Carotid artery compression by the hyoid bone.

An 83-year-old male presented with bilateral carotid stenosis. Stenosis on the left side was reported to be greater than 70%. A left carotid endarterectomy was undertaken to increase the lumen size and remove the atherosclerotic plaque. During surgery, the hyoid bone was observed to have a 2-cm calcified horn capable of compressing the carotid artery. This unusual compression was confirmed by radiographic images. In cases where the carotid artery is compressed by the hyoid bone, a carotid endarterectomy rather than a stent may be the procedure of choice.

Electrical artifact during intraoperative electromyographic neuromonitoring.

Acoustic electromyography is a commonly employed neuromonitoring modality for protecting cranial and peripheral nerves for a variety of neck, cranial, and spinal surgeries. An artifact resembling an electromyographic (EMG) response caused by contact between two metal instruments within the surgical field may contaminate the interpretation of mechanically-elicited activity that occurs from neural irritation during surgery. This artifact has been casually referred to as the "crossed swords" effect and has not been adequately described. A series of manipulations were devised to determine if this artifact: 1) required an electrolytic medium for its occurrence, 2) could be produced between a metal and nonmetal object, 3) could be detected in a control channel outside the surgical site, 4) could be detected in background waveforms using parameters for averaging a somatosensory evoked potential (SSEP), and lastly 5) could be quantified electrically. The metal-to-metal artifact could be produced when instruments made contact in a fluid medium. In contrast, metal-to-nonmetal contact did not produce the artifact in or outside a fluid medium. This artifact was not detected on a control channel from surface electrodes over the deltoid muscle. When tapped or rubbed, the artifact sounded like an EMG response, but the morphology was unique. Only when the two metals were rubbed together were the morphologies and acoustic "signatures" similar to an EMG response. Metal-to-metal contact in a fluid medium did not produce an artifact that could be detected in the background activity recorded using parameters for SSEPs. The electrical potential discharge was approximately 100 mV after the instruments stayed in solution and made contact after 150 seconds. This artifact is likely attributable to current discharge when two metals contact each other, a phenomenon referred to as a galvanic couple.

Intraoperative monitoring of the recurrent laryngeal nerve using acoustic, free-run, and evoked electromyography.

The purpose of this study was to explore advantages and disadvantages of electrodes used for monitoring of the recurrent laryngeal nerve (RLN) and to determine the postoperative outcome in 135 patients. A pilot study examined 11 patients to compare the clinical performance of two commercially available recording electrodes and three stimulation electrodes for RLN neuromonitoring. After determining the most reliable and consistent stimulating/recording electrode combination, 124 patients were then monitored. In a total of 135 patients there was no permanent iatrogenic nerve damage to the RLN, although 2 patients developed transient vocal hoarseness that resolved shortly postoperatively. An initial "searching" current for evoked electromyography (EMG) was delivered at 0.7 mA and then decreased to a value of 0.35 mA, which reliably elicited RLN stimulation with a minimal incidence of false-positive results. The combination of auditory feedback from the mechanically elicited EMG and a control channel involving EMG monitoring of an additional peripheral muscle improved the detection of artifact and improved the clinical efficacy of intraoperative electromyography. A video camera showed the surgical manipulation on the EMG screen, allowing the neurophysiologist to correlate dissection with RLN status and location. Auditory responses from the nerve helped to determine the type of distress the RLN was encountering.

The length of the retention interval, forgetting, and subjective similarity.

A long retention interval tends to result in the poor retention known as forgetting. A high subjective similarity between stimuli frequently produces their poor retention. Thus, a long retention interval may increase the subjective similarity between stimuli (the RIISS hypothesis), and this increase may produce forgetting. To examine this hypothesis, college students made speeded same-different discriminations between two lines or tones of different lengths or frequencies that were 400 ms or 3,300 ms apart, and they rated the similarity of these stimuli. The long interval produced poorer overall performance as expected, but also produced poorer performance on different than same stimuli, implying that it increased the subjective similarity between the initial and subsequent stimuli, and it also increased rated similarity, in support of the RIISS hypothesis. The position that stored stimuli lose less common information than distinctive information explains RIISS evidence better than does perturbation theory.