be resected. In the best case, the chosen trajectory preserves the bridging veins. Mobilization of the draining veins is important for gaining space, and their sacrifice should be avoided.

Brain relaxation can be achieved by osmotherapy and, most importantly, by release of CSF, mainly from the sulcal and callosal cisterns. This strategy is preferred over the use of rigid retractors so as to protect neural structures from pressure and tearing damage. Entrance to and advance within the interhemispheric fissure are achieved by blunt dissection with tailed cotton strips and balls.

When the corpus callosum is reached, an entrance of 10 to 15 mm is generally enough for removal of most lesions located in the frontal and middle parts of the lateral ventricles. The smoothest way of opening is to dissect along the plane of the fibers with fine-tipped bipolar forceps and small tailed cotton strips. When the ventricular cavity is entered, drainage of CSF leads to additional relaxation and can be augmented by incision of the septum pellucidum.

For better orientation in the presence of large tumor masses with severely distorted ventricles, the surgeon will find the thalamostriate vein located on the right side of the plexus in the right lateral ventricle and on the left side of the plexus in the left lateral ventricle. The further course of the plexus and vein leads to the internal cerebral vein, which serves as a guide for localization of the fornix and thalamus and thus acts as an important landmark.

Caution needs to be taken regarding the genu of the internal capsule, which reaches the surface of the ventricle lateral to the foramen of Monro where the thalamostriate vein turns medially toward the internal cerebral vein.^47–49 Recent publications show that complications related to this approach include mainly seizures, sensory-motor deficits, and visual and cognitive impairment.^14,23,50,51

The Anterior Transcortical Approach

This route provides excellent access to the frontal horns and bodies of the lateral cavities, and even the anterior part of the third ventricle can be exposed. This approach is most suitable for patients with large ventricles and for pathologies within the lateral frontal horn of the nondominant cerebral hemisphere. The working corridor is directed mainly through the middle frontal gyrus. With the patient in the supine position and the head turned between 10 and 15 degrees to the opposite side, the skin incision and craniotomy are placed over the main part of the middle frontal gyrus. The intraventricular landmarks are the same as for the transcallosal approach.

The advantage of the transcortical approach is that bridging veins are not a concern.⁴⁶ The disadvantage of this approach relative to the interhemispheric transcallosal approach is that not only are the commissural fibers dissected but also parts of the projection fibers and the short and long association fibers.

The Superior Frontal Sulcus Approach

As in the transcortical approach, the patient is placed in the supine position with elevation and flexion of the head, depending on the side in which the tumor is located. Instead of entering toward the lateral ventricle by opening the middle frontal gyrus as described earlier, the superior frontal sulcus is chosen for creation of the corridor. Neuronavigation can be used to plan and verify the exact trajectory. The advantages and disadvantages are the same as described for the transcortical approach. One has to be aware that the superior frontal sulcus can be short in length. Therefore, clear identification of it may not be possible in every case.⁵²

The Posterior Interhemispheric Transcingular Approach

The posterior interhemispheric transcingular approach is suitable for exposure of tumors of the atrium and the posterior horn of the lateral ventricle. The patient can be operated on in the prone or sitting position. The craniotomy is placed superior and inferior to the lambdoid suture, including the midline (as in the anterior interhemispheric approach), and can be varied according to the position of the superficial bridging veins. The posterior interhemispheric fissure is then opened widely to minimize retraction, and the precuneus and isthmus of the cingulate gyrus are opened to give access to the ventricle.⁵³ Because the posterior part of the optic radiation courses in the lateral wall of the atrium and posterior horn, one does not interfere with the fibers of the optic radiation when using this approach.⁵⁴

The Intraparietal Sulcus Approach

The intraparietal sulcus approach has been described for lesions of the medial and lateral portion of the trigone.^29,51,54,55 The ventricle is explored by opening the intraparietal sulcus and then dissecting the parietal white matter toward the ventricle. Although this approach leads to direct access to the trigone, one should be aware that it poses a risk for possible neurological complications, such as visual field defects, apraxia, and acalculia.

The Transsylvian Approach to the Temporal Horn

The proximal transsylvian approach was developed by Yasargil in 1967 for the treatment of vascular and neoplastic lesions in the mesial temporal area. Later, this approach was used for selective amygdalohippocampectomy.⁵⁶ The approach consists of pterional craniotomy and opening of the proximal part of the sylvian fissure with an incision about 3.0 to 5.0 cm long. Through a pial incision lateral to the M1 segment of the middle cerebral artery between the origin of the anterior temporal and temporopolar arteries, one can gain access to the temporal horn. In particular, limbic tumors of the amygdala, hippocampus, and parahippocampal area extending into the temporal horn can be removed with this approach without injuring the adjacent neocortex of the superior, middle, and inferior temporal gyrus and lateral temporo-occipital gyrus.

The Occipitotemporal Sulcus Approach

The occipitotemporal sulcus approach can be used to access lesions in the posterior part of the temporal horn.⁵¹ The occipitotemporal sulcus can be opened with a subtemporal craniotomy to allow access to the temporal horn. Placing a lumbar drain before surgery for release of CSF before opening the dura reduces the need for brain retraction. As is the case with other lateral transcortical approaches, there is a risk for postoperative visual field deficits.

Ependymomas

The first description of ependymomas was made by Bailey and Cushing in 1926.⁵⁷ Ependymomas account for about 2% to 9% of intracranial tumors, and they are more frequent in the pediatric population, with an incidence of 6% to 12% and a peak in the first 3 years of life. They are equally likely to occur in boys and girls.⁵⁸ Ependymomas arise from ependymal cells, and thus they are found in the entire ventricular system, especially in the infratentorial region.^59–63 These tumors usually tend to grow slowly and show perivascular pseudorosettes and ependymal rosettes as key features on histologic examination. Most ependymomas are classified as grade II tumors according to the World Health Organization (WHO) classification of 2007, but there also exists an anaplastic variant, and progression to it from lower grades has been described.^58,63,64 Therefore, histopathologic examination is recommended in any case. CT images of ependymomas appear isodense, with heterogeneous contrast enhancement. On MRI, they are well circumscribed, isointense to hypointense, and enhance heterogeneously.

Clinical symptoms arise from obstructive hydrocephalus, which leads to intracranial hypertension. In addition, cognitive changes are seen frequently, especially memory and attention deficits.⁶⁵

Surgery plays a key role in the treatment of ependymomas because gross-total resection (Fig. 138-4) is associated with improved prognosis.⁶⁶ If pathologic examination confirms malignant features and MRI studies show tumor remnants, radiotherapy should be discussed (Fig. 138-5).⁶⁷

FIGURE 138-4 A and B, Preoperative coronal magnetic resonance images (fluid-attenuated inversion recovery [FLAIR] sequence) of a 32-year-old man with symptoms of raised intracranial pressure caused by a large ependymoma that filled the left lateral ventricle. C-F, Postoperative computed tomography scans demonstrating total tumor removal. There were no postoperative neurological deficits; however, the patient needed placement of a ventriculoperitoneal shunt because of hydrocephalus.

FIGURE 138-5 Preoperative axial (A and B), coronal (C), and sagittal (D) magnetic resonance images (MRIs) of a 3-year-old girl with disturbed consciousness. Initially, an external ventricular drain was placed to treat the occlusive hydrocephalus. E, The child was operated on in the supine position with the aid of intraoperative neuronavigation. F-H, Gross-total removal of an anaplastic ependymoma was achieved as demonstrated on postoperative MRIs. The postoperative course was uneventful, and the young patient underwent chemotherapy.

Subependymomas

Subependymomas were first described by Scheinker in 1945.⁶⁸ Subependymomas are rare and account for just 0.2% to 0.7% of intracerebral tumors.^69,70 They are benign, slow-growing tumors, often attached to the ventricular wall, but they do not invade surrounding structures. Therefore, this pathology is classified as WHO grade I. Although they most commonly arise within the fourth ventricle, they are located within the lateral ventricles in up to 40% of patients.^58,71,72 Subependymomas show a male preponderance, with a male-to-female ratio of 2.3 : 1. Histologically, this tumor shows isomorphic nuclei in clustered patterns, a fibrillary matrix, and small cysts.⁵⁸ On CT these lesions appear as hypodense to isodense lobular masses with cystic components that do not usually show contrast enhancement. On MRI, this pathology appears as a solid to cystic tumor.

Depending on location and progression, subependymomas become clinically evident by obstruction of CSF pathways, with signs of increased intracranial pressure typically causing headache, nausea and vomiting, gait disturbances, or vertigo (Fig. 138-6). Patients most commonly become symptomatic between the ages of 40 and 60. Because of the benign natural history of these tumors, they remain clinically silent in many cases and are often detected only during autopsy studies.^69,72 At present, with easy access to cerebral imaging studies, a growing number of subependymomas are diagnosed incidentally.^70,72–74

FIGURE 138-6 Preoperative axial (A and B), coronal (C and D), and sagittal (E and F) magnetic resonance images (MRIs) of a 32-year-old woman (the patient shown in Fig. 138-3). The patient had severe headache, vomiting, and memory deficit. The solid, highly vascularized tumor, a subependymoma, was completely removed as shown on postoperative coronal (G) and sagittal (H) MRIs. There were no neurological or other deficits after the microsurgical procedure.

Management of patients in whom an incidental finding is diagnosed is still under debate. If clinical signs are absent, routine follow-up with imaging studies is recommended. If dynamic growth during follow-up or the development of clinical symptoms occurs, microsurgical removal of the mass is the treatment of choice. Because of the benign origin of this entity, radical extirpation defines cure. If imaging studies reveal residual tumor, further treatment options depend on the patient’s condition. If no further deficits have occurred, surveillance with MRI is justified. In patients with existing neurological deficits caused by the remnant mass, operative resection (or eventually radiotherapy) should be discussed.^70,72,74

Central Neurocytomas

These rare tumors were first described by Hassoun and colleagues in 1982.⁷⁵ This emphasizes the fact that this lesion was just recently determined to be distinct from other intraventricular pathologies and therefore has often been mistaken for another entity.⁷⁵ Overall, central neurocytomas represent only 0.1% to 0.5% of all intracranial tumors.^76,77 They generally occur in the lateral ventricles, with a predilection for the left frontal horn. Typically, they are detected between the second and fourth decades of life, with equal distribution between the sexes.^77–79 Histologic examination of central neurocytomas shows uniform round cells, perivascular pseudorosettes, and a honeycomb appearance, thus indicating their tendency to mimic the architectural patterns of intracerebral gliomas.^77,80 They are classified as WHO grade II tumors.⁵⁸

On CT and MRI, central neurocytomas appear hyperdense and hyperintense (with moderate contrast enhancement), respectively. The presence of necrosis, cysts, and calcifications in these tumors sometimes causes a heterogeneous appearance.^77,81 Differential diagnosis includes oligodendroglioma, ependymoma, and papilloma arising from the choroid plexus.^77,82

In most cases, central neurocytomas are slow growing and become clinically evident as a result of increased intracranial pressure from obstructive hydrocephalus that causes symptoms of headache, nausea, vomiting, gait disturbance, and cognitive deficits. Surgical removal remains the treatment of choice and defines cure (Fig. 138-7). Nevertheless, although central neurocytomas are generally considered to be benign, malignant courses with progression of remnant tumor and cerebral and spinal dissemination have been reported and associated with unfavorable clinical outcomes.^83–86 If radical removal cannot be achieved, adjuvant therapies such as radiation therapy and chemotherapy are options, but their benefits are still under debate. Reduction of tumor mass has been reported with both therapies.^{58,84,85,87,88}

FIGURE 138-7 Preoperative axial (A-C), coronal (D and E), and sagittal (F and G) magnetic resonance images of a 26-year-old woman with symptoms of raised intracranial pressure. The tumor (a central neurocytoma) was totally removed via the interhemispheric transcallosal approach. Postoperatively, mutism was observed for several days but completely resolved within the first week after surgery. No neurological or cognitive deficits were present thereafter. The patient has now been monitored for more than 12 years continuously and has shown an uneventful course.

Low-Grade Gliomas

Fibrillary astrocytomas and subependymal giant cell astrocytomas (SEGAs) can occur frequently within the lateral ventricles. The fibrillary component is the most frequent variant of common astrocytomas. On histopathologic examination, nuclear atypia is present, including enlarged, irregular hyperchromatic nuclei. Additionally, mucoid cysts can occur within the matrix. This tumor shows diffuse and infiltrative growth; giant cell astrocytomas are found in patients suffering from tuberous sclerosis. This coexistence is well documented in the literature, and the neoplasm is typically located in the vicinity of the foramen of Monro and can extend to the cavity of the lateral ventricle.^89–92 Unfortunately, astrocytomas are closely associated with morbidity and mortality in this particular setting.^91,93,94 SEGA is considered a benign and thus slow-growing tumor originating from the wall of the lateral ventricles. The lesion is structurally based on spindle and gemistocyte-like cells. In some cases, additional ganglion-like cells can be found. Clusters, perivascular pseudopalisades, and calcification are typical histologic characteristics. Consequently, SEGA was categorized as WHO grade I in 2007.^58,89 The tumor typically occurs in patients younger than 20 years.

On CT, this lesion appears hypodense and well circumscribed and shows contrast enhancement. On T1- and T2-weighted MRI, the tumor appears as a hypointense mass but in some cases can have high signal intensity on T2-weighted images (Fig. 138-8A). In all cases the tumor shows enhancement when contrast material is administered (Fig. 138-8B), with a somewhat heterogeneous appearance caused by the irregular occurrence of calcification.^91,92

FIGURE 138-8 A, This 33-year-old pregnant woman had severe headache, gait ataxia, and a slight memory deficit. Preoperative nonenhanced magnetic resonance images (MRIs) taken in the axial (top left, bottom left), coronal (top right), and sagittal (bottom right) planes demonstrate a large cystic tumor that is occupying the posterior portion of both lateral ventricles. Cyst evacuation and tumor biopsy were performed immediately to release the intracranial pressure. Histologic examination revealed a pilocytic astrocytoma. The patient quickly recovered from this procedure, and no further therapy was necessary during the following period of pregnancy. B, Contrast-enhanced coronal (top left), axial (bottom left), and sagittal (top middle) T2-weighted MRIs of the patient shown in A taken after uneventful delivery of the child. The patient then underwent elective surgery via the posterior interhemispheric subcallosal approach, and the tumor was removed completely, with preservation of the involved fornices on both sides. Postoperatively, the patient complained of a mild memory deficit for a few weeks; thereafter, no neurological or cognitive deficits were present, and follow-up MRI controls (top right, bottom middle and right) excluded any tumor recurrence.

Neurological symptoms are caused mainly by obstruction of CSF pathways, which leads to typical clinical symptoms related to the increased intracranial pressure; however, astrocytomas can bleed, which can result in intraventricular hemorrhage, depending on their location, and lead to sudden deterioration. If symptomatic lesions are diagnosed, surgical resection is the treatment of choice. With regard to incidental findings of ventricular gliomas, treatment is still controversial. In patients with small nonsymptomatic tumors, clinical follow-up with regular outpatient consultations and imaging studies is justified. If the lesion displays dynamic growth and can potentially displace CSF pathways, surgical removal in the absence of actual neurological deficits should be considered.^{89,91,92,95,96}

High-Grade Gliomas

The tendency toward malignant change in astrocytomas correlates with the patient’s age. High-grade gliomas of the lateral ventricle may frequently arise from the corpus callosum, the septum pellucidum, or the thalamus and show a predilection for the anterior horn of the lateral ventricle.⁹⁷

Anaplastic astrocytomas are malignant lesions (WHO grade III) with typical diffuse and infiltrating growth patterns (Fig. 138-9). The mean age at diagnosis peaks between 45 and 51 years. There is a slight male preponderance, with a male-to-female ratio that varies from 1.1 : 1 to 1.6 : 1.^98,99 Histologic features include increased cellularity, nuclear atypia, and mitotic activity. When anaplastic transformation is in progress, the nuclei vary in number, size, and shape. Additionally, abnormal mitoses can be detected.

FIGURE 138-9 Axial (A), sagittal (B), and coronal (C) contrast-enhanced T1-weighted magnetic resonance images of a 24-year-old man revealing a highly vascular (D) irregular tumor of the left atrium that infiltrated the surrounding structures. The patient was suffering from progressive headache and gait ataxia. E and F, He underwent microsurgical resection of the tumor via the intraparietal sulcus approach with the aid of the BrainLab neuronavigation system. Histologic examination confirmed the presence of an anaplastic glioma. G and H, Gross-total removal of the lesion was documented on postoperative computed tomography scans. In addition to surgery, the patient underwent subsequent radiochemotherapy.

Glioblastoma is the most malignant tumor known in the central nervous system. This tumor accounts for 12% to 15% of all intracranial tumors and shows astrocytic differentiation in 60% to 75% of cases. The mean age at diagnosis is 45 to 75 years, with a male-to-female ratio of 1.28 : 1. Histopathologic study reveals the typical malignant characteristics, such as nuclear atypia, cellular pleomorphism, a high mitotic rate, and necrosis. These are WHO grade IV tumors.^58,100

MRI may show the typical aspect of high-grade glioma, a central necrotic area surrounded by ring contrast enhancement. Whether to surgically resect a glioblastoma and to what extent depends on the patient’s neurological and neuropsychological status and the size, location, and extension of the tumor within the adjacent anatomic structures. In particular, if the fornices have been invaded, biopsy is preferred instead of extensive surgery.

Choroid Plexus Papillomas

Choroid plexus papillomas account for 0.5% to 0.6% of intracranial lesions in adults and for 2% to 5% of intracranial neoplastic lesions in children. They are among the most common tumors in children younger than 2 years. When these lesions are located in the lateral ventricle, the median age at diagnosis is 18 months, and there is no predilection to occur in either sex.⁵⁸ In around 20% of pediatric cases, these tumors show malignant transformation; approximately half of them are located within the atrium. They are similar in aspect to the glomus of the choroid plexus, being formed by a single cell layer of cuboid or cylindrical cells surrounded by a thin fibrovascular structure. In the latest WHO classification, choroid plexus papillomas are classified as grade I. In imaging studies, these tumors frequently contain calcifications, hemorrhagic elements, or cysts. In some cases, choroid plexus papillomas may fill the ventricular cavity, whereas in others, the ventricle may be markedly dilated ipsilaterally.

Surgical removal is the treatment of choice (Fig. 138-10). It is helpful to expose and interrupt the proximal arterial supply from the choroidal artery to devascularize the tumor at an early stage of the procedure. Debulking is then continued with the aid of an ultrasonic aspirator. At the end of the procedure, the remaining portions of the apparently healthy choroid plexus are resected as well to ensure complete tumor removal.^101–104

FIGURE 138-10 A and B, Preoperative axial contrast-enhanced T1-weighted magnetic resonance image of a 65-year-old man with cognitive deficits. Initially, a metastatic tumor was suspected because the patient had previously suffered from renal carcinoma. C, The tumor was approached via the right intraparietal sulcus. Surprisingly, histologic examination furnished evidence of a benign plexus papilloma that was completely removed, as seen on postoperative computed tomography (CT) (D). Similar to the previous patient, a large plexus papilloma within the right lateral ventricle is seen on this preoperative CT scan of a 48-year-old woman. E and F, The tumor was completely removed via a left parietal transsulcal/transcortical approach. Before surgery, the patient suffered from symptoms of raised intracranial pressure. The surgical procedure and postoperative course were uneventful.

Meningiomas

Meningiomas of the lateral ventricle originate from the stroma of the choroid plexus and arise at the tela choroidea. Ventricular meningiomas account only for 1% to 5% of all ventricular tumors and are located within the atrium in most cases.^105,106 They may show calcifications and, occasionally, cystic degeneration.¹⁰⁷ Usually, these tumors are highly vascularized (Fig. 138-11). The arterial supply stems from branches of the choroidal arteries, and they drain into the deep ventricular veins. Their histopathologic features and natural behavior are the same as those in any other location in the neural axis. Therefore, most intraventricular meningiomas are benign, slow-growing lesions (WHO grade I). Reports exist of a malignant course in some meningiomas, with recurrence and progression to atypical (WHO grade II) or anaplastic (WHO grade III) variants with the occurrence of metastases.^108–110

FIGURE 138-11 Preoperative axial (A and B), coronal (C), and sagittal (D and E) contrast-enhanced T1-weighted magnetic resonance images of a 58-year-old man revealing a highly vascular tumor (meningioma) of the left atrium that was severely compressing and distorting the surrounding structures. The patient had progressive headache, vertigo, and visual field disturbance. F, After being placed in the right park bench position, he underwent surgery with the aid of the BrainLab neuronavigation system. G and H, Note the significant vascularization as shown by digital subtraction angiography.