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Evaluation of petrosal sinus patency with 3-dimensional contrast-enhanced magnetic resonance venography in petroclival meningiomas for surgical strategy
Surgical Neurology 64 (2005) S2:67 – S2:71 www.surgicalneurology-online.com
Evaluation of petrosal sinus patency with 3-dimensional contrast-enhanced magnetic resonance venography in petroclival meningiomas for surgical strategy Haluk Deda, MDa,T, Ilhan Erden, MDb, Banu Yagmurlu, MDb Departments of aNeurosurgery and bRadiology, Ankara University School of Medicine, Ankara 06100, Turkey
Abstract
Background: The aim of this study was to perform a detailed anatomical analysis of petroclival venous structures as well as their patencies with 3D contrast-enhanced (CE) magnetic resonance venography (MRV) and to identify the potential contribution of these data to the therapeutic approach. Methods: Ten patients (8 women and 2 men) with unilateral petroclival meningioma were examined using 3D CE MRV in addition to conventional brain protocol. Both coronal source and multiplanar reconstructed images were evaluated for the anatomical orientation. Patency of the cavernous sinus, superior petrosal sinus (SPS), and inferior petrosal sinus (IPS) was assessed. Results: All the patients had a unilateral meningioma (7 on the right and 3 on the left) at the petroclival region. Both SPS and IPS were visualized with adequate intraluminal contrast enhancement in 6 patients, but IPS was absent in 3 on the lesion side, with a patent superior petrosal sinus as the drainage route. One patient had a partially occluded SPS, with IPS being the main course of cavernous sinus drainage. Conclusions: Cerebral venous anatomy is a challenge to display with noninvasive methods because of flow dynamics, and CE 3D imaging seems to be the modality of choice to evaluate the variational anatomy and patency, which is essential in petroclival meningiomas. Because the cavernous sinus drains into either IPS or SPS, the patent sinus should be protected in surgery if there is tumoral occlusion of the others. D 2005 Elsevier Inc. All rights reserved.
Keywords:
Cranial sinuses; Magnetic resonance angiography; Meningioma; Cavernous sinus; Surgical strategy
1. Introduction The intracranial venous system is very complex, with variable and often asymmetric anatomy, resulting in diagnostic difficulties and poor outcome of surgical procedures. With the advent of MR imaging, in particular, after the introduction of MR angiographic techniques, it became possible to visualize the venous system without
Abbreviations: CE, contrast-enhanced; IPS, inferior petrosal sinus; MR, magnetic resonance; MRV, magnetic resonance venography; PC, phase contrast; SPS, superior petrosal sinus; TOF, time of flight. T Corresponding author. Department of Neurosurgery, Ankara University School of Medicine, Ankara 06100, Turkey. E-mail address: [email protected] (H. Deda). 0090-3019/$ – see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.surneu.2005.07.056
invasive angiographic technique, which had been the longstanding gold standard [4,10]. Several reports have been published concerning the conventional MRV in demonstrating the venous occlusions relying on the inflow enhancement (TOF technique) or on phase changes (PC technique). However, both methods have limitations, including poor visualization of the low-caliber veins/ sinuses or slow flow in the lumen [8,14]. One of the major vascular complications of petroclival meningioma surgery is the occlusion of drainage of the cavernous sinus to varying degrees, causing temporal lobe infarction. Regarding the IPS and SPS as the main pathway draining the cavernous sinus, patency plays a crucial role in a number of situations such as predicting the possible venous infarction if both SPS and IPS are occluded or defining the right surgical approach in protecting the
S2:68
H. Deda et al. / Surgical Neurology 64 (2005) S2:67 – S2:71
Fig. 1. Three-dimensional spoiled gradient–recalled CE MRV image reformatted on the oblique-axial plane shows a large mass at the left petroclival region (asterisk) and the SPS demonstrating an intraluminal contrast enhancement consistent with patency (arrow), although the proximal part of the sinus is inside the tumor.
drainage route if one of the petrosal sinuses is occluded because of the tumor. SPS must be sacrificed during some skull-base approaches, but sometimes, sacrificing the SPS can be catastrophic for patients because of temporal lobe and brainstem infarction. Thus, we must know the cavernous sinus drainage before surgery. As mentioned previously, both TOF and PC techniques demonstrate only the large dural sinuses effectively; the impaired circulation involving these structures could be underestimated. The visibility of petrosal sinuses is very low with these techniques, especially on the nondominant side [10]; hence, 3D CE MRV technique becomes an important tool providing more extensive small vein detail and a better demonstration of venous anatomy [11]. 2. Materials and methods 2.1. Patients The study was performed over a period of 2 years between 2002 and 2004, including 10 patients with unilateral petroclival meningiomas having various features (8 women and 2 men; age range, 39-78 years; median age, 52 years). Patients were referred for MRV imaging, focusing on ipsilateral cavernous sinus, IPS, and SPS. All patients underwent both 2D TOF MRV (which is the routine technique) plus CE 3D dynamic venography examination. An informed consent for both the examination and administration of contrast material was obtained from all subjects.
Fig. 2. Axially oriented postcontrast T1-weighted image shows a right-sided petroclival meningioma, with intense homogeneous contrast enhancement infiltrating the right cavernous sinus (A). Two-dimensional TOF MRV (B) and volume-rendered images (C) demonstrate the tumoral infiltration of the invisible right IPS, whereas the contralateral-sided sinus is patent (arrow).
H. Deda et al. / Surgical Neurology 64 (2005) S2:67 – S2:71
2.2. MR examinations All examinations were performed with a superconducting 1.5-T MR system (Signa Horizon, Echo Speed, version 2.9.3; GE Medical Systems, Milwaukee, WI), with a standard head coil. We used a 3D spoiled gradient recalled pulse sequence in a centric k-space order with coronal acquisition from occiput to coronal suture using the following scan parameters: time to echo, minimum; flip angle, 308; bandwidth, 83.33; field of view, 32; slice thickness, 1.2 mm; matrix, 384 128; number of excitations, 1; and a slab containing approximately 60 to 80 sections. The examination consisted of 3 phases, each not exceeding 18 seconds and the first being the arterial phase given a delay time of 5 to 6 seconds for the contrast material to reach the brain. The consequent 2 phases were obtained following a 5-second delay after the first phase to get the venous system fully filled with contrast material. A commercially available MR-compatible injector (Spectris; Medrad, Pittsburgh, PA) was loaded with 20 mL of gadolinium-based contrast material and 5 mL of isotonic sodium chloride solution in a second syringe. Intravenous access was obtained with a 22-gauge catheter located in the right antecubital vein. Total amount of contrast material was injected after the saline infusion at a rate of 3 mL/s. Source image data were transferred to a commercially available workstation (Advantage Windows, version 3.1; GE Medical Systems) for image processing. The protocol included a maximum intensity projection algorithm to create angiograms of the intracranial venous system. Mostly, the second phase (occasionally, the third phase) was used for image processing, and in some cases, image subtraction (subtracting the first from the last phase) was performed to eliminate the arterial system from the view as much as possible. In all cases, targeted views, regions of interest, and surface rendering algorithm were used to optimize demonstration of selected sinuses. Two radiologists evaluated these images and determined whether the cavernous sinus, SPS, and IPS were visualized on the lesion side. Visualization of these structures was reported as visible, partially visible, or nonvisible. A completely visible structure implied that the lumen of the structure was entirely enhanced, either dominant or nondominant. If some segment of the vascular structure was indistinguishable form the tumor, it was noted as partially visible, and nonvisible indicated a nonenhancing vein with tumor existence in the region of interest.
3. Results All patients showed various degrees of tumoral infiltration at the cavernous sinus, which resulted in nonvisualization in 7 patients and partial visualization in 3. Nine patients had visible SPSs (Fig. 1), whereas one of them had an SPS infiltrated by the tumor proximally, and the distal part was considered as enhancing with retrograde or collateral flow probably from the ipsilateral IPS. Of 10 patients, 3 had
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Table 1 Visibility results of the targeted sinuses and lesion laterality Patient
Cavernous sinus
SPS
IPS
1 (right) 2 (right) 3 (left) 4 (right) 5 (left) 6 (right) 7 (right) 8 (left) 9 (right) 10 (right)
Partially visible Partially visible Nonvisible Nonvisible Nonvisible Partially visible Nonvisible Nonvisible Nonvisible Nonvisible
Visible Visible Visible Visible Visible Visible Visible Partially visible Visible Visible
Visible Visible Visible Visible Nonvisible Visible Nonvisible Visible Nonvisible Visible
nonvisual IPSs encaseated by the tumor (Fig. 2). Visibility assessment of the targeted sinuses is shown in Table 1 for each patient. 4. Discussion Evaluation of a patient with petroclival meningioma is of importance because of the vascular impact of the tumor, which may cause major sequelae, although the tumor itself is benign or might have been removed totally by surgery. To understand the mechanism of this influence, one must know the intracranial venous anatomy and drainage pathways concerning the cavernous sinus to predict the possible damage secondary to its occlusion by a petroclival meningioma or during the surgical procedures. The main tributaries of the cavernous sinuses are the superior ophthalmic vein, sylvian vein (superficial middle cerebral vein), inferior cerebral veins, and sphenoparietal sinus. The sinus mainly drains to the transverse sinus via the SPS and to the internal jugular via the IPS. The SPSs are small and narrow structures, each leaving the cavernous sinus posterolaterally and running in the margin of the tentorium cerebelli, finally ending by joining the transverse sinus where this curves down to become the sigmoid. The IPSs begin posteroinferiorly to the cavernous sinus and run back in a groove between the petrous temporal and basilar occipital bones, ending in the superior jugular bulb [3,5,9,15]. The anatomical orientation of the cavernous sinuses with drainage pathways is shown in Fig. 3. These relations are very important because infiltration of either of the petrosal sinuses by the tumor brings up the patent sinus as the main drainage pathway, which has to be protected during surgery. If both petrosal sinuses are occluded either by the tumor or as a surgical complication, the patient is at high risk for developing venous infarction, which might be lethal; preoperative embolization and obliteration of the IPS as a precaution to bleeding may also trigger this venous origin ischemic event [3]. In these patients, the main aim of cavernous sinus surgery is protection of the sylvian vein. In addition, the patency of the venous structures in the petroclival region may affect the choice of surgery from among the many approach routes available in the petrosal area [2,6,7]. Hence, an effective method is required for the
S2:70
H. Deda et al. / Surgical Neurology 64 (2005) S2:67 – S2:71
Fig. 3. The main tributaries and the sinuses into which cavernous sinuses drain are illustrated. 1 indicates cavernous sinus; 2, sigmoid sinus; 3, transverse sinus; 4, superior ophthalmic vein; 5, sphenoparietal sinus; 6, SPS; 7, IPS.
demonstration of the drainage pathways of the cavernous sinus. Conventional angiographic technique (digital subtraction angiography) was the gold standard tool for many years, but the recent advances in MR have made it possible to visualize the intracranial venous structures without any intervention. Good correlation has been shown between digital subtraction angiography and MRV, although some artifacts and potential diagnostic pitfalls exist within individual MR techniques [13]. Three methods have been introduced and are being used in routine applications: 2D TOF MRV, 3D PC MRV, and 3D CE MRV, each of which has its own advantages [12,13]. Time-of-flight technique is based on the principle of flowrelated enhancement, but it nevertheless has a minimum threshold, below which sufficient signal from flowing blood cannot be obtained, resulting in signal loss in a patent lumen [1]. This becomes a major problem when it comes to the small-caliber veins such as petrosal sinuses, which are the focus of this article, because they cannot be visualized with the TOF technique depending on the undetectable flow in the patent lumen, which may lead to misdiagnosis of an atretic or nondominant sinus as thrombosis [1,3,9]. Furthermore, TOF technique depends on the flow direction, which has a disadvantage of being insensitive to in-plane flow, resulting in signal loss resembling occlusion [9,12,13]. Blood signal intensity is higher when the image plane is perpendicular to the direction of flow, but saturation effect is induced when the plane is parallel to the flow. This causes signal loss in many veins and sinuses, which have blood flow in many planes and directions [13]. Three-dimensional PC MRV seems to cover these issues because it has the ability to quantify flow or even the flow
direction, but the need to predict the optimal velocity encoding variable, which is generally not known in advance, is the major disadvantage [13]. Even when these 2 methods are used together, delineation of petroclival venous structures is impossible [7]. Three-dimensional CE MRV is gaining wide clinical acceptance in venous applications, particularly in venoocclusive disease [13]. Unlike the previous 2 MR methods, it depends on the direct paramagnetic effect of gadolinium, which shortens the T1 relaxation time in the vascular lumen, and thus, it demonstrates the enhancement of the vascular structure of concern during first pass of the contrast material. This makes the method very sensitive to the luminal patency [9,12,13]. This brings an additional advantage in scan time, which is extremely short when compared against the other methods. The major advantages of 3D CE MRV are the much superior visualization of intracranial venous morphology including small veins and collaterals, greater suppression of unwanted background signal, and avoidance of saturation effects that are often problematic with TOF technique as mentioned previously [2,9,11,13]. The 3D nature of the data set also permits different postprocessing techniques that can optimize visualization of venous structures [13]. In our study, cavernous sinus, SPS, and IPS were all visualized on the contralateral side in all patients, although the vascular caliber was very narrow in some cases. On the tumor side, 3 patients had occluded IPSs, but SPSs were patent and served as the major drainage pathway of the cavernous sinus of concern. This is fundamental information for the surgeon to define the surgical approach with preemptory necessity of protection of the SPS to avoid a venous infarction immediately after surgery. This situation is reversed if the SPS is occluded, as seen in patient 8. The SPS was nonvisible at its proximal half segment, and the enhancement at the distal part was probably because of collateral or reverse directional flow with no clinical importance, leaving the IPS as the most important drainage access. The IPS drains the petroclival venous confluence, and sometimes, its size leads to hemorrhage in this area during surgery, particularly during removal of the dura around the petroclival fissure, which may raise the need for embolization of the IPS as a precautionary maneuver to reduce the bleeding [3]. On these occasions, knowledge of partial or total occlusion of the SPS is mandatory for the surgeon to avoid this embolization. Thus, patency of the IPS on the lesion side is of clinical importance in cases having occluded SPS. Preoperative MRV findings were in accord with the surgical findings, and preoperative MRV imaging contributed considerably to the management of the patients. Surgical approach and intraoperative management can be changed according to the preoperative imaging findings to best benefit the patient and surgeon. Three-dimensional CE MRV is a significantly faster method that better demonstrates small venous anatomy, including the petroclival venous structures, which have an
H. Deda et al. / Surgical Neurology 64 (2005) S2:67 – S2:71
outstanding role in surgical petrosal approach regarding petroclival meningiomas. This technique might allow a more accurate workup toward efficient therapy, considering the anatomical and hemodynamic features of the cavernous sinus and related venous structures. Although further studies with a larger pool of patients and follow-up data including surgical results and confirmation are needed, it is obvious that mapping of petroclival venous confluence before surgery is necessary not only for anatomical delineation but also for the patency information. Three-dimensional CE MRV seems to be the right diagnostic tool for this purpose. References [1] Ayanzen RH, Bird CR, Keller PJ, et al. Cerebral MR venography: normal anatomy and potential diagnostic pitfalls. AJNR Am J Neuroradiol 2000;21(1):74 - 8. [2] Cho CW, Al-Mefty O. Combined petrosal approach to petroclival meningiomas. Neurosurgery 2002;51(3):708 - 16. [3] Destrieux C, Velut S, Kakou MK, et al. A new concept in Dorello’s canal microanatomy: the petroclival venous confluence. J Neurosurg 1997;87(1):67 - 72. [4] Farb RIScott JN, Willinsky RA, et al. Intracranial venous system: gadolinium-enhanced three-dimensional MR venography with autotriggered elliptic centric-ordered sequence — initial experience. Radiology 2003;226(1):203 - 9.
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[5] Gailloud P, Fasel JH, Muster M, et al. Termination of the inferior petrosal sinus: an anatomical variant. Clin Anat 1997;10(2): 92 - 6. [6] Horgan MA, Anderson GJ, Kellogg JX, et al. Classification and quantification of the petrosal approach to the petroclival region. J Neurosurg 2000;93(1):108 - 12. [7] Iaconetta G, Fusco M, Samii M. The sphenopetroclival venous gulf: a microanatomical study. J Neurosurg 2003;99(2):366 - 75. [8] Kirchhof K, Welzel T, Jansen O, et al. More reliable noninvasive visualization of the cerebral veins and dural sinuses: comparison of three MR angiographic techniques. Radiology 2002;224(3):804 - 10. [9] Liang L, Korogi Y, Sugahara T, et al. Evaluation of the intracranial dural sinuses with a 3D contrast-enhanced MP-RAGE sequence: prospective comparison with 2D-TOF MR venography and digital subtraction angiography. AJNR Am J Neuroradiol 2001; 22(3):481 - 92. [10] Liauw L, van Buchem MA, Spilt A, et al. MR angiography of the intracranial venous system. Radiology 2000;214(3):678 - 82. [11] Lovblad KO, Schneider J, Bassetti C, et al. Fast contrast-enhanced MR whole-brain venography. Neuroradiology 2002;44(8):681 - 8 [Epub 2002 Jul 06]. [12] Pui MH. Cerebral MR venography. Clin Imaging 2004;8(2):85 - 9. [13] Scott JN, Farb RI. Imaging and anatomy of the normal intracranial venous system. Neuroimaging Clin N Am 2003;13(1):1 - 12. [14] Wetzel SG, Law M, Lee VS, et al. Imaging of the intracranial venous system with a contrast-enhanced volumetric interpolated examination. Eur Radiol 2003;13(5):1010 - 8 [Epub 2002 Nov 08]. [15] Williams PL, Warwick R, Dyson M, et al. The lymphatic system. Gray’s anatomy. 37th ed. London7 Churchill Livingstone; 1992. p. 799 - 804.
Evaluation of petrosal sinus patency with 3-dimensional contrast-enhanced magnetic resonance venography in petroclival meningiomas for surgical strategy Haluk Deda, MDa,T, Ilhan Erden, MDb, Banu Yagmurlu, MDb Departments of aNeurosurgery and bRadiology, Ankara University School of Medicine, Ankara 06100, Turkey
Abstract
Background: The aim of this study was to perform a detailed anatomical analysis of petroclival venous structures as well as their patencies with 3D contrast-enhanced (CE) magnetic resonance venography (MRV) and to identify the potential contribution of these data to the therapeutic approach. Methods: Ten patients (8 women and 2 men) with unilateral petroclival meningioma were examined using 3D CE MRV in addition to conventional brain protocol. Both coronal source and multiplanar reconstructed images were evaluated for the anatomical orientation. Patency of the cavernous sinus, superior petrosal sinus (SPS), and inferior petrosal sinus (IPS) was assessed. Results: All the patients had a unilateral meningioma (7 on the right and 3 on the left) at the petroclival region. Both SPS and IPS were visualized with adequate intraluminal contrast enhancement in 6 patients, but IPS was absent in 3 on the lesion side, with a patent superior petrosal sinus as the drainage route. One patient had a partially occluded SPS, with IPS being the main course of cavernous sinus drainage. Conclusions: Cerebral venous anatomy is a challenge to display with noninvasive methods because of flow dynamics, and CE 3D imaging seems to be the modality of choice to evaluate the variational anatomy and patency, which is essential in petroclival meningiomas. Because the cavernous sinus drains into either IPS or SPS, the patent sinus should be protected in surgery if there is tumoral occlusion of the others. D 2005 Elsevier Inc. All rights reserved.
Keywords:
Cranial sinuses; Magnetic resonance angiography; Meningioma; Cavernous sinus; Surgical strategy
1. Introduction The intracranial venous system is very complex, with variable and often asymmetric anatomy, resulting in diagnostic difficulties and poor outcome of surgical procedures. With the advent of MR imaging, in particular, after the introduction of MR angiographic techniques, it became possible to visualize the venous system without
Abbreviations: CE, contrast-enhanced; IPS, inferior petrosal sinus; MR, magnetic resonance; MRV, magnetic resonance venography; PC, phase contrast; SPS, superior petrosal sinus; TOF, time of flight. T Corresponding author. Department of Neurosurgery, Ankara University School of Medicine, Ankara 06100, Turkey. E-mail address: [email protected] (H. Deda). 0090-3019/$ – see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.surneu.2005.07.056
invasive angiographic technique, which had been the longstanding gold standard [4,10]. Several reports have been published concerning the conventional MRV in demonstrating the venous occlusions relying on the inflow enhancement (TOF technique) or on phase changes (PC technique). However, both methods have limitations, including poor visualization of the low-caliber veins/ sinuses or slow flow in the lumen [8,14]. One of the major vascular complications of petroclival meningioma surgery is the occlusion of drainage of the cavernous sinus to varying degrees, causing temporal lobe infarction. Regarding the IPS and SPS as the main pathway draining the cavernous sinus, patency plays a crucial role in a number of situations such as predicting the possible venous infarction if both SPS and IPS are occluded or defining the right surgical approach in protecting the
S2:68
H. Deda et al. / Surgical Neurology 64 (2005) S2:67 – S2:71
Fig. 1. Three-dimensional spoiled gradient–recalled CE MRV image reformatted on the oblique-axial plane shows a large mass at the left petroclival region (asterisk) and the SPS demonstrating an intraluminal contrast enhancement consistent with patency (arrow), although the proximal part of the sinus is inside the tumor.
drainage route if one of the petrosal sinuses is occluded because of the tumor. SPS must be sacrificed during some skull-base approaches, but sometimes, sacrificing the SPS can be catastrophic for patients because of temporal lobe and brainstem infarction. Thus, we must know the cavernous sinus drainage before surgery. As mentioned previously, both TOF and PC techniques demonstrate only the large dural sinuses effectively; the impaired circulation involving these structures could be underestimated. The visibility of petrosal sinuses is very low with these techniques, especially on the nondominant side [10]; hence, 3D CE MRV technique becomes an important tool providing more extensive small vein detail and a better demonstration of venous anatomy [11]. 2. Materials and methods 2.1. Patients The study was performed over a period of 2 years between 2002 and 2004, including 10 patients with unilateral petroclival meningiomas having various features (8 women and 2 men; age range, 39-78 years; median age, 52 years). Patients were referred for MRV imaging, focusing on ipsilateral cavernous sinus, IPS, and SPS. All patients underwent both 2D TOF MRV (which is the routine technique) plus CE 3D dynamic venography examination. An informed consent for both the examination and administration of contrast material was obtained from all subjects.
Fig. 2. Axially oriented postcontrast T1-weighted image shows a right-sided petroclival meningioma, with intense homogeneous contrast enhancement infiltrating the right cavernous sinus (A). Two-dimensional TOF MRV (B) and volume-rendered images (C) demonstrate the tumoral infiltration of the invisible right IPS, whereas the contralateral-sided sinus is patent (arrow).
H. Deda et al. / Surgical Neurology 64 (2005) S2:67 – S2:71
2.2. MR examinations All examinations were performed with a superconducting 1.5-T MR system (Signa Horizon, Echo Speed, version 2.9.3; GE Medical Systems, Milwaukee, WI), with a standard head coil. We used a 3D spoiled gradient recalled pulse sequence in a centric k-space order with coronal acquisition from occiput to coronal suture using the following scan parameters: time to echo, minimum; flip angle, 308; bandwidth, 83.33; field of view, 32; slice thickness, 1.2 mm; matrix, 384 128; number of excitations, 1; and a slab containing approximately 60 to 80 sections. The examination consisted of 3 phases, each not exceeding 18 seconds and the first being the arterial phase given a delay time of 5 to 6 seconds for the contrast material to reach the brain. The consequent 2 phases were obtained following a 5-second delay after the first phase to get the venous system fully filled with contrast material. A commercially available MR-compatible injector (Spectris; Medrad, Pittsburgh, PA) was loaded with 20 mL of gadolinium-based contrast material and 5 mL of isotonic sodium chloride solution in a second syringe. Intravenous access was obtained with a 22-gauge catheter located in the right antecubital vein. Total amount of contrast material was injected after the saline infusion at a rate of 3 mL/s. Source image data were transferred to a commercially available workstation (Advantage Windows, version 3.1; GE Medical Systems) for image processing. The protocol included a maximum intensity projection algorithm to create angiograms of the intracranial venous system. Mostly, the second phase (occasionally, the third phase) was used for image processing, and in some cases, image subtraction (subtracting the first from the last phase) was performed to eliminate the arterial system from the view as much as possible. In all cases, targeted views, regions of interest, and surface rendering algorithm were used to optimize demonstration of selected sinuses. Two radiologists evaluated these images and determined whether the cavernous sinus, SPS, and IPS were visualized on the lesion side. Visualization of these structures was reported as visible, partially visible, or nonvisible. A completely visible structure implied that the lumen of the structure was entirely enhanced, either dominant or nondominant. If some segment of the vascular structure was indistinguishable form the tumor, it was noted as partially visible, and nonvisible indicated a nonenhancing vein with tumor existence in the region of interest.
3. Results All patients showed various degrees of tumoral infiltration at the cavernous sinus, which resulted in nonvisualization in 7 patients and partial visualization in 3. Nine patients had visible SPSs (Fig. 1), whereas one of them had an SPS infiltrated by the tumor proximally, and the distal part was considered as enhancing with retrograde or collateral flow probably from the ipsilateral IPS. Of 10 patients, 3 had
S2:69
Table 1 Visibility results of the targeted sinuses and lesion laterality Patient
Cavernous sinus
SPS
IPS
1 (right) 2 (right) 3 (left) 4 (right) 5 (left) 6 (right) 7 (right) 8 (left) 9 (right) 10 (right)
Partially visible Partially visible Nonvisible Nonvisible Nonvisible Partially visible Nonvisible Nonvisible Nonvisible Nonvisible
Visible Visible Visible Visible Visible Visible Visible Partially visible Visible Visible
Visible Visible Visible Visible Nonvisible Visible Nonvisible Visible Nonvisible Visible
nonvisual IPSs encaseated by the tumor (Fig. 2). Visibility assessment of the targeted sinuses is shown in Table 1 for each patient. 4. Discussion Evaluation of a patient with petroclival meningioma is of importance because of the vascular impact of the tumor, which may cause major sequelae, although the tumor itself is benign or might have been removed totally by surgery. To understand the mechanism of this influence, one must know the intracranial venous anatomy and drainage pathways concerning the cavernous sinus to predict the possible damage secondary to its occlusion by a petroclival meningioma or during the surgical procedures. The main tributaries of the cavernous sinuses are the superior ophthalmic vein, sylvian vein (superficial middle cerebral vein), inferior cerebral veins, and sphenoparietal sinus. The sinus mainly drains to the transverse sinus via the SPS and to the internal jugular via the IPS. The SPSs are small and narrow structures, each leaving the cavernous sinus posterolaterally and running in the margin of the tentorium cerebelli, finally ending by joining the transverse sinus where this curves down to become the sigmoid. The IPSs begin posteroinferiorly to the cavernous sinus and run back in a groove between the petrous temporal and basilar occipital bones, ending in the superior jugular bulb [3,5,9,15]. The anatomical orientation of the cavernous sinuses with drainage pathways is shown in Fig. 3. These relations are very important because infiltration of either of the petrosal sinuses by the tumor brings up the patent sinus as the main drainage pathway, which has to be protected during surgery. If both petrosal sinuses are occluded either by the tumor or as a surgical complication, the patient is at high risk for developing venous infarction, which might be lethal; preoperative embolization and obliteration of the IPS as a precaution to bleeding may also trigger this venous origin ischemic event [3]. In these patients, the main aim of cavernous sinus surgery is protection of the sylvian vein. In addition, the patency of the venous structures in the petroclival region may affect the choice of surgery from among the many approach routes available in the petrosal area [2,6,7]. Hence, an effective method is required for the
S2:70
H. Deda et al. / Surgical Neurology 64 (2005) S2:67 – S2:71
Fig. 3. The main tributaries and the sinuses into which cavernous sinuses drain are illustrated. 1 indicates cavernous sinus; 2, sigmoid sinus; 3, transverse sinus; 4, superior ophthalmic vein; 5, sphenoparietal sinus; 6, SPS; 7, IPS.
demonstration of the drainage pathways of the cavernous sinus. Conventional angiographic technique (digital subtraction angiography) was the gold standard tool for many years, but the recent advances in MR have made it possible to visualize the intracranial venous structures without any intervention. Good correlation has been shown between digital subtraction angiography and MRV, although some artifacts and potential diagnostic pitfalls exist within individual MR techniques [13]. Three methods have been introduced and are being used in routine applications: 2D TOF MRV, 3D PC MRV, and 3D CE MRV, each of which has its own advantages [12,13]. Time-of-flight technique is based on the principle of flowrelated enhancement, but it nevertheless has a minimum threshold, below which sufficient signal from flowing blood cannot be obtained, resulting in signal loss in a patent lumen [1]. This becomes a major problem when it comes to the small-caliber veins such as petrosal sinuses, which are the focus of this article, because they cannot be visualized with the TOF technique depending on the undetectable flow in the patent lumen, which may lead to misdiagnosis of an atretic or nondominant sinus as thrombosis [1,3,9]. Furthermore, TOF technique depends on the flow direction, which has a disadvantage of being insensitive to in-plane flow, resulting in signal loss resembling occlusion [9,12,13]. Blood signal intensity is higher when the image plane is perpendicular to the direction of flow, but saturation effect is induced when the plane is parallel to the flow. This causes signal loss in many veins and sinuses, which have blood flow in many planes and directions [13]. Three-dimensional PC MRV seems to cover these issues because it has the ability to quantify flow or even the flow
direction, but the need to predict the optimal velocity encoding variable, which is generally not known in advance, is the major disadvantage [13]. Even when these 2 methods are used together, delineation of petroclival venous structures is impossible [7]. Three-dimensional CE MRV is gaining wide clinical acceptance in venous applications, particularly in venoocclusive disease [13]. Unlike the previous 2 MR methods, it depends on the direct paramagnetic effect of gadolinium, which shortens the T1 relaxation time in the vascular lumen, and thus, it demonstrates the enhancement of the vascular structure of concern during first pass of the contrast material. This makes the method very sensitive to the luminal patency [9,12,13]. This brings an additional advantage in scan time, which is extremely short when compared against the other methods. The major advantages of 3D CE MRV are the much superior visualization of intracranial venous morphology including small veins and collaterals, greater suppression of unwanted background signal, and avoidance of saturation effects that are often problematic with TOF technique as mentioned previously [2,9,11,13]. The 3D nature of the data set also permits different postprocessing techniques that can optimize visualization of venous structures [13]. In our study, cavernous sinus, SPS, and IPS were all visualized on the contralateral side in all patients, although the vascular caliber was very narrow in some cases. On the tumor side, 3 patients had occluded IPSs, but SPSs were patent and served as the major drainage pathway of the cavernous sinus of concern. This is fundamental information for the surgeon to define the surgical approach with preemptory necessity of protection of the SPS to avoid a venous infarction immediately after surgery. This situation is reversed if the SPS is occluded, as seen in patient 8. The SPS was nonvisible at its proximal half segment, and the enhancement at the distal part was probably because of collateral or reverse directional flow with no clinical importance, leaving the IPS as the most important drainage access. The IPS drains the petroclival venous confluence, and sometimes, its size leads to hemorrhage in this area during surgery, particularly during removal of the dura around the petroclival fissure, which may raise the need for embolization of the IPS as a precautionary maneuver to reduce the bleeding [3]. On these occasions, knowledge of partial or total occlusion of the SPS is mandatory for the surgeon to avoid this embolization. Thus, patency of the IPS on the lesion side is of clinical importance in cases having occluded SPS. Preoperative MRV findings were in accord with the surgical findings, and preoperative MRV imaging contributed considerably to the management of the patients. Surgical approach and intraoperative management can be changed according to the preoperative imaging findings to best benefit the patient and surgeon. Three-dimensional CE MRV is a significantly faster method that better demonstrates small venous anatomy, including the petroclival venous structures, which have an
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outstanding role in surgical petrosal approach regarding petroclival meningiomas. This technique might allow a more accurate workup toward efficient therapy, considering the anatomical and hemodynamic features of the cavernous sinus and related venous structures. Although further studies with a larger pool of patients and follow-up data including surgical results and confirmation are needed, it is obvious that mapping of petroclival venous confluence before surgery is necessary not only for anatomical delineation but also for the patency information. Three-dimensional CE MRV seems to be the right diagnostic tool for this purpose. References [1] Ayanzen RH, Bird CR, Keller PJ, et al. Cerebral MR venography: normal anatomy and potential diagnostic pitfalls. AJNR Am J Neuroradiol 2000;21(1):74 - 8. [2] Cho CW, Al-Mefty O. Combined petrosal approach to petroclival meningiomas. Neurosurgery 2002;51(3):708 - 16. [3] Destrieux C, Velut S, Kakou MK, et al. A new concept in Dorello’s canal microanatomy: the petroclival venous confluence. J Neurosurg 1997;87(1):67 - 72. [4] Farb RIScott JN, Willinsky RA, et al. Intracranial venous system: gadolinium-enhanced three-dimensional MR venography with autotriggered elliptic centric-ordered sequence — initial experience. Radiology 2003;226(1):203 - 9.
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