- Prone: The patient is placed prone, lying on rolls so that the abdomen is not compressed.
- Patient flexed: The patient is flexed so that the surgical field is elevated above the rest of the CSF column. The head should be dependent to the surgical field.
- Identification of the spinal levels for laminotomy or laminectomy: The first step of the operation is identification of the spinal levels requiring a laminotomy or laminectomy. This is straightforward for tumors in the cervical region, but as the tumor’s location moves caudally, x-ray will need to be considered unless markers were placed during preoperative imaging.
- Midline incision: A midline incision is made through the fascia down to the bone of the spinous processes of the levels to be exposed after incising the skin and subcutaneous fat.
- Cartilaginous cap: The cartilaginous cap at each spinous process can then be flicked off the bone. This will expose the subperiosteal plane of the spinous process. The muscle can then be pulled away from the bone. The ligamentous insertions along the spinous process and lamina are cut where they attach to the bone to allow the muscle to be mobilized to the lateral margins of the facet joints.
- Removal of the spinous processes and lamina: A laminectomy can be performed, but an alternative is to perform a laminotomy using a craniotome. The interlaminar space just caudal to the caudal-most lamina to be removed is enlarged using ronguers, and a power craniotome with a footed guard is used to cut the lamina just medial to the facet joints on both sides.
- Retraction of the laminar roof: “Trap-dooring” of the laminar roof is done by leaving intact the ligamentum flavum that joins the rostral most level of the laminotomy to the lamina just above and swinging the cadual end of the freed lamina rostrally to expose the soinal canal.
- Ultrasound: The adequacy of the exposure can be checked with the ultrasound (19).
- Dura opened: The dura is opened at midline over the tumor. It does not need to be opened over capping cysts unless they contain lump disease.
- Ultrasound: Ultrasound can then be used to locate cysts and main body of the tumor.
- Dorsal midline inspection: The dorsal midline of the spinal cord is inspected for a line of pial vessels disappearing into the spinal cord using the surgical microscope. This marks the median raphe.
Intervention – Tumor Resection
- Retraction: Retraction can be accomplished with specially designed plated bayonets. This avoids distortion of the cord by pial retraction sutures.
- Biopsies: Biopsies can be obtained before the resection starts. This allows for timely information from a frozen section and insures that specimens will be available for permanent study.
- Ultrasound: Ultrasound can be used to check for residual lumps of tumor.
- Control of bleeders: Hemostatic agents and tamponade are used to control bleeders. Cautery is not used at the margins of the tumor unless all else fails.
- Astrocytomas, gangliogliomas and other nonependymal gliomas: These tumors have in common infiltrating edges and no plane surrounding them. Consequently, their resection usually starts with a central debulking. It has been shown that for these tumors an 80% resection yields the same 5-year event-free survival rate as a 100% resection (10).
- Ependymomas: Ependymomas typically have a plane allowing for their separation from the cord’s parenchyma. An initial central debulking can be helpful if the tumor is large. It is then freed at the pole and gently lifted out of the cavity as it is separated from the cord laterally. As it is lifted, small vessels off the anterior spinal artery are looked for, cauterized, and cut at the point where they enter the tumor. Areas adherent to the cord are left.
- Hemangioblastomas: Hemangioblastomas frequently reach the pia of the dorsal surface, making the initial exposure straightforward. Pial attachments are cut, and the exposed surface of the tumor is cauterized to shrink it away from the cord (43). In a stepwise manner the surface is shrunk, bridging vessels are cut as they enter the tumor, and the cord is gently retracted away from the tumor to expose more of its surface, which is then cauterized. This can interfere with the perfusion of the surrounding cord since it shares blood supply with the tumor. Monitoring will warn of this circumstance with potentials suddenly dropping. Further work on the tumor should await return of the potentials.
- Cavernous malformations: Cavernous malformations are best resected after a hemorrhage, before the hematoma is resorbed (25). In this setting the hematoma is removed to expose the cavernoma, which is then shrunk by cautery and removed.
- Dura: The dura usually can be closed primarily. A duraplasty usually is not needed when a radical resection has been accomplished.
- Laminoplasty: If a laminotomy was performed at opening, a laminoplasty is performed (1). Metal miniplates and screws, although quick and convenient, can create artifact on MRI, making it difficult to following the patient for tumor recurrence. Resorbable plates and pins or suture is preferred.
- Drain: An epidural drain or drain dorsal to the repositioned lamina can be placed to prevent the muscle closure from being challenged by CSF. It should be tunneled out through a tract separate from the wound closure line.
- Muscle and fascia closed: Monofilament stitch, either dissolving or permanent, will not stretch and should be considered to maintain closure tightness. The fascia closure line is the barrier to CSF, and care should be taken that this layer is tight.
- Second drain: An additional drain can be place dorsal to the fascia as a “scout” for CSF leakage.
- Closure completion: The rest of the closure is by personal preference.