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Biomedical subjects

Herbert Chen

Publications and source records attributed to Herbert Chen.

At least 55 records · Page 3Linked to original sources
PubMed2004

Gastrointestinal carcinoid tumors: factors that predict outcome.

Gastrointestinal (GI) carcinoids are neuroendocrine tumors originating in multiple locations throughout the GI tract. The prognosis for patients with GI carcinoid tumors is diverse. To determine the factors that significantly affect prognosis, we reviewed our experience. Between 1992 and 2000 a total of 70 patients with GI carcinoid tumors underwent surgical resection at our institution. The patients were grouped into three categories based on the origin of the carcinoid tumor: foregut, midgut, hindgut. The mean age of the patients was 56 +/- 2 years. All patients with foregut carcinoids had symptoms upon presentation, whereas 61% of those with midgut carcinoids and only 37% of those with hindgut carcinoids had symptoms ( p < 0.001). The factors that most strongly affected survival on univariate analysis were a symptomatic presentation and the site of origin. Patients with foregut or midgut lesions had lower 5-year disease-free survivals than those with hindgut tumors. Moreover, the size of the primary tumor and the presence of liver metastases were not independent predictors of survival. Despite the larger tumor size and the higher incidence of liver metastases, patients with foregut carcinoids appear to have the same prognosis as those with midgut carcinoids. These data therefore suggest that the outcomes of patients with carcinoid tumors are highly dependent on the presence of symptoms and the site of origin.

Carcinoid Tumor↗
PubMed2004

The utility of frozen section evaluation for follicular thyroid lesions.

BACKGROUND: Because fine-needle aspiration cannot reliably discriminate between benign and malignant follicular thyroid lesions, some surgeons use intraoperative frozen section (FS) to guide operative management. To determine the utility of FS for these lesions, we reviewed our institutional experience. METHODS: Between 1994 and 2001, 152 patients underwent surgical resection for follicular neoplasms. RESULTS: The mean age of the patients was 47 years, and 76% were female. Forty-one (32%) FSs were reported as benign, 5 (4%) as malignant, and 3 (2%) as indeterminate, and in 80 (62%), the diagnosis was "follicular lesion, deferred to permanent histology." On paraffin section, all patients with malignant FSs had thyroid cancer, and all 41 patients with benign FSs had benign lesions. Thus, FS for diagnosis of follicular thyroid cancer had a sensitivity, specificity, positive predictive value, and accuracy of 67%, 100%, 100%, and 96%, respectively. In most cases (64%), FS rendered no additional information at the time of operation. Therefore, the cost per useful FS was $7800, which is higher than the charge of a completion thyroidectomy (approximately $6000). CONCLUSIONS: FS analysis for follicular lesions seems to be highly specific and accurate. However, because of the low sensitivity, routine use of FS is not cost-effective in patients with follicular thyroid lesions.

Adenocarcinoma, Follicular↗
PubMed2004

Subclinical Cushing's syndrome in adrenal incidentalomas.

Up to 20% of patients with adrenal incidentalomas have abnormal cortisol production, and can be classified as having subclinical Cushing's syndrome. Although these tumors do not secrete enough cortisol to lead to the development of overt Cushing's syndrome, they are likely playing a contributory role in the development of hypertension, diabetes, osteoporosis, and obesity. Studies suggest that many of these problems can be reversed with surgical treatment. Additionally, if this diagnosis is not sought out before pursuing an adrenalectomy for an incidentaloma, the patient can develop profound postoperative adrenal insufficiency.

Adenoma↗
PubMed2004

Does academic advancement impact teaching performance of surgical faculty?

BACKGROUND: An important reason for young surgeons entering academic practice is to educate trainees. As clinical and administrative responsibility increases, teaching time is decreased. We attempted to determine if the teaching performance of surgeons declines with career advancement. METHODS: Between July 1998 and June 2002, all faculty at our institution were evaluated by medical students on the surgical clerkship. Surgeons were scored on clinical teaching (CLINIC), operating room teaching (OR), and overall teaching (ALL) with the use of a 4-point scale. Surgeons were grouped by years in practice; group scores were compared with ANOVA. RESULTS: A total of 6345 evaluations were completed on 74 academic surgeons. Junior surgeons (< or = 5 years) performed better in operating room teaching (P < .001), clinical teaching (P<.001), and overall teaching (P < .001) compared with those in practice more than 5 years. When junior surgeons were compared with the most senior faculty (> or = 15 years), the difference in all categories was even greater (P < .001). Tenure status had no relationship to teaching ability. CONCLUSIONS: Junior faculty surgeons were perceived to be more effective teachers when compared to senior faculty. With career advancement, faculty may devote less energy to teaching and become less effective. Therefore, continued emphasis should be placed on strengthening education skills throughout the surgical career.

General Surgery↗
PubMed2004

Does propofol anesthesia affect intraoperative parathyroid hormone levels? A randomized, prospective trial.

BACKGROUND: Intravenous propofol (2,6-diisopropylphenol) infusion is used commonly for sedation/anesthesia during operations. Several authors have reported that propofol can interfere with intact parathyroid hormone (PTH) testing in vitro. Therefore, many surgeons avoid propofol during parathyroidectomy. METHODS: To determine whether propofol affects intraoperative PTH levels in vivo, we randomly assigned 34 patients (80% power; alpha < .05) with secondary hyperparathyroidism to undergo surgery for dialysis access. Patients were assigned randomly to local anesthesia with either propofol (n = 17 patients) or midazolam (n = 17 patients) sedation. PTH values were obtained before the procedure and at 10 minutes and 30 minutes after the start of the propofol or midazolam. RESULTS: Median preoperative serum PTH and calcium levels were 175 pg/mL (range, 27-2646 pg/mL) and 9.2 mg/dL (range, 8.1-10.8 mg/dL), respectively. There was no statistically significant difference between the PTH levels in the 2 groups at each of our time points. There was also no difference in the percentage of change from baseline in the PTH values between our 2 groups. No patient in either group had a sustained drop in their PTH level of greater than 50%. CONCLUSIONS: Intravenous propofol infusion does not alter PTH levels significantly during the operation. Therefore, we believe the intraoperative PTH assay can be used safely during propofol sedation when parathyroid surgical procedures are being performed.

Anesthetics, Intravenous↗
PubMed2004

Insulin-like growth factor 1 signaling in human gastrointestinal carcinoid tumor cells.

Background Insulin-like growth factor 1 (IGF-1) is an autocrine regulator of carcinoid tumors. Blockade of IGF-1 signaling has been proposed as a therapeutic target in the treatment of patients with carcinoid syndrome. We hypothesized that the induction of parallel raf-1/MEK1 pathways will block IGF-1-mediated chromogranin A (CgA) maintenance. Methods Human gastrointestinal carcinoid tumor cells (BON) were treated with IGF-1 (0-500 ng/mL). Raf-1/MEK1 activation was achieved with an estrogen-inducible raf-1 vector that was transduced into BON cells. Activation of IGF-1/raf-1 pathways was determined by phosphorylation of downstream targets p70s6 and ERK1/2. The secreted and intercellular levels of CgA were measured in conditioned media and whole cell extracts by Western and enzyme-linked immunosorbent assay analysis. Results IGF-1 and raf-1 pathways were activated successfully in BON cells, as shown by high levels of phosphorylated p70s6 and phosphorylated ERK1/2, respectively. Treatment of BON cells with IGF-1 stimulated the release of CgA, while high intracellular CgA levels were maintained. The activation of raf-1/MEK1 reversed the effect of IGF-1 treatment by the depletion of intracellular CgA. Conclusions The induction of the raf-1/MEK1 pathway blocks IGF-1-mediated intracellular neuroendocrine hormone regulation. Therefore, raf-1/MEK1 activation may be a viable method to block IGF-1-mediated cellular effects and serve as a therapeutic target in gastrointestinal carcinoid tumors.

Carcinoid Tumor↗
PubMed2004

Can thallium-pertechnetate subtraction scanning play a role in the preoperative imaging for minimally invasive parathyroidectomy?

PURPOSE: Preoperative Tc-99m sestamibi scanning can identify candidates for minimally invasive parathyroid surgery. However, a significant number of patients with single gland disease have negative scans and are not considered for the minimally invasive procedure. MATERIALS AND METHODS: To determine if T1-201/Tc-99m sodium pertechnetate subtraction scanning (TPSS) is a viable alternative imaging technique for patients with primary hyperparathyroidism (1 degrees HPTH), we reviewed our experience. The outcomes of 100 consecutive patients with 1 degrees HPTH who underwent preoperative TPSS and parathyroid exploration between 1995 and 2000 at our institution were retrospectively reviewed. RESULTS: The mean preoperative calcium and parathyroid hormone levels were 10.8 mg/dL and 220 pg/mL, respectively. The overall cure rate was 96%. Single gland disease was present in 88%. Of the 100 patients studied, 15 underwent both a Tc-99m sestamibi scan and TPSS, whereas the other 85 had only the TPSS. CONCLUSIONS: The sensitivity and positive predictive value of the TPSS were 73.3% and 90.4%, respectively. In the patients undergoing both TPSS and Tc-99m sestamibi scans, the results concurred in 60%. However, in 20% of the remaining patients, TPSS correctly localized the abnormal parathyroid(s) when Tc-99m sestamibi failed. TPSS has a comparable sensitivity and positive predictive value to Tc-99m sestamibi scanning. In patients with a negative Tc-99m sestamibi scan, TPSS can provide additional localizing information. As a result of the high positive predictive value of TPSS, a single parathyroid gland localized by TPSS alone can then be approached by minimally invasive parathyroidectomy.

Female↗
PubMed2004

Thallium-pertechnetate subtraction scanning in the preoperative localization of an ectopic undescended parathyroid gland.

Although bilateral exploration is highly effective in the treatment of primary hyperparathyroidism, minimally invasive parathyroidectomy has evolved into the procedure of choice when a single parathyroid lesion can be localized preoperatively. In this article, we discuss the utilization of thallium-pertechnetate subtraction scanning (TPSS) after technetium Tc-99m sestamibi scintigraphy failed to localize an ectopic parathyroid adenoma. Subsequently, radioguided resection of an undescended parathyroid adenoma inferior to the left submandibular gland was performed with surgical cure after a single procedure. This case report illustrates the importance of TPSS as a second-line modality in preoperative adenoma localization, thereby using minimally invasive techniques to successfully treat this patient's primary hyperparathyroidism.

Choristoma↗
PubMed2003

Utilization of fine-needle aspiration in patients undergoing thyroidectomy at two academic centers across the Atlantic.

Although fine-needle aspiration (FNA) has been accepted as a first-line test in patients with thyroid masses, the utilization of FNA varies even among experienced surgeons. To determine its utility we compared FNA results, pathology, and clinical results in patients who underwent thyroidectomy in two major endocrine centers on both sides of the Atlantic: one in the United States (US) and another in the United Kingdom (UK). Between January 1997 and March 1998 a total of 84 patients underwent thyroid surgery at the UK center, and 143 underwent thyroidectomy at the US center. The most common indication for thyroidectomy at the UK center was compressive goiter (CG), whereas follicular neoplasm (FN) was the most common indication at the US center. Bilateral thyroid resections, frozen section utilization, and thyroid cancer surgery were more common at the US center. Thyroidectomy for symptomatic multinodular goiter and Graves' disease was more prevalent at the UK center. Thyroid gland weights were also significantly greater in the UK, indicating a higher incidence of endemic goiter. FNA was more commonly employed in the US center (84% vs. 52%; p < 0.001). Despite the differing utilization of FNA at these major endocrine centers, only one thyroid cancer at each institution was not detected preoperatively (both patients had a benign FNA result). Therefore there were no clinically significant thyroid cancers found in patients who did not undergo preoperative FNA. In conclusion, FNA appears to be differentially utilized depending on the incidence of endemic goiter, Graves' disease, and thyroid cancer. In this series no clinically significant thyroid cancers were found in patients who did not undergo preoperative FNA. Therefore in the hands of experienced thyroid surgeons, FNA can be utilized selectively based on the clinical presentation.

Biopsy, Needle↗
PubMed2003

Medical student operative experience correlates with a match to a categorical surgical program.

BACKGROUND: Interest in general surgical residencies has decreased significantly. Because medical student clerkship experiences may affect specialty preferences, we attempted to determine if the degree of exposure to surgical procedures influenced career choices. METHODS: Operations observed by students who completed the third-year surgical clerkship between 1998 and 1999 were reviewed. These 146 medical students, who matched to residency training programs in March 2000, were then divided into three groups based upon residency fields. Surgical case exposures were then compared between the groups. RESULTS: The total number of operations observed was similar between the groups. However, students who matched into categorical general surgical programs participated in significantly more abdominal and general surgical procedures than those matching in surgical subspecialty or nonsurgical residencies (P < 0.01). CONCLUSIONS: There appears to be a correlation between surgical case exposure during the third-year clerkships and future residency fields. Thus, the degree of exposure to surgical procedures may influence medical student career choices.

Adult↗
PubMed2003

Do the best students go into general surgery?

BACKGROUND: Recent match trends by medical graduates have revealed a declining interest in general surgery. Our study evaluates the academic strength of recent graduates to determine the quality of those matching to general surgery residencies. METHODS: All third-year students rotating through the 8-week surgical clerkship from July 1998-June 2000 (n = 291) were followed at the University of Wisconsin Medical School. Each student completed 4 weeks of general surgery and 4 weeks of surgical subspecialties. Match data provided residency choices and students were divided into general surgery (GS), surgical subspecialty (SS), and nonsurgical (NS) residencies. Student performance was based upon National Board of Medical Experiences (NBME) surgery exam, class rank and Alpha Omega Alpha (AOA) status. RESULTS: Students at our institution scored at the national mean on the NBME exam. GS team, session, and timing of GS rotation had no relationship to exam score. Total number of operative cases observed was inversely related to exam performance (P = 0.02). Of students entering a GS career, most scored below the mean on the NBME exam, 46% graduated in the bottom two thirds of the class, and only 6% of AOA members entered a GS residency. CONCLUSION: Although many of the strongest medical students select surgical residencies, they choose to enter SS careers and not GS careers.

Career Choice↗
PubMed2003

Radioguided parathyroidectomy in patients with secondary and tertiary hyperparathyroidism.

BACKGROUND: To date there have been no reports on the feasibility of radioguided parathyroidectomy (RGP) in patients with secondary and tertiary hyperparathyroidism. METHODS: Twenty-three consecutive patients with secondary (n=5) or tertiary hyperparathyroidism (n=18) underwent RGP. Patients were injected with 10 mCi of technetium 99-sestamibi before surgery. All parathyroid glands were localized during operation with a neoprobe. RESULTS: The mean patient age was 50+/-3 years. The mean preoperative calcium and intact parathyroid hormone levels were 11.0+/-0.3 mg/dL and 400+/-107 pg/mL, respectively. Eighteen patients had 3- or 4-gland hyperplasia, 2 had double adenomas, 2 had forearm graft hyperplasia, 1 had 6-gland disease, and 3 had ectopic glands. All hyperplastic glands had ex vivo counts >20% of background (mean, 63%+/-6%), making frozen section unnecessary. When compared with 66 historical control subjects who underwent surgery without radioguidance for tertiary hyperparathyroidism, patients undergoing RGP had decreased operative times (96+/-8 minutes vs 151+/-15 minutes; P<.001) and lengths of stay (1.3+/-0.1 days vs 3.7+/-0.3 days; P<.001). CONCLUSIONS: RGP in patients with secondary and tertiary hyperparathyroidism is feasible, may reduce operative time, and permits omission of frozen section. Thus RGP appears to be a useful adjunct in the treatment of secondary and tertiary hyperparathyroidism.

Case-Control Studies↗
PubMed2003

The role of human achaete-scute homolog-1 in medullary thyroid cancer cells.

BACKGROUND: Human achaete-scute homolog-1 (hASH1) is a transcription factor that is expressed highly in neuroendocrine tumors such as medullary thyroid cancer (MTC). Thyroid C-cells do not develop in hASH1 knockout mice, which suggests that hASH1 is essential for normal C-cell development. METHODS: To determine the effect of raf-1 induction on hASH1 and hormone production, we used an estrogen inducible raf-1 construct in MTC cell line (TT) cells (TT-raf cells). TT or TT-raf cells were treated with control or 1 microM estradiol. After 48 hours, the cells were analyzed for levels of hASH1 and chromogranin A by Western blotting and for calcitonin production by enzyme-linked immunosorbent assay. RESULTS: Activation of raf-1 in the TT-raf cells resulted in high levels of phosphorylated MEK and ERK1/2, a morphologic transdifferentiation, and a decrease in chromogranin A and calcitonin levels that are associated with a reduction in hASH1 production. Furthermore, using MEK inhibitors, we demonstrated that these raf-1-mediated changes are dependent on MEK but not ERK1/2 activation. CONCLUSION: hASH1 down-regulation by raf-1 in MTC cells is associated with a significant decrease in hormone production. Thus, hASH1 appears to be important in the endocrine phenotype of MTC tumors and may serve as a molecular target for the treatment of patients with MTC.

Basic Helix-Loop-Helix Proteins↗
PubMed2003

Radioguided parathyroidectomy is equally effective for both adenomatous and hyperplastic glands.

OBJECTIVE: To determine the utility of radioguided parathyroidectomy for patients with hyperparathyroidism, we studied the properties of 180 resected, hyperfunctioning parathyroid glands. SUMMARY AND BACKGROUND DATA: Radioguided resection of hyperfunctioning parathyroid glands has been shown to be technically feasible in patients with parathyroid adenomas. Radioguided excision may obviate the need for intraoperative frozen section because excised parathyroid adenomas uniformly have radionuclide ex vivo counts >20% of background. The feasibility and applicability of radioguided techniques for patients with parathyroid hyperplasia are unclear. METHODS: Between March 2001 and September 2002, 102 patients underwent neck exploration for primary (n = 77) and secondary/tertiary (n = 25) hyperparathyroidism. All patients received an injection of 10 mCi of Tc-99m sestamibi the day of surgery. Using a gamma probe, intraoperative scanning was performed, looking for in vivo radionuclide counts > background to localize abnormal parathyroid glands. After excision, radionuclide counts of each ex vivo parathyroid gland were determined and expressed as a percentage of background counts.RESULTS Although patients with single adenomas had higher mean background radionuclide counts, the average in vivo counts of all enlarged glands were higher than background. Notably, in vivo counts did not differ between adenomatous and hyperplastic glands, suggesting equal sensitivity for intraoperative gamma detection. Ectopically located glands were identified in 22 cases and all were accurately localized using the gamma probe. Postresection, mean ex vivo radionuclide counts were highest in the single parathyroid adenomas and lowest in hyperplastic glands. Importantly, in all hyperplastic glands, the ex vivo counts were >20%. CONCLUSIONS: In patients with hyperparathyroidism, radioguided surgery is a sensitive adjunct for the intraoperative localization of both adenomatous and hyperplastic glands. In this series, all 180 enlarged parathyroids were located with the gamma probe. We have also shown that the ">20% rule" for ex vivo counts not only applies to parathyroid adenomas but also to hyperplastic glands. Therefore, radioguided resection is equally effective and informative for both adenomatous and hyperplastic glands.

Adenoma↗
PubMed2003

Raf-1 activation suppresses neuroendocrine marker and hormone levels in human gastrointestinal carcinoid cells.

Gastrointestinal carcinoid cells secrete multiple neuroendocrine markers and hormones including 5-HT and chromogranin A. The intracellular signaling pathways that regulate production of bioactive molecules are not completely understood. Our aim was to determine whether activation of the raf-1/MEK/MAPK signal transduction pathway in carcinoid cells could modulate production of neuroendocrine markers and hormones. Human pancreatic carcinoid cells (BON) were stably transduced with an estrogen-inducible raf-1 construct creating BON-raf cells. Activation of raf-1 in BON-raf cells led to a marked induction of phosphorylated MEK and ERK1/2 within 48 h. Importantly, raf-1 activation resulted in morphological changes accompanied by a marked decrease in neuroendocrine secretory granules by electronmicroscopy. Moreover, induction of raf-1 in BON-raf cells led to significant reductions in 5-HT, chromogranin A, and synaptophysin levels. Furthermore, treatment of BON-raf cells with MEK inhibitors PD-98059 and U-0126 blocked raf-1-mediated morphological changes and hormone suppression but not ERK1/2 phosphorylation. These results show that raf-1 induction suppresses neuroendocrine marker and hormone production in human gastrointestinal carcinoid cells via a pathway dependent on MEK activation.

Biomarkers, Tumor↗
PubMed2003

Radioguided parathyroidectomy for recurrent hyperparathyroidism caused by forearm graft hyperplasia.

One of the surgical options for symptomatic secondary hyperparathyroidism is a total parathyroidectomy with forearm implantation. Recurrence can occur and is most likely caused by hyperplasia of the small fragments of parathyroid tissue implanted in the forearm muscle. Forearm graft hyperplasia can be detected using Tc-99m sestamibi scanning of the forearm, which can show abnormal enhancement at the former graft site. In this report, we present the case of a 49-year-old gentleman with recurrent hyperparathyroidism caused by hyperplasia of forearm graft fragments. Unfortunately, no sutures or clips were placed at his initial surgery to identify the location of the parathyroid tissue in the forearm. Thus, we describe the first reported use of radioguided techniques using Tc-99m sestamibi injection and intraoperative gamma probe to localize parathyroid fragments in the forearm muscle. During our initial exploration, we found that injection of the tracer in the operative arm leads to prohibitively high levels of background activity. During a second exploration, the tracer was injected in the lower extremity, minimizing the background in the forearm and allowing the gamma probe to clearly identify two areas of abnormal parathyroid tissue. The intraoperative radioprobe allowed quick identification and removal of the abnormal parathyroid tissue in a case that was made particularly challenging by the absence of marking sutures.

Forearm↗