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|Year : 2014 | Volume
| Issue : 3 | Page : 290-295
Large/giant meningiomas of posterior third ventricular region: Falcotentorial or velum interpositum?
Sanjay Behari, Kuntal Kanti Das, Ashish Kumar, Anant Mehrotra, Arun K Srivastava, Rabi N Sahu, Awadhesh K Jaiswal
Department of Neurosurgery, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
|Date of Submission||18-Mar-2014|
|Date of Decision||06-Jun-2014|
|Date of Acceptance||08-Jun-2014|
|Date of Web Publication||18-Jul-2014|
Professor, Department of Neurosurgery, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh - 226 014
Source of Support: None, Conflict of Interest: None
Surgical excision of rare, large-to-giant posterior third ventricular (PTV) meningiomas [including velum-interpositum meningiomas (VIM; postero-superior venous complex displacement; without falco-tentorial attachment) and falco-tentorial meningiomas (FTM; falco-tentorial attachment; displacing major veins antero-inferiorly)] is extremely challenging. To study the management nuances in the excision of large-to-giant PTV meningiomas. Tertiary care referral center. Four patients with large (>3 cm; n = 2) and giant (>5 cm; n = 2) meningiomas (FTM = 2; VIM = 2, mean tumor size = 4.9 cm) underwent occipital transtentorial approach (OTT) for tumor excision. One also underwent a second-stage supracerebellar infratentorial (SCIT) approach. The side of approach was determined by lateral tumor extension and venous displacement (right = 3, left = 1). Near-total removal or subtotal excision (<10% remaining) with radiotherapy was performed in 2 patients each, respectively. At follow-up (mean: 14.75 months), clinical improvement without tumor recurrence/re-growth was achieved. Extent of excision was determined by position of great vein of Galen; tumor attachment to falco-tentorium or major veins; its consistency; its lateral and inferior extent; and, presence of a good tumor-neuraxial arachnoidal plane. OTT is the preferable approach for large-to-giant meningiomas as it provides a wider corridor and better delineation of tumor-neurovascular arachnoidal interface.
Keywords: Falco-tentorial, giant meningiomas, occipital transtentorial approach, posterior third ventricular meningiomas, supracerebellar infratentorial approach, surgery, velum interpositum
|How to cite this article:|
Behari S, Das KK, Kumar A, Mehrotra A, Srivastava AK, Sahu RN, Jaiswal AK. Large/giant meningiomas of posterior third ventricular region: Falcotentorial or velum interpositum?. Neurol India 2014;62:290-5
|How to cite this URL:|
Behari S, Das KK, Kumar A, Mehrotra A, Srivastava AK, Sahu RN, Jaiswal AK. Large/giant meningiomas of posterior third ventricular region: Falcotentorial or velum interpositum?. Neurol India [serial online] 2014 [cited 2021 Jan 16];62:290-5. Available from: https://www.neurologyindia.com/text.asp?2014/62/3/290/136934
| » Introduction|| |
Posterior third ventricular (PTV) tumors form less than (<) 1% all intracranial tumors, of which meningiomas constitute 1-6%. , Large (greater than[>]3 cm)-to- giant (>5 cm) PTV meningiomas constitute an extremely rare subgroup. Their insinuation between deep veins in the posterior incisural space and close proximity to critical neuraxial structures makes their surgical excision challenging. We discuss the surgical nuances; the differentiating features between velum interpositum meningiomas (VIM) and falcotentorial meningiomas (FTM); and, review the pertinent literature.
| » Materials and Methods|| |
Four patients with large (>3 cm; n = 2) and giant (>5 cm; n = 2) PTV meningiomas (M:F = 1:1; mean age = 55 years; FTM = 2, VIM = 2, mean tumor size = 4.9 cm; mean symptom duration: 11.7 months, range: 5-24 months) underwent occipital transtentorial approach (OTT) for tumor excision. One patient also underwent a second-stage supracerebellar infratentorial (SCIT) approach for residual lesion. Excision was labeled as 'near total' when no residual tumor was visualized on postoperative enhanced CT scans; and, as 'subtotal' when <10% residual tumor remained.
The clinico-radiological findings are summarized in [Table 1]. On CT scans, the patients had a hyperdense, uniformly enhancing, rounded lesion located in the PTV area. On contrast enhanced MR images, the deep venous system was displaced supero-laterally in one patient, superiorly in one patient and antero-inferiorly in two patients. All patients had obstruction of the aqueduct causing a tri-ventricular hydrocephalus.
Patient 2 had already undergone a ventriculo-peritoneal shunt elsewhere before definitive surgery. Patient 1 was initially taken up for endoscopic third ventriculostomy and biopsy of the lesion. In this patient and also in the remaining two patients (patients 3 and 4), an external ventricular drainage through the trigonal area of the lateral ventricle was instituted prior to the interhemispheric dissection in the parieto-occipital region.
In all patients, an OTT approach using a three-quarter prone position with ipsilateral head turning (to facilitate gravitational-dependent retraction of the occipital lobe) was instituted. The side of approach was right in 3 patients and left in 1 patient. A second-stage SCIT approach in sitting position was used in one patient to resect part of the tumor that had infiltrated across the vein of Galen to the contralateral side as well as infratentorially above the superior vermis. In the two patients with a VIM (cases 1 and 2) [Figure 1],[Figure 2] and [Figure 3], no falcotentorial tumor attachment could be found during surgery; in the two cases with a FTM (cases 3 and 4) [Figure 4] and [Figure 5], the falcotentorial attachment had to be disconnected and the residual tumor within the edges of the tent coagulated. Near-total excision was performed in 2 patients whereas in 2 patients, subtotal excision (with < 10% residual tumor remaining) was done [Table 1].
|Figure 1: (Patient 1): (a) Contrast axial CT scan; (b) axial; and (c) sagittal MRI showing the giant uniformly enhancing meningioma causing triventricular hydrocephalus and shifting of the GVC to the left and superiorly; (d) Postoperative contrast axial CT scan showing tumor excision using right occipital transtentorial approach. The venous shifts are still seen; and, (e) Clinical photograph showing upgaze palsy and ophthalmoparesis|
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|Figure 2: (Patient 1): Occipital transtentorial approach. (a) CSF drainage using ventricular catheter augmented gravity-dependent parietooccipital retraction; (b) Interhemispheric retraction reveals tumor (straight arrow) in posterior incisural space; (c) intratumoral decompression; (d) tentorium division parallel to straight sinus (curved arrow) gives large fi eld of view; (e) intratumoral decompression on contralateral side; (f) Operative cavity. No tentorial attachment seen|
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|Figure 3: (Patient 2): (a) Contrast axial CT scan; (b) axial; and (c) coronal; (d) sagittal MRI showing large uniformly enhancing VIM with extension towards left trigone causing hydrocephalus; (e) venous drainage is through enlarged veins on medial surface of parieto-occipital lobes; (f) Postoperative contrast axial CT scan showing residual tumor close to GVC above and relief of hydrocephalus due to functioning third ventriculostomy|
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|Figure 4: (Patient 3): (a) axial; (b) sagittal; and, (c) coronal contrast MRI showing the giant FTM with venous complex anteroinferior to the lesion with greater right-sided extension; (d and e) postoperative contrast axial CT scans showing a thin rim of tumor left contralateral to the vein of Galen and close to the thalamic/hypothalamic area|
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|Figure 5: (Patient 4): (a) Contrast axial CT scan; (b) axial; and (c) sagittal; (d) coronal contrast MRI showing a giant FTM with right sided extension and dural-tail sign; and, (e) sagittal reconstructed CT scan showing near total excision|
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During the SCIT approach in sitting position, a minor venous bleed resulted in air embolism that could successfully be managed by continuous operative site irrigation, closing the venous breech using surgicel and fibrin glue, and aspirating the circulating air through the central venous catheter. Partial tumor excision was performed in this patient. This patient also developed homonymous hemianopia that has significantly improved at follow-up examination (case 2). A patient developed postoperative pneumonia that resolved with antibiotics and chest physiotherapy. The two patients with subtotal resection underwent radiotherapy (cases 2 and 4). The patients resumed normal lifestyle without recurrence/increase in residual disease at a mean follow up of 14.75 months.
| » Discussion|| |
Both VIMs and the antero-inferiorly projecting FTMs may be considered as "pineal region meningiomas". ,,, The VIMs, arising from the double-layered pia forming the third ventricular roof, lack a dural attachment; in FTMs, however, a significant dural attachment is present.  The VIMs are supplied by the posterior-choroidal arteries  and displace the Galenic venous complex (GVC) postero-superiorly. FTMs are supplied by tentorial branches of the cavernous internal carotid artery (ICA) and cause antero-inferior displacement of the GVC. VIMs have been further classified into dorsal and ventral leaf lesions.  Dorsal leaf meningiomas push the vein of Galen ventrally while ventral leaf meningiomas push the venous complex dorsally, a subtle distinction not possible in the large/giant lesions seen in the present study.
A very important CT feature of PTV meningiomas is the presence of an eccentric rather than a central intratumoral calcification characteristic of intrinsic pineal tumors. , The peripheral calcification is actually the calcification present within the compressed yet normal pineal gland.  The dural-tail sign is better appreciated on coronal images and may help in differentiating the two variants of pineal region meningiomas.  The displacement of the GVC, evident on angiogram, helps in defining the type of lesion and the side of the surgical approach. Long-standing compression on the GVC may often lead to development of alternate drainage pathways. The most important ones are from the basal vein of Rosenthal through the lateral mesencephalic and anterior pontomesencephalic vein to the petrosal vein; and, from the Galenic system through the internal cerebral vein or the enlarged veins on the medial surface of the parietal or occipital lobes.  The latter pattern was evident in Case no 2.
In these large to giant lesions, an OTT approach is preferable to the SCIT approach, ,,,,, as it permits a wider surgical corridor and a greater cranio-caudal view (especially for excision of tumors high above the tentorium and also for accessing their inferior pole extending infratentorially anterior to the anterior cerebellar vermis). It facilitates excision of lateral tumor extensions and allows better tumor dissection from the venous complex located in the region. In the dire eventuality of a venous injury, it is much easier to control bleeding while accessing the operative site from a cranio-caudal direction. The three-quarter prone position decreases the risk of postoperative hemorrhage at the surgical site as it avoids the development of negative pressure within the veins (that creates a false sense of security while achieving hemostasis in sitting position). The incidence of pneumocephalus and venous air embolism are also minimized. An ipsilateral head-tilt facilitates gravity-dependent opening up of the posterior interhemispheric corridor that is usually devoid of anastomotic veins. The OTT approach also avoids the vermian retraction essential in the SCIT approach (that may precipitate hemorrhage from tentorial bridging veins or even cerebellar mutism). ,,,,, The considerations for choosing the side of approach were the lateral extensions of the tumor; and the side of shift of the GVC in the quadrigeminal cistern. In the presence of a pre-existing homonymous hemianopia, retraction of the ipsilateraloccipital lobe should be avoided to prevent a bilateral homonymous field defect from developing. In patient 2, therefore, once postoperative homonymous hemianopia was detected following the initial OTT approach, a second stage SCIT (rather than a contra-lateral OTT approach) was preferred.
Various innovative surgical approaches for giant PTV meningiomas include combining the two approaches,  a trans-sinus approach through a non-dominant sinus,  a combined occipital-suboccipital approach by ligating the transverse sinus and cutting the tentorium  and, the occipital bitranstentorial-falcine approach. ,
In the present series, residual tumor was left when the great vein of Galen or the basal vein of Rosenthal traversed through the tumor extensions and a proper tumor-vein interface could not be defined; the tumor attachment to the falx or tentorium could not be separated but had to be coagulated; a proper arachnoidal plane separating the lesion from the brain stem, collicular plate, cerebellum or pulvinar of the thalamus was lacking; significant lateral and inferior tumor extensions were present; and, visualization of the contralateral tumor extension beyond the vein of Galen was difficult. Neuronavigation-assisted surgery may often lead to erroneous results in this location due to brain-shift induced by ventricular decompression and by tumor excision. 
Adjuvant radiation therapy [(RT); given in two patients with subtotal tumor excision] improves overall and progression-free survival in WHO grade II and III meningiomas and in inoperable, recurrent and residual meningiomas, irrespective of their grade.  In grade I meningiomas (found in our patients), perhaps a "wait and watch" policy and administration of RT at the first sign of recurrence/re-growth would also have been a valid strategy.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
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