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Michael W Yeh

Publications and source records attributed to Michael W Yeh.

13 recordsLinked to original sources
PubMed2007

Minimally invasive parathyroidectomy using the lateral focused miniincision approach: Is there a learning curve for surgeons experienced in the open procedure?

BACKGROUND: Minimally invasive parathyroidectomy (MIP) has gained acceptance as the standard of care for management of primary hyperparathyroidism in which a single adenoma can be localized. The aim of this study was to determine if there is a learning curve for MIP using the lateral focused miniincision approach performed by surgeons experienced in open parathyroidectomy. STUDY DESIGN: This is a retrospective case series comprising all parathyroid operations undertaken by three surgeons in the University of Sydney Endocrine Surgical Unit from 2003 to 2005. Outcomes of the experienced surgeon were compared with those of the two surgeons commencing practice. RESULTS: There were 699 parathyroidectomies performed in the Unit during the 36-month period (experienced surgeons: 438 versus commencing physicians: 261). Of the parathyroidectomies performed, 57% done by experienced surgeons were minimally invasive compared with 38% of those performed by surgeons commencing practice (p < 0.001). There were no differences in the number of complications (p = 0.21), conversions to open exploration (p = 0.6), and cure rates (p = 0.9) in the MIP patients in both groups. The initial (first 131 patients) and subsequent (next 130 patients) parathyroidectomy experiences of surgeons commencing practice were examined. In the initial experiences, 28% of the cases were minimally invasive compared with 48% in the subsequent experiences (p < 0.001). There were no differences in the number of complications (p = 0.3), conversions to open exploration (p = 0.9), and cure rates (p = 0.9). CONCLUSIONS: For surgeons experienced in open parathyroidectomy, there is no technical learning curve using the lateral focused miniincision technique for MIP. There is, however, a learning curve for patient selection.

Clinical Competence↗
PubMed2006

Completion thyroidectomy for malignancy after initial minimal access thyroid surgery.

BACKGROUND: Minimal access thyroid surgery (MATS), carried out through a lateral 2.5-cm incision, provides excellent clinical and cosmetic outcomes when carried out for small (<3 cm), single nodules. However, if the final pathology shows thyroid malignancy and a completion thyroidectomy is required, the small lateral incision requires conversion to a standard collar incision and the second operation must be carried out in the presence of previous lateral dissection. The aim of this study is to determine if there is any demonstrable disadvantage to completion thyroidectomy for malignancy after MATS when compared with the same procedure after conventional hemithyroidectomy. METHODS: This retrospective cohort study examined all patients undergoing completion thyroidectomy for malignancy in the University of Sydney Endocrine Surgical Unit from January 2002 to January 2005. Outcome measures were complication rates, final scar length and patient's self-assessment of scar appearance. RESULTS: A total of 106 patients underwent MATS during the study period, 11 of whom required completion thyroidectomy for malignancy. During the same period, 42 patients required completion thyroidectomy for malignancy after previous conventional hemithyroidectomy. There was no difference in complication rates between the two groups. The two complications in the study consisted of one case of flap oedema (control) and one case of keloid scar (MATS). Mean final incision length, scar appearance and patient's satisfaction with scar did not differ between the two groups. CONCLUSION: There is no demonstrable disadvantage when completion thyroidectomy for malignancy is required after MATS.

Adult↗
PubMed2006

Use of the ligaSure vessel sealing system in laparoscopic adrenalectomy.

Laparoscopic adrenalectomy is the operation of choice for benign adrenal lesions. During laparoscopic surgery, vessels are usually ligated with diathermy, ligaclips, staplers or ultrasonic coagulators. Use of the electrothermal bipolar vessel sealer (LigaSure; Valleylab, Boulder, CO, USA) has recently been described in a variety of procedures, not including adrenalectomy. This article is a retrospective study of 28 patients undergoing laparoscopic adrenalectomy within the University of Sydney Endocrine Surgical Unit at the Royal North Shore Hospital using the LigaSure vessel sealing system. Between July 2004 and August 2005, 28 consecutive patients underwent laparoscopic adrenalectomy using the LigaSure vessel sealing system to divide feeding adrenal vessels as well as the adrenal vein. There were no bleeding complications. The LigaSure vessel sealing system can be safely used to secure haemostasis, including division of the adrenal vein, in laparoscopic adrenalectomy.

Adrenalectomy↗
PubMed2006

New surgical consultants: is there a learning curve?

The purpose of this study was to determine whether newly established surgeons who have completed dedicated post-fellowship training are able to achieve surgical outcomes comparable to their more experienced peers. A cross-sectional study of consecutive patients undergoing total thyroidectomy (TT) or completion thyroidectomy was carried out. Outcomes measured included unplanned return to the operating theatre, postoperative infection, permanent recurrent laryngeal nerve (RLN) injury and permanent hypoparathyroidism. Outcomes were categorized according to whether surgery was carried out by an established surgeon (ES) or a newly appointed surgeon (NAS). Eight hundred and nine TT and completion thyroidectomy procedures were carried out in the period January 2002 to December 2004. Of these, 515 (64%) were carried out by ES and 294 (36%) were carried out by NAS. The overall rate of permanent hypoparathyroidism and RLN injury was 1.4% (12/809) and 0.6% (5/809), respectively. The rate of permanent hypoparathyroidism was not significantly different between the two categories of surgeon (ES 1.35% vs NAS 1.7%; P = 0.7). The incidence of permanent RLN injury was not different between the two groups (ES 0.8% vs NAS 0.3%; P = 0.4). For NAS, the rate of permanent RLN injury for the first two years of independent practice did not differ significantly from 3 to 4 years of practice (0/123 vs 1/171; P = 0.4). Indications for surgery between the two groups were similar, with ES carrying out TT for benign goitre in 42% and cancer in 28%, and NAS 44 and 32%, respectively. Surgical outcomes for the newly established endocrine surgeon following subspecialty training are equivalent to those achieved by more experienced surgeons.

Adult↗
PubMed2006

Differentiated thyroid cancer cell invasion is regulated through epidermal growth factor receptor-dependent activation of matrix metalloproteinase (MMP)-2/gelatinase A.

Mechanisms of invasion in thyroid cancer remain poorly understood. We hypothesized that signaling via the epidermal growth factor receptor (EGFR) stimulates thyroid cancer cell invasion by altering the expression and cleavage of matrix metalloproteinases (MMPs). Papillary and follicular carcinoma cell lines were treated with EGF, the EGFR tyrosine kinase inhibitor AG1478, and the MMP inhibitors GM-6001 and Col-3. Flow cytometry was used to detect EGFR. In vitro invasion assays, gelatin zymography, and quantitative reverse transcription-PCR were used to assess the changes in invasive behavior and MMP expression and activation. All cell lines were found to overexpress functional EGFR. EGF stimulated invasion by thyroid cancer cells up to sevenfold (P<0.0001), a process that was antagonized completely by AG1478 and Col-3, partially by GM-6001, but not by the serine protease inhibitor aprotinin. EGF upregulated expression of MMP-9 (2.64- to 8.89-fold, P<0.0001) and membrane type-1 MMP (MT1-MMP, 1.97- to 2.67-fold, P<0.0001). This effect was blocked completely by AG1478 and partially by Col-3. The activation of MMP-2 paralleled MT1-MMP expression. We demonstrate that MMPs are critical effectors of invasion in the papillary and follicular thyroid cancer cell lines studied. Invasion is regulated by signaling through EGFR, an effect mediated by augmentation of gelatinase expression and activation. MMP inhibitors and growth factor antagonists may be effective tumoristatic agents for the treatment of aggressive thyroid carcinomas.

Adenocarcinoma, Follicular↗
PubMed2005

Phaeochromocytoma: current concepts.

The discovery of novel mutations in genes encoding succinate dehydrogenase subunits has revealed that familial phaeochromocytomas are much more common than previously thought. Genetic screening should be offered to patients with apparently sporadic phaeochromocytomas and their first-degree relatives. An increasing proportion of phaeochromocytomas present preclinically on genetic testing or as "incidentalomas" on abdominal imaging, rather than with classic symptoms and signs. Clinical suspicion should prompt measurement of plasma levels of free metanephrine or 24-hour urinary catecholamine and metanephrine levels, followed, if positive, by tumour localisation studies. With appropriate perioperative care, surgical management of phaeochromocytomas is safe and effective. Most tumours can be removed laparoscopically.

Adrenal Gland Neoplasms↗
PubMed2005

Potential pitfalls in the diagnosis of phaeochromocytoma.

Six patients being evaluated for phaeochromocytoma had misleading investigative findings: all initially had raised urinary catecholamine levels, and five had adrenal masses on imaging studies. Adrenalectomy in these five patients revealed only one pathologically confirmed phaeochromocytoma. Tricyclic antidepressant use produced misleading elevations in urinary catecholamine levels in three patients. 24-hour urine studies should be performed at least twice, after eliminating confounding factors (stressors, medications).

Adrenal Gland Neoplasms↗
PubMed2005

Endovascular repair of an actively hemorrhaging gunshot injury to the abdominal aorta.

Endovascular stents have had a limited role in the management of trauma and vascular emergencies involving active hemorrhage. We describe a patient with delayed rupture of the infrarenal aorta after intra-abdominal sepsis caused the breakdown of a primary aortic repair. A stent-graft repair was performed, as concomitant injuries did not allow anterior access to the aorta. This report describes the successful endovascular repair of an actively hemorrhaging penetrating abdominal aortic injury. Endovascular approaches to aortic injuries may be valuable in settings where a hostile abdomen precludes traditional open repair.

Abdominal Injuries↗
PubMed2004

False-negative fine-needle aspiration cytology results delay treatment and adversely affect outcome in patients with thyroid carcinoma.

Clinicians have become reliant on fine-needle aspiration (FNA) cytology in the diagnosis of thyroid nodules. We encountered several patients who had thyroid cancer at operation despite having had FNAs that never showed malignant or suspicious cells. Hence, we retrospectively studied 100 consecutive patients with histologically proven thyroid cancer who had undergone preoperative FNA. Fourteen of these patients had cancers that were not detected by FNA, three of whom developed widespread disease. The sensitivity of FNA was 79%, the false-negative rate 21%, and the inadequate rate 12%. FNA was less sensitive in detecting follicular and Hürthle cell carcinomas compared to papillary carcinomas. FNAs interpreted by cytopathologists at a major university center were more sensitive than those performed elsewhere. A single false-negative FNA delayed surgical treatment by 28 months, sometimes despite clinical evidence suggesting malignancy. Subjects whose tumors were not detected by FNA experienced delayed treatment, had higher rates of vascular and capsular invasion, and were more likely to have persistent disease at follow up (hazard ratio 2.28). False-negative results remain a concern in the cytologic diagnosis of thyroid cancer. Although FNA is a useful test, clinical findings should overrule cytologic data in order for timely treatment to occur.

Adenocarcinoma, Follicular↗
PubMed2003

The heat shock protein 90-binding geldanamycin inhibits cancer cell proliferation, down-regulates oncoproteins, and inhibits epidermal growth factor-induced invasion in thyroid cancer cell lines.

Heat shock protein 90 (HSP90) serves as a chaperone protein and plays a critical role in tumor cell growth and/or survival. Geldanamycin, a specific inhibitor of HSP90, is cytotoxic to several human cancer cell lines, but its effect in thyroid cancer is unknown. We, therefore, investigated the effect of geldanamycin on cell proliferation, oncoprotein expression, and invasion in human thyroid cancer cell lines. We used six thyroid cancer cell lines: TPC-1 (papillary), FTC-133, FTC-236, FTC-238 (follicular), XTC-1 (Hürthle cell), and ARO (anaplastic). We used the dimethyl-thiazol-diphenyltetrazolium bromide assay, a clonogenic assay, an apoptotic assay, and a Matrigel invasion assay. We evaluated oncoprotein expression using Western blots and flow cytometry. After 6 d of treatment with 50 nM geldanamycin, the percent inhibition of growth was 29.4% in TPC-1, 97.5% in FTC-133, 96.7% in FTC-236, 10.8% in FTC-238, 70.9% in XTC-1, and 45.5% in ARO cell lines. In the FTC-133 cell line, geldanamycin treatment decreased clonogenicity by 21% at a concentration of 50 nM; geldanamycin induced apoptosis and down-regulated c-Raf-1, mutant p53, and epidermal growth factor (EGF) receptor expression; geldanamycin inhibited EGF-stimulated invasion. In conclusion, geldanamycin inhibited cancer cell proliferation, down-regulated oncoproteins, and inhibited EGF-induced invasion in thyroid cancer cell lines.

Adenocarcinoma, Follicular↗
PubMedDate not supplied

Two hundred consecutive parathyroid ultrasound studies by a single clinician: the impact of experience.

OBJECTIVE: To assess the ability of ultrasound studies, performed by an experienced clinician, to predict surgical findings and provide precise anatomic localization of abnormal parathyroid glands. METHODS: We retrospectively examined 200 consecutive parathyroid ultrasound studies performed by a single experienced clinician in our unit. All patients subsequently underwent parathyroidectomy, with histopathologic confirmation of abnormal parathyroid tissue. The correlation between the ultrasound and surgical findings was assessed. RESULTS: Of the 200 study patients, 197 (98.5%) were cured of their disease at the initial operation. Ultrasound studies correctly predicted the surgical findings in 88% of patients, including 168 of 180 (93%) with single gland disease and 7 of 20 (35%) with multiple gland disease (MGD). In all cases in which a single adenoma was identified, precise information regarding its location relative to adjacent anatomic structures was provided. In 92% of these cases, anatomic details correlated closely with surgical findings. Ectopic and descended superior adenomas were most frequently missed. Patients with two nonlocalizing studies (scintigraphy and ultrasonography) had a >50% likelihood of having MGD. CONCLUSION: In experienced hands, parathyroid ultrasonography is a highly sensitive technique that provides both localization of enlarged parathyroid glands and precise anatomic detail. Thus, in this study, focused parathyroidectomy was possible in 76.5% of patients. MGD remains difficult to diagnose preoperatively. Nonlocalizing studies should alert the surgeon to a high probability of MGD and prompt the performance of 4-gland exploration.

Adenoma↗