Micro-endoscopic system for functional assessment of neural circuits in deep brain regions: Simultaneous optical and electrical recordings of auditory responses in mouse's inferior colliculus.

In vivo Ca2+ imaging is a powerful method for the functional assessment of neural circuits. Although multi-photon excitation fluorescence microscopy has been widely used, observation of circuits in deep brain regions remains challenging. Recently, observing these deep regions has become possible via an endoscope consisting of an optical fiber bundle or gradient-index lens. We have designed a micro-endoscope system that enables simultaneous optical recording of fluorescence and electrical recording of neural activity. Using this system, we recorded auditory responses by simultaneously detecting changes in the fluorescence intensity of a Ca2+ indicator dye, multi-unit activities (MUA), and local field potentials (LFP) in the mouse's inferior colliculus (IC). Such simultaneous optical and electrical recordings enabled detailed comparison of electrically recorded phenomena (MUA and LFP) and optically recorded Ca2+ response. By systematically changing sound frequency and intensity, we determined the frequency tuning of the recording site. The best frequency shifted higher as the probe advanced more deeply, demonstrating that the system is capable of optically measuring the dorso-ventral organization of IC (i.e., tonotopicity). Thus, our new micro-endoscope system will be useful in the neurophysiological studies of a wide range of brain circuits, including those within the auditory system.

A multiport MR-compatible neuroendoscope: spanning the gap between rigid and flexible scopes.

OBJECTIVE Rigid endoscopes enable minimally invasive access to the ventricular system; however, the operative field is limited to the instrument tip, necessitating rotation of the entire instrument and causing consequent tissue compression while reaching around corners. Although flexible endoscopes offer tip steerability to address this limitation, they are more difficult to control and provide fewer and smaller working channels. A middle ground between these instruments-a rigid endoscope that possesses multiple instrument ports (for example, one at the tip and one on the side)-is proposed in this article, and a prototype device is evaluated in the context of a third ventricular colloid cyst resection combined with septostomy. METHODS A prototype neuroendoscope was designed and fabricated to include 2 optical ports, one located at the instrument tip and one located laterally. Each optical port includes its own complementary metal-oxide semiconductor (CMOS) chip camera, light-emitting diode (LED) illumination, and working channels. The tip port incorporates a clear silicone optical window that provides 2 additional features. First, for enhanced safety during tool insertion, instruments can be initially seen inside the window before they extend from the scope tip. Second, the compliant tip can be pressed against tissue to enable visualization even in a blood-filled field. These capabilities were tested in fresh porcine brains. The image quality of the multiport endoscope was evaluated using test targets positioned at clinically relevant distances from each imaging port, comparing it with those of clinical rigid and flexible neuroendoscopes. Human cadaver testing was used to demonstrate third ventricular colloid cyst phantom resection through the tip port and a septostomy performed through the lateral port. To extend its utility in the treatment of periventricular tumors using MR-guided laser therapy, the device was designed to be MR compatible. Its functionality and compatibility inside a 3-T clinical scanner were also tested in a brain from a freshly euthanized female pig. RESULTS Testing in porcine brains confirmed the multiport endoscope's ability to visualize tissue in a blood-filled field and to operate inside a 3-T MRI scanner. Cadaver testing confirmed the device's utility in operating through both of its ports and performing combined third ventricular colloid cyst resection and septostomy with an endoscope rotation of less than 5°. CONCLUSIONS The proposed design provides freedom in selecting both the number and orientation of imaging and instrument ports, which can be customized for each ventricular pathological entity. The lightweight, easily manipulated device can provide added steerability while reducing the potential for the serious brain distortion that happens with rigid endoscope navigation. This capability would be particularly valuable in treating hydrocephalus, both primary and secondary (due to tumors, cysts, and so forth). Magnetic resonance compatibility can aid in endoscope-assisted ventricular aqueductal plasty and stenting, the management of multiloculated complex hydrocephalus, and postinflammatory hydrocephalus in which scarring obscures the ventricular anatomy.

Transventricular fenestration of the lamina terminalis: the value of a flexible endoscope: technical note.

BACKGROUND: Recently, the authors demonstrated the technical feasibility of a transventricular translaminar terminalis ventriculostomy with a rigid endoscope. A major problem with this technique remains the contusion of the fornix at the foramen of Monro. Here, the authors evaluated alternative approaches and techniques, including the use of a flexible endoscope. MATERIAL AND METHODS: Feasibility of two approaches-anterior and posterior of the coronal suture-was evaluated on magnetic resonance images and in cadaveric brains. Two different trajectories were selected. Lamina terminalis (LT) fenestration was performed with a rigid and a flexible endoscope using two approaches in 10 fixed cadaver brains. RESULTS: Using the posterior approach 2 cm behind the coronal suture with the two endoscopes caused moderate to severe damage to foramen and fornix. Using the standard approach (Kocher point) with the flexible endoscope avoided damage of these structures. After completion of the anatomical investigation, the authors successfully performed a transventricular fenestration of the LT with the flexible endoscope in one clinical case. CONCLUSION: Rigid scopes provide brilliant optics and safe manipulation with the instruments. However, with the rigid scope, a transventricular opening of the LT is only possible with acceptance of structural damage to the foramen of Monro and the fornix. In contrast, opening of the LT via a transventricular route with preservation of the anatomical structures can be achieved with a flexible steerable endoscope even via a standard burr hole. Thus, if a standard third ventriculostomy is not feasible, endoscopic opening of the LT might represent an alternative, particularly with a flexible scope in experienced hands.

Transendoscopic intraoperative recording of gelastic seizures from a hypothalamic hamartoma.

OBJECT: The differential diagnosis of hypothalamic masses in children includes hamartomas, which are associated with gelastic seizures and endocrine dysfunction. The purpose of this study was to utilize transendoscopic electroencephalography (EEG) recording at the time of tissue biopsy to further assist in diagnosis, determination of prognosis, and treatment planning. METHODS: We present the case of an infant with gelastic seizures and a large hypothalamic mass lesion. Despite a clinical and radiographic presentation typical of hypothalamic hamartoma (HH), slight growth on serial imaging raised concern for a diagnosis of intrinsic neoplasm. Biopsy of the lesion was recommended. RESULTS: Transventricular, endoscopic biopsy, was undertaken, with concurrent intraoperative, transendoscopic EEG recording using a standard epilepsy depth recording macroelectrode. Numerous electrographic seizures were recorded. Histopathology revealed a HH. CONCLUSION: This is the first report of intraoperative macroelectrode recording of electrographic seizures transendoscopically from a HH. This technique may prove useful for diagnosis, prognosis and treatment planning, as well as to guide transendoscopic therapeutic interventions for HH.