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Howard M. Eisenberg, Charles Y. Liu, and Oren Sagher

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Robert G. Grossman, Charles Y. Liu, and Amit Verma

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Charles Y. Liu and Alfredo Quinones-Hinojosa

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Daniel J. Hoh, Charles Y. Liu, and Michael Y. Wang

Object

Effective methods for fixation of the axis include C1–2 transarticular and C-2 pedicle screw placement. Both techniques pose a risk of vertebral artery (VA) injury in patients with narrow pedicles or an enlarged, high-riding VA. Pars screws at C-2 avoid the pedicle, but can cause VA injury with excessively long screws. Therefore, the authors evaluated various entry points and trajectories to determine ideal pars screw lengths that avoid breaching the transverse foramen.

Methods

Both pars were studied on 50 CT scans (100 total). Various pars lengths were assessed using 2 entry points and 3 trajectories (6 measurements). Entry point A was the superior one-fourth of the lateral mass. Entry point B was 3-mm rostral to the inferior aspect of the lateral mass. Using entry points A and B, Trajectory 1 was the minimum distance to the transverse foramen; Trajectory 2 was the maximum distance to the transverse foramen; and Trajectory 3 was the steepest angle to the pars/C-2 superior facet junction without transverse foramen breach.

Results

The mean patient age was 46 ± 17 years, and 84% of the CT scans reviewed were obtained in men. There was no significant difference in right or left measurements. Entry point B demonstrated greater pars lengths for each trajectory compared with entry point A (p < 0.0001). For both entry points, Trajectory 3 provided the greatest pars length. Using Trajectory 3 with entry point B, 84, 95, and 99% had a pars length that measured ≥ 18, 16, and 14 mm, respectively. Using Trajectory 3 with Entry point A, only 41, 64, and 87% had a pars length that measured ≥ 18, 16, and 14 mm, respectively.

Conclusions

Using an entry point 3-mm rostral to the inferior edge of the lateral mass and a trajectory directed toward the superior facet/pars junction, 99% of partes interarticularis in this study would tolerate a 14-mm screw without breach of the transverse foramen.

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Yvette D. Marquez, Michael Y. Wang, and Charles Y. Liu

Over the course of the past few decades, it has become apparent that in contrast to previously held beliefs, the adult central nervous system (CNS) may have the capability of regeneration and repair. This greatly expands the possibilities for the future treatment of CNS disorders, with the potential strategies of treatment targeting the entire scope of neurological diseases. Indeed, there is now ample evidence that stem cells exist in the CNS throughout life, and the progeny of these stem cells may have the ability to assume the functional role of neural cells that have been lost. The existence of stem cells is no longer in dispute. In addition, once transplanted, stem cells have been shown to survive, migrate, and differentiate. Nevertheless, the clinical utility of stem cell therapy for neurorestoration remains elusive. Without question, the control of the behavior of stem cells for therapeutic advantage poses considerable challenges. In this paper, the authors discuss the cellular signaling processes that influence the behavior of stem cells. These signaling processes take place in the microenvironment of the stem cell known as the niche. Also considered are the implications attending the replication and manipulation of elements of the stem cell niche to restore function in the CNS by using stem cell therapy.

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Gabriel Zada, Eisha Christian, Charles Y. Liu, and Steven L. Giannotta

Object

Aneurysms of the anterior communicating artery (ACoA) can be a considerable challenge to treat surgically based on variations in the anatomy and morphological features of the ACoA complex. The fenestrated aneurysm clip can be a simple and practical tool in the operative management of ACoA aneurysms. The goal in this study was to characterize the particular surgical situations in which the use of a fenestrated clip facilitates the clip ligation of ACoA aneurysms.

Methods

The authors present their operative strategy and techniques for the use of fenestrated clips in the treatment of ACoA aneurysms.

Results

One hundred ninety-nine patients underwent surgical clipping of an ACoA aneurysm at the authors' institution between the years 1991 and 2008. Of these patients, fenestrated aneurysm clips were used in 20 cases (10%). The following structures were enclosed in the clip aperture: ipsilateral A2 artery, 12 patients (60%); ipsilateral A1 artery, 4 patients (20%); ipsilateral A1 artery plus recurrent artery of Heubner, 1 patient (5%); ACoA, 1 patient (5%); frontopolar artery, 1 patient (5%); and no structures, 1 patient (5%). Aneurysms approached from the left side more frequently required fenestrated clips than did right-sided aneurysms (80 vs 20%, p = 0.0073). In all cases, patency of the A2 vessels was confirmed on postoperative angiography. In 2 patients, small remnant aneurysm necks were identified on postoperative angiography.

Conclusions

The use of fenestrated aneurysm clips can minimize tedious and potentially dangerous dissection of adherent branch vessels, while maintaining the integrity of structures placed within the clip aperture. The ACoA aneurysms pointing in a superior direction are more likely to require clip fenestration around the A2 vessel, whereas those pointing in an inferior direction are more likely to require clip fenestration around the A1 vessel. The parallel approximation of the fenestrated clip blades makes them especially useful in the treatment of large or giant aneurysms.

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Charles Y. Liu, Brian Lee, Nicholas Boulis, and Ali R. Rezai

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Christopher J. Stapleton, Charles Y. Liu, and Martin H. Weiss

Growth hormone (GH)–secreting pituitary adenomas represent a common source of GH excess in patients with acromegaly. Whereas surgical extirpation of the culprit lesion is considered first-line treatment, as many as 19% of patients develop recurrent symptoms due to regrowth of previously resected adenomatous tissue or to continued growth of the surgically inaccessible tumor. Although medical therapies that suppress GH production can be effective in the management of primary and recurrent acromegaly, these therapies are not curative, and lifelong treatment is required for hormonal control. Stereotactic radiosurgery has emerged as an effective adjunctive treatment modality, and is an appealing alternative to conventional fractionated radiation therapy. The authors reviewed the growing body of literature concerning the role of radiosurgical procedures in the treatment armamentarium of acromegaly, and identified more than 1350 patients across 45 case series. In this review, the authors report that radiosurgery offers true hormonal normalization in 17% to 82% of patients and tumor growth control in 37% to 100% of cases across all series, while minimizing adverse complications. As a result, stereotactic radiosurgery represents a safe and effective treatment option in the multimodal management of primary or recurrent acromegaly secondary to GH-secreting pituitary adenomas.

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Gabriel Zada, Charles Y. Liu, Dawn Fishback, Peter A. Singer, and Martin H. Weiss

Object

The goal of this study was to assess the incidence of symptomatic and occult hyponatremia in patients who had undergone transsphenoidal pituitary surgery.

Methods

Patients who underwent transsphenoidal surgery at the University of Southern California University Hospital between 1997 and 2004 had serum sodium levels drawn on an outpatient basis on postoperative Day 7. Patient records were retrospectively reviewed to determine the incidence of, and risk factors for, symptomatic and asymptomatic hyponatremia.

Two hundred forty-one patients had routine serum sodium levels drawn as outpatients on postoperative Day 7. Twenty-three percent of these patients were found to be hyponatremic (Na ≤ 135 mEq/L). The overall incidence rate of symptomatic hyponatremia in the 241 patients was 5%. The majority of hyponatremic patients (80%) remained asymptomatic, whereas 20% became symptomatic. In patients with symptomatic hyponatremia, the mean sodium level at diagnosis was 120.5 mEq/L, compared with 128.4 mEq/L in asymptomatic, hyponatremic patients (p < 0.0001). Female patients were more likely to develop hyponatremia than male patients (33% compared with 22%, p < 0.03). Fifty-two percent of patients who had transient diabetes insipidus (DI) early in their postoperative course subsequently developed hyponatremia, compared with 21% of those who did not have DI (p < 0.001). Patient age, tumor type, and tumor size did not correlate with development of delayed hyponatremia. Outpatients with moderately and severely low sodium levels were 5 and 12.5 times more likely, respectively, to be symptomatic than were patients with mild hyponatremia.

Conclusions

Delayed hyponatremia occurs more frequently than was previously suspected in patients who have undergone transsphenoidal surgery, especially in female patients and those who have previously had transient DI. The majority of hyponatremic patients remain asymptomatic. Obtaining a serum sodium value on an outpatient basis 1 week after pituitary surgery is helpful in recognition, risk stratification, and subsequent intervention, and may prevent potentially serious complications.

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Daniel R. Kramer, Krista Lamorie-Foote, Michael Barbaro, Morgan B. Lee, Terrance Peng, Angad Gogia, George Nune, Charles Y. Liu, Spencer S. Kellis, and Brian Lee

OBJECTIVE

Stimulation of the primary somatosensory cortex (S1) has been successful in evoking artificial somatosensation in both humans and animals, but much is unknown about the optimal stimulation parameters needed to generate robust percepts of somatosensation. In this study, the authors investigated frequency as an adjustable stimulation parameter for artificial somatosensation in a closed-loop brain-computer interface (BCI) system.

METHODS

Three epilepsy patients with subdural mini-electrocorticography grids over the hand area of S1 were asked to compare the percepts elicited with different stimulation frequencies. Amplitude, pulse width, and duration were held constant across all trials. In each trial, subjects experienced 2 stimuli and reported which they thought was given at a higher stimulation frequency. Two paradigms were used: first, 50 versus 100 Hz to establish the utility of comparing frequencies, and then 2, 5, 10, 20, 50, or 100 Hz were pseudorandomly compared.

RESULTS

As the magnitude of the stimulation frequency was increased, subjects described percepts that were “more intense” or “faster.” Cumulatively, the participants achieved 98.0% accuracy when comparing stimulation at 50 and 100 Hz. In the second paradigm, the corresponding overall accuracy was 73.3%. If both tested frequencies were less than or equal to 10 Hz, accuracy was 41.7% and increased to 79.4% when one frequency was greater than 10 Hz (p = 0.01). When both stimulation frequencies were 20 Hz or less, accuracy was 40.7% compared with 91.7% when one frequency was greater than 20 Hz (p < 0.001). Accuracy was 85% in trials in which 50 Hz was the higher stimulation frequency. Therefore, the lower limit of detection occurred at 20 Hz, and accuracy decreased significantly when lower frequencies were tested. In trials testing 10 Hz versus 20 Hz, accuracy was 16.7% compared with 85.7% in trials testing 20 Hz versus 50 Hz (p < 0.05). Accuracy was greater than chance at frequency differences greater than or equal to 30 Hz.

CONCLUSIONS

Frequencies greater than 20 Hz may be used as an adjustable parameter to elicit distinguishable percepts. These findings may be useful in informing the settings and the degrees of freedom achievable in future BCI systems.