Vincent N. Carrasco

Cochlear Implantation in Children with Congenital Inner Ear Malformations

Objective/Hypothesis: To assess the audiologic and surgical outcomes for pediatric cochlear implant patients with inner ear malformations.

Cochlear implant performance in senior citizens

Cochlear implants are indicated for elderly patients with severe-to-profound hearing loss (sensorineural hearing loss ≥ 70 dB). Their use has been limited, possibly by the misconception that elderly patients will perform poorly. To document the performance of older adults (≥65 years old), we undertook a retrospective analysis of our postlingually deafened adult patients who underwent implantation with the CLARION Multi-Strategy Cochlear Implant and underwent formal audiologic analysis (sentence recognition [Central Institute for the Deaf, CID] and monosyllabic word recognition [consonant-noun-consonant, CNC]). Both younger (n = 20; mean age = 46.9 years) and older (n = 16; mean age = 71.5 years) adults showed statistically significant increases in CID and CNC scores after cochlear implantation. No statistically significant difference could be detected in operative time, anesthesia time, length of hospitalization, or CID or CNC scores between the two age groups. We conclude that age should not be a criterion for deciding who should receive cochlear implants. (Otolaryngol Head Neck Surg 2000;123:419-24.)

Cochlear implantation in common cavity malformations using a transmastoid labyrinthotomy approach

The transmastoid facial recess approach has become the standard technique for cochlear implantation. Although this approach has been used for implantation in patients with common cavity deformities, it is not without increased risk to the facial nerve. Using a direct approach to the common cavity that circumvents the facial recess, we have successfully implanted four patients with common cavity deformities. An aberrant facial nerve in one patient would have precluded placement of the electrode array using standard cochlear implant techniques. As demonstrated in these four patients, the direct approach to the common cavity is an effective approach for placement of the electrode array, minimizes risk to the facial nerve, and may decrease the likelihood of postoperative cerebrospinal fluid leaks. Intraoperative video footage demonstrates the feasibility and facility of this approach in patients with common cavity deformities.

Radiation therapy of glomus jugulare tumors.

The relative effectiveness of surgery versus radiation therapy as the primary treatment for glomus jugulare tumors remains controversial. Literature can be cited to support either modality as primary therapy. This inability to reach a definitive consensus as to the best treatment for this disease is due to the lack of adequate information on patients who are staged, consistently treated, and followed for a sufficient period of time. The value of radiation therapy both as primary treatment and for surgical salvage is examined.

Defect reconstruction and cerebrospinal fluid management in neurotologic skull base tumors with intracranial extension

Intracranial extension (ICE) is the spread of tumor into the subarachnoid space through dura or along cranial nerve roots. The single‐stage removal of the skull base tumor with its ICE has been confounded by cerebrospinal fluid management and defect reconstruction.

Effect of sodium nitroprusside on compound action potential thresholds in the gerbil cochlea

The presence of active nitric oxide synthase (NOS) in the spiral ganglion cells of the cochlea suggests that the neuromodulator nitric oxide (NO) may play a role in hearing. This study investigated the effects of sodium nitroprusside (SNP), an NO donor, upon cochlear function mediated through its activation of guanylate cyclase. In gerbils, cochlear compound action potential (CAP) thresholds were recorded after cochlear perfusions of control and test solutions in four experimental groups. Perfusions were performed using the following: artificial perilymph solution (APS); the NO donor SNP; the guanylate cyclase inhibitor methylene blue (MB); and sodium dodecyl sulfate (SDS), which facilitates MB entrance into cells. SNP caused significant elevations of CAP thresholds from baseline (25 dB SPL +/- 1.54 dB to 64.3 dB SPL +/- 2.54 dB). SNP with MB also resulted in significant CAP threshold elevations (29.4 dB SPL +/- 4.27 dB to 38.1 dB SPL +/- 4.0 dB); however, these elevations were significantly lower than those seen in SNP perfusions without MB. Drilling perfusion holes and perfusion of APS, APS/SDS, and MB/SDS/APS solutions did not significantly affect CAP thresholds. These results suggest that the NO donor nitroprusside does affect cochlear neuromodulation and effects this mediation in part through NO activation of guanylate cyclase.

Catecholaminergic Innervation of the Inner Ear

Cochlear blood flow has been shown to be controlled, in part, by the sympathetic nervous system. We have used immunocytochemical staining for tyrosine hydroxylase (TH) to further demonstrate the extent of catecholaminergic innervation of the cochlea. Deeply anesthetized Mongolian gerbils were systemically perfused with phosphate-buffered saline, followed by 4% paraformaldehyde. The cochleae were dissected out and post-fixed for 3 hours in 4% paraformaldehyde. They were then incubated in anti-TH antibody and subsequently processed using the avidin-biotin immunoperoxidase method. Microscopic examination of whole-mounted tissue revealed many immunoreactive fibers on the spiral modiolar artery. TH-positive fibers have also been found on both radiating arterioles and radial collecting venules, which has not been previously reported. With innervation of these small vessels, blood flow in the cochlea may be segmentally controlled. We also further describe the organization of TH-positive fibers in the osseous spiral lamina.

Volume registration using the 3D core

The core is a multiscale object description extracted directly from an image in which the significance of object features depends on the scale at which the object is currently being considered. Core descriptions extracted from the same object using different imaging modalities display remarkable similarities despite noise and variations imposed by the imaging devices. Core based registration methods have been successfully employed in examples of 3D registration that would have caused boundary or contour based methods to fail. In this paper, we present an overview of the core, and describe its properties that make it a promising approach toward registration. Our current core-based method of registration is also presented. Results of the registration of 3D volumes from both a single imaging modality and from two different modalities are given.

Measurement of cochlear blood flow: intravital fluorescence microscopy

A technique is described for directly observing in vivo cochlear microvasculature in the gerbil for physiologic and experimentally induced changes in vessel diameter and blood flow velocity. Measurements are made from computer processed video images of surgically exposed microvessels. These images are obtained using intravital fluorescence microscopy (IFM) with epi-illumination. The Mongolian gerbil is an ideal animal model for circulatory studies of the inner ear. It has a stable heart rate and blood pressure under urethane/alpha-chloralose anesthesia and its cochlea is surgically accessible. A window is created over the feeding artery (anterior inferior cerebellar artery) and over the stria vascularis of the second turn of the cochlea, atraumatically exposing radiating arterioles and strial capillaries. Our system of IFM provides images that are videorecorded, digitally analyzed with a computer image processor, and enhanced according to the type of measurement desired. Velocity measurements are obtained by tracking plasma gaps or single fluorescent labeled red blood cells through successive frames of the videorecorded images. This experimental technique allows us to analyze circulatory responsiveness to a variety of vasoactive drugs administered regionally to the cochlea in concentrations not affecting systemic circulation.

Role of Nitric Oxide in Kainic Acid-induced Elevation of Cochlear Compound Action Potential Thresholds

Nitric oxide (NO) has specifically been found to mediate the effects of excitatory amino acids in the central nervous system (CNS). Excitatory amino acids are the primary neurotransmitters at the cochlear hair cell afferent nerve synapse. Recent studies in our laboratory demonstrate that NO synthase is an active enzyme in the spiral ganglion cells of the cochlea. Given our current understanding of neurotransmission in the cochlea, it is reasonable to postulate that the actions of NO in cochlear neuronal tissue are similar to the actions of NO in the CNS, and that NO acts as a neurotransmitter/neuromodulator in the cochlea. In addition, NO is implicated as a mediator of excitotoxicity in the CNS and may therefore play a similar role in excitotoxicity in the cochlea. To further elucidate the role of NO in cochlear excitotoxicity, this study investigated the effects of 7-nitroindazole (7-NI), a competitive inhibitor of neuronal nitric oxide synthase, with regard to kainic acid (KA)-induced elevation of compound action potential (CAP) thresholds. KA is a conformationally restricted analog of glutamate with well-known excitotoxic effects on SGCs and previously described inhibitory actions on cochlear CAP thresholds. In anesthetized gerbils, CAP thresholds were recorded before and after cochlear perfusions with control solutions of artificial perilymph solution and test solutions of KA. 7-NI was administered i.p. prior to KA perfusion in an effort to block its depolarizing and toxic effects. Results showed that cochlear perfusion with KA caused significant elevation (p < 0.05) of the mean CAP threshold. This threshold shift was significantly reduced (p < 0.05) in animals pretreated with 7-NI. These results indicate that NO is involved in the toxic effects on CAP thresholds elicited by KA in the cochlea.