Stephen M. Pirris

Corridor surgery: the current paradigm for skull base surgery.

IntroductionClival chordomas are rare tumors, especially in the pediatric population. In this report, we present the case of a 3-year-old boy who was found to have a large posterior pharyngeal, clival, and posterior fossa tumor detected on a CT scan after a closed head injury.DiscussionFurther questioning revealed a history of ataxia and dysphagia. Imaging confirmed severe extrinsic brain stem compression. The tumor was resected in multiple stages utilizing a minimally invasive endoscopic endonasal technique along with open transfacetal, transcondylar approach through the carotid–vertebral window. The child suffered no permanent complications as a result of our treatment and his dysphagia significantly improved. Although a complete resection was not feasible due to vascular encasement by the tumor, extensive decompression was obtained with minimal morbidity.ConclusionWe present this case to illustrate a new paradigm of skull base surgical approaches for large clival lesions in pediatric patients that allows aggressive resection with minimal morbidity.

Operating room radiation exposure in cone beam computed tomography-based, image-guided spinal surgery: clinical article.

OBJECT Surgeon and operating room (OR) staff radiation exposure during spinal surgery is a concern, especially with the increasing use of multiplanar fluoroscopy in minimally invasive spinal surgery procedures. Cone beam computed tomography (cbCT)-based, 3D image guidance does not involve the use of active fluoroscopy during instrumentation placement and therefore decreases radiation exposure for the surgeon and OR staff during spinal fusion procedures. However, the radiation scatter of a cbCT device can be similar to that of a standard 64-slice CT scanner and thus could expose the surgeon and OR staff to radiation during image acquisition. The purpose of the present study was to measure radiation exposure at several unshielded locations in the OR when using cbCT in conjunction with 3D image-guided spinal surgery in 25 spinal surgery cases. METHODS Five unshielded badge dosimeters were placed at set locations in the OR during 25 spinal surgery cases in which cbCT-based, 3D image guidance was used. The cbCT device (O-ARM) was used in conjunction with the Stealth S7 image-guided platform. The radiology department analyzed the badge dosimeters after completion of the last case. RESULTS Fifty high-definition O-ARM spins were performed in 25 patients for spinal registration and to check instrumentation placement. Image-guided placement of 124 screws from C-2 to the ileum was accomplished without complication. Badge dosimetry analysis revealed minimal radiation exposure for the badges 6 feet from the gantry in the area of the anesthesiology equipment, as well as for the badges located 10-13 feet from the gantry on each side of the room (mean 0.7-3.6 mrem/spin). The greatest radiation exposure occurred on the badge attached to the OR table within the gantry (mean 176.9 mrem/spin), as well as on the control panel adjacent to the gantry (mean 128.0 mrem/spin). CONCLUSIONS Radiation scatter from the O-ARM was minimal at various distances outside of and not adjacent to the gantry. Although the average radiation exposure at these locations was low, an earlier study, undertaken in a similar fashion, revealed no radiation exposure when the surgeon stood behind a lead shield. This simple precaution can eliminate the small amount of radiation exposure to OR staff in cases in which the O-ARM is used.

Gamma Knife Radiosurgery for Benign Tumors With Symptoms From Brainstem Compression

PURPOSE This study evaluated the role of radiosurgery in the management of symptomatic patients with brainstem compression from benign basal tumors. METHODS AND MATERIALS Over a 17-year, period 246 patients (202 vestibular schwannomas and 44 meningiomas) with brainstem compression from benign skull-base tumors were managed with Gamma Knife radiosurgery. Median tumor volumes were 3.9 cm(3) (range, 0.8-39.0 mL) and 6.6 mL (range, 1.6-25.1 mL) for vestibular schwannomas and meningiomas, respectively. For both tumors, a median marginal dose of 13 Gy was prescribed. Median follow-up of patients was 65 months for vestibular schwannomas and 60 months for meningiomas. Patients were categorized into four groups on the basis of the tumor-brainstem relationship on neuroimaging. RESULTS Preservation of function was stratified according to grade of brainstem compression. We analyzed the effect of radiosurgery on symptoms of brainstem compression. The tumor control rate was 100 % for meningioma and 97% for vestibular schwannomas (although 5% required an additional procedure such as a ventriculoperitoneal shunt). In patients with vestibular schwannoma, serviceable hearing was preserved in 72.0%. Balance improved in 31.9%, remained unchanged in 56.5%, and deteriorated in 11.6% of patients who had imbalance at presentation. Balance improved significantly in patients who had less tumor compression (p = 0.0357) after radiosurgery. Symptoms improved in 43.2% of patients with meningioma. CONCLUSION Radiosurgery is a minimally invasive option for patients with benign basal tumors that indent or distort the brainstem. A high tumor growth control rate and satisfactory rate of neurological preservation and symptom control can be obtained with radiosurgery.

Improving the Informed Consent Process for Surgery

OBJECTIVE:Obtaining and documenting informed consent is of vital importance to physicians. We developed a procedure-based consent form that facilitates patient discussion and validated this process by surveying the patient regarding elements of the consent process, using an independent evaluator. METHODS:One hundred and twenty consecutive outpatients were evaluated before different neurosurgery procedures. The consent form listed specific diagnoses, procedures, alternatives (eight listed), and risks (22 listed), and each point discussed was checked off by the surgeon. Between 10 and 20 minutes later, each element was questioned by one lay-member of the office staff. A group of patients not at risk for cognitive decline were resurveyed months later. RESULTS:One hundred and twenty (100%) of 120 of patients answered correctly regarding their diagnosis and the planned procedure. Four hundred and twenty-eight alternative treatments were discussed, and 420 (98.1%) of the 428 were recalled correctly. Of 1207 risks that were discussed, 1176 (97.4%) were recalled correctly. When a subset of the patients were reevaluated at a mean of 4.5 months later, all 20 patients correctly recalled their procedure and diagnosis. Of 79 alternatives discussed with patients before surgery, 73 (92.4%) were subsequently recalled. Of 217 risks discussed before surgery, 199 (91.7%) were recalled. Although the immediate or delayed recall rates were high (>90%), there was a reduction in the recall rate over time (alternatives, P = .007; risks, P < 0.0001). CONCLUSION:A consent process designed for an individual surgeon’s practice was validated and showed high rates of patient recall in the postprocedural period. We think that this method to obtain and document informed consent should be considered for use by physicians.

A retrospective study of iliac crest bone grafting techniques with allograft reconstruction: do patients even know which iliac crest was harvested? Clinical article.

OBJECT Considerable biological research has been performed to aid bone healing in conjunction with lumbar fusion surgery. Iliac crest autograft is often considered the gold standard because it has the vital properties of being osteoconductive, osteoinductive, and osteogenic. However, graft site pain has been widely reported as the most common donor site morbidity. Autograft site pain has led many companies to develop an abundance of bone graft extenders, which have limited proof of efficacy. During the surgical consent process, many patients ask surgeons to avoid harvesting autograft because of the reported pain complications. The authors sought to study postoperative graft site pain by simply asking patients whether they knew which iliac crest was grafted when a single skin incision was made for the fusion operation. METHODS Twenty-five patients underwent iliac crest autografting with allograft reconstruction during instrumented lumbar fusion surgery. In all patients the autograft was harvested through the same skin incision but with a separate fascial incision. At various points postoperatively, the patients were asked if they could tell which iliac crest had been harvested, and if so, how much pain did it cause (10-point Numeric Rating Scale). RESULTS Most patients (64%) could not correctly determine which iliac crest had been harvested. Of the 9 patients who correctly identified the side of the autograft, 7 were only able to guess. The 2 patients who confidently identified the side of grafting had no pain at rest and mild pain with activity. One patient who incorrectly guessed the side of autografting did have significant sacroiliac joint degenerative pain bilaterally. CONCLUSIONS Results of this study indicate the inability of patients to clearly define their graft site after iliac crest autograft harvest with allograft reconstruction of the bony defect unless they have a separate skin incision. This simple, easily reproducible pilot study can be expanded into a larger, multiinstitutional investigation to provide more definitive answers regarding the ideal, safe, and cost-effective bone graft material to be used in spinal fusions.

Load sharing and stabilization effects of anterior cervical devices.

Study Design Biomechanical human cadaveric cervical flexibility testing with direct load-sharing measurement. Objective To determine if the flexibility and load-sharing characteristics of a functional spinal unit were affected by anterior treatments for cervical pathologies. Summary of Background Data With advancements in polymers, anterior cervical plates have used thermoplastics including recent designs from biodegradable polylactide acids. However, the difference in material properties between metal and polymer can be significant. Methods Thirteen cervical spine specimens were subjected to 5 treatments at C4-C5. Each treatment for each specimen was subjected to multidirectional flexibility testing. The third cycle was used for treatment comparisons. Results With the integrated load cell spacer, the mean range of motion for the functional spinal unit measured on average 104%±40% normalized to the intact control. The mean biodegradable and titanium plate were 55%±31% and 40%±36%, respectively. Both plates exhibited statistically lower mean range of motions (P=0.001 and P<0.001) compared with spacers. The load transmitted through the interbody space was 54%±20%, 43%±20%, and 33%±15% on average for the spacer, biodegradable, and titanium plate constructs, respectively. No statistically significant difference was detected between the biodegradable plate and spacer (P=0.214). Conclusions From this research, a biodegradable plate offers immediate postoperative stability significantly different than spacer alone treatments but with graft load sharing that is statistically no different. Thus, the intrinsic lower native material modulus of elasticity of biodegradable polymers has biomechanical implications. However, clinical evidence, particularly for long-term outcomes, will be required in understanding the efficacy of biodegradable polymers.

Compression fracture in the middle of a chronic instrumented fusion that developed into pseudarthrosis after balloon kyphoplasty.

There are only 2 documented cases of vertebral compression fractures occurring within a solid lumbar fusion mass: one within the fusion mass after hardware removal and the other within the levels of the existing instrumentation 1 year postoperatively. The authors report a case of fracture occurring in a chronic (> 30 years) solid instrumented fusion mass in a patient who underwent kyphoplasty. The pain did not improve after the kyphoplasty procedure, and the patient developed a posterior cleft in the fusion mass postoperatively. The patient, a 46-year-old woman, had undergone a T4-L4 instrumented fusion with placement of a Harrington rod when she was 12 years old. Adjacent-segment breakdown developed, and her fusion was extended to the pelvis, with pedicle screws placed up to L-3 to capture the existing fusion mass. Almost 2 years after fusion extension, she fell down the stairs and suffered an L-2 compression fracture, which is when kyphoplasty was performed without pain relief, and she then developed a cleft in the posterior fusion mass that was previously intact. She refused further surgical options. This case report is meant to alert surgeons of this possibility and allow them to consider the rare occurrence of fracture within the fusion mass when planning extension of chronic spinal fusions.

Biomechanical Cyclical Loading on Cadaveric Cervical Spines in a Corpectomy Model

Approved posterior cervical spinal fixation systems have been submitted to the U.S. Food and Drug Administration with results from standardized test protocols from the ASTM. The bench top mechanical studies are designed to minimize biologic and laboratory variability. However, for implant tests such as ASTM F1717 to be more clinically relevant, anatomical and physiologic considerations must be understood. The specific aim of this study was to determine if a human cadaveric cervical spine with a corpectomy and posterior fixation was effective in maintaining stability prior to and following cyclical loading. Six fresh frozen cadaveric human cervical specimens were harvested and prepared. A C5 corpectomy was performed. Posterior cervical instrumentation was implanted from C3 and C7 spanning across the C4–C6 defect. Each specimen followed an established pure moment test protocol to characterize the instrumented spine in flexion extension, lateral bending, and axial torsion at ±2.5 N m and axial compressive loading to 150 N. Subsequently, each specimen was subjected to 10 000 flexion extension cycles. Following the cyclical loading, each specimen was characterized a second time via the same test protocol. Statistical analyses were then performed on the third cycle data between the two pure moment tests. The mean FE bending range of motion (ROM) was 18.0° ± 10.7° prior to the 10 000 cyclical bending protocol. Following cyclical loading, the mean ROM measured 22.0° ± 19.9°. In axial compression, the mean ROM was 4.1 mm ± 1.9 mm prior to cycling and 4.2 mm ± 1.4 mm post-cycling. A statistically significant difference was detected only in the axial torsion mode of loading (p = 0.030). Although the ASTM standard provides consistent test methodologies, biomechanical cadaveric testing remains an important step in the validation of all spinal instrumentation. The pure moment biomechanical cadaveric test protocol for the same construct was capable of detecting significant changes pre- and post-flexion extension fatigue cycling only in the axial torsion mode of loading.