Fig. 9.1
Anatomical subclassification of tentorial meningiomas. Tentorial meningiomas are classified based on the tumor location. The four groups include the incisural type, falcotentorial type, lateral type, and posterior type
Incisural Type
Surgical excision of meningiomas involving the tentorial incisura is a significant technical challenge, mainly due to access, especially for medially located lesions, as well as their relationship to the brain stem, cranial nerves, temporal lobe, blood vessels, and venous sinuses.
Meningiomas arising from the tentorial incisura grow up around the interpeduncular, crural, and ambient cisterns . Since they sometimes encase cranial nerves and blood vessels, such as the superior cerebellar artery or trochlear nerve, resection of the tumor requires great care to avoid any neurological dysfunction. If the tumor is huge, the tumor compresses the brain stem and adheres to it, thus making total resection relatively difficult.
Surgical Planning
Preoperative brain MRI scans and preoperative vascular studies (MRA, CTA, or angiogram) should be evaluated to identify the location of tumor extension, as well as the relationship to the brain stem, any encasement of vessels, and involvement of the cavernous sinus. In the case of incisura type, the venous system is crucial for planning surgery. Evaluation of the transverse and sigmoid sinuses and their connection at the torcular Herophili is important for lateral and posterior approaches. The venous drainage pattern of the temporal lobe, including the vein of Labbe and basal temporal veins and the relationship between the superior petrosal sinus and petrosal vein, is also important to avoid any venous complications.
Different surgical approaches have been proposed for tentorial incisura meningiomas. A retrosigmoid approach and an anterior or combined transpetrosal approach are most frequently performed.
The retrosigmoid approach is appropriate for infratentorial tumor extension or older patients. This approach is simple and quickly performed, with no risk of temporal retraction. Its disadvantage is limited access to the prepontine region and clivus. If it is necessary to gain more access to the cerebellopontine angle, careful removal of the petrous apex with a high-speed drill is useful. The limits of this exposure are defined by the trigeminal nerve medially and the seventh and eighth cranial nerves laterally. If the petrosal vein is well developed, the surgical corridor is more obstructed.
The transpetrosal approach is reserved for relatively large meningiomas invading the cerebellopontine angle at the lateral incisura and the supratentorial region. By using the transpetrosal approach, the surgeon’s operative distance to these regions is shorter than with the retrosigmoid approach , and a more multi-angled corridor leads to better control of the basilar artery and perforating vessels, with minimal retraction of the cerebellum and temporal lobe.
Illustrative Case
Case 1: Retrosigmoid Approach (Fig. 9.2)
A 43-year-old woman presented with a 1-year history of left facial pain. MR imaging demonstrated a mass lesion at the left tentorial incisura . The size of the tumor was 25 mm. The tumor compressed the brain stem slightly, and there was no edema into the brain stem. The tumor was excised via a retrosigmoid approach. The tumor had a well-defined plane of dissection from the brain stem and cranial nerves. The tumor could be totally removed with preservation of the petrosal veins, and there were no postoperative complications .
Fig. 9.2
Case 1. Preoperative axial (a) and coronal (b) T1-weighted magnetic resonance images with gadolinium showing the left incisural type of tentorial meningioma. Postoperative axial (c) and coronal (d) T1-weighted magnetic resonance images with gadolinium showing no tumor residual via a retrosigmoid approach
Case 2: Retrosigmoid Approach with Drilling of the Petrous Apex (Fig. 9.3)
A 52-year-old woman presented with a 2-year history of headache. Neurological examination showed instability of tandem gait. MR imaging demonstrated a mass lesion at the left tentorial incisura with extension into Meckel’s cave. The tumor was removed via a retrosigmoid approach. After internal debulking of the tumor, the petrous apex was drilled out, and Meckel’s cave was opened. Most of the tumor was resected except for around the porous part of the trochlear nerve. There were no postoperative complications .
Fig. 9.3
Case 2. Preoperative axial (a) and coronal (b) T1-weighted magnetic resonance images with gadolinium showing the left incisural type of tentorial meningioma. Postoperative axial (c) and coronal (d) T1-weighted magnetic resonance images with gadolinium showing near-total resection of the tumor via a retrosigmoid approach with drilling of the petrous bone. After internal debulking of the tumor (e), the left SCA is exposed (f). The tumor is peeled from the brain stem (g), and the petrous apex is drilled out (h). The tumor in Meckel’s cave is removed (i), and most of the tumor is resected, except for just around the porous part of the trochlear nerve (j). SCA superior cerebellar artery
Case 3: Anterior Transpetrosal Approach (Fig. 9.4)
A 67-year-old woman presented with a 1-year history of left facial pain. MR imaging demonstrated a mass lesion at the left tentorial incisura . Although the size of the tumor was not very large, the tumor compressed the brain stem slightly. The tumor was excised via a left anterior transpetrosal approach. The trigeminal nerve was compressed caudally, so that the tumor inside Meckel’s cave was removed easily, and the tentorium was incised along the posterior edge of the tumor. The tumor was totally removed (Simpson G1), and there was no neurological worsening .
Fig. 9.4
Case 3. Preoperative axial (a) and coronal (b) T1-weighted magnetic resonance images with gadolinium showing the left incisural type of tentorial meningioma. Postoperative axial (c) and coronal (d) T1-weighted magnetic resonance images with gadolinium showing total removal of the tumor via an anterior transpetrosal approach. After opening of Meckel’s cave (e), internal debulking of the tumor is performed. The tumor is carefully peeled from the trochlear nerve (f), and the tentorium is detached from the tumor (g). The tumor located around the trigeminal nerve and brain stem is removed (h). Residual tentorium, which was the origin of the tumor, is resected completely (i), and the tumor is totally removed (j)
Case 4: Combined Transpetrosal Approach (Fig. 9.5)
A 39-year-old man presented with a 2-month history of gait disturbance. MR imaging showed a large mass lesion at the right tentorial incisura . The tumor severely compressed the brain stem and medial temporal lobe. Resection of the tumor was performed via a combined transpetrosal approach. The tumor adhered tightly to the midbrain at the interpeduncular cistern, leaving a small residual amount of tumor along the right oculomotor nerve. Subtotal resection of the tumor was performed with transient right oculomotor nerve palsy and left hemiparesis. These symptoms improved completely within 3 months .
Fig. 9.5
Case 4. Preoperative axial (a) and coronal (b) T1-weighted magnetic resonance images with gadolinium showing the large right incisural type of tentorial meningioma. Postoperative axial (c) and coronal (d) T1-weighted magnetic resonance images with gadolinium showing near-total resection of the tumor via a right combined transpetrosal approach. After cutting of the superior petrosal sinus (e) and opening of Meckel’s cave, internal debulking of the tumor is performed (f, g). The proximal portion of the right SCA is exposed (h). The distal portion of the right SCA and brain stem are peeled from the tumor (i). Near-total resection of the tumor is achieved with a small residual tumor along the right oculomotor nerve (j). SPS superior petrosal sinus, SCA superior cerebellar artery, * residual tumor
Falcotentorial Type
Meningiomas arising from the falcotentorial junction are relatively rare, and only isolated case reports or small series related to surgical technique are available in the literature [1, 3]. Because of the lesion’s depth from the surface and its anatomical proximity to critical neural and vascular structures, surgical access and technique are complex issues. A variety of factors, including the tumor location and the patency of the vein of Galen and the straight sinus, influence surgery and the outcomes. Falcotentorial meningiomas are difficult to treat, but they can be well controlled by meticulous strategy.
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