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Endolymphatic hydrops (ELH), hearing loss and neuronal degeneration occur together in a variety of clinically significant disorders, including Meniere's disease (MD). However, the sequence of these pathological changes and their relationship to each other are not well understood. In this regard, an animal model that spontaneously develops these features postnatally would be useful for research purposes. A search for such a model led us to the Phex Hyp-Duk mouse, a mutant allele of the Phex gene causing X-linked hypophosphatemic rickets. The hemizygous male (Phex Hyp-Duk /Y) was previously reported to exhibit various abnormalities during adulthood, including thickening of bone, ELH and hearing loss. The reported inner-ear phenotype was suggestive of progressive pathology and spontaneous development of ELH postnatally, but not conclusive. The main focuses of this report are to further characterize the inner ear phenotype in Phex Hyp-Duk /Y mice and to test the hypotheses that (a) the Phex Hyp-Duk /Y mouse develops ELH and hearing loss postnatally, and (b) the development of ELH in the Phex Hyp-Duk /Y mouse is associated with obstruction of the endolymphatic duct (ED) due to thickening of the surrounding bone. Auditory brainstem response (ABR) recordings at various times points and histological analysis of representative temporal bones reveal that Phex Hyp-Duk /Y mice typically develop adult onset, asymmetric, progressive hearing loss closely followed by the onset of ELH. ABR and histological data show that functional degeneration precedes structural degeneration. The major degenerative correlate of hearing loss and ELH in the mutants is the primary loss of spiral ganglion cells. Further, Phex Hyp-Duk /Y mice develop ELH without evidence of ED obstruction, supporting the idea that ELH can be induced by a mechanism other than the blockade of longitudinal flow of endolymphatic fluid, and occlusion of ED is not a prerequisite for the development of ELH in patients.

The TMEDIC is a safe and effective method to repair transtemporal meningoencephalocele obviating the need for a middle fossa craniotomy in certain cases.

OBJECTIVEThere is no definitive or consensus classification system for the jugular bulb position that can be uniformly communicated between a radiologist, neurootologist, and neurosurgeon. A high-riding jugular bulb (HRJB) has been variably defined as a jugular bulb that rises to or above the level of the basal turn of the cochlea, within 2 mm of the internal auditory canal (IAC), or to the level of the superior tympanic annulus. Overall, there is a seeming lack of consensus, especially when MRI and/or CT are used for jugular bulb evaluation without a dedicated imaging study of the venous anatomy such as digital subtraction angiography or CT or MR venography.METHODSA PubMed analysis of “jugular bulb” comprised of 1264 relevant articles were selected and analyzed specifically for an HRJB. A novel classification system based on preliminary skull base imaging using CT is proposed by the authors for conveying the anatomical location of the jugular bulb. This new classification includes the following types: type 1, no bulb; type 2, below the inferior margin of the posterior semicircular canal (SCC), subclassified as type 2a (without dehiscence into the middle ear) or type 2b (with dehiscence into the middle ear); type 3, between the inferior margin of the posterior SCC and the inferior margin of the IAC, subclassified as type 3a (without dehiscence into the middle ear) and type 3b (with dehiscence into the middle ear); type 4, above the inferior margin of the IAC, subclassified as type 4a (without dehiscence into the IAC) and type 4b (with dehiscence into the IAC); and type 5, combination of dehiscences. Appropriate CT and MR images of the skull base were selected to validate the criteria and further demonstrated using 3D reconstruction of DICOM files. The microsurgical significance of the proposed classification is evaluated with reference to specific skull base/posterior fossa pathologies.RESULTSThe authors validated the role of a novel classification of jugular bulb location that can help effective communication between providers treating skull base lesions. Effective utilization of the above grading system can help plan surgical procedures and anticipate complications.CONCLUSIONSThe authors have proposed a novel anatomical/radiological classification system for jugular bulb location with respect to surgical implications. This classification can help surgeons in complication avoidance and management when addressing HRJBs.

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These recent advances have expanded our understanding and will allow for the development of targeted therapeutic interventions aimed at preventing the progression oochleovestibular deterioration.

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