J. Diaz Day

Vagus Nerve Stimulation Activates Central Nervous System Structures in Epileptic Patients During PET H215O Blood Flow Imaging

OBJECTIVE To determine the central areas of activation by vagal nerve stimulation (VNS) in epilepsy. VNS is a promising neurosurgical method for treating patients with partial and secondary generalized epilepsy. The anti-epileptic mechanism of action from VNS is not well understood. METHODS We performed H2(15)O PET blood flow functional imaging on three patients with epilepsy in a vagal nerve stimulation study (E04 Protocol with Cyberonics). The three patients included two that had previous epilepsy surgery but continued to have frequent seizures. Seizure onset was frontal in two patients and bitemporal in the third patient. Twelve PET scans per subject were acquired every 10 minutes with a Siemens 953/A scanner. In 6 stimulus scans, VNS was activated for 60 seconds (2 mA, 30 Hz) commensurate with isotope injection. In 6 control scans no VNS was administered. No clinical seizures were present during any scan. Three way ANOVA with linear contrasts subject, task, repetition) of coregistered images identified significant treatment effects. RESULTS The difference between PET with VNS and without revealed that left VNS activated right thalamus (P < 0.0006), right posterior temporal cortex (P < 0.0003), left putamen (P < 0.0002), and left inferior cerebellum (P < 0.0009). CONCLUSIONS VNS causes activation of several central areas including contralateral thalamus. Localization to the thalamus suggests a possible mechanism to explain the therapeutic benefit, consistent with the role of the thalamus as a generator and modulator of cerebral activity.

Endoscopically assisted microneurosurgery.

SummaryTechnological developments in neuroendoscopy are leading to an expansion of applications into the realm of microneurosurgical procedures. The new dimension that using an endoscope provides requires insight into different neuroanatomical aspects and a new kind of strategy in planning a microneurosurgical procedure. To gain some new insights into these exciting aspects of neurosurgery we have explored the sellar, parasellar, and posterior fossa regions in 50 fresh anatomical specimens and used various types of endoscopes to observe the surgically relevant neurotopographical details. We then utilized this experience in 33 clinical cases during microsurgical approaches for various lesions (posterior fossa tumors — 12 cases, sellar and parasellar tumors — 8 cases, transsphenoidal procedures for pituitary adenoma — 7 cases, transventricular procedures — 6 cases). In the laboratory we found that familiar neuroanatomical structures are seen in a completely different aspect from what we are accustomed. Orientation is at times difficult, which requires rehearsal and special handling of the endoscope for complex clinical procedures. We found that certain structures that are hardly noticed in routine anatomical views become very important when utilizing the endoscope (i.e., different arachnoid membranes and trabeculae). Importantly, the dimensions of a microsurgical approach can be greatly enlarged with the endoscope, making it possible to look behind structures and “around corners”. We present our findings with respect to important anatomical details relevant to utilizing the endoscope as an adjunct to microneurosurgical procedures and our clinical data. We have concluded that the neuroendoscope can be a safe and helpful adjunct in many microneurosurgical procedures.

Working area and angle of attack in three cranial base approaches

OBJECTIVE This study was designed to quantify the operative exposure obtained in the pterional, orbitozygomatic, and modified orbitozygomatic with maxillary extension surgical approaches. METHODS The pterional and orbitozygomatic approaches and a variation of the orbitozygomatic osteotomy that included an extra centimeter of bone resection in the inferior direction (“maxillary extension”) were performed on cadaveric heads. For each surgical exposure, the working area was determined by using triangles defined with anatomic points. The “angle of attack” of the approaches for the same target point was determined with the use of a robotic microscope. RESULTS The maximum allowable angle of attack was significantly greater with the orbitozygomatic approach (37.2 ± 4.7 degrees) than that with the pterional approach (27.1 ± 4.3 degrees) (P < 0.001). The angle of attack with the maxillary extension (42.0 ± 4.9 degrees) was significantly greater than that with the orbitozygomatic approach (P < 0.001). The working areas were 281, 343, and 371 mm2 for the pterional, orbitozygomatic, and maxillary extension approaches, respectively. The orbitozygomatic approach with maxillary extension had a significantly larger working area than the pterional approach (P = 0.011). CONCLUSION Increments in bony removal open a wider angle in which to work more than they increase the actual amount of working area. Increasing the amount of bone removed by using an orbitozygomatic approach instead of a pterional approach converts a narrow space into a wide portal, allowing surgeons to work closer to the surgical target while decreasing the need for brain retraction. Extending the orbitozygomatic approach into the maxillary region also improves the exposure area and angle, but less significantly.

The retrosigmoid approach to acoustic neurinomas: technical, strategic, and future concepts

SummaryThe retrosigmoid approach continues to be the most widely employed strategy for the surgical resection of acoustic neuromas. The results with respect to facial nerve function are uniformly reported to be quite high. The great emphasis currently is upon improving results with regard to the conservation of useful hearing. This paper focuses on the anatomical and strategic surgical factors that we currently consider to be important to maximizing our current results. The future aspects of this trend toward improved success in conserving hearing in these patients is also discussed.

Pigmented villonodular synovitis of the temporomandibular joint: a rare tumor of the temporal skull base

Musculoskeletal tumors are not usually encountered at the skull base. Benign lesions such as cholesterol granuloma, cholesteatoma, fibrous dysplasia, and Paget disease are common examples of such tumors arising from the bone of the cranial base. The authors report a case involving an adult male patient with the rare finding of pigmented villonodular synovitis of the temporomandibular joint. This case is reported as an example of another lesion to consider in the differential diagnosis. Due to the complexity of the anatomy at the cranial base, radical resection as recommended for the usual sites of occurrence in major joints is problematic. Because of the reported high recurrence rates at other sites, as radical excision as possible with vigilance for recurrence is recommended.