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The Tentorial Sinuses
CHAPTER 8
The Tentorial Sinuses ALIREZA SHOAKAZEMI • R. SHANE TUBBS
ANATOMY The tentorial sinuses (Figs. 8.1 and 8.2) are often encountered with neurosurgical approaches1,2 and should not be confused with the prenatal tentorial sinus (tentorial vein of Markowski; inferior cerebral vein of Streeter). Gibbs and Gibbs first described the presence of these postnatal sinuses, primarily fed by the superior cerebellar veins and drained into the transverse sinuses.3,4 Drainage of the tentorium cerebelli is dependent on two groups of vessels: the dural sinuses of the tentorium cerebelli and the afferent tentorial veins.5 In contrast to other intracranial sinuses, the intratentorial dural sinuses are not held open and tend to collapse.5 These sinuses show variable thickness and appear as a separation of the two leaflets of the tentorium with some arachnoid granulations, mainly at entry point into transverse sinuses.5 The complexity and versatility of these venous structures mandates a reliable and reproducible method of classification. A reliable method of classification can assist a neurosurgeon to plan a safe surgical corridor and to prevent potential morbidities associated with sacrifice or inadvertent injury of this category of venous sinuses. Tentorial sinuses are grossly categorized into two constant, paired, bilateral but mostly asymmetric venous channels.2,5,6 The medial group is formed by the coalescence of the veins from the superior surface of the cerebellum (Fig. 8.3), and the lateral group is commonly formed by the convergence of veins arising from the basal and lateral surface of the temporal and occipital lobes.2 The medial group of intratentorial sinuses arises between 15–25 mm from the midline and 10–25 mm from the transverse sinus.5 The lateral tentorial sinus (LTS), in most cases, arises at a point on the tentorium 30–40 mm from the midline, 2–10 mm from the transverse sinus, and 10 mm from petrous ridge.5 Both groups of intratentorial sinuses normally carry venous blood from the supratentorial and infratentorial compartments, and they also substantially contribute to the venous drainage of the floor of the middle cranial fossa.5 On the other hand, in certain circumstances,
these sinuses act as a potential connection between the supratentorial and infratentorial sinuses. LTS. This group of sinuses arises within the lateral part of the tentorium cerebelli, and after pursuing a lateral course, it drains into the terminal segment of the transverse sinus and transverse-sigmoid junction on each side.2,6,7 The basal and lateral occipital and temporal venous system contributes significantly in the formation of the LTS on each side.6 Configuration of the LTS has been classified into three categories based on neuroradiologic and cadaveric study findings: type I: venous candelabra configuration, type II: multiple independent veins, and type III: venous lakes within the tentorium, the most common type of sinuses.6,8 Rhoton et al. classified venous branches of LTS into eight groups: (1) anterior temporal vein, (2) anterior temporobasal vein, (3) middle temporobasal vein, (4) posterior temporobasal vein, (5) occipitobasal vein, (6) posterior temporal vein, (7) vein of Labbé, and (8) middle temporal vein.2,6,7 Medial tentorial sinus (MTS). This group normally courses medially and empties into the straight sinus and transverse sinus confluence.2 This category is mainly responsible for the drainage of the superior cerebellar surface.6 In a cadaveric study, Matsushima et al. described four types of tentorial venous sinuses.1 In this study, the draining pattern was used as the classification criteria. • Group I (tentorial sinuses draining the cerebral hemispheres): In this group, several cerebral veins converged at the superior surface of the tentorium to form bridging veins. They were commonly present near the transverse sinuses. In this study, the vein of Labbé was included in this category.1 • Group II (tentorial sinuses draining the cerebellum): In this category, bridging veins from the cerebellar tentorial surface formed the tentorial sinuses. This group of sinuses drained into the torcular or the dural sinuses nearby.1 • Group III: This group formed near the tentorial edge of the straight sinus. They were frequently small with no bridging veins.
Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses. https://doi.org/10.1016/B978-0-323-65377-0.00008-8 Copyright © 2020 Elsevier Inc. All rights reserved.
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Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses
FIG. 8.1 Cadaveric example of the tentorial sinuses. The supratentorial brain has been removed.
FIG. 8.2 Cadaveric example of the tentorial sinuses. This right-sided tentorial sinus is seen draining into
the straight sinus.
FIG. 8.3 Posterior view of the supracerebellar region noting superior cerebellar veins draining superiorly
into the tentorial sinus on the left side. (Courtesy Dr. Albert Rhoton.)
CHAPTER 8 The Tentorial Sinuses • Group IV: This group was a rare subtype found in cadaveric studies. The basal vein of Rosenthal terminated as a bridging vein to the tentorial free edge forming a tentorial sinus. The presence of venous sinuses in the tentorium cerebelli is reported in about 86% of cases in some cadaveric studies.4 Special attention to detect the presence of these sinuses in imaging is of paramount importance.
TENTORIAL BRIDGING VEINS This group of bridging veins is a part of the superficial group of cerebral veins that are involved with the draining of the lateral surface of the temporal lobe and the basal surface of the temporal and occipital lobes into the tentorial sinuses, transverse sinuses, or superior petrosal sinuses at the tentorial margin.2 This group of bridging veins, except for the vein of Labbé, which normally drains into the transverse sinus, converges on the preoccipital notch to drain into the LTS. For ease of classification, a group of veins that empty into the LTS can be subdivided into two groups. The lateral branches include the anterior temporal vein, middle temporal vein, posterior temporal vein, and vein of Labbé.6 The medial branches are composed of the anterior temporobasal vein, middle temporobasal vein, posterior temporobasal vein, and occipitobasal veins.6 There have been some controversies with regard to the predominant type of LTS. Miabi et al. found type III to be the most common type, whereas Guppy et al. found type II to be the most common in a cadaveric study.6,8
EMBRYOLOGY Padget explained the formation and development of the intracranial venous channels.9 She highlighted that the venous development is frequently accompanied by the reversal of flow direction and that posteroinferior and middle cerebral veins drain a part of the neopallium into the transverse sinuses behind the sigmoid sinus.9 Butler et al. reported the results of a human embryonic study depicting cranial venous anatomy.10 During the embryonic phase, the posterior tentorial fold runs along the superior border of the otic capsule and then sweeps onto the posterior surface of the otic capsule.
PATHOLOGY The tentorial sinuses can be the main venous drainage pathway in conditions, such as vein of Galen aneurysms and holoprosencephaly, in which the posterior dural venous sinuses are absent are compromised.6 In
89
these conditions, interventional radiology or surgical manipulation of this group of vessels should be considered more carefully. This group of sinuses can be affected with other pathologies that normally affect other sinuses, such as tumors and vascular anomalies.
IMAGING Understanding the location and different types of tentorial sinuses facilitates an easier detection of these sinuses on different imaging modalities. Although an LTS is commonly detectable by catheter angiogram or magnetic resonance imaging (MRI) (Figs. 8.4–8.6), it is commonly misinterpreted as a cortical vein close to the vein of Labbé.6 Miabi et al. investigated the accuracy of the conventional T1-weighted, spin-echo, contrastenhanced MR imaging to visualize the LTS and found this method to be reliable for detecting this category of sinuses.6 Although in the majority of cases, the previously mentioned LTS and MTS anatomic classifications are reflected in imaging findings, case reports of a tentorial sinus draining the telencephalic and diencephalic tributaries of the basal vein has been reported in the literature.11 Braun et al. on a neuroradiologic study found that the LTSs are taking up the contrast via the superficial veins of the temporal and occipital lobes (anterior circulation angiography), whereas the MTSs are more obvious during vertebral angiography studies.5 In radiologic studies, two types of venous formations can be found: an inverted cone and a rectilinear formation.5 Choosing the appropriate imaging modality, interpreting the resultant data, and determining the architecture of the sinuses in anticipation of performing a surgery, which can potentially involve manipulation or sacrifice of these sinuses, can prevent potential morbidities accompanied by the chosen surgical approach.
SURGERY Certain neurosurgical approaches involve manipulation or sectioning of the tentorial sinuses or adjacent venous structures.1 Special attention to the presence, location, and anatomic configuration of the tentorial sinuses is crucial to prevent devastating intraoperative bleeding and potential postoperative complications associated with damage to these sinuses.4 For ease of classification, surgical approaches can be categorized according to the part of the TS that can potentially be affected.
90
Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses
FIGS. 8.4–8.6 Coronal MRIs illustrating the tentorial sinuses.
CHAPTER 8 The Tentorial Sinuses
91
FIGS. 8.4–8.6, cont’d
1. Surgical approaches that can affect the LTS. Certain surgical approaches that involve manipulation of the posterior temporal lobe area can have a deleterious effect on the LTS venous structures with possible resultant venous infarction.6 Collaboration between a neurosurgeon and neuroradiologist before a middle cranial fossa approach, which can potentially involve retraction and damage to the LTS, is of paramount importance. To define the LTS type, termination of the vein of Labbé and venous drainage dominance and presence of sphenoparietal sinus should be considered before embarking a surgical approach.6 To define the type of LTS can be helpful to modify a surgical approach accordingly. Other approaches in which the LTS can be affected are the transoccipital transtentorial, infratentorial supracerebellar, and subtemporal transtentorial approaches.1 Some authors recommended avoiding dividing the tentorium cerebelli in patients displaying type I or III LTS.6 The possibility of a tentorial sinus acting as a collateral circulation should be
considered when sacrifice of the sinus is considered.4 2. Surgical approaches that can affect the MTS. A supracerebellar infratentorial approach can potentially affect the venous structures of the bridging veins, which empty into the MTSs. Similar approaches to tentorial meningiomas often manipulate the MTSrelated bridging veins.
REFERENCES 1. Matsushima T, Suzuki SO, Fukui M, Rhoton AL, de Oliveira E, Ono M. Microsurgical anatomy of the tentorial sinuses. J Neurosurg. 1989;71(6):923–928. 2. Rhoton AL. Rhoton’s Cranial Anatomy and Surgical Approaches. LWW; 2007. 3. Gibbs EL, Gibbs FA. The cross section areas of the vessels that form the torcular and the manner in which flow is distributed to the right and to the left lateral sinus. Anat Rec. 1934;59(4):419–426. 4. Muthukumar N, Palaniappan P. Tentorial venous sinuses: an anatomic study. Neurosurgery. 1998;42(2):363–371.
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Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses
5. Braun JP, et al. Anatomical and neuroradiological study of the veins of the tentorium and the floor of the middle cranial fossa, and their drainage to dural sinuses. J Neuroradiol. 1978;5(2):113–132. 6. Miabi Z, et al. Delineation of lateral tentorial sinus with contrast-enhanced MR imaging and its surgical implications. AJNR Am J Neuroradiol. 2004;25(7):1181–1188. 7. Oka K, et al. Microsurgical anatomy of the superficial veins of the cerebrum. Neurosurgery. 1985;17(5):711–748. 8. Guppy KH, et al. Venous drainage of the inferolateral temporal lobe in relationship to transtemporal/transtentorial approaches to the cranial base. Neurosurgery. 1997;41(3):615–619; discussion 619–20.
9. Padget DH. The cranial venous system in man in reference to development, adult configuration, and relation to the arteries. Am J Anat. 1956;98(3):307–355. 10. Butler H. The development of certain human dural venous sinuses. J Anat. 1957;91(4):510–526. 11. Terbrugge K, Lasjaunias P. Tentorial sinus. Radiologic and anatomic features of a case. Surg Radiol Anat. 1988;10(3):243–246.
The Tentorial Sinuses ALIREZA SHOAKAZEMI • R. SHANE TUBBS
ANATOMY The tentorial sinuses (Figs. 8.1 and 8.2) are often encountered with neurosurgical approaches1,2 and should not be confused with the prenatal tentorial sinus (tentorial vein of Markowski; inferior cerebral vein of Streeter). Gibbs and Gibbs first described the presence of these postnatal sinuses, primarily fed by the superior cerebellar veins and drained into the transverse sinuses.3,4 Drainage of the tentorium cerebelli is dependent on two groups of vessels: the dural sinuses of the tentorium cerebelli and the afferent tentorial veins.5 In contrast to other intracranial sinuses, the intratentorial dural sinuses are not held open and tend to collapse.5 These sinuses show variable thickness and appear as a separation of the two leaflets of the tentorium with some arachnoid granulations, mainly at entry point into transverse sinuses.5 The complexity and versatility of these venous structures mandates a reliable and reproducible method of classification. A reliable method of classification can assist a neurosurgeon to plan a safe surgical corridor and to prevent potential morbidities associated with sacrifice or inadvertent injury of this category of venous sinuses. Tentorial sinuses are grossly categorized into two constant, paired, bilateral but mostly asymmetric venous channels.2,5,6 The medial group is formed by the coalescence of the veins from the superior surface of the cerebellum (Fig. 8.3), and the lateral group is commonly formed by the convergence of veins arising from the basal and lateral surface of the temporal and occipital lobes.2 The medial group of intratentorial sinuses arises between 15–25 mm from the midline and 10–25 mm from the transverse sinus.5 The lateral tentorial sinus (LTS), in most cases, arises at a point on the tentorium 30–40 mm from the midline, 2–10 mm from the transverse sinus, and 10 mm from petrous ridge.5 Both groups of intratentorial sinuses normally carry venous blood from the supratentorial and infratentorial compartments, and they also substantially contribute to the venous drainage of the floor of the middle cranial fossa.5 On the other hand, in certain circumstances,
these sinuses act as a potential connection between the supratentorial and infratentorial sinuses. LTS. This group of sinuses arises within the lateral part of the tentorium cerebelli, and after pursuing a lateral course, it drains into the terminal segment of the transverse sinus and transverse-sigmoid junction on each side.2,6,7 The basal and lateral occipital and temporal venous system contributes significantly in the formation of the LTS on each side.6 Configuration of the LTS has been classified into three categories based on neuroradiologic and cadaveric study findings: type I: venous candelabra configuration, type II: multiple independent veins, and type III: venous lakes within the tentorium, the most common type of sinuses.6,8 Rhoton et al. classified venous branches of LTS into eight groups: (1) anterior temporal vein, (2) anterior temporobasal vein, (3) middle temporobasal vein, (4) posterior temporobasal vein, (5) occipitobasal vein, (6) posterior temporal vein, (7) vein of Labbé, and (8) middle temporal vein.2,6,7 Medial tentorial sinus (MTS). This group normally courses medially and empties into the straight sinus and transverse sinus confluence.2 This category is mainly responsible for the drainage of the superior cerebellar surface.6 In a cadaveric study, Matsushima et al. described four types of tentorial venous sinuses.1 In this study, the draining pattern was used as the classification criteria. • Group I (tentorial sinuses draining the cerebral hemispheres): In this group, several cerebral veins converged at the superior surface of the tentorium to form bridging veins. They were commonly present near the transverse sinuses. In this study, the vein of Labbé was included in this category.1 • Group II (tentorial sinuses draining the cerebellum): In this category, bridging veins from the cerebellar tentorial surface formed the tentorial sinuses. This group of sinuses drained into the torcular or the dural sinuses nearby.1 • Group III: This group formed near the tentorial edge of the straight sinus. They were frequently small with no bridging veins.
Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses. https://doi.org/10.1016/B978-0-323-65377-0.00008-8 Copyright © 2020 Elsevier Inc. All rights reserved.
87
88
Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses
FIG. 8.1 Cadaveric example of the tentorial sinuses. The supratentorial brain has been removed.
FIG. 8.2 Cadaveric example of the tentorial sinuses. This right-sided tentorial sinus is seen draining into
the straight sinus.
FIG. 8.3 Posterior view of the supracerebellar region noting superior cerebellar veins draining superiorly
into the tentorial sinus on the left side. (Courtesy Dr. Albert Rhoton.)
CHAPTER 8 The Tentorial Sinuses • Group IV: This group was a rare subtype found in cadaveric studies. The basal vein of Rosenthal terminated as a bridging vein to the tentorial free edge forming a tentorial sinus. The presence of venous sinuses in the tentorium cerebelli is reported in about 86% of cases in some cadaveric studies.4 Special attention to detect the presence of these sinuses in imaging is of paramount importance.
TENTORIAL BRIDGING VEINS This group of bridging veins is a part of the superficial group of cerebral veins that are involved with the draining of the lateral surface of the temporal lobe and the basal surface of the temporal and occipital lobes into the tentorial sinuses, transverse sinuses, or superior petrosal sinuses at the tentorial margin.2 This group of bridging veins, except for the vein of Labbé, which normally drains into the transverse sinus, converges on the preoccipital notch to drain into the LTS. For ease of classification, a group of veins that empty into the LTS can be subdivided into two groups. The lateral branches include the anterior temporal vein, middle temporal vein, posterior temporal vein, and vein of Labbé.6 The medial branches are composed of the anterior temporobasal vein, middle temporobasal vein, posterior temporobasal vein, and occipitobasal veins.6 There have been some controversies with regard to the predominant type of LTS. Miabi et al. found type III to be the most common type, whereas Guppy et al. found type II to be the most common in a cadaveric study.6,8
EMBRYOLOGY Padget explained the formation and development of the intracranial venous channels.9 She highlighted that the venous development is frequently accompanied by the reversal of flow direction and that posteroinferior and middle cerebral veins drain a part of the neopallium into the transverse sinuses behind the sigmoid sinus.9 Butler et al. reported the results of a human embryonic study depicting cranial venous anatomy.10 During the embryonic phase, the posterior tentorial fold runs along the superior border of the otic capsule and then sweeps onto the posterior surface of the otic capsule.
PATHOLOGY The tentorial sinuses can be the main venous drainage pathway in conditions, such as vein of Galen aneurysms and holoprosencephaly, in which the posterior dural venous sinuses are absent are compromised.6 In
89
these conditions, interventional radiology or surgical manipulation of this group of vessels should be considered more carefully. This group of sinuses can be affected with other pathologies that normally affect other sinuses, such as tumors and vascular anomalies.
IMAGING Understanding the location and different types of tentorial sinuses facilitates an easier detection of these sinuses on different imaging modalities. Although an LTS is commonly detectable by catheter angiogram or magnetic resonance imaging (MRI) (Figs. 8.4–8.6), it is commonly misinterpreted as a cortical vein close to the vein of Labbé.6 Miabi et al. investigated the accuracy of the conventional T1-weighted, spin-echo, contrastenhanced MR imaging to visualize the LTS and found this method to be reliable for detecting this category of sinuses.6 Although in the majority of cases, the previously mentioned LTS and MTS anatomic classifications are reflected in imaging findings, case reports of a tentorial sinus draining the telencephalic and diencephalic tributaries of the basal vein has been reported in the literature.11 Braun et al. on a neuroradiologic study found that the LTSs are taking up the contrast via the superficial veins of the temporal and occipital lobes (anterior circulation angiography), whereas the MTSs are more obvious during vertebral angiography studies.5 In radiologic studies, two types of venous formations can be found: an inverted cone and a rectilinear formation.5 Choosing the appropriate imaging modality, interpreting the resultant data, and determining the architecture of the sinuses in anticipation of performing a surgery, which can potentially involve manipulation or sacrifice of these sinuses, can prevent potential morbidities accompanied by the chosen surgical approach.
SURGERY Certain neurosurgical approaches involve manipulation or sectioning of the tentorial sinuses or adjacent venous structures.1 Special attention to the presence, location, and anatomic configuration of the tentorial sinuses is crucial to prevent devastating intraoperative bleeding and potential postoperative complications associated with damage to these sinuses.4 For ease of classification, surgical approaches can be categorized according to the part of the TS that can potentially be affected.
90
Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses
FIGS. 8.4–8.6 Coronal MRIs illustrating the tentorial sinuses.
CHAPTER 8 The Tentorial Sinuses
91
FIGS. 8.4–8.6, cont’d
1. Surgical approaches that can affect the LTS. Certain surgical approaches that involve manipulation of the posterior temporal lobe area can have a deleterious effect on the LTS venous structures with possible resultant venous infarction.6 Collaboration between a neurosurgeon and neuroradiologist before a middle cranial fossa approach, which can potentially involve retraction and damage to the LTS, is of paramount importance. To define the LTS type, termination of the vein of Labbé and venous drainage dominance and presence of sphenoparietal sinus should be considered before embarking a surgical approach.6 To define the type of LTS can be helpful to modify a surgical approach accordingly. Other approaches in which the LTS can be affected are the transoccipital transtentorial, infratentorial supracerebellar, and subtemporal transtentorial approaches.1 Some authors recommended avoiding dividing the tentorium cerebelli in patients displaying type I or III LTS.6 The possibility of a tentorial sinus acting as a collateral circulation should be
considered when sacrifice of the sinus is considered.4 2. Surgical approaches that can affect the MTS. A supracerebellar infratentorial approach can potentially affect the venous structures of the bridging veins, which empty into the MTSs. Similar approaches to tentorial meningiomas often manipulate the MTSrelated bridging veins.
REFERENCES 1. Matsushima T, Suzuki SO, Fukui M, Rhoton AL, de Oliveira E, Ono M. Microsurgical anatomy of the tentorial sinuses. J Neurosurg. 1989;71(6):923–928. 2. Rhoton AL. Rhoton’s Cranial Anatomy and Surgical Approaches. LWW; 2007. 3. Gibbs EL, Gibbs FA. The cross section areas of the vessels that form the torcular and the manner in which flow is distributed to the right and to the left lateral sinus. Anat Rec. 1934;59(4):419–426. 4. Muthukumar N, Palaniappan P. Tentorial venous sinuses: an anatomic study. Neurosurgery. 1998;42(2):363–371.
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Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses
5. Braun JP, et al. Anatomical and neuroradiological study of the veins of the tentorium and the floor of the middle cranial fossa, and their drainage to dural sinuses. J Neuroradiol. 1978;5(2):113–132. 6. Miabi Z, et al. Delineation of lateral tentorial sinus with contrast-enhanced MR imaging and its surgical implications. AJNR Am J Neuroradiol. 2004;25(7):1181–1188. 7. Oka K, et al. Microsurgical anatomy of the superficial veins of the cerebrum. Neurosurgery. 1985;17(5):711–748. 8. Guppy KH, et al. Venous drainage of the inferolateral temporal lobe in relationship to transtemporal/transtentorial approaches to the cranial base. Neurosurgery. 1997;41(3):615–619; discussion 619–20.
9. Padget DH. The cranial venous system in man in reference to development, adult configuration, and relation to the arteries. Am J Anat. 1956;98(3):307–355. 10. Butler H. The development of certain human dural venous sinuses. J Anat. 1957;91(4):510–526. 11. Terbrugge K, Lasjaunias P. Tentorial sinus. Radiologic and anatomic features of a case. Surg Radiol Anat. 1988;10(3):243–246.