Benson P. Yang

Thoracic pedicle subtraction osteotomy for fixed sagittal spinal deformity.

Study Design. A retrospective clinical study. Objective. To find the corrective capacity of a thoracic pedicle subtraction osteotomy (PSO), determine if segmental correction is dependent on level, and to compute the impact of thoracic PSO on regional and global spinal balance. Summary of Background Data. PSO is a technique popularized in the lumbar spine primarily for the correction of fixed sagittal imbalance. Despite several studies describing the clinical and radiographic outcome of lumbar PSO, there is no study in literature reporting its application in the thoracic spine. Methods. We retrospectively analyzed patients with fixed thoracic kyphosis who underwent thoracic PSOs for sagittal realignment. Segmental pedicle screw instrumentation and intraoperative neurophysiologic monitoring was used in all patients. Data acquisition was performed by reviewing medical charts and radiographs to determine sagittal correction (segmental/regional/global) and complications. Clinical outcome using the Scoliosis Research Society-22 (SRS-22) instrument was determined by interview. Results. A total of 25 thoracic PSOs were performed (mean: 1.7 PSOs/patient, range: 1–3) in 15 patients (9 M/6 F). The study population had an average age of 56 years (range, 36–81 years) and was followed up after surgery for a mean of 3.5 years (range, 24–75 months). The osteotomies were carried out in the proximal thoracic spine (T2–T4, n = 6), midthoracic spine (T5–T8, n = 12), and distal thoracic spine (T9–T12, n = 7). Mean correction at the PSO for all 25 levels was 16.3° ± 9.6°. Stratified by region of the spine, thoracic PSO correction was as follows: T2–T4 = 10.7° ± 15.8°, T5–T8 = 14.7° ± 4.6°, and T9–T12 = 23.9° ± 4.1°. Mean thoracic kyphosis (T2–T12 Cobb angle) was improved from 75.7° ± 30.9° to 54.3° ± 21.4° resulting in a significant regional sagittal correction of 21.4° ± 13.7° (P < 0.005). Global sagittal balance was improved from 106.1 ± 56.6 to 38.8 ± 37.0 mm yielding a mean correction of 67.3 ± 54.7 mm (P < 0.005). One patient, in whom there was segmental translation during osteotomy closure, had a decline in intraoperative somatosensory-evoked potentials. No patient sustained a temporary or permanent neurologic deficit after surgery. The mean SRS-22 Questionnaire score at final follow-up was 82.4 ± 10.2. Conclusion. Thoracic PSO can be performed safely. Segmental sagittal correction appears to vary based on the region of the thoracic spine the PSO is performed. The distal thoracic segments, which more closely resemble lumbar segments in morphology, rendered the greatest sagittal correction after PSO, approximately 24°. There was no case of neurologic injury associated with thoracic PSO, and clinical outcomes according to the SRS-22 instrument were generally favorable.

Percutaneous lumbar pedicle screw placement aided by computer-assisted fluoroscopy-based navigation: perioperative results of a prospective, comparative, multicenter study.

Study Design. Institutional review board-approved, prospective, multicenter, comparative study. Objective. To assess the accuracy and utility of a computer-assisted fluoroscopic navigation method for percutaneous placement of lumbar pedicle screws compared with conventional fluoroscopic placement. Summary of Background Data. Recent reports indicate that cortical breaches during percutaneous pedicle screw placement can exceed 15%. Computed tomography (CT)- and fluoroscopy-based navigation systems may facilitate increased placement accuracy with reduced radiation exposure and operative times. Methods. Patients were alternately assigned to either the Guidance or Control group. The Guidance group underwent lumbar pedicle screw placement using the oblique visualization technique and computer-assisted fluoroscopic navigation. The Control group underwent lumbar pedicle screw placement per standard percutaneous technique aided by fluoroscopy alone. Baseline demographics, visual analog scale (VAS) pain scores, and American Spinal Injury Association scores were obtained preoperatively and in the immediate postoperative period. Fluoroscopy times and guidewire insertion times were recorded intraoperatively. All postoperative CT scans were reviewed by an independent spine surgeon to grade screw placement accuracy. Results. Forty-two patients (210 screws) were assigned to the Guidance group and 34 patients (152 screws) were assigned to the Control group. Use of Guidance resulted in reduced average fluoroscopy usage per pedicle [6.6 sec (SD = 5.1) vs. 9.6 sec (SD 6.2), P < 0.001] and more expedient placement of guidewires per pedicle [3.65 min (SD = 2.31) vs. 4.43 min (SD = 2.56), P = 0.003]. The Guidance group experienced less than half of the breach rate of the Control group (3.0% vs. 7.2%, P = 0.055) and reduced breach magnitudes. None of the breaches resulted in a corresponding neurological deficit or required revision. All patient-reported outcomes were significantly improved after surgery and there were no significant differences in average postoperative VAS scores between treatment groups. Conclusion. Use of Guidance reduces fluoroscopy and insertion times with increased accuracy compared with conventional fluoroscopic methods of percutaneous pedicle screw insertion.

A Method For Calculating The Exact Angle Required During Pedicle Subtraction Osteotomy For Fixed Sagittal Deformity: Comparison With The Trigonometric Method

OBJECTIVE: Pedicle subtraction osteotomy (PSO) has emerged as a powerful procedure for correcting fixed sagittal deformity. There has only been one attempt to quantify the magnitude of correction needed to restore sagittal balance; the trigonometric method for calculating the desired PSO angle is an approximation. We propose a method for calculating the exact angle required for PSO and explore how this angle differs from that obtained via the trigonometric method in illustrative cases. METHODS: We conducted a mathematical analysis of the spine with application in illustrative cases. The trigonometric method calculates the necessary angular correction at the axial level of the PSO, but along the sacral vertical line. However, the angular measurement should take place at the true axis of rotation, the apex of the PSO. Measurements were taken from full-length standing x-rays, and both methods were explored. RESULTS: The trigonometric method for calculating PSO angle is an exact measurement only if the apex of the PSO site lies on the sacral vertical line. As the apex of the PSO site moves anterior to that line, the trigonometric approximation underestimates the actual angle. As the apex of the PSO moves posterior to that line, the trigonometric approximation overestimates the actual angle. CONCLUSION: The trigonometric method for calculating the PSO angle required for surgical deformity correction is an approximation, but its validity in clinical practice was confirmed by this study. The exact angle is obtained by a method centered on the apex of the PSO site. Although the difference between these angles is small, it is an important conceptual point for spine surgeons. Measurement of the exact angle is easily performed and should replace the trigonometric method for calculating the required PSO angle when standard digital measurement tools are available.

Surgical management of superficial siderosis

BACKGROUND CONTEXT Superficial siderosis is a rare condition resulting from the presence of chronic bleeding into the subarachnoid space usually causing gait instability and deafness. The surgical management of superficial siderosis depends on localizing the source of hemorrhage. PURPOSE The surgical treatment of this rare condition has not been well described in the literature. We present a case illustrating the surgical treatment for superficial siderosis. STUDY DESIGN Case report. PATIENT SAMPLE The authors describe the case report of a 70-year-old gentleman with gait instability and deafness found to have an abnormal communication between the spinal epidural venous plexus and the subarachnoid space. METHODS The source of hemorrhage into the subarachnoid space was identified to be a fistula in the ventral thoracic dural. A costotransversectomy approach was undertaken at the T4-T5 level to expose the fistula. The abnormal communication was patched and sealed. RESULTS The patients symptoms remained stable on follow-up at 15 months with no worsening of his symptoms. CONCLUSIONS Superficial siderosis is a neurologic disorder that arises from chronic hemosiderin deposition into the subarachnoid space. The progressive nature of the disease can be halted if a source of hemorrhage can be found and treated surgically.

Traumatic Retroclival Epidural Hematoma in a Child

Accessible online at: www.karger.com/pne A 5-year-old boy was struck by a motor vehicle while crossing at an intersection. His Glasgow Coma Scale score was 7 in the field and he was noted to have periods of apnea. A rigid cervical collar was applied at the accident scene. Shortly after arrival in the hospital, his Glasgow Coma Scale score deteriorated to 3 and he was intubated for mechanical ventilation. Plain films of the cervical spine confirmed a normal relationship among the bony structures at the occipitoatlantal junction. However, CT scan suggested the presence of an acute hematoma interposed between the clivus and the brain stem (fig. 1). MRI of the cervical spine revealed an extensive retroclival hematoma that extended inferiorly through the craniocervical junction to end posterior to the odontoid process (fig. 2). The dura and tectorial membrane appeared to be stripped off the clivus by the hematoma. Ligamentous instability was assumed and the child was taken to the operating room for halo vest fixation. Within 2 days, the boy improved and was extubated. He was transferred for rehabilitation after 10 days with poor fine motor control and mild right-sided weakness. At a followup visit 4 weeks after the accident, he was neurologically intact and the retroclival hematoma was no longer apparent on CT scan. Several structures comprise the ligamentous anatomy of the craniocervical junction. The odontoid process is held against the anterior arch of the atlas by the transverse part of the cruciform ligament. The cruciform ligament Fig. 1. CT scan of the head demonstrates a prominent hyperdense mass posterior to the clivus.

Massive cerebral arterial air embolism following arterial catheterization.

Microscopic cerebral arterial air embolism (CAAE) has been described in many patients undergoing cardiac surgery as well as other invasive diagnostic and therapeutic procedures. However, massive CAAE is rare. We report a 42-year-old woman who initially presented with thalamic and basal ganglia hemorrhages. Shortly after a radial arterial catheter was inserted, the patient suffered a generalized seizure and CT demonstrated intra-arterial air in bilateral cerebral hemispheres.

A novel mathematical model of the sagittal spine.

Study Design. Development of a mathematical model with application to a cohort of healthy volunteers. Objectives. To derive a smooth mathematical function representing the sagittal spinal curve from individual vertebral elements. To generate normative data using this model. Summary of Background Data. Current concepts of spinal sagittal balance center on the C7 plumb line. While elegant in its ease of use, this method oversimplifies the true complexity of the spine. If the spinal curve could be expressed as a smooth mathematical function, the ability to analyze sagittal balance would be greatly enhanced. Methods. Lateral full-length radiographs of 18 normal volunteers were examined. The posterosuperior aspect of each vertebral body was chosen as a representative point for the spinal sagittal curve. A cubic spline function was derived from these points. From this function, the area under the curve (AUC) and average sagittal positions of the thoracic, lumbar, and thoracolumbar segments were calculated. Results. Assuming an average vertebral column height of 60 cm with anterior being positive, the average position of the posterosuperior aspect of C7 relative to S1 was −2.8 cm (±3.0). The average thoracolumbar AUC was −161 cm2 (±83). The average lumbar and thoracic AUCs were 0 cm2 (±17) and −157 cm2 (±68), respectively. The average sagittal position over the thoracolumbar curve was −3.3 cm (±1.7). The average sagittal positions of the lumbar and thoracic subcurves were 0.1 cm (±1.1) and −5.1 cm (±2.2), respectively. Intraobserver and interobserver reliabilities were excellent. Conclusions. A mathematical model of the sagittal spine that retains the spines segmental nuances was derived using cubic spline interpolation. The average sagittal position of the thoracolumbar spine, a calculation based on the AUC, is a less variable measure of sagittal balance than the C7 plumb line. The model and normative data generated from it will allow more insightful investigations of spinal deformity and more quantitative evaluations of corrective outcomes.

Remote Cerebellar Hemorrhage after Craniotomy

A 15-year-old boy with von Willebrand’s disease, seizures and prior resection of pleomorphic xanthoastrocytoma had radiographic regrowth of tumor. Following factor VIII replacement, he underwent repeat craniotomy and resection of the left temporal pleomorphic xanthoastrocytoma. In the postoperative period, he had slurred speech and developed marked bradycardia requiring administration of atropine. CT scan of the head showed cerebellar hemorrhage remote from the site of craniotomy ( fi g. 1 ). Prothrombin and activated partial thromboplastin times were normal; no additional factor replacement was indicated. The patient was treated with mannitol and decadron with signifi cant improvement in cerebellar edema and no further episodes of extreme bradycardia. Remote cerebellar hemorrhage following supratentorial craniotomy probably results from venous infarction secondary to disruption of the deep draining veins of the cerebellum [1, 2] . Most cases described to date are in adults undergoing neurosurgical procedures with penetration into the cerebrospinal fl uid cisterns or the ventricular system [3] . Among several published series, there are only isolated reports of remote cerebellar hemorrhage in children [2, 3] . The relative fullness of the pediatric brain may prove protective against cerebellar drooping,

Images in Neuro-Oncology. Selective Invasion of the Anterior Commissure in Glioblastoma Multiforme

3 weeks of increasingly frequent episodes of lightheadedness and confusion. On physical exam, she demonstrated deficits in attention and short-term memory. Testing of her language, motor, and sensory faculties did not disclose any focality. MRI of the brain showed a 16mm · 23mm mass centered in the anterior right temporal lobe. Peculiarly, there was an enhancing track that originated at the mass, spanned the anterior commissure exclusively, and extended into the contralateral medial temporal lobe (Fig. 1). Axial contrast-enhanced T1-weighted MR images show the main tumor mass in the anterior right temporal lobe (A), at the level of the anterior commissure (B), and across into the contralateral anterior temporal lobe (C). Sagittal midline contrast-enhanced T1-weighted MR image demonstrates isolated enhancement within the anterior commissure (D). Antiepileptic therapy was commenced for suspected complex partial seizures. Stereotactic biopsy of the right temporal mass identified the lesion to be glioblastoma multiforme. The patient underwent radiation therapy and concomitant chemotherapy. Spread of malignant cells across the midline via the corpus callosum is a well-described, prognostically unfavorable phenomenon that has been dubbed ‘butterfly glioma’. The remarkable aspect of this case is the contralateral invasion of glioblastoma multiforme by way of the anterior commissure, with no radiographic evidence of corpus callosal involvement. The anterior commissure is a small white-matter tract that links the right and left olfactory areas, including cortical regions in the anterior temporal lobes. To date, the functional significance of this phylogenetically primitive structure remains elusive. This case illustrates the specific fibertracking invasivity of certain malignant gliomas. While the corpus callosum comprises the interhemispheric conduit for the frontal, parietal, occipital, and posterior temporal lobes, the anterior commissure interconnects the anterior temporal lobes and must be closely inspected for neoplastic infiltration for tumors in this vicinity. Bihemispheric tumor extension has clinical implications with regard to prognosis and management strategies.