Faculty Bibliography

Two of the most significant developments in neurosurgery over the past ten years have been the application of intraoperative navigational units and the widespread use of 'skull base' surgical techniques. These developments have independently revolutionized the way in which neurosurgeons approach intracranial pathology. The combination of these two developments has had a profound effect in our clinical practice to improve outcome and extend our capabilities. This ability to see around the corner, 'x-ray' vision as some have called it, provides an added measure of safety for the patient while allowing the surgeon to treat the lesion in a more aggressive fashion

The influence of excitatory transmission on postsynaptic structure is well established in developing animals, but little is known about the role of synaptic inhibition. We addressed this issue in developing gerbils with two manipulations designed to decrease glycinergic transmission in an auditory nucleus, the lateral superior olive (LSO), before the onset of sound-evoked activity. First, contralateral cochlear ablation functionally denervated the glycinergic pathway from the medial nucleus of the trapezoid body (MNTB) to the LSO, while leaving the excitatory pathway intact. Second, continuous release of a glycine receptor antagonist, strychnine (SN), was used to decrease transmission. The strength of excitatory and inhibitory synapses was examined with whole-cell recordings from LSO neurons in a brain-slice preparation. The percentage of LSO neurons exhibiting MNTB-evoked IPSPs was reduced in both ablated and SN-treated animals. In those neurons displaying IPSPs, the amplitude was significantly reduced. This decrease was accompanied by an 8 mV depolarization in the IPSP equilibrium potential. In contrast, the ipsilaterally evoked EPSPs were of unusually long duration in experimental animals. These long-duration EPSPs were significantly shortened by hyperpolarizing the neuron to -90 mV or exposing them to aminophosphonopentanoic acid (AP-5), an NMDA receptor antagonist. Membrane hyperpolarization and AP-5 had little effect in control neurons. In addition, LSO neurons from ablated or SN-treated animals displayed broad rebound depolarizations after membrane hyperpolarization, and these were abolished in the presence of Ni2+. Because both cochlear ablation and SN-rearing were initiated before the onset of sound-evoked activity, the results suggest that spontaneous glycinergic transmission influences the development of postsynaptic properties, including the IPSP reversal potential, NMDA receptor function, and a Ca2+ conductance

Laryngomalacia is a well-recognized cause of airway obstruction and inspiratory stridor in infants. As children grow and become more active, laryngomalacia may manifest in different, unexpected ways. Otherwise healthy athletes may generate enough inspiratory force to draw the aryepiglottic folds into the endolarynx, causing a subtotal glottic obstruction. This problem may be overlooked or attributed to asthma, lack of fitness, or functional abnormalities. The purpose of this report is to review the prevalence, diagnosis, and treatment of exercise-induced laryngomalacia (EIL) in children and young adults. To study the incidence and diagnosis of this disorder, we examined 10 healthy volunteers. Fiberoptic laryngoscopy was used to videotape each subject's larynx during active exercise on a stationary bicycle. All volunteers demonstrated altered laryngeal dynamics with exercise, and 1 of the 10 volunteers developed laryngomalacia. Anatomically, it appears that the aryepiglottic fold serves as the critical point of obstruction. When symptomatic, laryngomalacia may be treated with supraglottoplasty. We have had experience with 2 EIL patients in the last 12 months who have undergone carbon dioxide laser microlaryngoscopy. Both patients benefited significantly from surgery. We conclude that EIL is underdiagnosed but responds well to treatment

Expression of a sarcoma proto-oncogene, c-lyn, was mapped in the adult rat brain using immunohistochemistry. Lyn protein was prevalent in restricted cell populations of the olfactory bulb and the basal forebrain which included nuclei of accumbens, fundal striatum, bed stria, ventral pallidum and central amygdala as well as deep entorhinal and pyriform cortices. Tightly packed Lyn-positive cells formed discrete multiple stripes crossing perpendicular to the rostral limb of the anterior commissure, and intense masses surrounding the caudal limb. In the thalamus, the habenula, anterodorsal nucleus and medial geniculate body, together with the paraventricular hypothalamic nuclei, had prominent reactive neuronal somata and dendrites in the neuropil. The lateral septal nucleus also had intense Lyn-positive neurons with overlapping dendritic fields. In addition, scattered neurons were evenly distributed throughout the striatum. The red, interpeduncular, auditory and trigeminal tract nuclei were intensely reactive. The cerebellar molecular layer was uniformly labeled except for a few isolated fiber bundles in the lowest part of this layer. The granule cells adjacent to the Purkinje cell layer appeared in reactive patches. In the spinal cord, the posteromarginal nucleus had intense labeling. The significance of this highly localized distribution pattern of Lyn protein may be related to connections forming functional compartments serving signal transduction within specific central nervous system circuitry

Two groups of children received periodic documentation of their middle ear status by pneumatic otoscopy in the first year of life and had hearing sensitivity estimated by multiple auditory brainstem response (ABR) assessments during the same period. One group was considered otitis media (OM)-positive, with repeated bilateral episodes of OM and mild conductive hearing loss. The second group was considered OM-free with normal middle ear function bilaterally and normal hearing sensitivity in the first year of life. Children's higher-order auditory abilities were examined at 4, 6 and 9 years of age. Various measures such as speech recognition-in-competition, visual-auditory learning, sound blending, auditory memory, and masking level difference estimates were utilized to probe the children's auditory abilities. Results show that children with a first-year history of otitis media demonstrate deficits in the long term in some aspects of higher-order auditory processing. Performance appears to be associated with the mild hearing loss experienced during an important period of early development.

Loss of auditory neurons is commonly associated with sensorineural deafness, and may result from either direct neuronal injury or be a consequence of sensory hair cell loss (i.e. loss of source of trophic factors). Developmental studies and in vitro studies of adult neurons have begun to identify growth factors important for the development, maintenance, and rescue/repair of auditory neurons. Specific neurotrophic factors have been shown to enhance the auditory neurons' ability to withstand traumatic loss of target tissue connections and toxic injury. Promising initial in vivo studies confirm that specific neurotrophins are able to support neuronal survival and promote neuronal repair in an intact animal following injury to the cochlea. Further study into unique methods and routes of growth factor delivery will provide insights into the possibility of neurotrophic growth factors to act as drugs for the treatment of injured or stressed auditory neurons.

A potential side effect of tracheotomy in the pediatric population is poor speech development. It has been well documented that children with tracheotomies have delays in expressive and receptive language out of proportion to the child's degree of intellectual functioning. While numerous methods of augmentative devices have been proposed, none are ideal for the child with a tracheotomy. Of the choices available, the Passy-Muir valve is best suited for use in the pediatric population. We present a method of selection of patients for Passy-Muir valve placement currently in use at Blythedale Children's Hospital. The criteria employed include measurement of trans-tracheal pressures. This has not previously been presented in the literature, but has been found to be of significant value in determining who will benefit most from Passy-Muir valve placement.

The presence of dysphagia, drooling, and stridor in an adult subsequent to thermal or caustic injury should alert the treating physician to the possibility of injury to the supraglottic structures with resultant epiglottitis. These adults possess many of the features seen in acute infectious epiglottitis and should be handled with the same consideration for potential upper airway obstruction. Epiglottic injuries of this type should be suspected in adults with mental disorders or communication difficulties