Avoidance If Structural Pitfalls in Spinal Meningioma Resection
Avoidance If Structural Pitfalls in Spinal Meningioma Resection
Creating a surgical avenue through which to resect an intraspinal meningioma requires dissection of the musculoligamentous structures of the spine. Variable vertebral components must be removed to create a corridor to the intraspinal compartment. The cardinal principles of intraspinal tumor resection are to minimize the intraoperative risk of deformation and traumatic injury of the spinal cord. Therefore, the appropriate planning for access to and removal of the osseous elements is critical. Of equal importance is the consideration of the biomechanics of the spine. In cases of potential spinal instability instrumentation-assisted fusion should be performed at the time of tumor resection. The authors discuss the techniques for creating access to these tumors and propose a simple classification scheme to assist with this decision-making process.
The incidence of spinal meningiomas includes up to 46.7% of intraspinal tumors, and resection is considered their primary treatment modality. Radiotherapy and chemotherapy are not indicated as the primary modalities. The majority of the tumors occur in the thoracic region (7582%), and there is a female predominance. Roux, et al., reported that one third of the lesions were posterolateral within the canal and greater than one third were located anterolaterally.
Preoperative imaging studies and surgical planning are of paramount importance. The dimensions and location of the tumor should be determined, as well as intraspinal position of the spinal cord, its condition, and the presence of extradural or -spinal extension. These factors will help determine the nature of the surgical corridor required to resect the tumor. The required extent of partial vertebral bone removal is planned to create the desired corridor to the targeted lesion. Absolute predictors of delayed spinal deformity or instability after spinal tumor excision include multilevel laminectomy, interference with the facet joints, and corpectomy. Relative risk factors for deformity and deformity progression are the spinal level of involvement and the preexistence of deformity. Treatment of cervicothoracic and thoracolumbar regions is associated with a higher risk than other levels because of the change in the axis of motion and in degree of mobility occurring at these junctions. Because oblique approaches require variable degrees of structural excision (facets, laminae, and pars interarticularis) depending on individual anatomy, the postoperative risk of instability is also variable.
Failure to address the possibility of acquired instability and/or adjacent-segment hypermobility will result in deformity and possibly chronic pain. An understanding of the basic spinal biomechanics permits minimal bone removal and maximal exposure, providing secure access to the meningioma.
Intraoperative ultrasonography allows assessment of the adequacy of the surgical corridor in the craniocaudal and mediolateral directions when excising intraspinal tumors. The extent of bone removal is measured using a marked dissector (Fig. 1). Once the initial plan is completed, ultrasonography is conducted to evaluate access to the tumor's margins. If inadequate, additional bone is removed to provide unobstructed surgical access. Additionally the appearance of the ultrasonic image will help differentiate between meningioma and nerve sheath tumors in cases in which the preoperative diagnosis is equivocal; in contrast to neuroma, for example, meningioma has uniform echogenicity and is hyperechoic without cysts. This is important because the principles of tumor resection differ between meningioma and nerve sheath tumor. In addition preoperative MR imaging may fail to distinguish between meningioma and nerve sheath tumor.
(Enlarge Image)
Intraoperative photographs showing measurement of the dural exposure after bone removal.
Creation of the transosseous corridors is based on spinal morphological features and biomechanics (Fig. 2). The three surgical approaches for creation of such a corridor are illustrated in Fig. 3. The "A" approaches require removal of the posterior elements to various degrees without interfering with the anterior column. In the "B" approaches the anterior vertebral columns are removed, and the "C" approaches involve a combination of the A and B maneuvers. Access to an intraspinal meningioma requires one to choose among the A approaches. Transosseous B and C approaches are reserved for the resection of vascular lesions such as cavernomas and arteriovenous malformations. The latter approaches may also be required in cases of predominantly anterior duralbased and heavily calcified meningiomas. Approaches B and C are more likely to interfere with spinal anatomy and function ( Table 1 ).
(Enlarge Image)
Upper and Center: Photographs showing anatomical dissection of a sheep spine, via a unilateral approach. Greater bone removal combined with costotranversectomy when indicated allows increased access to the spinal canal. Lower: Illustration providing an axial perspective of the extended bone removal for increased exposure.
(Enlarge Image)
Classification scheme of approaches to intraspinal meningiomas.
Creating a surgical avenue through which to resect an intraspinal meningioma requires dissection of the musculoligamentous structures of the spine. Variable vertebral components must be removed to create a corridor to the intraspinal compartment. The cardinal principles of intraspinal tumor resection are to minimize the intraoperative risk of deformation and traumatic injury of the spinal cord. Therefore, the appropriate planning for access to and removal of the osseous elements is critical. Of equal importance is the consideration of the biomechanics of the spine. In cases of potential spinal instability instrumentation-assisted fusion should be performed at the time of tumor resection. The authors discuss the techniques for creating access to these tumors and propose a simple classification scheme to assist with this decision-making process.
The incidence of spinal meningiomas includes up to 46.7% of intraspinal tumors, and resection is considered their primary treatment modality. Radiotherapy and chemotherapy are not indicated as the primary modalities. The majority of the tumors occur in the thoracic region (7582%), and there is a female predominance. Roux, et al., reported that one third of the lesions were posterolateral within the canal and greater than one third were located anterolaterally.
Preoperative imaging studies and surgical planning are of paramount importance. The dimensions and location of the tumor should be determined, as well as intraspinal position of the spinal cord, its condition, and the presence of extradural or -spinal extension. These factors will help determine the nature of the surgical corridor required to resect the tumor. The required extent of partial vertebral bone removal is planned to create the desired corridor to the targeted lesion. Absolute predictors of delayed spinal deformity or instability after spinal tumor excision include multilevel laminectomy, interference with the facet joints, and corpectomy. Relative risk factors for deformity and deformity progression are the spinal level of involvement and the preexistence of deformity. Treatment of cervicothoracic and thoracolumbar regions is associated with a higher risk than other levels because of the change in the axis of motion and in degree of mobility occurring at these junctions. Because oblique approaches require variable degrees of structural excision (facets, laminae, and pars interarticularis) depending on individual anatomy, the postoperative risk of instability is also variable.
Failure to address the possibility of acquired instability and/or adjacent-segment hypermobility will result in deformity and possibly chronic pain. An understanding of the basic spinal biomechanics permits minimal bone removal and maximal exposure, providing secure access to the meningioma.
Intraoperative ultrasonography allows assessment of the adequacy of the surgical corridor in the craniocaudal and mediolateral directions when excising intraspinal tumors. The extent of bone removal is measured using a marked dissector (Fig. 1). Once the initial plan is completed, ultrasonography is conducted to evaluate access to the tumor's margins. If inadequate, additional bone is removed to provide unobstructed surgical access. Additionally the appearance of the ultrasonic image will help differentiate between meningioma and nerve sheath tumors in cases in which the preoperative diagnosis is equivocal; in contrast to neuroma, for example, meningioma has uniform echogenicity and is hyperechoic without cysts. This is important because the principles of tumor resection differ between meningioma and nerve sheath tumor. In addition preoperative MR imaging may fail to distinguish between meningioma and nerve sheath tumor.
(Enlarge Image)
Intraoperative photographs showing measurement of the dural exposure after bone removal.
Creation of the transosseous corridors is based on spinal morphological features and biomechanics (Fig. 2). The three surgical approaches for creation of such a corridor are illustrated in Fig. 3. The "A" approaches require removal of the posterior elements to various degrees without interfering with the anterior column. In the "B" approaches the anterior vertebral columns are removed, and the "C" approaches involve a combination of the A and B maneuvers. Access to an intraspinal meningioma requires one to choose among the A approaches. Transosseous B and C approaches are reserved for the resection of vascular lesions such as cavernomas and arteriovenous malformations. The latter approaches may also be required in cases of predominantly anterior duralbased and heavily calcified meningiomas. Approaches B and C are more likely to interfere with spinal anatomy and function ( Table 1 ).
(Enlarge Image)
Upper and Center: Photographs showing anatomical dissection of a sheep spine, via a unilateral approach. Greater bone removal combined with costotranversectomy when indicated allows increased access to the spinal canal. Lower: Illustration providing an axial perspective of the extended bone removal for increased exposure.
(Enlarge Image)
Classification scheme of approaches to intraspinal meningiomas.
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