Papillary thyroid carcinoma of thyroglossal duct cyst: a retrospective analysis.

BACKGROUND: The incidence of thyroglossal duct cyst (TDC) carcinoma is uncommon (approximately 1%) and rarely reported in the literature. Treatment modalities have included tumourectomy, Sistrunk's procedure and/or total thyroidectomy. AIM: To try and determine the most adequate surgical approach for papillary thyroid carcinoma (PTC) arising in TDC. RESULTS: We reviewed the clinical charts of 22 patients with PTC of TDC treated between January 1974 and December 2008 (0.63% of the total of 3458 patients with PTC treated over that period). All patients underwent the Sistrunk's procedure. Fourteen (64%) were submitted to total thyroidectomy and 11 of these patients were ablated with lodine131. Seven (50%) of the 14 patients treated with total thyroidectomy had tumour both in the thyroid gland and in TDC but lymph node metastases were present only in four. None of the patients died of the disease and all of them are still alive without recurrence with a mean follow-up of 8 years (range: 2-27 years). The mean survival rate of the patients submitted to total thyroidectomy (n= 14) was not statistically different from that of patients treated with the Sistrunk's procedure alone (9.23 +/- 7.65 vs. 8.95 +/- 6.22, p= 0.940). CONCLUSION: Papillary thyroid carcinoma arising in thyroglossal duct cysts is a very rare malignant tumour. In spite of the multifocal character of several of our cases, their analysis showed that the prognosis in the vast majority of patients with TDC carcinoma is excellent. Moreover, we found no relation between outcome and surgical procedure.

Calibration of (109)Cd KXRF systems for in vivo bone lead measurements: weighted least-squares regression with different weighting functions.

The use of iteratively reweighted least squares (IRLS) has recently been described as an alternative to ordinary least squares with heteroscedastic data, in the calibration of (109)Cd KXRF systems for in vivo bone lead measurements. This work addresses the use of weighted least squares (WLS) with two different weighting functions and no iteration, with that same data set. The functions are defined as the inverse of the variance of observed ratios of lead to coherent peak amplitudes and the inverse of the square of the error reported by the Marquardt fitting program for these ratios. The results show that if no iteration is implemented when using WLS, then the two weighting functions are highly inefficient in homogenizing the residual variance. Moreover, both methods estimate much more imprecise calibration intercepts and slopes than did the IRLS method. Work is in progress to investigate the implementation of IRLS with these weighting functions, with the focus on the selection of the best function for residuals to be used in each iteration stage.

Calibration of (109)Cd KXRF systems for in vivo bone lead measurements: the guiding role of the assumptions for least-squares regression in practical problem solving.

The use of least-squares regression to probe the level of lead contamination of plaster of Paris standards in the calibration of (109)Cd KXRF systems for bone lead measurement, as well as the use of iteratively reweighted least-squares (IRLS) in the case of violation of the assumptions for ordinary least-squares (OLS), is discussed here. One common violation is non-uniform residual variance, which makes the use of OLS inappropriate due to strong influence of points with large variance on the calibration line and variance of the slope and intercept. Comparison between OLS and IRLS in that case showed that IRLS estimates of the intercept are significantly smaller and more precise than OLS estimates, while a less marked increase in the calibration slope is observed when IRLS is used. Moreover, OLS underestimates bone lead concentrations at low levels of lead exposure and overestimates those concentrations at higher levels. These discrepancies are smaller in magnitude than the measurement uncertainty of conventional systems, except for high concentrations. For the newly developed cloverleaf systems, the suggested differences at bone lead concentrations below 17 ppm are comparable to the minimum detection limit, but are larger than the measurement uncertainty for bone lead concentrations above 60 ppm.

The effect of covariance between the K alpha and the K beta lead peak concentrations on the uncertainty in the result of in vivo (109)Cd KXRF bone lead measurement.

The effect of covariance between the K alpha and K beta lead peak concentrations on the uncertainty in the (109)Cd K x-ray fluorescence measurement of lead in bone is addressed here. It is commonly believed that this covariance arises as a result of the mutual dependence of the ratios of x-ray to coherent amplitudes on the same coherent peak amplitude. Previous work assumes statistical independence between spectral quantities of interest, crudely estimates the uncertainties in the lead peak concentrations, and suggests that the effect of covariance on the measurement uncertainty is small and can be ignored. Consequently, the current method followed by most laboratories reports the measurement uncertainty as if the fluctuations in the measured peak concentrations were independent. The robustness of such assumption, however, is undermined by existing epidemiological data. This paper assesses the magnitude of the covariance effect, using a method based on the observed significant correlations between the ratios of x-ray to coherent peak amplitudes in series of repeat phantom measurements. The revised uncertainties following this approach can exceed the uncertainties estimated by the accepted method by as much as 40%, which suggests a much stronger effect of covariance on the measurement uncertainty than previously reported.