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Biomedical subjects

D Y Chan

Publications and source records attributed to D Y Chan.

At least 37 records · Page 2Linked to original sources
PubMed2000

Renal ablative cryosurgery in selected patients with peripheral renal masses.

OBJECTIVES: To present the preliminary results of renal ablative cryosurgery in selected patients. METHODS: Seven patients were treated, all of whom had small peripheral tumors and chose not to undergo partial or radical nephrectomy. Four patients underwent a rib-sparing flank incision; the remaining three underwent laparoscopy. All tumors were biopsied before cryoablation. Intraoperative ultrasound was used to monitor the cryolesion. RESULTS: There were no intraoperative complications. The estimated blood loss averaged 111 mL. To date, 6 of the 7 patients have undergone at least one follow-up computed tomography scan (14.2 months average follow-up); all these scans demonstrated partial resolution of the lesion. Clinically, the patients tolerated the procedure without any renal complications or significant changes in creatinine. CONCLUSIONS: This limited clinical trial has demonstrated the feasibility of treating small peripherally located renal tumors with cryosurgery with minimal morbidity and a favorable outcome. Further studies are necessary to determine the long-term efficacy of this treatment modality.

Aged↗
PubMed2000

Focal hepatic ablation using interstitial photon radiation energy.

BACKGROUND: Intratumoral ablative therapy is being used increasingly for the treatment of primary and secondary hepatic malignancies. The interstitial point-source photon radiosurgery system (PRS) is a novel ablative technique that uses radiation therapy similar in dosimetry to interstitial brachytherapy. STUDY DESIGN: To determine the feasibility, toxicity, and local tissue destructive capabilities of the PRS in the liver, preliminary studies in a nontumor-bearing canine model were examined. A 6-month survival study was conducted. Each animal received three radiation treatments, in the right, central, and left hepatic regions. Three low-dose treatments were delivered to each of six animals (group A), generating a 2.0-cm-diameter radiated sphere with a dose of 20 Gy at the lesion edge. Three high-dose treatments were delivered to each of six animals (group B), generating a 3.0-cm-diameter radiated sphere with 20 Gy at the lesion edge. RESULTS: The treatment reproducibly generated sharply demarcated hepatic ablative lesions proportional to the administered dose. Mean lesion diameter at 1 month was 1.6+/-0.2 cm in group A and 3.4+/-1.0 cm in group B. Lesion size was independent of intrahepatic location, including near vascular structures. PRS therapy, when applied to portal structures, resulted in hilar damage. Hilar damage appeared to be associated with arteriolar thrombosis and bile duct injury. Treatment of regions adjacent to large hepatic veins and the IVC was not associated with vessel thrombosis or stricture. CONCLUSIONS: PRS ablation is a generally well-tolerated method that results in consistent, well-demarcated, symmetric lesions of complete necrosis with minimal adjacent parenchymal injury. Application of such an approach for the treatment of liver tumors is promising.

Animals↗
PubMed2000

Feasibility of ablating normal renal parenchyma by interstitial photon radiation energy: study in a canine model.

BACKGROUND AND PURPOSE: A miniature photon radiosurgery system (PRS) has been described as an alternative to surgical resection and external-beam radiation for tumors and may now offer an alternative for ablation of renal lesions. We evaluated the feasibility of ablation by PRS in a normal parenchyma canine model. MATERIALS AND METHODS: Twelve mongrel dogs were used in this survival study. In the left and right kidneys of each animal, a peripheral lesion and central-hilar lesion, respectively, were induced with PRS. The probes were placed in the renal parenchyma, and local radiation of 15 Gy at a radius of 1.3 cm was delivered over 10 minutes. Serum electrolytes were measured serially. Computed tomography scans were obtained, and the animals were sacrificed for pathologic correlation. In a separate study, the liver received three additional treatments of 10 to 20 minutes of radiation. RESULTS: Eleven dogs survived this 6-month study and were sacrificed as scheduled. One animal expired after 2 weeks from radiation-induced fulminant hepatic failure with normal renal function. No other complications were observed. The average lesion size was 2.5 cm in diameter. Histologic analysis confirmed coagulative necrosis with sharp demarcation from the surrounding parenchyma. CONCLUSION: Preliminary studies demonstrate the feasibility of PRS ablation of the renal parenchyma. Further tumor model testing will be important to determine the ultimate efficacy of local photon radiation energy.

Animals↗
PubMed2000

Effect of time delay on surgical performance during telesurgical manipulation.

BACKGROUND: Telementoring allows a less experienced surgeon to benefit from an expert surgical consultation, reducing cost, travel, and the learning curve associated with new procedures. However, there are several technical limitations that affect practical applications. One potentially serious problem is the time delay that occurs any time data are transferred across long distances. To date, the effect of time delay on surgical performance has not been studied. MATERIALS AND METHODS: A two-phase trial was designed to examine the effect of time delay on surgical performance. In the first phase, a series of tasks was performed, and the numbers of robotic movements required for completion was counted. Programmed incremental time delays were made in audiovisual acquisition and robotic controls. The number of errors made while performing each task at various time delay intervals was noted. In the second phase, a remote surgeon in Baltimore performed the tasks 9000 miles away in Singapore. The number of errors made was recorded. RESULTS: As the time delay increased, the number of operator errors increased. The accuracy needed to perform remote robotic procedures was diminished as the time delay increased. A learning curve did exist for each task, but as the time delay interval increased, it took longer to complete the task. CONCLUSIONS: Time delay does affect surgical performance. There is an acceptable delay of <700 msec in which surgeons can compensate for this phenomenon. Clinical studies will be needed to evaluate the true impact of time delay.

Evaluation Studies as Topic↗
PubMed2000

Mini-percutaneous nephrolithotomy.

Standard percutaneous nephrolithotomy is highly effective for the removal of renal calculi. However, significant morbidity has been associated with this procedure. Consequently, many urologists inappropriately defer to a less effective procedure to reduce patient morbidity. This practice may increase the total number of procedures needed for treatment and result in a substantial increase in health care costs. Mini-percutaneous nephrolithotomy using a 13F ureteroscopy sheath is described to reduce the morbidity associated with standard percutaneous nephrolithotomy while maintaining its efficiency and effectiveness for stone removal. The indications and technique for mini-percutaneous nephrolithotomy and our results are summarized.

Cystoscopy↗
PubMed2000

Extensively necrotic cystic renal cell carcinoma: a clinicopathologic study with comparison to other cystic and necrotic renal cancers.

Renal cell carcinomas often show varying degrees of necrosis and cystic change. The prognostic importance of necrosis so extensive that only a few tumor cells can be identified is not clear. We gathered clinicopathologic and follow-up data on a group of eight such cases ("type I"). These patients were compared with two other groups of renal cell carcinomas: those with extensive necrosis (>50%), yet with readily identifiable tumor ("type II"), and cancers with extensive cystic change not resulting from necrosis, usually multiloculated ("type III"). The groups showed similar demographic characteristics, and within each group there was great variation in tumor size. Conventional (clear cell) histology was more common than papillary morphology in all groups. The type II neoplasms tended to be of higher nuclear grade and pathologic stage than the other groups. While one of six type I patients with follow up progressed 131 months after diagnosis, eight of 20 type II patients showed progression. None of the six type III patients with follow up progressed. We conclude that renal cell carcinomas showing extensive necrosis are capable of aggressive behavior, and patients with these lesions cannot be assured of cure following surgery. Pathologists must be aware of this entity and extensively sample any renal lesion showing extensive necrosis. The tumors showing a greater amount of viable neoplastic cells yet at least 50% necrosis had a higher rate of progression than did the type I patients. The lack of progression of any of the type III cases supports the idea that type III multiloculated cystic renal cell carcinomas may carry a distinctly better prognosis than other forms of renal cell carcinoma.

Adult↗
PubMed1999

Partial nephrectomy for centrally located tumors.

INTRODUCTION: Interest in nephron-sparing surgery has been spurred by the good long-term results of patients treated with partial nephrectomy. Partial nephrectomy entails the complete resection of renal tumor while leaving behind clear surgical margins and maximum functional renal parenchyma. TECHNICAL CONSIDERATIONS: We prefer to access the renal tumor by a flank incision. Intraoperative sonography is used to define the operative lesion and to search for multicentric tumors. A vascular clamp is placed on the renal hilum for vascular control. Regional hypothermia protects the kidney during renal ischemia. The perinephric fat is excised in situ with the renal tumor. Tumor base biopsies ensure negative margins. Meticulous dissection and tying of vessels improves hemostasis. Diluted methylene blue is directly injected into the renal pelvis to inspect for any intrarenal leakage. The argon beam coagulator is used routinely, and collagen (Avitene) is placed into the renal defect for hemostasis. The renal parenchyma and Gerota's fascia are reapproximated anatomically. A small drain is left in place, and the wound is closed in the usual manner. CONCLUSIONS: Recent studies continue to report that conservative surgery is as effective as radical nephrectomy for renal cell carcinoma, but the judgments in patient selection and operative management are paramount in determining its success.

Humans↗
PubMed1999

Laparoscopic renal cryoablation: acute and long-term clinical, radiographic, and pathologic effects in an animal model and application in a clinical trial.

OBJECTIVES: To evaluate renal cryosurgery by studying the feasibility of laparoscopic delivery and the radiographic characteristics and histopathologic effects in a porcine model using different freeze cycles. On the basis of the results, a clinical trial of laparoscopic cryosurgical ablation in select patients with clinical stage T1 renal tumors was started. MATERIALS AND METHODS: Twelve kidneys from six farm pigs underwent cryosurgery. Each kidney was treated with two freeze cycles to -180 degrees C. Six kidneys were retroperitonealized, and six were not. An abdominal CT scan was performed at various times to evaluate for the presence of urinoma or hematoma and to monitor lesion changes. Organs were harvested at times ranging from 24 hours to 13 weeks. Radiographic and histopathologic changes were recorded for each time period. Eight patients with small (average 2-cm) exophytic renal masses underwent laparoscopic biopsy and cryosurgical ablation using a 3- or 4.8-mm probe (Cryomedical Sciences Inc., Rockville, MD) for one 15-minute or two 5-minute freeze cycles to a temperature of -180 degrees C to extend the ice ball at least 7 mm beyond the tumor margin. RESULTS: Dense adhesions between the bowel and cryoablated renal tissue were encountered in all non-retroperitonealized kidneys, but no fistula formation was present. The retroperitonealized kidneys had minimal adhesion formation. None of the animals developed a urinary fistula. At 24 hours and 1 week, CT scanning demonstrated an enhancement defect corresponding to the region of the ice ball with no urinoma or hematoma. At 13 weeks, only a nonenhancing cortical defect was seen. At immediate harvest, hemorrhage was noted in the area of the ice ball with a sharp demarcation at the edge of the freeze zone. At 1 week, four distinct zones were seen: central necrosis, inflammatory infiltrate, hemorrhage, and fibrosis with regeneration. At 13 weeks, the necrotic tissue had been replaced with a circumscribed area of fibrosis. There were no intraoperative or postoperative complications in the eight patients. The estimated blood loss was 140 mL, and the mean hospital stay was 3.5 days. At a mean clinical follow-up of 7.7 (range 1-18) months and radiographic follow-up of 5 months; there have been no tumor recurrences or significant changes in the serum creatinine concentration. At 24 hours, there was an enhancement defect in the area of the ice ball. The CT images at 13 weeks showed a nonenhancing cortical defect in the area of the ice ball. CONCLUSIONS: Cryosurgery can be readily delivered laparoscopically, creating a discrete lesion at the time of treatment that appears to be consistent over time. In the animal studies, complete tissue necrosis developed in the freeze zone, followed by reabsorption, and by 13 weeks, fibrous tissue had replaced the defect. In the animal and human trials, there were no operative complications, urinomas, hematomas, or bowel or urinary fistulas. Follow-up imaging in human trials revealed a persistent nonenhancing defect in the area of the freeze zone. Long-term clinical follow-up will be necessary to determine the cancer-free survival rate.

Aged↗
PubMed1999

Retroperitoneal access for transperitoneal laparoscopy in patients at high risk for intra-abdominal scarring.

BACKGROUND AND PURPOSE: Adhesions from prior extensive open abdominal surgery can make initial transperitoneal access for laparoscopy hazardous. An alternative to open port placement is a retroperitoneal approach to the peritoneal cavity. We describe our retroperitoneal access for transperitoneal laparoscopy and evaluate the success of the subsequent laparoscopic procedure. PATIENTS AND METHODS: Eight patients with a history of abdominal surgery have undergone retroperitoneal access to the peritoneum prior to a laparoscopic urologic procedure. With the patient in a lateral decubitus position, the retroperitoneum is entered with a 10-mm Visiport device (US Surgical Corp., Norwalk, CT) along the posterior axillary line. A working space is bluntly created, the peritoneum identified anterior to the colon, and the endoscope passed through a peritoneotomy. The abdomen is then inspected, transperitoneal ports are strategically placed under direct vision, and the intended procedure is commenced. RESULTS: In all cases, retroperitoneal access to the peritoneum and subsequent trocar placement was successful. In five cases, the intended procedure was completed laparoscopically. In a case of bilateral ureterolysis, one side was completed laparoscopically; however, the other required open conversion. In two nephrectomies for xanthogranulomatous pyelonephritis (XGP), open conversion was necessary because of fibrosis. CONCLUSION: Retroperitoneal access to the peritoneal cavity permits safe and effective port placement when previous abdominal surgery makes initial transabdominal access difficult. However, despite successful access, in patients at risk for extensive perinephric fibrosis (e.g., XGP), a high incidence of open conversion may be expected.

Abdomen↗
PubMed1999

Laparoscopic testicular denervation for chronic orchalgia.

PURPOSE: No specific cause is identified in most cases of chronic orchialgia. Nonsurgical therapies, including management at a chronic pain clinic, are generally recommended. Only when multiple conservative measures fail are patients offered surgical intervention, such as orchiectomy. We evaluate laparoscopic testicular denervation as an organ preserving and minimally invasive surgical alternative. MATERIALS AND METHODS: Since 1993, 9 patients with chronic orchialgia have undergone transperitoneal laparoscopic testicular denervation after nonsurgical modalities failed. Using 1, 10 mm. and 1 or 2, 5 mm. ports, the gonadal vessels were isolated circumferentially and divided cephalad to the vas deferens and its vasculature. Preoperative treatment modalities, morbidity and outcome were documented. A cord block provided temporary relief in all 9 patients. Analog scales were used to assess long-term pain relief (0 no pain to 100 worst pain) and activity levels (0 bedrest to 100 no restrictions). RESULTS: Average symptom duration before laparoscopic testicular denervation was 4.1 years. Of 9 patients 8 had undergone prior scrotal surgery. Failed nonsurgical modalities included anti-inflammatory drugs in 7 patients, antibiotics in 6, pain clinic consultations in 4 and antidepressant medications in 2. Mean pain score decreased from 69.4 (range 35 to 90) preoperatively to 30.6 at a mean followup of 25.1 months. Excluding the 2 cases that had no pain relief (less than 10-point reduction), average pain score decreased from 69 to 19 postoperatively (mean reduction 71%). Activity levels improved in all cases. There were no significant complications, including testis atrophy. One patient who had no pain relief underwent subsequent hydrocelectomy for pain, which also failed. CONCLUSIONS: Laparoscopic testicular denervation can provide significant long-term pain relief and appears to be a reasonable alternative in select cases with chronic orchialgia refractory to medical therapy. Larger series and prospective evaluations are necessary.

Adult↗
PubMed1999

Laparoscopic donor nephrectomy: standard of care or unnecessary risk of organ loss?

Laparoscopic donor nephrectomy was developed to remove disincentives to live donation. It has been demonstrated to decrease the length of hospitalization, postoperative pain, time to convalescence and activity, while providing an optimal cosmetic result. Initial reports suggest that laparoscopic donor nephrectomy is feasible and equivalent to open donor nephrectomy.

Humans↗
PubMed1998

Surgery in advanced and metastatic renal cell carcinoma.

Curative surgery in more advanced renal cell carcinoma is limited to solitary metastases or regional disease. Response to systemic immunotherapy continues to be reported; however, most responses are limited and not durable. Only randomized, prospective clinical trials will prove the efficacy of systemic therapy.

Journal Article↗
PubMed1989

Refractive index gradient of human lenses.

We report nondestructive measurements and the modeling of the refractive index profiles in human lenses. Results in the equatorial and sagittal planes are compared with destructive measurements of refractive index, modeled data as well as with microdensitometric measurements of protein concentration. These comparisons highlight the differences between current models and measured data on human lenses.

Adolescent↗
PubMed1988

Nondestructive method of constructing three-dimensional gradient index models for crystalline lenses: I. Theory and experiment.

A nondestructive method of constructing the three-dimensional refractive index profile of crystalline lenses is presented. The technique is based on earlier work in which the refractive index profile is deduced from measuring the refraction of a set of light rays that traverse the lens in a particular plane. However, the present approach requires fewer assumptions about the form of the refractive index profile so that the deduced results are less likely to reflect preconceived notions about the form of the refractive index distribution. An accurate model for the bovine crystalline lens has been constructed with the present approach. Without further adjustable parameters, our three-dimensional model of the lens refractive index profile is able to predict accurately the refraction of meridional rays that traverse the lens in the sagittal plane. Preliminary data on human lenses are also presented.

Adolescent↗
PubMed1984

The Smoluchowski-Poisson-Boltzmann description of ion diffusion at charged interfaces.

A theoretical description of ion diffusion in the electric field set up by the double layer in the neighborhood of a charged interface is presented. Such a description is needed for the understanding of diffusion-controlled chemical kinetics and transport of ionic species in a variety of systems of interest in biophysics, electrochemistry, and colloid science. The ion dynamics are taken to be governed by the Smoluchowski diffusion equation and the average electrostatic field is obtained from the nonlinear Poisson-Boltzmann equation. Diffusion in finite regions with partially absorbing boundaries of planar, cylindrical, or spherical geometry is considered. The complete analytical solution of the Smoluchowski-Poisson-Boltzmann equation for counterions between two planar charged interfaces is given. Simple expressions are derived for certain useful integral quantities, viz., mean absorption times and absorption probabilities, in all geometries considered. Finally, lateral counterion diffusion and its consequences for surface re-encounter-enhanced chemoreception is considered.

Diffusion↗
PubMed1978

Evidence for variation in the number of functional gene copies at the AmaR locus in Chinese hamster cell lines.

The hypothesis of functional hemizygosity has been examined for the alpha-amanitin resistant (AmaR, a codominant marker) locus in a series of Chinese hamster cell lines. AmaR mutants were obtained from different cell lines, e.g., CHO, DHW, M3- 1 and CHO-Kl, at similar frequencies. After fractionation of different RNA polymerase activities in the extracts by chromatographic procedures, the sensitivity of the mutant RNA polymerase II towards alpha-amanitin was determined. While all of the RNA polymerase II activity in mutant CHO and CHO-Kl lines became resistant to alpha-amanitin inhibition, only about 50% of the activity is highly resistant in AmaR mutants of CHW and M3- 1 cell lines. The remaining activity in the latter cell lines shows alpha-amanitin sensitivity similar to that seen with the wild-type enzyme. This behaviour is similar to that observed with a 1:1 mixture of resistant and sensitive enzymes from CHO cells. These results, therefore, strongly indicate that while only one functional copy of the gene affected by alpha-amanitin is present in CHO and CHO-Kl cells, two copies of this gene are functional in the CHW and M3-1 cell lines.

Amanitins↗
PubMed1978

Evidence for functional hemizygosity at the Emtr locus in CHO cells through segregation analysis.

The hypothesis of functional hemizygostiy at the emetine-resistant (Emtr, a non-X-linked recessive marker) locus in Chinese hamster ovary (CHO) cells has been examined by segregation analysis. The frequencies and the rates of segregation of the Emtr and Thgr (thioguanine-resistant, an X-linked recessive mutation) markers were determined from hybrids constructed between an Emtr-Thgr CHO cell line and various other Chinese hamster lines (V79, M3-1, CHO, GM7S, CHW and CHL). Thgr segregants were obtained at similar frequencies (10(-2)-10(-3)) from all the hybrids. The frequency of segregation of the Emtr marker, however, was similar to that of Thgr only in the CHO x CHO hybrids and was much lower (10(-4)-10(-6)) than the CHO x other Chinese hamster hybrids. Similar results were obtained when the segregation rates for the two markers from various hybrids were determined. These results are consistent with the hypothesis that in CHO cells, the gene responsible for Emtr is present in a single (functional) copy, whereas two copies of this gene are present in other Chinese hamster lines examined.

Cell Line↗