Edward Tarlov

Organization of vestibulo-oculomotor projections in the cat

Summary Unilateral stereotaxic lesions were made in restricted portions of the cat vestibular nuclei, and the resulting axonal degeneration was stained by the Nauta 23 method. Vestibular projections to the extraocular motor nuclei arise only in the superior vestibular nucleus (SV) and in rostral portions of the medial vestibular nucleus (RMV), the regions which receive the central projections of the semi-circular canal ganglia. Fibers ascending from these two regions follow separate courses. From caudal portions of the SV, a few fibers pass medially to the ipsilateral VI nucleus. The majority of ascending SV fibers pass rostromedially into the ipsilateral MLF from which they enter the ipsilateral trochlear and III nuclei. Within caudal portions of the III nuclei, fibers decussate and turn caudally to distribute to the contralateral trochlear nucleus. Fibers passing to the contralateral extraocular motor nuclei cross the midline within the III nuclei. From the RMV, ascending fibers pass medially into the ipsilateral VI nucleus. The projections from rostral portions of the RMV decussate rostral to those from caudal portions of the RMV. A few fibers are distributed to the contralateral VI nuclei. Ascending fibers pass in the contralateral MLF to the EOM nuclei bilaterally. Both the SV and RMV project to the interstitial nuclei of Cajal and the nuclei of Darkschewitsch; from the SV, this projection is predominantly ipsilateral, while from the RMV it is predominantly contralateral. Extensive areas of overlap between the projections of the SV and RMV exist. Small regions within the SV and RMV have wide projection fields within the EOM nuclei. The projection fields of restricted regions of the SV and RMV are depicted in detail. This vast and beautiful intricacy of organization provides direct pathways over which a relatively few neurons within the superior and medial vestibular nuclei can influence the activity of large numbers of extraocular muscle motor neurons. Conversely, small groups of extraocular muscle motor neurons receive projections from large areas in the superior and medial vestibular nuclei. The delicate influences of the vestibular system on coordinated eye movements must depend on such exquisite organization.

Heuristic map of myotomal innervation in humans using direct intraoperative nerve root stimulation.

OBJECTIVE Considerable overlap exists in nerve root innervation of various muscles. Knowledge of myotomal innervation is essential for the interpretation of neurological examination findings and neurosurgical decision-making. Previous studies relied on cadaveric dissections, animal studies, and cases with anomalous anatomy. This study investigates the myotomal innervation patterns of cervical and lumbar nerve roots through in vivo stimulation during surgeries for spinal decompression. METHODS Patients undergoing cervical and lumbar surgeries in which nerve roots were exposed in the normal course of surgery were included in the study. Electromyography electrodes were placed in the muscle groups that are generally accepted to be innervated by the roots under study. These locations included levels above and below the spinal levels undergoing decompression. After decompression, a unipolar neural stimulator probe was placed directly on the nerve root sleeve and constant current stimulation in increments of 0.1 mA was performed. Current was raised until at least a 100 μV amplitude-triggered electromyographic response was noted in 1 or more muscles. All muscles that responded were recorded. RESULTS A total of 2295 nerve root locations in 129 patients (mean age 57 ± 15 years, 47 female [36%]) were stimulated, and 1589 stimulations met quality criteria and were analyzed. Four hundred ninety-five stimulations were performed on roots contributing to the cervical and brachial plexus from C-3 to T-1 (31.2%), and 1094 (68.8%) were roots in the lumbosacral plexus between L-1 and S-2. The authors were able to construct a statistical map of the contributions of each cervical and lumbosacral nerve root for the set of muscle groups monitored in the protocol. In many cases the range of muscles innervated by a specific root was broader than previously described in textbooks. CONCLUSIONS This is the largest data set of direct intraoperative nerve root stimulations during decompressive surgery, demonstrating the relative contribution of root-level motor input to various muscle groups. Compared with classic neuroanatomy, a significant number of roots innervate a broader range of muscles than expected, which may account for the variability of presentation between patients with identical number and location of compressed roots.

Total One-Stage Suboccipital Microsurgical Removal of Acoustic Neuromas of All Sizes: With Emphasis on Arachnoid Planes and on Saving the Facial Nerve

Clinical suspicion is essential for early diagnosis of acoustic neuroma. No absolutely characteristic pattern of hearing loss occurs, and atypical presentations are the rule. The diagnosis of acoustic neuroma is possible by tests that can be performed on an outpatient basis. A hearing loss for high tones with impaired speech discrimination is frequently seen. Testing of the acoustic reflexes and particularly the brain stem auditory-evoked responses (BAER) are becoming the most reliable methods of defining hearing loss in patients suspected of having an acoustic neuroma. High-resolution, thin-sectioning, overlapping-cut CT scanning including CT pneumography when necessary and polytomography of the internal auditory meatus are the mainstays of radiologic evaluation. Complete removal of the tumor at one operation is usually possible by the suboccipital retromastoid route with preservation or restoration of normal brain stem function and preservation of facial nerve function. Preservation of hearing has occasionally been accomplished, and the potential occasionally exists for restoration of hearing in patients with favorable smaller tumors, which have not acquired extensive arterial supply in common with the cochlea. The two factors that most influence results are early diagnosis and gentleness of surgical manipulation of the tissues that is made possible by magnification and illumination with the operating microscope.

Studies of suspected neurotransmitters in the vestibuloocular pathways.

Isolated fresh cat trochlear and oculomotor nuclei, which contain the axon terminals of inhibitory neurons whose cell bodies are in the superior vestibular nucleus (SVN), actively synthesize and store [3H]GABA, [14C]acetylcholine, [3H]dopamine and [3H]tyramine from labeled precursors of these compounds. Twelve to 14 days following lesions of the ipsilateral superior vestibular nucleus or its efferent pathway to the oculomotor and trochlear nuclei, at a time when there is extensive degeneration of superior vestibular nucleus axon terminals in these nuclei, the synthesis and storage of GABA in the ipsilateral trochlear nucleus is markedly reduced compared to that in the contralateral trochlear nucleus; the synthesis of acetylcholine, dopamine and tyramine is not measurably affected. The oculomotor nuclei, which unlike the trochlear nuclei receive a heavy bilateral projection from the SVN, show no asymmetric decrease after SVN lesions in their ability to synthesize any of the compounds tested. The data support the identity of GABA as an inhibitory transmitter in the superior vestibular nucleus-trochlear nucleus pathway.

Percutaneous and open microsurgical techniques for relief of refractory tic douloureux.

In the younger patient with trigeminal neuralgia refractory to medical treatment, microsurgical operation is warranted. If a truly significant compressive artery is found in relation to the posterior root, microvascular decompression is carried out. If no convincing evidence of a compressive vascular lesion is found at operation, the posterior root is partially sectioned. Most patients with tic douloureux are elderly and in these, and in all patients who prefer a minor procedure, I favor the simple low morbidity percutaneous radiofrequency technique. In these days of informed consent, patients should preoperatively be made aware of the advantages of both kinds of operations and participate in choosing the procedure which best suits the individuals health and preferences.

Stereotactic Computed Tomographic-Guided Functional Neurosurgery Using the Redesigned Gouda Frame

The Gouda frame has been used to perform thalamotomy successfully. Computer-generated coordinates were used without the need of ventriculography.