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Biomedical subjects

S J Millen

Publications and source records attributed to S J Millen.

At least 19 recordsLinked to original sources
PubMed1999

Vestibular compensation in guinea pigs given intravenous lidocaine after unilateral labyrinthectomy.

Intravenous lidocaine has been reported to alleviate vertigo in Meniere's disease and suggested as a possible antivertigo agent after unilateral labyrinthectomy in a study of cats. To further evaluate the effects of intravenous lidocaine on the acute phase of postural compensation, we subjected 13 pigmented guinea pigs to unilateral labyrinthectomy. Seven received intravenous lidocaine (4 mg/kg) immediately after labyrinthectomy. The other six served as controls and received an equivalent-volume injection of normal saline solution. Total body curvature, trunk curvature, yaw head tilt, and roll head tilt were measured at frequent intervals for up to 30 hours after surgery. Both groups had immediate difficulties with posturing that gradually improved. The lidocaine group tended to exhibit delayed postural compensation, but this was only statistically significant for roll head tilt. These results do not show improvement in postural compensation from unilateral labyrinthectomy after the administration of intravenous lidocaine. A species-specific effect on the vestibular pathways is suggested, and we conclude that further evaluation of lidocaine and the vestibular system is warranted.

Animals↗
PubMed1997

Functional MR of the primary auditory cortex: an analysis of pure tone activation and tone discrimination.

PURPOSE: To use functional MR imaging to measure the effect of frequency (pitch), intensity (loudness), and complexity of auditory stimuli on activation in the primary and secondary auditory cortexes. METHODS: Multiplanar echo-planar images were acquired in healthy subjects with normal hearing to whom auditory stimuli were presented intermittently. Functional images were processed from the echo-planar images with conventional postprocessing methods. The stimuli included pure tones with a single frequency and intensity, pure tones with the frequency stepped between 1,000, 2,000, 3,000, or 4,000 Hz, and spoken text. The pixels activated by each task in the transverse temporal gyrus (TTG) and the auditory association areas were tabulated. RESULTS: The pure tone task activated the TTG. The 1,000-Hz tone activated significantly more pixels in the TTG than did the 4,000-Hz tone. The 4,000-Hz tone activated pixels primarily in the medial TTG, whereas the 1,000-Hz tone activated more pixels in the lateral TTG. Higher intensity tones activated significantly more pixels than did lower intensity tones at the same frequency. The stepped tones activated more pixels than the pure tones, but the difference was not significant. The text task produced significantly more activation than did the pure tones in the TTG and in the auditory association areas. The more complex tasks (stepped tones and listening to text) tended to activate more pixels in the left hemisphere than in the right, whereas the simpler tasks activated similar numbers of pixels in each hemisphere. CONCLUSION: Auditory stimuli activate the TTG and the association areas. Activation in the primary auditory cortex depends on frequency, intensity, and complexity of the auditory stimulus. Activation of the auditory association areas requires more complex auditory stimuli, such as the stepped tone task or text reading.

Acoustic Stimulation↗
PubMed1995

Functional magnetic resonance imaging of the central auditory pathway following speech and pure-tone stimuli.

Functional magnetic resonance imaging (FMRI) is a new noninvasive technique for imaging cerebral function. Studies of the human central auditory pathway examined responses in eight normal hearing volunteers following auditory stimuli, including narrative speech and pure-tone audiometry. The activation demonstrated by FMRI is modeled on an increase in regional blood flow with increased neuronal activity. The FMRI signals represent deoxyhemoglobin concentration changes in capillaries within the region of the brain that is activated. Brain activation was imaged in the superior temporal gyrus during text reading and pure tones. Activation in both text and pure-tone presentation did not vary with the intensity of the auditory stimulus and elicited a dominant response in the left temporal lobe. These observations demonstrate the capability of FMRI to correlate anatomic and functional relationships in the human central auditory pathway.

Acoustic Stimulation↗
PubMed1994

The effect of intracranial surgical trauma on gadolinium-enhanced magnetic resonance imaging.

Gadolinium-enhanced magnetic resonance imaging (MRI) is currently the gold standard for diagnosis of an acoustic neuroma. Its status is diagnosis of a recurrent or residual neuroma is not nearly as clear. A pilot study of 36 postoperative cases showed enhancement in 100% of the patients at the operative site. To examine the role of surgical trauma and biodegradable packing on enhanced MRI, an animal study was designed. Cats and monkeys that underwent posterior fossa surgical procedures had preoperative and postoperative MRI and histologic correlation of any enhanced area. Areas of postoperative enhancement should not be considered as diagnostic of tumor. Further studies are necessary to develop a criteria for recurrent tumor diagnosis with enhanced MRI.

Adult↗
PubMed1994

Absent round window reflex: possible relation to step-wise hearing loss.

The diagnosis of perilymphatic fistula can be confusing and prone to error. The signs and symptoms can be extremely varied, and currently there is no clinical or laboratory test that accurately predicts the presence of this entity. The only reliable method of diagnosis, namely surgical exploration, is often frustrating as, commonly, no evidence of an active fistula is found. Four children initially believed to have a perilymphatic fistula were found on exploration instead to have an absent round window reflex with normal mobility of the ossicular chain. These children presented with a history of abrupt, step-wise decreases in their hearing thresholds that frequently progressed from a mixed to a purely sensorineural loss. No anatomic abnormalities were found on high-resolution computed tomography. The authors theorize that this finding may represent altered fluid dynamics within the inner ear. Whether it signifies a prior fistula that has spontaneously healed remains to be confirmed. A review of the literature along with possible pathophysiologic mechanisms is presented.

Adolescent↗
PubMed1993

Surgical management of CSF otorhinorrhea following retrosigmoid removal of cerebellopontine angle tumors.

Cerebrospinal fluid (CSF) otorhinorrhea continues to be one of the most common complications following surgery for cerebellopontine angle (CPA) tumors. For retrosigmoid approaches, this complication has been reported to occur in 12-19 percent of patients. Nearly all prior surgical attempts at control have included middle ear and eustachian tube obliteration along with packing of the mastoid. This article reviews 165 retrosigmoid procedures (January 1982-December 1990) for removal of CPA tumors, with a leak rate of 9.8 percent (16 cases), 7.2 percent (12 cases) requiring surgical control. An operative technique involving only mastoid obliteration is presented. This approach is less invasive as it limits the scope of the surgical field and also maintains the integrity of the middle ear for potential preservation of hearing. This approach has resulted in control in 100 percent of the patients, without reoperation. The routes of the CSF leak, the technique, and the rationale for its use are presented.

Cerebellar Neoplasms↗
PubMed1990

Gadolinium-enhanced magnetic resonance imaging in facial nerve lesions.

We present our 2-year experience with a contrast enhancement agent in magnetic resonance imaging (MRI) examining facial nerve pathology. Characteristics of the agent gadolinium diethylenetriamine pentaacetic acid are reviewed. The radiographic capability to differentiate pathologic vs. normal facial nerves based on enhancement and a change in signal intensity generated by the nerve is demonstrated. Experience with facial nerve disorders including Bell's palsy, facial nerve neuromas, a facial nerve graft site, postoperative facial paralysis, and traumatic facial paralysis is presented. The ability to image the facial nerve in Bell's palsy provides an entirely new means of examining this disorder, and its implications are discussed. The ability to enhance the paralyzed facial nerve in the temporal bone after posterior fossa surgery supports a previously held concept as to the pathophysiology of this problem.

Adult↗
PubMed1989

MR imaging of facial nerve enhancement in Bell palsy or after temporal bone surgery.

The authors evaluated magnetic resonance (MR) images obtained with intravenously administered gadolinium in ten patients who had facial paralysis and no facial nerve tumor. In patients with either Bell palsy (four patients) or facial paralysis after temporal bone surgery (six patients), intratemporal facial nerve enhancement was seen. Facial nerve enhancement on MR images proved to be a nonspecific finding.

Facial Nerve↗
PubMed1989

Gadolinium-enhanced magnetic resonance imaging in temporal bone lesions.

A 2-year experience with an enhancement agent in magnetic resonance imaging (MRI) is examined through case presentations. Characteristics of the agent Gadolinium DTPA/Dimeglumin are reviewed. Radiographic capabilities in enhanced versus unenhanced MRI are compared. Temporal bone lesions, including acoustic neuromas and facial nerve neuromas, are presented. Recent experience with facial nerve enhancement in Bell's palsy is also presented. Greater accuracy in defining small temporal bone lesions and increased delineation of facial nerve involvement appear to be significant benefits with enhanced MRI.

Adult↗
PubMed1987

MR detection of tumor in the internal auditory canal.

The MR appearance of 15 tumors within or near the internal auditory canal was analyzed in detail and compared with the subsequent surgical observations. In most cases, nonenhanced MR showed the precise extent of the intracanalicular and extracanalicular tumor despite minor variations in appearance. In a case of facial nerve neurinoma, the extent to which the tumor invaded the canal was underestimated by MR. Gadolinium-DTPA enhancement is expected to eliminate uncertainties in MR imaging of the internal auditory canal.

Cerebellar Neoplasms↗
PubMed1986

Retrosigmoid intracanalicular vestibular nerve section: an alternative surgical approach for Menière's disease.

Selective vestibular nerve section has been shown to be an extremely effective treatment for control of vertigo in Menière's disease. In recent years the retrolabyrinthine approach has popularized this form of treatment. An alternative to the retrolabyrinthine approach is presented. It consists of a retrosigmoid intracanalicular dissection, and approach used for acoustic neuroma surgery. A review of the surgical technique, the rationale for its selection over the retrolabyrinthine approach, and the initial results and operative complications during its first eighteen months of use are presented.

Humans↗
PubMed1985

Surface-coil magnetic resonance imaging of the internal auditory canal.

Computed tomography is effective for detecting acoustic neuromas, but not for resolving individual nerves in the internal auditory canal. Surface-coil magnetic resonance (MR) images of the internal auditory canal were obtained using a 1.5 T superconducting magnet, a 13.5-cm-diameter surface coil, 3- and 5-mm-thick slices, and partial-saturation pulse sequences. Cranial nerves VII and VIII (three branches) were identified on MR images in volunteers and on corresponding cryomicrotomic sections. The nerves were obscured in one patient with an acoustic neuroma. Because high-resolution surface-coil images can demonstrate specific nerves in the internal auditory canal, MR should be a sensitive study to evaluate cranial nerves VII and VIII in patients with facial paralysis and neurosensory hearing loss that is congenital or caused by small acoustic neuromas.

Facial Nerve↗
PubMed1985

Mixed glioma of the cerebellopontine angle.

A rare case of mixed ependymoma and astrocytoma of the cerebellopontine angle is reported. Its clinical presentation, characteristics on evaluation, and prognosis are compared with those of the acoustic neuroma and glioma. The central form of von Recklinghausen's disease and familial multiple lipomatosis as it applies to the patient is also discussed.

Astrocytoma↗
PubMed1984

Magnetic resonance imaging of the internal auditory canal.

Three patients with exclusively or predominantly intracanalicular neuromas and 5 with presumably normal internal auditory canals were examined with prototype 1.4- or 1.5-tesla magnetic resonance (MR) scanners. MR images showed the 7th and 8th cranial nerves in the internal auditory canal. The intracanalicular neuromas had larger diameter and slightly greater signal strength than the nerves. Early results suggest that minimal enlargement of the nerves can be detected even in the internal auditory canal.

Facial Nerve↗