Cavernous Sinus (eBook)

Preface 5
Contents 6
List of contributors 8
Chapter 1. Anatomy of the cavernous sinus 10
The middle cranial base and cavernous sinus 11
The transition between the cavernous sinus and orbit 34
Venous anatomy of the lateral sellar compartment 41
Central skull base anatomy as seen through the endoscope 58
Chapter 2. Surgical approaches to the central skull base 63
Evolution from the classical pterional to the contemporary approach to the central skull base 64
Extended endoscopic endonasal transsphenoidal approach to supra- parasellar tumors 78
Chapter 3. Neuromonitoring in central skull base surgery 90
Neuromonitoring in central skull base surgery 91
Chapter 4. Surgical treatment of vascular lesions in the central skull base 107
Surgical treatment of large/giant carotid–ophthalmic and other intradural internal carotid artery aneurysms 108
Surgical treatment of basilar apex aneurysms – surgical approaches and techniques 117
Aneurysms of the intracavernous ICA: current treatment 127
Chapter 5. Surgical treatment of tumorous lesions in the central skull base 137
Cavernous sinus meningiomas 138
Surgery of cavernous sinus meningiomas: advantages and disadvantages 152
Trigeminal neurinomas: surgical considerations 162
Bypasses for cavernous sinus tumors: history, techniques, and current status 177
Giant pituitary tumors: surgical treatment of 265 cases 188
Chapter 6. Radiosurgery in treatment of central skull base tumors 202
The role of Gamma Knife surgery in the management of non- meningeal tumors of the cavernous sinus 203
Subject index 218

Neuromonitoring in central skull base surgery (p. 89-90)

W. Eisner, T. Fiegele

Neurosurgical Department, Medical University Innsbruck, Innsbruck, Austria

Introduction

Intraoperative electrophysiological monitoring has become increasingly common in neurosurgery. Such methods prevent postoperative deficits by warning the surgeon of the imminent injury to neuronal structures. Monitoring sensorimotor, cognitive (language and short term memory), and cranial nerve function (except hearing) during cerebellopontine angle operations has been well established.

Yet monitoring the function of nuclei and fiber tracts in the floor of the fourth ventricle and cranial nerves traversing the central skull base is more demanding – ranging from recording site challenges (e.g., within the orbit) to interpreting the more subtle electrophysiological findings. Preserving motor cranial nerve function has long been a problem for skullbase surgeons. Currently, however, the continuous recording of compound muscle action potentials (CMAPs) from muscles enervated by cranial nerves III–XII makes it possible to monitor skull base and cavernous sinus operations as reliably as those performed in the cerebellopontine angle.

Problems in central skull base surgery

Space occupying lesions occurring at the central skull base endanger three primary systems: (1) cranial nerves I–VI include four motor nerves, two sensory nerves, and one of the mixed functions. Lesions extending from the central skull base to the foramen magnum may affect any or all cranial nerves, I–XII. (2) The vascular system of the anterior circulation, including connections with the posterior circulation, as it impacts the cerebral hemispheres and basal ganglia. (3) The hypothalamic and hypophyseal system (concerned with endocrine function) is beyond the scope of this article. The basis for intraoperative electrophysiological monitoring involves stimulating various cranial motor nerves, then recording subclinical contractions of the muscles they innervate. Continuous recording of muscle activity during surgical dissection has the capacity to reveal contact with or injury to a cranial nerve. The percentage reduction of a supramaximal CMAP compared to that at the beginning of the operation indicates the percentage of functional neuron loss.

Historical overview

On 14 July 1898, Dr. Fedor Krause in Berlin first described the use of cranial nerve monitoring during posterior fossa surgery to section a cochlear nerve for tinnitus. He noted that .. . .unipolar faradic irritation of the facial nerve trunk with the weakest possible current of the induction apparatus resulted in contractions of the right facial region, especially of the orbicularis oculi, as well as of the branches supplying the nose and the mouth . . .. [65]. The patient exhibited facial paresis immediately following surgery which almost completely resolved by the next day. Krause also noted contractions of the shoulder, which he thought were due to the stimulation of the spinal accessory nerve that .. . .had undoubtedly been reached by the current, because it was, together with the acusticus, bathed in liquor that had trickled down . . ... Thus, Krause was not only the first to describe locating a cranial nerve by electrical stimulation, but also the first to encounter the confounding problem of an artifact being produced by the spread of current! Frazier used a similar technique during an operation for the relief of vertigo, and pointed out the importance of preserving the facial nerve, which he noted could be identified by "galvanic current". [36].