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Biomedical subjects

D Y Chan

Publications and source records attributed to D Y Chan.

At least 19 recordsLinked to original sources
PubMed2001

Interaortocaval renal artery dissection for right laparoscopic donor nephrectomy.

Laparoscopic donor nephrectomy is gaining increasing popularity because the procedure helps reduce disincentives to live kidney donation and has increased the live kidney donor pool. The left kidney of the donor is the preferred allograft because the right renal vein is shorter. Similarly, the right renal artery might be foreshortened because it hides behind the inferior vena cava during laparoscopic transperitoneal dissection. There are instances, however, in which it is not practical to take the left kidney due to vascular anomalies or asymmetric function. We describe a novel technique for obtaining greater renal arterial length utilizing laparoscopic interaortocaval dissection.

Aorta↗
PubMed2001

Density functional theory of charged colloidal systems.

The phase behavior of charged colloidal systems has been studied recently by the density functional theory formalism (DFT) [R. van Roij, M. Dijkstra, and J. P. Hansen, Phys. Rev. E 59, 2010 (1999)]. A key feature of this approach is the appearance of a density and temperature-dependent effective Hamiltonian between the charged colloids. Under certain approximations, the effective Hamiltonian is made up only of a sum of position-independent one-body or volume terms and two-body colloid-separation dependent terms. In the limit of low colloidal densities, the DFT results do not reduce to the familiar Debye-Hückel limiting law nor do the results agree with previous work based on an identical approach but were developed using traditional statistical-mechanical methods [B. Beresford-Smith, D. Y. C. Chan, and D. J. Mitchell J. Colloid Interface Sci. 105, 216 (1985)]. This paper provides a reconciliation of these differences and comments on the significance of the one-body volume terms in the effective Hamiltonian of a system of charged colloids in determining thermodynamics and phase behavior.

Journal Article↗
PubMed2001

Laparoscopic radical nephrectomy: cancer control for renal cell carcinoma.

PURPOSE: We evaluated the clinical efficacy of laparoscopic versus open radical nephrectomy in patients with clinically localized renal cell carcinoma. MATERIALS AND METHODS: Between 1991 and 1999, 67 laparoscopic radical nephrectomies were performed for clinically localized, stages cT1/2 NXMX, pathologically confirmed renal cell carcinoma. During this period 54 patients who underwent open radical nephrectomy with pathologically confirmed stages pT1/2 NXMX disease were also identified. Medical and operative records were retrospectively reviewed and telephone followup was done to assess patient status. RESULTS: In the laparoscopic and open groups average tumor size was 5.1 (range 1 to 13) and 5.4 cm. (range 0.2 to 18), respectively, which was not statistically significant. No patient had laparoscopic port site, wound or renal fossa tumor recurrence in either group. All patients were followed at least 12 months. In the laparoscopic group 2 cancer specific deaths occurred at a mean followup of 35.6 months. In the open group there were 2 cancer specific deaths and 3 cases of disease progression at a mean followup of 44 months. Kaplan-Meier disease-free survival and actuarial survival analysis revealed no significant differences in the laparoscopic and open radical nephrectomy groups. Also, no differences were noted in the complication rate. CONCLUSIONS: Laparoscopic radical nephrectomy is an effective alternative for localized renal cell carcinoma when the principles of surgical oncology are maintained. Initial data show shorter patient hospitalization and effective cancer control with no significant difference in survival compared with open radical nephrectomy.

Adult↗
PubMed2001

Laparoscopic nephroureterectomy for the treatment of transitional cell carcinoma of the upper urinary tract.

OBJECTIVES: To establish the safety and efficacy of laparoscopic and laparoscopic-assisted nephroureterectomy. METHODS: Since 1993, 25 patients with a minimum of 12 months of follow-up underwent nephroureterectomy using a total laparoscopic or laparoscopic-assisted technique. Four patients had specimen morcellation for tissue removal. All patients had regular follow-up with physical examinations, interval cystoscopy, and radiographs, depending on the metastatic potential of the tumor. Retrospective chart review was performed and assessed for operative time, blood loss, tumor pathologic stage, complications, and outcome. One patient was excluded because of an open conversion due to multiple previous abdominal surgeries and failure to progress. RESULTS: The mean operating time was 329 minutes but decreased with experience. The median hospital stay was 4 days. Tumor stage was directly related to tumor grade. Associated bladder tumors (prior history or recurrent tumors) occurred in 50% of the patients. Ipsilateral ureteral stump site recurrence occurred in 1 patient. Although no port site seeding occurred, 1 patient, whose tumor was discovered histologically after laparoscopic pyeloplasty for presumed benign disease, developed recurrence in the renal fossa and metastatic disease. Two patients developed liver metastasis. CONCLUSIONS: Total laparoscopic and laparoscopic-assisted nephroureterectomy are acceptable alternatives to open surgery in the treatment of transitional cell carcinoma of the upper urinary tract. Tumor morcellation did not appear to adversely affect patient outcome. As with open nephroureterectomy, tumor grade is the most important prognostic indicator of local, bladder, and metastatic recurrence. No port site seeding was observed in either the total laparoscopic or laparoscopic-assisted groups.

Adolescent↗
PubMed2001

Determinants of continence in the bladder exstrophy population: predictors of success?

OBJECTIVES: To delineate factors that may predict eventual urinary continence after bladder neck reconstruction (BNR) in the bladder exstrophy population. METHODS: The records of 65 patients who underwent all phases of bladder exstrophy reconstruction at our institution between 1975 and 1997 with greater than 1-year follow-up were reviewed and data analyzed. RESULTS: Fifty patients (77%) are continent day and night and voiding per urethra without need for augmentation or intermittent catheterization. Nine (14%) patients have social continence, dry for more than 3 hours during the day. Two patients required continent diversion for continence after failed BNR. Four patients are completely incontinent. The mean age of BNR was 4 years with a mean and median capacity of 93 and 85 cc (range 45 to 175). Analysis of bladder capacity measurements prior to BNR revealed that patients with a bladder capacity greater than 85 cc median capacity at the time of BNR had better outcomes. No correlation was found between the age of BNR and obtaining eventual continence. The mean time to daytime continence was 14 months (range 4 to 21) and the mean time to nighttime continence was 22 months (range 11 to 33). CONCLUSIONS: Determinants of continence in the bladder exstrophy population are multifactorial. In our experience, 77% of patients are completely dry, day and night, and 91% can achieve social continence, being dry for at least 3 hours. However, with careful evaluation of bladder capacity and bladder growth, urinary continence may be improved in this population with better patient selection.

Bladder Exstrophy↗
PubMed2001

Does capsular incision at radical retropubic prostatectomy affect disease-free survival in otherwise organ-confined prostate cancer?

OBJECTIVES: To evaluate the influence of isolated, histologically identified capsular incision (CI) (exposure of benign or malignant glands to the inked surgical margin in the setting of organ-confined disease) on disease progression after anatomic radical retropubic prostatectomy (RRP) for clinically localized prostate cancer. METHODS: Between March 1993 and September 1999, 4747 men underwent RRP at the Johns Hopkins Hospital; 107 men (2.3%) were diagnosed with CI in otherwise organ-confined disease; 92 (86%) had at least 6 months (mean 30) of follow-up. We matched these CI cases (based on surgeon, age, clinical stage, final pathologic Gleason grade, and preoperative serum prostate-specific antigen level) one-for-one with controls in three additional pathologically defined groups and compared the freedom from disease progression (prostate-specific antigen level greater than 0.2 ng/mL and/or local palpable recurrence) after RRP. RESULTS: The actuarial 3-year likelihood of freedom from disease progression was 87.8% for the CI group, 96.4% for men with organ-confined disease (P = 0.10), 91.3% for men with extraprostatic extension and negative surgical margins (P = 0.99), and 73.9% for men with positive surgical margins resulting from extraprostatic extension (P <0.01). No statistically significant difference was found in the actuarial likelihood of freedom from disease progression between men with CI into benign glands (n = 22) and men with CI into tumor (n = 70) (P = 0.93). CONCLUSIONS: No statistically significant difference was found in the likelihood of early recurrence between patients with isolated CI and other specimen-confined disease. Patients with isolated CI have a significantly lower likelihood of early recurrence than patients with positive surgical margins due to extraprostatic extension, regardless of whether the CI is into benign glands or tumor. Long-term follow-up is necessary to confirm these findings.

Adult↗
PubMed2001

Image-guided therapy in urology.

Technological breakthroughs have advanced the fields of urology, radiology, and minimally invasive surgery. Today, the various imaging modalities are increasingly applied to guiding therapy. Among the procedures now in use or under development are percutaneous cyst drainage or sclerotherapy; tissue ablation with high-intensity focused ultrasound, cold, heat, or photon radiation; and conformal radiation and brachytherapy. As current limitations are overcome, image-guided therapy will expand.

Animals↗
PubMed2001

Does increased needle biopsy sampling of the prostate detect a higher number of potentially insignificant tumors?

PURPOSE: Several studies have documented that increased biopsy sampling, that is 6 versus 12 biopsy cores, can detect more prostate cancer. It is unknown whether increased sampling of the prostate will detect a higher number of potentially insignificant tumors. MATERIALS AND METHODS: We searched the surgical pathology files at The Johns Hopkins Hospital for patients in whom prostate needle biopsy was performed by a single urologist between April 1993 and April 2000, and subsequently underwent radical prostatectomy. Patients who underwent radical prostatectomy and had 8 core biopsies or less between March 1994 and August 1999 were also studied. Clinically significant tumors were defined as those with volume greater than 0.5 cc, Gleason score 7 or greater or nonorgan confined disease. RESULTS: A total of 297 patients with a mean age of 60 years (range 36 to 75) were evaluated. Group 1 consisted of 107 men with 8 core biopsies or less, including 51 with 6, and group 2 comprised 190 men with 9 cores or greater, including 145 with 12. The 2 groups were equal in regard to prostate specific antigen, age, digital rectal examination and transrectal ultrasound gland volume at biopsy. The only difference between the groups was a higher number of cores with cancer in group 2 (mean 2.8 versus 2.1, p = 0.0006). Of the patients who underwent radical prostatectomy 59.6% had Gleason score 6 or less, 26.3% 3+4, 6.7% 4+3 and 7.4% 8 to 9. There were 12.4% of patients with positive margins, 36.4% extraprostatic extension, and 5.4% seminal vesicle invasion and/or lymph node metastasis. Tumor volumes averaged 1.1 cc (range 0.01 to 10.7) and 60.9% of tumors were greater than 0.5 cc. Clinically significant tumors were seen in 77.4% of patients in group 1 and 74.6% in group 2. There was no significant difference in Gleason score, margin status, tumor volume, seminal vesicle invasion, or lymph node metastasis between groups 1 and 2, or in a subset analysis of men with 6 versus 12 core biopsies. However, patients in whom cancer was diagnosed with 9 core biopsies or greater were more likely to have organ confined disease (p = 0.02). CONCLUSIONS: Although increased sampling of the prostate does not increase the detection of potentially insignificant tumors, it does appear to detect earlier stage cancer.

Adult↗
PubMed2000

Laparoscopic nephrectomy for autotransplantation.

Proximal ureteral injuries often require extensive reconstruction to repair. Management options include nephrectomy, ileal ureter interposition, extensive spiral bladder flaps, or autotransplantation. We report a patient who sustained a proximal ureteral avulsion and underwent a less invasive repair by way of a laparoscopic nephrectomy and subsequent autotransplantation.

Adult↗
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↗