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October2012 Vol.49 Issue:      4 Table of Contents
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The Posterior Interhemispheric Approach to the Posterior Incisural Space and Adjacent Structures: Surgical Experience in 11 Cases

Wael M. Nazeem1, Amr K. Elsamman2

Departments of Neurosurgery, Beni Suif University1, Cairo University2; Egypt



Background: Deep midline lesions related to the posterior incisural area in the brain, although rare, pose a challenge in their surgical management due to proximity to vital structures and lengthy corridors. Objective: To assess the efficacy of the posterior intrehemispheric (PI) approach to lesions in the pineal region and adjoining area. Methods:  Eleven cases with lesions related to the pineal region were surgically treated using the PI approach. Six cases had neoplastic lesion and one had inflammatory mass. Four cases had vascular lesions in the territory of the posterior cerebral artery (PCA), 2 arteriovenous malformations (AVMs) and 2 aneurysms. Transcallosal approach through the splenium was utilized in 5 patients. Endoscopic third ventriculostomy and ventriculo peritoneal shunt were used to treat pre operative hydrocephalus. Results: Total excision was achieved in 50% of neoplastic lesions, subtotal resection in the rest and the inflammatory mass. Total removal of the AVM’s and successful clipping of the aneurysms was achieved also. Redo was carried on in 2 patients, one patient for unsatisfactory decompression and the other for reestablishing the pathology which revealed inflammation. Transient hemianopia occurred in one patient. One patient died due to brainstem compression with poor preoperative clinical condition. Conclusion: The posterior interhemispheric approach is safe, effective with low incidence of complications. The flap can be flexibly designated. It can be combined with the infratentorial approach in the same or another sitting for better outcome. [Egypt J Neurol Psychiat Neurosurg.  2012; 49(4): 347-352]

 Key Words: pineal, posterior cerebral artery, posterior incisural space, posterior third ventricle, posterior interhemispheric approach, transtentorial, transcallosal, three quarter prone.

Correspondence: Wael M. Nazeem, Depatment of  Neurosurgery,  Faculty of Medicine, Beni Suif University, Egypt.   Tel.: 01111696222    e-mail:




The pineal region lies in the depth of the brain with intimate relation to important vascular and neural structures. The quadrigemianl cistern includes the deep venous system and the pineal gland. It is related dorsally to the splenium of corpus callosum, ventrally to the tegmentum of midbrain, posteriorly to the falcotentroail junction and anteriorly to the posterior part of the third ventricle. Adjacent structures as the ambient cistern, the posterior part of the thalamus and the vermis of the cerebelleum are also closely related.1-4

Although lesions in this area are quite rare, they impose a challenge for neurosurgeons because of the vitality of related structures, the diversity of anatomy, and the importance of structures in different pathways to this area.2,4-7

Benign and encapsulated tumors should be totally removed with better chance of subsequent resolution of associated hydrocephalus. Biopsy of malignant tumors may miss the possible multiple pathology which mandates additional adjuvant therapy. In addition, there is evidence that debulcking of malignant tumors enhances the effect of adjuvant therapy.2,7-9

Several approaches appeared but few became superior, as the corridors to this important region are not without risk. So, modifications of the approaches and even patient positioning are developed for better surgical outcome and maximal lesion control.2,5,7-9,10-16

Lesions with upward, lateral extension or involving the posterior third ventricle or thalamus are the subject for the posterior interhemispheric (PI) approach. This approach gives the possibility to reach the pineal region and adjacent structures through different angles and modifications and positions.3,5,9,12,17,18


Aim of the Work:

To assess the efficacy of the posterior intrehemispheric (PI) approach to lesions in the pineal region and adjoining area and to discuss several arguments regarding the technicality and outcome. 




This study was held at Cairo university hospitals. Eleven cases with lesions related to the pineal region and surrounding structures were operated upon. The age of patients ranged from 10 to 62 years, three were children. Male patient were 7 while female were 4.

Seven patients had space occupying lesions, six proved to be neoplastic and one inflammatory. Two patients had ruptured intracranial aneurysm form the posterior cerebral artery (PCA), one P2P and the other P3. Two other patients with arteriovenous malformation (AVM) fed from the PCA.

After the initial computed tomography (CT) brain, magnetic resonance imaging (MRI) was done in patients with tumors, inflammatory lesions and AVM’s. Angiographic studies whether CT angiography (CTA), digital subtraction angiography (DSA) or both were done in patients with  vascular lesions.  Other requirements for surgical preparation were done including laboratory and medical evaluation.

The choice of patient’s position and the flap design were selected for best lesion approach and according to surgeon‘s preference. The sitting position was utilized in 4 patients, the three quarters (3/4) prone in 3, the park bench in 2, while the prone and semi-sitting each was used in one patient. The craniotomy flap was always crossing the superior sagittal sinus (SSS), while its relation to the transverse sinus is justified according to the lesion location and extent. Unless the lesion mandates an approach form the left side (like the P2P aneurysm was left), we go from the right side. In patients who were positioned in the ¾ prone and park bench, the side of approach was always the dependent which aids with gravity in minimizing brain retraction.

Even in patients with cerebrospinal fluid (CSF) diversion, ventricular tapping was helpful in limiting retraction time or even using retractless technique all through. Initial retraction was applied only in some cases in the sitting position.

Tentorial opening for reaching the posterior fossa was done in 6 patients. Removing few millimeters from the splenium was done in 4 patients. In one patient the approach was parieto-occipital transcallosal through the splenium. No additional posterior fossa (infratentorial supracerebellar), transfalcine, nor trans-sinus approach in the same sitting were utilized, although some were put in consideration. The lesions were characteristically large in size and some tumors were non suckable or even tough like the falcotentorial meningioma.

Hydrocephalus was treated with ETV in 3 out of 6 patients; the other 3 were subjected for V/P shunt before surgery. In one patient temporary ventriculo-subgaleal (V/S) shunt was done before definitive V/P shunt.

We didn’t use cavitron ultrasonic aspirator (CUSA), laser, or navigation due to their unavailability.




Total excision was achieved in 3 out of 6 (50 %) patients with neoplasms. In those with subtotal excision the huge size of the neoplasm and the thalamic invasion hindered more aggressive removal. Debulcking of the inflammatory mass was done. The neoplasms were proved histologically to be as the following, 3 pineoblastoma, 1 thalamic gliobalstoma multiformis [GBM], 1 germinaoma, and 1 falcotentorial meningioma (Figure 1).

Two patients were reoperated because of unsatisfactory debulcking and for confirming the pathology in the patient with inflammation. The first patient had huge pineoblastoma, reviewing the images revealed that transfalcine and/or infratentorial views may have helped in more radical removal.

To avoid splenial incision we had 4 patients in which a retrocallsoal approach was used with removal of few mm from the splenium with additional retraction to access the posterior 3rd ventricle (Figure 3).

The two included aneurysms were successfully clipped, although intraoperative rupture of the P2P aneurysm occurred during dissection. Also both AVM’s were totally excised after occlusion of the feeders with postoperative angiographic confirmation (Figure 2).

We had a single mortality in a patient with initial Glasgow Coma Scale (GCS) of 5 due to brainstem compression and the patient’s condition didn’t improve with total tumor excision. One patient had temporary field deficit that improved on follow up.

No veins whether bridging nor deep were sacrificed.

No air embolism, hematomas, infection, or ocular muscle palsy complicated our patients.



Figure 1. Falcotentorial meningioma that was removed totally. The patient was operated in ¾ prone with the right sided (side of approach) down. Tentorial incision was done. A,B,C show the preoperative MRI with contrast. Small arrows in B & D show the flap extension. Dotted arrows in B show the view angles obtained by the approach.


Figure 2. A left P2P aneurysm that was operated through a left parieto occipital PI approach with splenial incision in the semisitting position. A, B & C show the preoperative CTA. The image in A was reverted so the left side of the patient is on the left of the image, to compare with reconstructed CTA in C & intraoperative view in D. In D small arrows outline the aneurysm, the PCA between the bipolar blades for temporary control as the aneurysm ruptured. Aneu= aneurysm, BA= basilar artery, BV = basal vein, Du= dura reflected on the sagittal sinus, PCA= posterior cerebral artery.


Figure 3. Thalamic GBM operated by PI occipital transtentorial retrocallosal in ¾ prone, with removal of few millimeters of the splenium. A & B preoperative MRI. The arrow in B shows the trajectory chosen. C postoperative CT. D,E, & F intraoperative images. D after tentorial opening, E shows the opening done in the splenium, In D, E dotted arrows point to the vein of Galen, and solid arrow to the splenium. F the proximal end of the V/P shunt in the depth of the field after debulcking with retraction on the splenium. Du= dura reflected on the SSS, Fx = flax, T = tentorial medial side after its opening, S = Sucker end.





The posterior incisural region is a deep midline area that resides at the center of the cranium, which means equal distance form any point in the skull.5

Surgery of the pineal region, although developed at the beginning of the previous century, was considered dangerous till the early 1980’s. The advancement of microsurgical techniques, neurosnaestheria, and imaging led to improvement of precision and safety.9

Surgery of pineal region tumors aims at complete excision of benign tumors, and biopsy and debulcking of malignant ones. Although appreciable advancement of adjuvant therapy occurred, biopsy alone may miss another pathology upon which additional therapy is given. Also there are reports that debulcking ameliorates the benefits of adjuvant therapy.2,8,9,17

The anatomy of the lesion is the factor upon which the surgical approach is choosen. Mastering the surgical anatomy of  different approaches in different positions is the key for good surgical outcome.2-5,8,9,12,13,19

Among other approaches, the infratentorial supracerebellar is still favored in some instances. It obviates retraction on the occipital lobe and working close to deep venous system. On the other hand, difficulties are encountered in lesions with anterior extension towards the third ventricle, above the deep veins or laterally. Other approaches as the trancortical transventricualr, anterior transcallosal tranventricualr transvelum intepositum, transcallosal interforniceal, frontal subchoroidal, and lateral infratentorial are rarely used. 5,13

The posterior interhemispheric (PI) approach is superior to approach lesions with anterior extension into the 3rd ventricle or the thalamus, lateral or superior extension above the deep veins. It also gives the opportunity for modifying the flap site and size and approaches the lesion from multiple pathways for a better lesion control and even with different positions. The occipital tranincisural (with or without the transtentorial, transfalcine, or transplenial), parietal trancscallosal, combined supratentorial infratentorial (with or without transinus) approaches can be considered part of or modifications of the PI approach to access tumor extensions. The modifications of the approach or even 2 stage procedure can be of value in attacking lesions that are large or extending into different comaprtments.5-8,12,14,15,17

Several positions can be used; the sitting, semi setting, ¾ prone, lateral decubitus (or park bench) and the prone. The ¾ prone or park bench on the same side of the lesion or the non-dominant (right) in midline lesions, give the advantage of minimizing the brain retraction by utilizing the gravity. Avoiding retraction lessens the incidence of postoperative hemianopsia. On the contrary the lateral approaches may cause anatomical disorientation.5,11-15

We had only one case of transient hemianopsia in a patient operated in sitting position, although retraction in those patients was carried only initially. Even in cases with preoperative cerebrospinal fluid (CSF) diversion, ventricular tapping reduces the need for retraction. Other studies agree that postoperative visual field defect is usually transient.5,6,9,15

The bony flap and the skin incision are designed according to the corridor(s) suggested from tumor extension based on the preoperative radiology. In all cases in this study, the flap was crossing the midline with variable length and distance from the transverse sinus. This agrees with the view of several authors that the flap size and relation to the transverse sinus is flexibly designed according to the desired trajectory but should reach or cross the midline. 5,12,17

We didn’t have to sacrifice any bridging veins due to their paucity in the occipital region and we had only one case of parieto-occipital PI approach. It is reported that sacrifice of one or two bridging veins, if necessary, in the parietal region usually has no negative consequences. 6, 12,17

The occipital approach with tentorial incision was done in 6 patients in this study, while in 4 patients suctioning of few millimeters of the splenium was required for accessing the third ventricle. The parietao occipital transcallosal (through the splenium) approach was used in one patient.

Out of 6 neoplastic lesions, total excision was achieved in 3 (50%). Decompression was aimed in one patient with thalamic mass to avoid injury of internal cerebral veins. In one patient a part of the lesion was blocked by the falx and the patient was re-operated. The neoplastic lesions in our cases were significantly huge in size. We had a case of falcoterntorial meningioma (medial type) that was removed totally without deficits.

The incision in the splenium is always intended to be kept to the minimum if needed. Trial of working behind the splenium is usually tried with or without additional very small splenial incision (Figure 3).

In another patient debulcking of an inflammatory mass was done and the patient was reopearted for pathological reevaluation.

Several studies report that sacrificing one or more deep veins may be done to obtain more excision as collateral venous channels develop, but others reject this. We didn’t try to occlude any deep vessel to reach that goal or to investigate the patient with angiography to verify the presence of collateral venous channels peroepratively.6,9,12,20-24

In this study 4 patients with vascular lesions (2 AVM’s and 2 aneurysms of the PAC) were included. Total excision of the malformations and safe aneurysmal clipping were achieved. The approach was occipital in three patients with lateral extension of the flap in the AVM’s. In one patient the approach was parietal transcallosal to approach a P2P aneurysm.

In one patient we had to go through the splenium to access the ambient cistern for clipping of the P2P aneurysm. This is another point of argument, as some studies advocate avoiding splenial incision to avoid hemihalexia while others deny complications.5,9,12,17

Other approaches to reach the PCA in the ambient cistern is the subtemporal. It is known that this part of the PCA is the most difficult to reach.4,25-28

Hydrocephalus is suggested to be managed before definitive tumor management, but in cases of benign or encapsulated lesions there is a good chance for resolving the CSF pathway with complete tumor excision. In our study, the hydrocephalus issue was managed before tumor attack as the lesions didn’t look to be benign.17



The posterior interhemispheric approach to the posterior incisural space and the adjoining structures can be considered safe, effective with low complication rate. The flap size and extension can be flexibly changed according to lesion location and surgeon’s preference. Different corridors, angles and patient positions, can be combined for better lesion access. Surgical knowledge of different approaches with alternative options gives the maximum benefit for the patients.


[Disclosure: Authors report no conflict of interest]




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الملخص العربي


المسار الخلفي بين نصفي المخ للفراغ الخلفي الشقي والمناطق المجاورة


الهدف من هذا البحث هو تقييم فاعلية المسار الخلفي بين الفصين للوصول إلى الإصابات في منطقة الجسم الصنوبري والمناطق المجاورة. أيضاً لمناقشة أوجه الاتفاق و الاختلاف في الأسلوب والنتائج.

تم إجراء هذا البحث على احد عشر حالة في منطقة الجسم الصنوبري والمناطق المحيطة. ستة حالات كانت تعاني من أورام، حالة واحدة من التهاب، حالتين تمدد شرياني وحالتين عيوب شرياني وريدية تم استخدام عدة أوضاع جراحية مثل الجلوس، شبه الجلوس، المقلوب على الوجه وثلاث أرباع المقلوب على الوجه. تم عمل قطع في الخيمة في ست حالات وقطع في الجسم السفلي في خمس حالات. ست حالات كانت تعاني من استسقاء المخ وتم أتعامل قبل الجراحة الأساسية عن طريق المنظار في ثلاث حالات و الصمام في ثلاث حالات أخرى.

تم استئصال الورم بالكامل في 50% من حالات الأورام واستئصال غير كامل في باقي الأورام وحالة الالتهاب. الحالات الدموية تم التعامل الناجع معها. أعيدت الجراحة مرتين، الأولى لعدم كفاية الاستئصال، والثانية لعدم الاقتناع بنتيجة التحليل.

يوجد حالة وفاة واحدة بسبب الضغط على جذع المخ وجدير بالذكر أن حالة المريض كانت سيئة قبل المجيء للمستشفى.

يخلص هذا البحث إلى أن المسار الخلفي بين النصفين هو مسار امن، فعال، وقليل المضاعفات.


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