En bloc resection of a primary tumor is a significant undertaking, even in the most experienced hands. We therefore recommend referring these cases to quaternary centers with experience in primary spine tumor surgery.
En bloc resections
Terminology is essential in primary tumor management.
An en bloc resection refers to a surgical attempt to remove a tumor in one piece without violating it.
On the other hand, an intralesional resection or a curettage refers to a deliberate intralesional resection.
An en bloc resection needs to be associated with a pathological margin description to be correctly defined.
Four types of margins are described:
Intralesional – resection margin is within tumoral tissue
Marginal – resection margin is within a reactional zone or pseudocapsule (in the spine, the epidural margin is often marginal)
Wide – resection margin is within normal tissue
Radical – this is extracompartmental resection and, as such, does not apply to spine tumors
Three conditions need to be met for an en bloc resection to be deemed possible.
If we consider the spinal canal as a ring, there needs to be enough circumference of that ring to be removed piecemeal to allow delivery of the neural element.
Access to the nerve root sleeve at its dural origin is required. This might only be achievable after mobilization.
In the cervical spine, one vertebral artery needs to remain patent. Preoperative assessment of cerebral vasculature is useful to determine dominance and assess for patency of the posterior communicating artery.
If these conditions are not met, an en bloc resection will not be possible without a planned transgression of the tumor.
In this illustration, the spinal canal is circumferentially surrounded by a tumor. There is not enough uninvolved portion of the ring to allow an en bloc resection.
Proper planning is instrumental in the management of primary spine tumors. A multidisciplinary approach may be required depending on the localization of the tumor.
Note: A gastrostomy/tracheostomy can be considered for high cervical tumors on a case by case basis.
Embolization procedures are recommended to reduce operative blood loss in hypervascular tumors, especially during more extensive resections.
Embolization should be considered for hypervascular tumors, such as giant cell tumors, aneurysmal bone cysts, and hemangiomas.
The role of the embolization is:
To reduce the vascularity of the tumor
To facilitate dissection around the tumor
Mapping of spinal cord vascular supply and vertebral artery anatomy
Embolization on its own may also have a therapeutic effect.
This image shows the embolization of a hypervascular tumor.
A posterior approach followed by an anterior approach is generally recommended for a cervical tumor involving the vertebral body.
During the posterior approach, the uninvolved part of the spinal ring will be resected in a piecemeal fashion, and osteotomies and soft tissue dissections will be performed.
A wide visualization is essential in these cases, and a laminectomy involving one level above and below the tumor is recommended.
The goal is to achieve:
Good visualization of normal and abnormal anatomy
Safe decompression of the neural elements
Appropriate posterior tumor mobilization allows the tumor to be delivered during the anterior approach.
En bloc resection is a destabilizing procedure. As such, long constructs are required.
As a general rule, three vertebrae above and below the tumor are included in the construct. In multilevel tumors, or when there is poor bone quality, this construct can be extended.
As the procedure is often curative, it is important to verify that the spine is reconstructed in good alignment, and a solid bony union should be attempted.
The C7 vertebra can be instrumented with either pedicle screw fixation or lateral mass screw fixation, depending on the patient’s anatomy.
Anterior reconstruction of the disc space or vertebral body following a complete corpectomy should be performed using a cage and plate.
Alternatively, an expandable cage or PMMA can be used.
Every case is unique.
To illustrate the surgical principle of an en bloc resection with posterior release and anterior delivery in the cervical spine, we will use a C5 tumor located in segments 4–9 of the WBB classification. The ipsilateral vertebral artery is involved.
Insert all screws according to the preoperative plan.
If one vertebral artery needs to be sacrificed in part of the tumor resection, instrumentation of the contralateral side should be well planned to avoid a contralateral vertebral artery injury. One strategy to decrease the risk of vertebral artery injury is to use a C2 laminar screw instead of a pedicle screw.
If C1 instrumentation is indicated, lateral mass screws are used.
Consideration is given to using pedicle or laminar screws when doing an occiput to C2 fusion, as the starting point for pars screws often compromises the facet joint.
Lateral mass screws vs pedicle screws (C3–C7)
Fixation can be achieved with either lateral mass screws, pedicle screws, or a combination of the two.
Because lateral mass fixation is generally sufficient and carries less risk, pedicle screw fixation is limited to rare cases where lateral mass fixation would be insufficient or is not possible. A pedicle screw is most often used in C7 if instrumented.