David M. Vernick

Stapedectomy Results in a Residency Training Program

As the total number of stapedectomy procedures has declined, the adequacy of residency training for this procedure must be evaluated. Results of 5 years of stapedectomies performed by the resident otology service at the Massachusetts Eye and Ear Infirmary from Oct 1, 1979, through Sept 30, 1984, are reviewed and compared with other published results. A suggestion is made for improving the residency teaching program.

Clones of Chinese hamster cells cultivated in vitro not permanently resistant to azaguanine

Abstract The frequency of clones not permanently resistant to azaguanine (AG) was measured in Chinese hamster ovary cells (CHO) grown in vitro by plating them in 7.5 μg/ml AG and isolating a number of clones in the course of 5 experiments. Such isolated clones were propagated to a point at which their resistance to both AG and the reverse selective medium, HAT, could be determined. Out of a total of 13 clones isolated, 4 of these could not be distinguished from the parent CHO line, either on the basis of their growth in a gradient of AG concentrations or the reverse selective HAT medium or on the basis of their mutation frequency to resistance to 30 μg/ml AG. All four of the apparent phenocopies were isolated from plates in which although lower numbers of cells were seeded, a higher frequency of clones able to grow in AG was yielded. This suggests that the higher “mutation” frequencies obtained at lower cell densities are due to the appearance of phenocopies which occur only under these conditions. It is concluded that under low plating density conditions, the lower levels of AG (7.5 μg/ml) are not satisfactory for mutagenesis and mutation rate studies.

Hyperlipidemia in association with childhood sensorineural hearing loss.

In adults there has been an association noted between hyperlipidemia and sensorineural hearing loss. Etiologic considerations include hyperviscosity of the serum, vascular occlusion and an increased susceptibility to noise. Until now this correlation, to our knowledge, has not been made in the pediatric population. Several children with bilateral fluctuating sensorineural hearing losses have been identified with hyperlipidemia. The fluctuations in hearing varied with lipid levels. With dietary controls, the cholesterol levels returned to what would be near the norm for the pediatric population and hearing returned to near baseline. Unexplained fluctuating sensorineural hearing losses in children warrant the consideration of hyperlipidemia. Discovering a potentially reversible etiology for hearing loss is significant but more importantly, may lead to the early detection of hyperlipidemia in the young patient.

Bilateral congenital middle ear cholesteatomas

Congenital middle ear choleslcatomas remain of interest because of their relative rarity and unknown origin. A 4‐month‐old child presenting with bilateral congenital middle ear cholestcatomas forms the basis for this report. The nature of the epithelial debris found suggests an external origin. An extended transcanal tympanotomy approach for removal, based upon an operative experience of 11 similar ears, will be discussed.

Hearing Loss in Osteogenesis Imperfecta: Characteristics and Treatment Considerations

Osteogenesis imperfecta (OI) is the most common heritable disorder of connective tissue. It is associated with fractures following relatively minor injury, blue sclerae, dentinogenesis imperfecta, increased joint mobility, short stature, and hearing loss. Structures in the otic capsule and inner ear share in the histologic features common to other skeletal tissues. OI is due to mutations involving several genes, the most commonly involved are the COL1A1 or COL1A2 genes which are responsible for the synthesis of the proalpha-1 and proalpha-2 polypeptide chains that form the type I collagen triple helix. A genotype/phenotype relationship to hearing loss has not been established in OI. Hearing loss is commonly found in OI with prevalence rates ranging from 50 to 92% in some studies. Hearing loss in OI may be conductive, mixed, or sensorineural and is more common by the second or third decade. Treatment options such as hearing aids, stapes surgery, and cochlear implants are discussed.

Infralabyrinthine Approach to the Internal Auditory Canal

Multiple surgical procedures have been developed to expose the contents of the internal auditory canal. These include the middle fossa approach, the posterior fossa approach, the retrolabyrinthine approach, and the retrosigmoid approach. Each has its own unique benefits, as well as disadvantages. A new posterior-inferior approach to the internal auditory canal (the infralabyrinthine approach) has been developed. This approach affords exposure of at least the medial half of the internal auditory canal while remaining extradural and extralabyrinthine. By dissecting below the posterior semicircular canal, and remaining extradural, hearing is preserved. The dissection can proceed far enough laterally in the internal auditory canal to separate the cochlear and vestibular nerve divisions. Further anatomic considerations, as well as clinical applicability, will be discussed.

Mutagenesis studies on cultured mammalian cells. The sensitivity of the asparagine-requiring phenotype to several chemical agents ☆

The effect of several chemical agents on the mutation frequency from asparagine dependence to asparagine independence has been studied in Jensen sarcoma cells. It was found that ethylmethanesulfonate brought about a dramatic exponential increase, while nitrosoguanidine was not lighly effective as a mutagen, causing only a modest increase in mutation frequency, and quinacrine HCl was ineffective. The results presented here are compared with those obtained in other systems and with our previous work on the effects of UV on mutation induction in the asparagine system. They suggest that the basis of the asparagine requirement of mammalian cell lines resides in a specific genetic alteration in nuclear DNA which is corrected by the mutagenic action of the agents tested here.

Ultraviolet-induced mutations to asparagine independence in Jensen sarcoma cells in vitro

Abstract UV-irradiation induces an exponential increase in the frequency of mutation from asparagine requirement to asparagine non-requirement in Jensen sarcoma cells grown in vitro . The corrected mutation frequency increases from the spontaneous rate of 5.1·10 −6 per cell to 1248·10 −6 per cell with a dose of 180 erg/mm 2 of 254 nm UV A substantial increase was oberved even without correction for survivors, and no significant difference was observed in the UV sensitivity of asparagine-requiring and non-requiring Jensen clones. When Jensen cells were plated at low densities in a feeder layer of LMTK-cells inactivated by HAT medium, an increase in the cloning ability of the former was observed as compared to appropriate controls without the feeder layer, but the increase was constant over all doses of UV tested. Revertants are stable and possess measurable asparagine synthetase. It is concluded that UV is an extremely effective mutagen in this system.

Extramedullary hematopoiesis of the middle ear in a patient with thalassemia

Extramedullary hematopoiesis, the formation of blood cells outside trabecular bone, is not an uncommon phenomenon. It occurs as a result of an increased demand on the hematopoietic system from anemia combined with an ineffective response by the bone marrow. It has been associated with both congenital and acquired anemias, as well as bone marrow infiltrating diseases such as myelofibrosis, leukemia, and osteitis fibrosa cystica.‘J There are only two other reported cases of extramedullary hematopoiesis occurring in the middle ear. Both cases were young black patients with sickle cell disease.lOz’l This is the first reported case of extramedullary hematopoiesis in the middle ear occurring in a patient with thalassemia.

The effects of anesthesia on middle-ear effusions

Surgeons occasionally note a discrepancy between preoperative assessment of middle‐ear effusion and operative observation during the placement of ventilating tubes in childrens ears. This study was designed to determine whether this variance is secondary to the effects of inhalation anesthesia or misinterpretation of the preoperative exam. Observations were recorded by three distinctly different methods of measurement: the surgeon, the MD‐2 Impedance Analyzer, and the Acoustic Otoscope® immediately before and after induction of anesthesia. These results were then analyzed and compared with the operative findings. Anesthetic induction was shown to cause alteration in the presence of middle‐ear fluid in less than 10% of cases.