Naoki Inamura

Effect of kainic acid upon N1 latency.

Although the N1 latency of whole nerve action potential is one of the important pieces of information obtained from ECochG, there are some conflicting opinions as to whether or not it is prolonged in scnsorineural hearing loss. Kainic acid (KA) is known to destroy neurons selectively through an action at glutamatergic synapses. Therefore, a model of “neural deafness” was made by perfusing the scala tympani with KA solution. The effect of KA upon cochlear microphonics was minimal. Although the N1 amplitude was markedly suppressed by KA, the N1 latency was neither prolonged nor shortened. The result obtained in the present study strongly suggests that the N1 latency is not prolonged in “neural deafness.”

Gas Analysis of the Middle Ear Cavity in Normal and Pathological Conditions

The gas of the tympanic bulla was measured using 18 normal and 14 tube-obstructed guinea pigs. The concentrations of CO2 and O2 were 4.8 +/- 1.0% and 7.2 +/- 1.8% in normal animals, and 4.3 +/- 1.6% and 8.1 +/- 2.0% in tube-obstructed animals, respectively. The bulla was opened to room air and then closed again. The recovery process of each gas was examined. In normal animals, CO2 and O2 were exponentially changed toward the pre-open value with time. The time constants of this recovery process were 15 min and 97 min in CO2 and O2, respectively. In tube-obstructed animals, however, this quick recovery of CO2 was significantly delayed (time constant, 50 to 80 min), although there was no effect upon the recovery of O2. This delayed recovery of CO2 is likely to be due to the edema of the mucous membrane.

Saccular and Cochlear Endolymphatic Potentials in Experimentally Induced Endolymphatic Hydrops of Guinea Pigs

Saccular and cochlear endolymphatic potentials (SEP and CEP) were recorded in 33 normal animals. We confirmed that SEP is not produced in the saccule per se, but is a potential leak from the cochlea. CEP was reduced to one-tenth of the original value when it reached the saccule. Endolymphatic hydrops was provoked in 32 animals, and CEP and SEP were successfully recorded in 29 and 20 cases, respectively. The measurements were performed in the 2nd, 4th and 12th postoperative week. Both CEP and SEP decreased in magnitude as time elapsed after the surgery. This reduction is attributed to the strial dysfunction. In advanced hydrops, CEP transmission to the saccule is greatly inhibited. It is concluded that the saccular dysfunction can occur in the hydropic ear.

Cochlear Potentials of Guinea Pigs with Experimentally Induced Renal Failure

In order to investigate the relationship between renal failure and hearing loss, the authors made a guinea pig model with experimentally induced renal failure and examined cochlear potentials (N1, CM and EP). When renal damage was greater, the amplitudes of N1 and CM were decreased and the latency of N1 was prolonged, but EP was within normal range. The sensory cells of the cochlea were considered responsible for the hearing loss in the guinea pig model. No pathological alterations of the cochlea were revealed by a light microscopy. It is suggested that the etiology of the hearing loss was due mainly to metabolic disturbances such as uremic toxins, electrolyte imbalance or endocrine abnormalities.

Pathophysiology and Prognosis of Sudden Deafness with Special Reference to the N1 Latency

Electrocochleography (ECochG) was performed in 84 patients with sudden deafness which were classified into 3 groups according to the ECochG findings, i.e. the unchanged N1 latency, the prolonged N1 latency and the absence of N1 response. The cause of hearing loss in the first group was thought to be strial, postsynaptic or mild cochlear damage and that in the second to be vascular, sensory or neural damage. The first group showed a better prognosis than those of the other two.

Effect of hypothermia on the cochlear potentials

The effects of hypothermia upon the cochlear potentials were studied in 30 guinea pigs. Particular attention was paid to the transient increase in AP amplitude at a moderate temperature. CM and AP were recorded via an Ag-AgCl lead placed on the round window membrane. Although the CM amplitude and threshold, and the AP latency and threshold were both impaired concomitant with the lowering of body temperature, the AP amplitude exhibited a transient increase at the beginning of cooling (peak at 30 degrees C) and a decrease thereafter. Narrow-band analysis of AP revealed that this phenomenon was most prominent in the high-frequency region. When the cochlear efferent fibers (crossed and uncrossed olivocochlear bundle) were cut, this transient increase in AP amplitude disappeared. This phenomenon seems to be due to the difference in sensitivity to hypothermia between the efferent and afferent fiber systems.

A Case of Extramedullary Plasmacytoma of the Maxilla with the Expression of Cytokeratin.

We report a case of extramedullary plasmacytoma of the maxilla, which was difficult to diagnose definitively by conventional histopathology because of the presence of epithelial antigens.A 62-year-old male with a 7-month-history of unilateral epiphora and nasal obstruction followed by swelling of his left cheek is presented. Physical findings, CT scanning and MRI imaging revealed a maxillary tumor, T4N0M0. Blood test, serum and urine protein analyses and bone marrow examination showed no abnormality. No other systemic lesion was found in X-rays and 67Ga- and 99mTc-scintigrams. Exploratory resection was performed, and the tumor was pathologically diagnosed as an undifferentiated carcinoma on the basis of its morphological features and positive immunohistochemical examination for epithelial markers such as cytokeratin and epithelial membrane antigen (EMA). The patient received preoperative local irradiation of 40Gy, and underwent total maxillectomy followed by irradiation of 50Gy and administration of cisplatin and 5-fluorouracil.Nineteen months after the surgery, the patient manifested a tumor in the thyroid region with high serum gamma-globulin and IgG levels. In addition, IgG-kappa-type myeloma protein was detected by immunoelectrophoresis of the serum. The patient underwent subtotal thyroidectomy. Although the tumor cells of the surgical specimen still exhibited epithelial markers, electron microscopic observation, immunohistochemical examination and Southern blot analysis demonstrated rough endoplasmic reticulum-rich cytoplasm, kappa (+) lambda (-) of Ig light chain and rearranged bands of Ig heavy chain, which are characteristic of plasmacytoma. The tumor was, consequently, diagnosed as extramedullary plasmacytoma. Serum gamma-globulin and IgG levels returned to the normal range 4 months after the second surgery.In conclusion, we emphasize that plasmacytoma may express epithelial antigens, and thus the importance of multiple supplementary methods to diagnose this neoplasm.

Extirpation of Epipharyngeal Cyst with KTP/532 Laser; A Report of Two Cases.

Epipharyngeal cysts were removed by KTP/532 laser from a 54-year-old male and a 68-year-old male. The chief complaint of both patients was a sensation of a foreign body on the epipharynx. MRI revealed a lateral cyst on the right wall of the epipharynx in both patients. Each cyst had a smooth surface and a high intensity signal in T2 weighted pulse sequences. The symptoms totally disappeared, and no recurrence of cysts had been observed for 3 months and more after treatment. The application of KTP/532 laser extirpation to epipharyngeal cysts caused little bleeding and no obvious complications.