Minimally Invasive Microsurgical Resection of Spinal Intradural Extramedullary Lesions

53 Minimally Invasive Microsurgical Resection of Spinal Intradural Extramedullary Lesions

Dragos Catana, Mohammed Aref, Jetan Badhiwala, Brian Vinh, Saleh Almenawer, and Kesava (Kesh) Reddy

53.1 Minimally Invasive Resection of T9–T10 Intradural Extramedullary Spinal Tumor

53.1.1 Clinical Findings

• A 24-year-old male presented with left-sided abdominal pain and paresthesias.

• The pain began insidiously but progressively worsened over several months. It followed a bandlike distribution at the level of the umbilicus.

• There were no signs or symptoms of myelopathy, and there was no history of urinary or fecal incontinence.

• MRI of the spine showed a left-sided intradural, extramedullary lesion at the T9–T10 level causing mass effect on the spinal cord and near-complete obliteration of the CSF spaces (Fig. 53.1). The lesion avidly enhanced with gadolinium administration (Fig. 53.2). There was no obvious dural tail.

• The differential diagnosis included schwannoma, neurofibroma, and meningioma (Video 53.1).

53.1.2 Preoperative Plan

• The patient was selected to undergo minimally invasive microsurgical resection of the T9–T10 intradural spinal lesion using the METRx (Minimal Exposure Tubular Retractor) tubular retractor system (Medtronic, Memphis, TN), with possible sacrifice of the left T9 nerve root.

• Lower limb and sphincteric somatosensory evoked potentials (SSEP) and motor evoked potentials (MEP) were monitored throughout the operation.

• The patient was positioned prone on a Jackson table. The upper limbs were flexed at the elbow, with the forearms oriented cranially. Pressure points were carefully padded.

53.1.3 Surgical Procedure

• The T9 lamina was localized using lateral fluoroscopy and counting from the sacrum up to the lower thoracic region.

• Under fluoroscopic guidance, a 2-mm K-wire was advanced through a small skin incision over the left T9 lamina, starting 2 cm off midline and aiming medially. The smallest size tubular retractor was guided over the K-wire, and the paraspinal muscles were dissected off the lamina in the subperiosteal plane in a mediolateral fashion. The K-wire was removed, and tubular retractors were sequentially placed over each other to dilate and distract the soft tissues. The mediolateral blunt dissection was repeated at each step, along with fluoroscopic confirmation of placement (Fig. 53.3).

• The depth of the surgical corridor was measured using the markings on the dilators, and an appropriate length of final tubular METRx Quadrant retractor was chosen.

• The flexible arm attached to the table rail was used to secure the final tubular retractor in place and to allow for appropriate angulation.

Fig. 53.1 Axial T1-weighted MRI with gadolinium contrast demonstrating an intradural left-eccentric enhancing lesion with associated mass effect on the spinal cord.

Fig. 53.2 Sagittal T1-weighted MRI with gadolinium contrast demonstrating an enhancing intradural lesion at the T9–T10 level.

Fig. 53.3 Fluoroscopic image demonstrating the insertion of the final tubular retractor over the T9 lamina.

53.1.4 Microscopic Findings

• The microscope was brought into the surgical field and appropriately positioned over the surgical corridor. Paraspinal muscles not displaced with the sequential dilation technique were dissected with monopolar electrocautery to expose the bony lamina. The lamina was thinned out with a high-speed pneumatic drill; the thinned bone was then resected with Kerrison rongeurs along the epidural plane. The exposure was extended by undercutting the upper and lower laminae. Bone wax was applied for hemostasis.

• A sharp hook and a bayoneted blade were used to perform the initial durotomy. (Sutures may be used at the dural edges for epidural hemostasis to prevent blood from entering the intradural space. Alternatively, the dural edge may be lifted up using a micro hook.)

• A nerve stimulator was used to identify neuronal tissue. The tumor margins were identified in a systematic fashion. The left T9 nerve root could not be dissected off the tumor mass. Therefore, a decision was made to sacrifice the root.

• The tumor capsule was cauterized with low-setting bipolar electrocautery and was sharply dissected. The mass was debulked in a piecemeal fashion using standard bimanual technique. The resulting mobile capsule was dissected from surrounding structures using standard microsurgical techniques and hemostasis was achieved.

• The dural edges were re-approximated with 7–0 Prolene suture, starting just above the apex. An angled bayoneted microdriver was used in conjunction with microforceps. The assistant provided gentle countertraction using a bayoneted suture pusher during the repair. A Valsalva maneuver confirmed watertight closure, and a fibrin sealant (e.g., Tisseel) was used to augment the repair.

• The tubular retractor was gently removed and soft tissue hemostasis was achieved with bipolar electrocautery. The fascia was re-approximated with 2–0 Vicryl interrupted sutures. Finally, the skin was re-approximated with a 3–0 Monocryl running subcuticular suture.

• The final incision was ~ 25 mm long.

53.1.5 Results

• The patient was discharged home on the following day (postoperative day 1). On follow-up, the patient’s pain, numbness, and paresthesias had improved significantly. Postoperative MRI showed complete tumor resection.

53.1.6 Tips

• Careful study of preoperative MRI and fluoroscopic images for exact level identification is essential.

• The shortest possible final tubular retractor length provides more degrees of freedom for microinstruments when working in the tubular corridor.

• Lateral bone removal is limited by the facet to avoid destabilizing the spine.

• Use of the flexible arm is essential to angle the tube superomedially, superolaterally, inferomedially, and inferolaterally to improve visualization throughout the procedure.

• It is important to use fluoroscopic guidance when inserting the K-wire and subsequent tubes to avoid entering the interlaminar space and causing secondary neuronal injury.

53.2 Minimally Invasive Resection of L3 Intradural Spinal Tumor

53.2.1 Clinical Findings

• A 59-year-old male with a history of resection of an L3 intra-dural dermoid tumor 5 years earlier presented with a history of worsening back pain, along with difficulty ambulating and paresthesias in both legs (but more intense on the right side), and recent urinary incontinence.

• MRI of the lumbar spine showed recurrence of the intradural lesion at L3 (Fig. 53.4, Fig. 53.5).