Jeffrey S. Henn

Meningovenous Structures of the Petroclival Region: Clinical Importance for Surgery and Intravascular Surgery

OBJECTIVE The goals of this investigation were to perform a detailed analysis of petroclival microanatomic features, to investigate the course of the abducens nerve in the petroclival region, and to identify potential causes of injury to neurovascular structures when anterior transpetrosal or transvenous endovascular approaches are used to treat pathological lesions in the petroclival region. METHODS Petroclival microanatomic features were studied bilaterally in seven cadaveric head specimens, which were injected with colored silicone before microdissection. Another cadaveric head was used for histological section analyses. RESULTS A lateral or medial location of the abducens nerve dural entrance porus, relative to the midline, was correlated with the course and angulation of the abducens nerve in the petroclival region. The angulation of the abducens nerve was greater and the nerve was closer to the petrous ridge in the lateral type, compared with the medial type. The abducens nerve exhibited three changes in direction, which represented the angulations in the petroclival region, at the dural entrance porus, the petrous apex, and the lateral wall of the internal carotid artery. The abducens nerve was covered by the dural sleeve and the arachnoid membrane, which became attenuated between the second and third angulation points. The abducens nerve was anastomosed with the sympathetic plexus and fixed by connective tissue extensions to the lateral wall of the internal carotid artery and the medial wall of Meckel’s cave at the third angulation point. There were two types of trabeculations inside the sinuses around the petroclival region (tough and delicate). CONCLUSION The petroclival part of the abducens nerve was protected in a dural sleeve accompanied by the arachnoid membrane. Therefore, the risk of abducens nerve injury during petrous apex resection via the anterior transpetrosal approach, with the use of the transvenous route through the inferior petrosal sinus to the cavernous sinus, should be lower than expected. The presence of two anatomic variations in the course of the abducens nerve, in addition to findings regarding nerve angulation and tethering points, may explain the relationships between adjacent structures and the susceptibility to nerve injury with either surgical or endovascular approaches. Venous anatomic variations may account for previously reported cases of subarachnoid hemorrhage with the endovascular approach.

Subtonsillar Approach to the Foramen of Luschka: An Anatomic and Clinical Study

OBJECTIVEConventional approaches to tumors of the foramen of Luschka are limited because the foramen is viewed from either the fourth ventricle laterally (transvermian approach) or the cerebellopontine angle medially (suboccipital approach). The definitive approach is subtonsillar, because the foramen of Luschka is actually the end of the natural cleavage plane between the cerebellar tonsil and the medulla. We describe the microsurgical anatomic features of the foramen of Luschka region and the operative technique for the subtonsillar approach to this region. METHODSIn the anatomic study, five formalin-fixed, silicone-injected, cadaveric heads were used. In the clinical study, the records for five patients treated via the subtonsillar approach were examined; several illustrative cases are presented. RESULTSThe foramen of Luschka is formed by the tela choroidea and the rhomboid lip and exists at the lateral end of the cerebellomedullary fissure, which is a natural cleavage plane between the cerebellar tonsil and the medulla. The subtonsillar approach is performed via a suboccipital craniotomy; the patient is positioned in the lateral decubitus position, with the tumor side down. After the cerebellar tonsil is freed from arachnoid adhesions, it can be retracted rostrodorsally from the medulla, to expose the cerebellomedullary fissure. Clinically, the tela choroidea and rhomboid lip are significantly attenuated by tumor expansion. Therefore, by dissecting in a subtonsillar manner around the tumor, one can reach the foramen of Luschka without traversing any neural tissue. CONCLUSIONThe subtonsillar approach yields a panoramic view to the foramen of Luschka laterally and up to the middle cerebellar peduncle superiorly. This approach minimizes the distance between the tumor and the surgeon, while maximizing neural preservation. We think this is the definitive approach to this difficult region of the posterior fossa.

Pars screw fixation of a hangman's fracture: technical case report.

OBJECTIVE AND IMPORTANCE: Traumatic spondylolisthesis of the axis may be treated by external immobilization or surgical fixation. CLINICAL PRESENTATION: We report the case of a 23-year-old man who sustained an Effendi Type II fracture of the axis, for which halo immobilization did not provide adequate stability. INTERVENTION: The unstable fracture was treated by placing lag screws in the pars interarticularis of C2, which reduced the fracture directly but sacrificed no normal spinal motion. The patient developed a solid fusion, and cervical alignment was normal at his 6-month follow-up examination. CONCLUSION: Although this technique has been reported previously, it is more commonly used in multilevel cervical fusions than for stand-alone repair of C2. Management options, anatomy, and technical considerations for the treatment of traumatic spondylolisthesis are reviewed.

Thoracoscopic Placement of Dual-rod Instrumentation in Thoracic Spinal Trauma

OBJECTIVE AND IMPORTANCE:Traditionally, thoracic fractures that require anterior stabilization are treated through an open thoracotomy approach. Thoracoscopic instrumentation avoids many of the complications associated with an open thoracotomy but is technically challenging. We report the first cases of dual-rod internal fixation systems placed thoracoscopically for thoracic spinal trauma. CLINICAL PRESENTATION:Two male patients sustained midthoracic spinal trauma falling from motorcycles in separate incidents. Both injuries led to unstable spinal columns, but the patients had no neurological deficits and had minimal spinal cord compression. One patient had a complex spiral fracture from T6 to T8; the other had T7 burst and T8 compression fractures. Based on the complex morphological features of the patients’ fractures, anterior internal fixation was the treatment of choice for both. The two available options for an anterior stabilization were open thoracotomy and thoracoscopic instrumentation. Because extensive decompression was unnecessary, a thoracoscopic approach was used. INTERVENTION:A dual-rod internal fixation system (Medtronic Sofamor Danek, Inc., Memphis, TN) was placed with two screws each in the T6 and T9 vertebral bodies of each patient. Thoracoscopy was used for direct visualization of the operative site with fluoroscopic guidance for screw placement. Surgery was completed without complications, and both patients did well afterward. Upright and supine x-rays demonstrated that the constructs were stable at 10 weeks and 6 months, respectively. CONCLUSION:Thoracoscopic instrumentation offers the advantages of a minimally invasive approach but is technically challenging. The characteristics of dual-rod fixation systems (small-profile components and step-wise insertion) provide the best biomechanical profile and facilitate thoracoscopic instrumentation.

Reoperation for acute hemispheric stroke after carotid endarterectomy: is there any value?

OBJECTIVE Because the clinical benefit of urgent investigation and carotid rerepair for acute stroke complicating carotid endarterectomy (CEA) is uncertain, the results of this approach were examined in a large series of patients. METHODS In a consecutive series of 700 CEAs, 24 patients (3.4%) had a postoperative stroke. Thirteen of these 24 patients experienced major hemispheric deficits (hemiplegia with or without aphasia, forced eye deviation, and decreased consciousness) that prompted either immediate surgical reexploration or cerebral angiography with reoperation on the basis of angiogram results; these 13 patients are the subject of this report. Neurological improvement was attributed to carotid reopening when affected muscle strength increased to antigravity power within 6 hours of reoperation. RESULTS Of the 13 patients with severe postoperative deficits, 5 (38%) had the deficits when they awakened, 7 deficits occurred within 12 hours of surgery, and the only intracerebral hemorrhage in this series occurred 8 days after surgery. Five patients underwent urgent reoperation without angiography, and carotid occlusions were found and repaired in two patients. In another patient, the carotid was patent, and an intra-arterial injection of tissue plasminogen activator (20 mg) was given. In the seven patients who underwent cerebral angiography as the first step, two carotid occlusions and one residual stenosis with thrombus were found and repaired on an urgent basis. Surgical reopening of occluded arteries was followed by improvement in two of four patients, and early improvement was noted in one patient with a stenosis correction as well as in the patient who received intraoperative tissue plasminogen activator. Four patients who underwent urgent reoperation did not demonstrate a benefit soon after surgery. Two patients died, two were left with major deficits and five with moderate deficits, and four patients eventually had good recovery at a minimum of 6 months of follow-up. CONCLUSION In this series, approximately one-half of hemispheric strokes complicating CEA had an underlying correctable lesion (occlusion or stenosis), and these patients typically had delayed-onset strokes. Approximately one-half of these patients improved early as a result of reopening, although computed tomography revealed new infarcts in most of them. Urgent carotid repair may benefit a minority of selected patients who have a major stroke after CEA.

A new table-fixed retractor for anterior odontoid screw fixation

The authors describe a unique retraction device adapted for anterior odontoid screw placement. A rigidly fixed tubular retractor system obviates the need for dissecting the longus colli muscles as well as for excessive retraction of the trachea, esophagus, and recurrent laryngeal nerve. The proper trajectory for screw placement can be determined by fine manipulation of the retractor as determined by biplanar fluoroscopy. The retractor is then rigidly fixed in position. The tubular corridor permits the odontoid screw to be placed in the usual fashion.