Benjamin P. C. Wei

Intraoperative round window recordings to acoustic stimuli from cochlear implant patients.

Hypothesis Acoustically evoked neural and hair cell potentials can be measured from the round window (RW) intraoperatively in the general population of cochlear implant recipients. Background Cochlear implant performance varies greatly among patients. Improved methods to assess and monitor functional hair cell and neural substrate before and during implantation could potentially aid in enhanced nontraumatic intracochlear electrode placement and subsequent improved outcomes. Methods Subjects (1–80 yr) undergoing cochlear implantation were included. A monopolar probe was placed at the RW after surgical access was obtained. The cochlear microphonic (CM), summating potential (SP), compound action potential (CAP), and auditory nerve neurophonic (ANN) were recorded in response to tone bursts at frequencies of 0.25 to 4 kHz at various levels. Results Measurable hair cell/neural potentials were detected to 1 or more frequencies in 23 of 25 subjects. The greatest proportion and magnitude of cochlear responses were to low frequencies (<1,000 Hz). At these low frequencies, the ANN, when present, contributed to the ongoing response at the stimulus frequency. In many subjects, the ANN was small or absent, whereas hair cell responses remained. Conclusion In cochlear implant recipients, acoustically evoked cochlear potentials are detectable even if hearing is extremely limited. Sensitive measures of cochlear and neural status can characterize the state of hair cell and neural function before implantation. Whether this information correlates with speech performance outcomes or can help in tailoring electrode type, placement or audiometric fitting, can be determined in future studies.

Can we prevent cochlear implant recipients from developing pneumococcal meningitis

The restoration of hearing to persons with severely or profoundly impaired hearing by means of a cochlear implant is one of the great achievements of bionics applied to medicine. However, pneumococcal meningitis in implant recipients has received high profile public attention as a result of the US Food and Drug Administrations public health notification and recent media attention. Worldwide, 118 of the 60,000 people who received cochlear implants over the past 20 years have acquired meningitis, causing deep concern in the international medical community. This review provides answers to pediatricians, internists, and infectious diseases doctors who have patients with cochlear implants and who have questions about the safety of the cochlear implant from both the clinical and scientific research perspectives. Both clinical and laboratory research support the notion that pneumococcal meningitis is more likely in patients who receive cochlear implantation, and that the surgical insertion technique and the cochlear implant design should be nontraumatic, and that all cochlear implant recipients should be offered vaccination against Streptococcus pneumoniae.

DETERMINING NORMAL VALUES FOR INTRA-ABDOMINAL PRESSURE

Background:  Intra‐abdominal pressure (IAP) measurements can be used for the early detection and management of the abdominal compartment syndrome. IAP values are widely thought to be atmospheric or subatmospheric. However, there are no reports that describe normal IAP values using urinary bladder pressure measurements in patients not suspected of having a raised IAP level. This study sought to determine these normal values to aid our interpretation of IAP measurements in post‐surgical patients or patients with suspected increased IAP.

Threshold shift: effects of cochlear implantation on the risk of pneumococcal meningitis

Objectives The study goals were to examine whether cochlear implantation increases the risk of meningitis in the absence of other risk factors and to understand the pathogenesis of pneumococcal meningitis post cochlear implantation. Study Design and Setting Four weeks following surgery, 54 rats (18 of which received a cochleostomy alone, 18 of which received a cochleostomy and acute cochlear implantation using standard surgical techniques, and 18 of which received a cochlear implant) were infected with Streptococcus pneumoniae via three different routes of bacterial inoculation (middle ear, inner ear, and intraperitoneal) to represent all potential routes of bacterial infection from the upper respiratory tract to the meninges. Results The presence of a cochlear implant reduced the threshold of bacteria required to cause pneumococcal meningitis from all routes of infection in healthy animals. Conclusion The presence of a cochlear implant increases the risk of pneumococcal meningitis regardless of the route of bacterial infection. Significance Early detection and treatment of pneumococcal infection such as otitis media may be required, as cochlear implantation may lead to a reduction of infectious threshold for meningitis.

Pneumococcal meningitis threshold model: a potential tool to assess infectious risk of new or existing inner ear surgical interventions

Hypothesis: A minimal threshold of Streptococcus pneumoniae is required to induce meningitis in healthy animals for intraperitoneal (hematogenous), middle ear, and inner ear inoculations, and this threshold may be altered via recent inner ear surgery. Background: There has been an increase in the number of reported cases of cochlear implant-related pneumococcal meningitis since 2002. The pathogenesis of pneumococcal meningitis is complex and not completely understood. The bacteria can reach the central nervous system (CNS) from the upper respiratory tract mucosa via either hematogenous route or via the inner ear. The establishment of a threshold model for all potential routes of infection to the CNS in animals without cochlear implantation is an important first step to help us understand the pathogenesis of the disease in animals with cochlear implantation. Methods: Fifty-four otologically normal adult Hooded Wistar rats (27 receiving cochleostomy and 27 controls) were inoculated with different amounts of bacterial counts via three different routes (intraperitoneal, middle ear, and inner ear). Rats were monitored during 5 days for signs of meningitis. Blood, cerebrospinal fluid, and middle ear swabs were taken for bacterial culture, and brains and cochleae were examined for signs of infection. Results: The threshold of bacterial counts required to induce meningitis is lowest in rats receiving direct inner ear inoculation compared with both intraperitoneal and middle ear inoculation. There is no change in threshold between the group of rats with cochleostomy and the control (Fishers exact test, p < 0.05). Conclusion: A minimal threshold of bacteria is required to induce meningitis in healthy animals and is different for three different routes of infection (intraperitoneal, middle ear, and inner ear). Cochleostomy performed 4 weeks before the inoculation did not reduce the threshold of bacteria required for meningitis in all three infectious routes. This threshold model will also serve as a valuable tool, assisting clinicians to quantitatively analyze if the presence of a cochlear implant or other CNS prostheses alter the risk of meningitis.

Pneumococcal meningitis: development of a new animal model.

Hypothesis: The rat is a suitable animal to establish a model for the study of pneumococcal meningitis postcochlear implantation. Background: There has been an increase in the number of cases of cochlear implant-related meningitis. The most common organism identified was Streptococcus pneumoniae. Whether cochlear implantation increases the risk of pneumococcal meningitis in healthy subjects without other risk factors remains to be determined. Previous animal studies do not focus on the pathogenesis and risk of pneumococcal meningitis postimplantation and are based on relatively small animal numbers, making it difficult to assess the cause-and-effect relationship. There is, therefore, a need to develop a new animal model allowing direct examination of the pathogenesis of meningitis in the presence of a cochlear implant. Methods: Eighteen nonimplanted rats were infected with 1 × 106 and 1 × 108 colony-forming units (CFU) of a clinical isolate of S. pneumoniae via three different inoculation routes (middle ear, inner ear, and i.p.) to examine for evidence of meningitis during 24 hours. Six implanted rats were infected with the highest amount of bacteria possible for each route of inoculation (4 × 1010 CFU i.p., 3 × 108 CFU middle ear, and 1 × 106 CFU inner ear) to examine for evidence of meningitis with the presence of an implant. The histological pattern of cochlear infections for each of the three different inoculating routes were examined. Results: Pneumococcal meningitis was evident in all 6 implanted animals for each of the three different routes of inoculation. Once in the inner ear, bacteria were found to enter the central nervous system via either the cochlear aqueduct or canaliculi perforantes of the osseous spiral lamina, reaching the perineural and perivascular space then the internal acoustic meatus. The rate, extent, and pattern of infection within the cochleae depended on the route of inoculation. Finally, there was no evidence of pneumococcal meningitis observed in 18 nonimplanted rats inoculated at a lower concentration of S. pneumoniae when observed for 24 hours postinoculation. Conclusion: Meningitis in implanted rats after inoculation with a clinical isolate of S. pneumoniae is possible via all three potential routes of infection via the upper respiratory tract. The lack of meningitis observed in the 18 nonimplanted rats suggests that longer postinoculation monitoring periods are required to ensure whether or not meningitis will develop. Based on this work, we have developed a new animal model that will allow quantitative risk assessment of meningitis postcochlear implantation, and the assessment of the efficacy of potential interventional strategies in future studies.

Mesenteric Castleman's disease in childhood

and rarely occurs in children. In 70% of cases, it occurs in the mediastinum. 3–5 The neck, retroperitoneum, pancreas, pelvic cavity and the axillary and inguinal lymph nodes are uncommon sites of involvement. 4,6 Furthermore the mesenteric Castleman’s disease is very rare. To our knowledge only 12 cases have been reported. 4,7–9 Surgical excision of the affected lymph node plays an important role in treatment of this disease. We encountered a case of the mesenteric Castleman’s disease in a paediatric surgical patient. Information from the literature research on this entity and the pathological findings are included in this report. An 8-year-old boy with no underlying health problems presented to his local doctor with symptoms of tonsillitis. Routine blood tests showed: hypochromic microcystic anaemia (haemoglobin level of 90 g/L), thrombocytosis (platelets count of 558 × 10 9 /L) and elevated erythrocyte sedimentation rate (ESR of 118 mm/h). His white cell count was normal. His iron study was difficult to interpret in the context of high acute inflammatory markers. The stool and the urine microscopy and culture were negative. His chest X-ray was normal. The patient did not have any symptoms or signs of chronic systemic infections, malignancy, gastrointestinal blood loss or malabsorption. His dietary history was satisfactory. He had a trial of 6 weeks iron replacement therapy in which he had no response to the treatment. Further investigations showed the presence of hypergammaglobulinaemia. However, tests for Coeliac disease were negative. He had a normal Meckels’ scan, and normal endoscopic studies of upper and lower gastrointestinal tracts. A small bowel barium series did not reveal Crohn’s disease of the small bowel or a duplication cyst. However, it revealed a mass of 4 × 5 cm displacing between the loops of bowel. Subsequent ultrasound imaging showed a well circumscribed 5-cm mass with heterogeneous echogenicity at the level of the bifurcation of the aorta. He was referred to the paediatric surgical clinic for the evaluation of this mass. The patient underwent laparotomy and a 4 × 5cm irregular yellow-tan ovoid solid mass arising from ileal mesentery was resected. Histology of the mass showed a lymph node consisting of a large number of lymphoid follicles with germinal centres separated by bands of dense hyaline connective tissue. Numerous plasma cells were present (Fig. 1). Only occasional vessels with a thick hyaline wall are seen in the germinal centres. The features are consistent with Castleman’s disease of the plasma cell type. The patient had an unremarkable recovery postoperatively. His anaemia, platelets count, inflammatory markers and immunoglobulin level improved at the 3-month follow up.

Intraoperative Real-time Cochlear Response Telemetry Predicts Hearing Preservation in Cochlear Implantation.

Aim: To monitor cochlear function during cochlear implantation and determine correlations with postoperative acoustic hearing. Background: Cochlear response telemetry measures cochlear function directly from cochlear implant electrodes. We have adapted this system to provide real-time cochlear response telemetry (RT-CRT) monitoring of a patients acoustic hearing as the cochlear implant electrode array is inserted. Methods: Eighteen subjects (1 child and 17 adults) with sloping high frequency hearing loss were implanted with Cochlear Ltd slim straight arrays (CI422/CI522). Tone bursts (500 Hz, 100–110 dB) were presented at 14 Hz continuously during the array insertion. RT-CRT amplitudes were correlated with surgical manoeuvres recorded on the video from the operating microscope and with postoperative pure tone audiograms. Results: Despite an excellent overall rate of complete or partial hearing preservation (79%), RT-CRT identified that in 47% of these implantations there was transient or permanent reduction in the amplitude of the cochlear microphonic (CM). Patients with a preserved CM at the end of insertion had on average 15 dB better low-frequency hearing preservation. The CM amplitude was most vulnerable during the last few millimeters of insertion or when inadvertent movement of the array occurred after full insertion. Physical contact/elevation of the basilar membrane is hypothesized as a likely mechanism of hearing loss rather than overt physical trauma. Conclusion: RT-CRT can be used to predict early postoperative hearing loss and to potentially refine surgical technique. In the future, feedback of RT-CRT may prove to be a valuable tool for maximizing preservation of residual hearing or providing feedback on electrode contact with the basilar membrane.

Pneumococcal meningitis post cochlear implantation: potential routes of infection and pathophysiology

OBJECTIVE This review describes the current concept of pneumococcal meningitis in cochlear implant recipients based on recent laboratory studies. It examines possible routes of Streptococcus pneumoniae infection to the meninges in cochlear implant recipients. It also provides insights into fundamental questions concerning the pathophysiology of pneumococcal meningitis in implant recipients. DATA SOURCES Medline/PubMed database; English articles after 1960. Search terms: cochlear implants, meningitis, pneumococcus, streptococcus pneumonia. REVIEW METHODS Narrative review. All articles relating to post-implant meningitis without any restriction in study designs were assessed and information extracted. RESULTS The incidence of pneumococcal meningitis in cochlear implant recipients is greater than that of an age-matched cohort in the general population. Based on the current clinical literature, it is difficult to determine whether cochlear implantation per se increases the risk of meningitis in subjects with no existing risk factors for acquiring the disease. As this question cannot be answered in humans, the study of implant-related infection must involve the use of laboratory animals in order for the research findings to be applicable to a clinical situation. The laboratory research demonstrated the routes of infection and the effects of the cochlear implant in lowering the threshold for pneumococcal meningitis. CONCLUSION The laboratory data complement the existing clinical data on the risk of pneumococcal meningitis post-cochlear implantation.

Hydrocele of the canal of nuck

Hydrocele of the canal of nuck is a rare condition in females of which there are approximately 500 cases in the known literature. It is caused by incomplete obliteration of the processus vaginalis peritonei, a tubular fold of peritoneum that invaginate the inguinal canal anterior to the gubernaculum and is analogous to the tunica vaginalis testis in the male. Commonly if the processus remains patent, it forms a pathway for an indirect inguinal hernia. However, if it is partially obliterated proximally, an encysted hydrocele can result. Herein we report the case of a hydrocele in a 26-year-old female presenting with an intermittent right groin lump. Differentials included a femoral hernia, inguinal lymphadenopathy, epidermal cyst or tumour (sarcoma, lipoma, leiomyoma). Ultrasound examination demonstrated a 6 cm dumb bell shaped anechoic structure with its waist at the superficial ring, consistent with a hydrocele. The diagnosis was subsequently confirmed on surgical exploration.