Electrophysiological aspects of the middle ear muscle reflex in the rat: latency, rise time and effect on sound transmission.

The latency, the rise time and the influence of the acoustic reflex on sound transmission were investigated in the adult rat during ketamin anesthesia. This was done by recordings of the cochlear microphonics (CM) and electromyographic (EMG) recordings of the reflex responses of the tensor tympani muscle. The acoustic reflex was elicited by contralateral acoustic stimuli of which the intensity and frequency was varied. Ipsilaterally, the effect on sound transmission was determined by estimating the change in amplitude of the CM's of ipsilateral administered subliminal stimuli. It was shown that both the tensor tympani muscle and the stapedius muscle contribute in the reflex. The latency as well as the rise time of the reflex determined by CM recordings showed to be short (minimal values: 12 and 7 ms respectively). The mean latency of the tensor tympani muscle reflex, measured by EMG, was about 7 ms. The attenuation of 0.25-8 kHz tone bursts upto 115 dB SPL is limited to a mean maximum of 15 dB SPL. The maximal attenuation was shown to occur at 1 kHz. Frequencies above 2 kHz appeared to be the best elicitor of the middle ear muscle reflex.

A tumour in the cerebellopontine angle region: an unusual case.

This paper describes a nearly 60-year old patient with unilateral hearing loss, developed in one year, and complaints of tinnitus and dizziness. Additional findings were unilateral peripheral facial paresis and a diminished corneal reflex. The cause was found to be a metastasis of an anaplastic carcinoma, localized at the site of the internal acoustic porus.

Ear surgery in Treacher Collins syndrome.

The autosomal dominant hereditary Treacher Collins syndrome manifests itself phenotypically in dysmorphogenesis of particularly the first, but also the second branchial arch system. Consequently, 50% of patients with Treacher Collins syndrome have a congenital, generally pure conductive hearing loss resulting from a major or minor ear anomaly. The outcome of surgery to improve patients' hearing varies and is sometimes even disappointing. Thorough analysis of 33 cases (39 operated ears) and the strict application of a classification for the anomaly to each ear enabled us to gain insight into the most suitable surgical policy and to form a prognosis for reconstructive ear surgery.

Immunohistochemistry of Nasopharyngeal (Waldeyer's ring equivalent) lymphoid tissue in the rat.

Previously we have described the presence of Waldeyer's ring equivalent (WRE) lymphoid tissue in the rat, and pointed out the importance of such an experimental model for studying the immunological role of nasopharyngeal lymphoid tissue. Here we extend this work with immunohistological data in terms of compartmentalization and distribution of the various lymphoid and non-lymphoid cells of this WRE lymphoid tissue in situ. WRE tissue consists of distinct T cell and B cell areas. B cell areas predominate; they are located directly under the mucosal epithelium and consist mainly of follicles. These follicles frequently contain a germinal center with IgD negative B cells interspersed with scattered CD4 (helper/inducer) T cells. Follicular dendritic cells are present in the germinal centers. T cell areas, on the other hand, are predominantly present at the abluminal side of the WRE in interfollicular areas. In these areas high endothelial venules and both CD4 and CD8 (suppressor/cytotoxic) T cell populations with a clear preponderance of CD4 over CD8 cells can be observed. MHC class II positive interdigitating dendritic cells are also scattered throughout these T cell areas. Mononuclear phagocytes (ED1-positive monocytes/macrophages) are scattered throughout the WRE, but especially in the T cell areas. A subpopulation of (ED3-positive) mononuclear phagocytes, e.g., the lymphoid tissue macrophage, is exclusively scattered between the small blood vessels along the abluminal side of the lymphoid tissue. Here, plasma cells, including those of the IgA type, are located. The data show that nasopharyngeal lymphoid tissue in the rat can be considered as an immunologically fully equipped and active mucosal lymphoid organ presumably executing similar immune functions as the tonsils in the human Waldeyer's ring.

The Waldeyer ring equivalent in the rat. A model for analysis of oronasopharyngeal immune responses.

By means of serial sectioning of the head and neck a paired, rod shaped, parachoanic lymphoid organ was identified in Lewis rats. Histological, ultrastructural studies and FACS analysis showed this organ to be a lympho-epithelial organ with high endothelial venules (HEV) and a preponderance of B over T and T helper over T suppressor cells. Consequently this organ resembles the pharyngeal tonsil of man, and it is called the Waldeyer ring equivalent (WRE). The lymphatic drainage of this organ occurs predominantly to the deep, and to a lesser extent to the superficial cervical lymph nodes. Migration studies with 51Cr labeled cells show that the WRE lymphoid cells migrate into the lymphoid organs with HEV (peripheral lymph nodes. Peyer patches and WRE). In this respect they resemble peripheral lymph node cells more than cells from the Peyer patches. Thus the WRE lymphoid tissue in the rat is undoubtedly involved in local oronasopharyngeal immune surveillance and may also contribute to mucosal and systemic immune responses.

Tension pneumoperitoneum as an early complication after adenotonsillectomy.

Pneumoperitoneum as a result of pneumomediastinum has been described already. Amongst the causes pneumoperitoneum due to a complication of adenotonsillectomy, has not previously been described. We describe a five-year-old girl with tension pneumoperitoneum with respiratory and circulatory insufficiency half an hour after adenotonsillectomy. Removal of the intra-abdominal air with a 14 gauge needle restored normal respiration and circulation.

Treacher-Collins syndrome. Management of major and minor anomalies of the ear.

12 patients suffering from a Treacher-Collins syndrome, or mandibulo-facial dysostosis, were operated on in the Nijmegen University Hospital between 1960 and 1990. An early diagnosis is generally reached when there is a congenital atresia of the auditory canal. Auditory rehabilitation with a conventional prosthesis of the bone or a BAHA is preferable to surgical reconstruction. In minor cases, deafness must be screened as early as possible, with a bone hearing aid prosthesis. Surgical exploration can be performed at best as the age of 10, but the chances of success are less than those of other functional reconstructions because of the associated malformation.

An additional classification for congenital aural atresia. Its impact on the predictability of surgical results.

An additional classification of type II of congenital aural atresia (to Altmann) is presented. This subclassification proved to be useful in predicting the change on a servicable hearing level after a canal plasty procedure. Also a correlation has been noted between the postoperative hearing level and the degree of malformation of the auricle. In type II A atresia the rate of success is so good, that a small group of patients with unilateral atresia and this class of anomally can also be expected to benefit from surgery.

Surgical treatment of congenital aural atresia.

The divergent views concerning indications, ideal age for surgery, and surgical approach to achieve better hearing illustrate the complexity of cases of congenital aural atresia. Whether the anomaly is unilateral or bilateral also influences the criteria on which the surgical decision is based. In the thirty-six ears operated on between 1972 and 1983 using the canal plasty technique, the average hearing gain was 20 dB, with 18 ears having an air conduction threshold of 35 dB or better after a long follow-up.

The facial nerve coursing across the promontory with a persistent stapedial artery.

A case of congenital bilateral conductive deafness is described. Some years ago absence of the oval window was found in the left ear. Exploratory tympanotomy of the right ear revealed a large persistent stapedial artery while the facial nerve took its course from the geniculate ganglion straight down across the promontory anteriorly of the stapedial artery.

Arachnoid cyst simulating intrameatal acoustic neuroma.

A very rare cause of perception deafness wass found in a child with an intrameatal arachnoid cyst. This case is the second reported in the literature.