Special Somatic Sensory Afferent Systems Overview

The special somatic sensory afferent systems include the auditory, vestibular, and visual systems. Auditory and vestibular afferent information is received by cranial nerve VIII, which projects to central pathways. Cranial nerve II carries afferent visual information to central pathways. This chapter reviews the receptors and structural components of these special somatic sensory afferent systems. The ossicular chain (malleus, incus, and stapes) within the air-filled middle ear serves as a transformer that bridges the impedance mismatch between sound vibrations in air on the large tympanic membrane and the resulting vibrations onto the small stapedial footplate.

Understanding the Radiobiology of Vestibular Schwannomas to Overcome Radiation Resistance

Vestibular schwannomas (VS) are benign tumors arising from cranial nerve VIII that account for 8–10% of all intracranial tumors and are the most common tumors of the cerebellopontine angle. These tumors are typically managed with observation, radiation therapy, or microsurgical resection. Of the VS that are irradiated, there is a subset of tumors that are radioresistant and continue to grow; the mechanisms behind this phenomenon are not fully understood. In this review, the authors summarize how radiation causes cellular and DNA injury that can activate (1) checkpoints in the cell cycle to initiate cell cycle arrest and DNA repair and (2) key events that lead to cell death. In addition, we discuss the current knowledge of VS radiobiology and how it may contribute to clinical outcomes. A better understanding of VS radiobiology can help optimize existing treatment protocols and lead to new therapies to overcome radioresistance.

Posterior petrous face meningiomas presenting with Ménière’s-like syndrome: a case series and review of the literature

OBJECTIVE Ménière’s disease is an inner ear disorder classically characterized by fluctuating hearing loss, tinnitus, and aural fullness accompanied by episodic vertigo. While the pathogenesis of Ménière’s remains under debate, histopathological analyses implicate endolymphatic sac dysfunction with inner ear fluid homeostatic dysregulation. Little is known about whether external impingement of the endolymphatic sac by tumors may present with Ménière’s-like symptoms. The authors present a case series of 7 patients with posterior fossa meningiomas that involved the endolymphatic sac and new onset of Ménière’s-like symptoms and review the literature on this rare clinical entity. METHODS A retrospective review of patients undergoing resection of a posterior petrous meningioma was performed at the authors’ institution. Inclusion criteria were age older than 18 years; patients presenting with Ménière’s-like symptoms, including episodic vertigo, aural fullness, tinnitus, and/or hearing loss; and tumor location overlying the endolymphatic sac. RESULTS There were 7 cases of posterior petrous face meningiomas involving the vestibular aperture presenting with Ménière’s-like symptoms. Imaging and intraoperative examination confirmed no cranial nerve VIII compression or labyrinthine artery involvement accounting for audiovestibular symptoms. Of the 7 patients in the series, 6 experienced significant improvement or resolution of their vertigo, and all 7 had improvement or resolution of their tinnitus after resection. Of the 5 patients who had preoperative hearing loss, 2 experienced improvement or resolution of their ipsilateral preoperative hearing deficit, whereas the other 3 had unchanged hearing loss compared to preoperative evaluation. CONCLUSIONS Petrous face meningiomas overlying the endolymphatic sac can present with a Ménière’s syndrome. Early recognition and microsurgical excision of these tumors is critical for resolution of most symptoms and stabilization of hearing loss.

Dyslexia & the Pons

Introduction Dyslexia is a learning disorder. It is centered on the Pons. It affects between 5 to 17% of the population. The Pons is where the balance takes place. People with Dyslexia have trouble with balance. The Pons is also central to the sub consciousness, which is tied in with REM sleep. The sleep equation therefore applies. The Pons is involved in communication by facial expression. People with Dyslexia is a communication disorder since those with it have trouble linking visual and hearing senses. The Cranial Nerve VIII, Vestibular Nerve, responsible for hearing comes out of the Pons. The tracts for sight and hearing pass through the Lateral Geniculate Body (LGB) and the Medical Geniculate Body. (MGB) which are located on the anterior of the Thalamus. Reading and wringing, which is a problem with Dyslexia, involves both seeing and hearing. We translate visual signal to vocal words and writing. Dyslexia also have trouble with writing letters. They do letter backwards. The is an orientation problem. It may have to do with the left hemisphere which usually is responsible for language (Broca’s and Wernicke’s Areas). The Pons too is responsible for communication, especially the nonverbal facial recognition.

Beyond Antoni: A Surgeon's Guide to the Vestibular Schwannoma Microenvironment

Introduction Vestibular schwannomas (VS) are histologically benign tumors arising from cranial nerve VIII. Far from a homogenous proliferation of Schwann cells, mounting evidence has highlighted the complex nature of the inflammatory microenvironment in these tumors. Methods A review of the literature pertaining to inflammation, inflammatory molecular pathways, and immune-related therapeutic targets in VS was performed. Relevant studies published up to June 2020 were identified based on a literature search in the PubMed and MEDLINE databases and the findings were synthesized into a concise narrative review of the topic. Results The VS microenvironment is characterized by a dense infiltrate of inflammatory cells, particularly macrophages. Significantly higher levels of immune cell infiltration are observed in growing versus static tumors, and there is a demonstrable interplay between inflammation and angiogenesis in growing VS. While further mechanistic studies are required to ascertain the exact role of inflammation in angiogenesis, tumor growth, and Schwann cell control, we are beginning to understand the key molecular pathways driving this inflammatory microenvironment, and how these processes can be monitored and targeted in vivo. Conclusion Observational research has revealed a complex and heterogeneous tumor microenvironment in VS. The functional landscape and roles of macrophages and other immune cells in the VS inflammatory infiltrate are, however, yet to be established. The antiangiogenic drug bevacizumab has shown the efficacy of targeted molecular therapies in VS and there is hope that agents targeting another major component of the VS microenvironment, inflammation, will also find a place in their future management.

The nervous system

HistoryPresenting symptomsThe rest of the historyExaminationThe outline examinationGeneral inspection and mental stateCognitive functionSpeech and languageCranial nerve examinationCranial nerves II, III, IV, and VICranial nerve I: olfactoryCranial nerve V: trigeminalCranial nerve VII: facialCranial nerve VIII: vestibulocochlearCranial nerves IX and XCranial nerve XI: accessoryCranial nerve XII: hypoglossalMotor: applied anatomyMotor: inspection and toneMotor: upper limb powerMotor: lower limb powerTendon reflexesOther reflexesPrimitive reflexesSensory: applied anatomySensory examinationCoordinationSome peripheral nervesGaitThe unconscious patientImportant presenting patternsThe elderly patient

Hearing Preservation After Translabyrinthine Vestibular Schwannoma Excision: Audiometry and Electrocochleography Results

Objectives: To describe a case of inadvertent hearing preservation following a classical translabyrinthine resection of a vestibular schwannoma of the internal auditory canal in an otherwise healthy patient. Methods: Herein, we describe the case of an otherwise healthy patient who underwent resection of an intracanalicular vestibular schwannoma via a translabyrinthine approach. Furthermore, as part of an ongoing study aimed at characterizing hearing changes due to intraoperative events, cochlear hair cell and nerve activity were monitored using electrocochleography throughout surgery. Unexpectedly, the patient maintained serviceable hearing following surgery. As a result, we are able to provide electrophysiologic evidence of cochlear hair cell activity at various stages of this surgery. Results: Hair cell responses across tested frequencies were detectable prior to and following completion of the translabyrinthine procedure. Neural integrity of the auditory division of cranial nerve VIII was maintained throughout. Lastly, postoperative audiometric testing supported the patient’s subjective assertion of serviceable hearing in the surgical ear. Conclusion: Our results suggest that some degree of hair cell and neural integrity can be maintained throughout the course of the translabyrinthine approach, and if preservation of the auditory division of cranial nerve VIII is feasible, a functional amount of hearing preservation is attainable.