Autofluorescence-Guided Total Thyroidectomy in Low-Volume, Nonparathyroid Institutions.

Importance: Hypoparathyroidism following thyroid surgery is a serious complication that occurs frequently when surgery is performed by low-volume thyroid surgeons without experience in parathyroid surgery. Objective: To evaluate the occurrence of hypoparathyroidism following total thyroidectomy after the introduction of autofluorescence in low-volume, nonparathyroid institutions. Design, Setting, and Participants: This prospective, multicenter cohort study, with a follow-up period of up to 1 year, was conducted in Denmark at 2 low-volume nonparathyroid institutions between January 2021 and November 2023. All adult patients referred for total thyroidectomy were assessed for eligibility (n = 90). Only patients with no history of thyroid surgery were considered (n = 89). Patients who only underwent lobectomy (n = 6) or declined to participate (n = 5) were excluded. All included patients completed follow-up. The prospective cohort was compared with a historical cohort of successive patients undergoing primary total thyroidectomy from 2016 to 2020 (before autofluorescence was available). Intervention: Included patients underwent autofluorescence-guided total thyroidectomy. Main outcomes and Measures: Rate of hypoparathyroidism. Immediate hypoparathyroidism was defined as the need for active vitamin D postoperatively, whereas permanent hypoparathyroidism was considered when there still was a need for active vitamin D 1 year after surgery. Results: Seventy-eight patients underwent autofluorescence-guided surgery (mean [SD] age, 55.6 [13.1] years; 67 [86%] female) and were compared with 89 patients in the historical cohort (mean [SD] age, 49.7 [12.8] years; 78 [88%] female). The rate of immediate hypoparathyroidism decreased from 37% (95% CI, 27%-48%) to 19% (95% CI, 11%-30%) after the introduction of autofluorescence (P = .02). Permanent hypoparathyroidism rates decreased from 32% (95% CI, 22%-42%) to 6% (95% CI, 2%-14%) (P < .001), reaching 0% at the end of the study. More parathyroid glands were identified with autofluorescence (75% [95% CI, 70%-80%] vs 61% [95% CI, 56%-66%]) (P < .001) and less parathyroid glands were inadvertently excised (4% [95% CI, 1%-11%] vs 21% [95% CI, 13%-31%]) (P = .001). Conclusions and Relevance: In this cohort study of autofluorescence-guided thyroid surgery in low-volume, nonparathyroid institutions, the use of autofluorescence was associated with a significant decrease in both immediate and permanent hypoparathyroidism. When autofluorescence was used, hypoparathyroidism rates were comparable with those of high-volume surgeons who also perform parathyroid surgery.

Suppression of Acoustic Streaming in Shape-Optimized Channels.

Acoustic streaming is an ubiquitous phenomenon resulting from time-averaged nonlinear dynamics in oscillating fluids. In this theoretical study, we show that acoustic streaming can be suppressed by two orders of magnitude in major regions of a fluid by optimizing the shape of its confining walls. Remarkably, the acoustic pressure is not suppressed in this shape-optimized cavity, and neither is the acoustic radiation force on suspended particles. This basic insight may lead to applications, such as acoustophoretic handling of nm-sized particles, which is otherwise impaired by the streaming.

Theory of acoustic trapping of microparticles in capillary tubes.

We present a semianalytical theory for the acoustic fields and particle-trapping forces in a viscous fluid inside a capillary tube with arbitrary cross section and ultrasound actuation at the walls. We find that the acoustic fields vary axially on a length scale proportional to the square root of the quality factor of the two-dimensional (2D) cross-section resonance mode. This axial variation is determined analytically based on the numerical solution to the eigenvalue problem in the 2D cross section. The analysis is developed in two steps: First, we generalize a recently published expression for the 2D standing-wave resonance modes in a rectangular cross section to arbitrary shapes, including the viscous boundary layer. Second, based on these 2D modes, we derive analytical expressions in three dimensions for the acoustic pressure, the acoustic radiation and trapping force, as well as the acoustic energy flux density. We validate the theory by comparison to three-dimensional numerical simulations.

Bulk-driven acoustic streaming at resonance in closed microcavities.

Bulk-driven acoustic (Eckart) streaming is the steady flow resulting from the time-averaged acoustic energy flux density in the bulk of a viscous fluid. In simple cases, like the one-dimensional single standing-wave resonance, this energy flux is negligible, and therefore the bulk-driven streaming is often ignored relative to the boundary-driven (Rayleigh) streaming in the analysis of resonating acoustofluidic devices with length scales comparable to the acoustic wavelength. However, in closed acoustic microcavities with viscous dissipation, two overlapping resonances may be excited at the same frequency as a double mode. In contrast to single modes, the double modes can support a steady rotating acoustic energy flux density and thus a corresponding rotating bulk-driven acoustic streaming. We derive analytical solutions for the double modes in a rectangular-box-shaped cavity including the viscous boundary layers, and use them to map out possible rotating patterns of bulk-driven acoustic streaming. Remarkably, the rotating bulk-driven streaming may be excited by a nonrotating actuation, and we determine the optimal geometry that maximizes this excitation. In the optimal geometry, we finally simulate a horizontal 2×2, 4×4, and 6×6 streaming-roll pattern in a shallow square cavity. We find that the high-frequency 6×6 streaming-roll pattern is dominated by the bulk-driven streaming as opposed to the low-frequency 2×2 streaming pattern, which is dominated by the boundary-driven streaming.

Theory of pressure acoustics with viscous boundary layers and streaming in curved elastic cavities.

The acoustic fields and streaming in a confined fluid depend strongly on the viscous boundary layer forming near the wall. The width of this layer is typically much smaller than the bulk length scale set by the geometry or the acoustic wavelength, which makes direct numerical simulations challenging. Based on this separation in length scales, the classical theory of pressure acoustics is extended by deriving a boundary condition for the acoustic pressure that takes viscous boundary-layer effects fully into account. Using the same length-scale separation for the steady second-order streaming, and combining it with time-averaged short-range products of first-order fields, the usual limiting-velocity theory is replaced with an analytical slip-velocity condition on the long-range streaming field at the wall. The derived boundary conditions are valid for oscillating cavities of arbitrary shape and wall motion, as long as both the wall curvature and displacement amplitude are sufficiently small. Finally, the theory is validated by comparison with direct numerical simulation in two examples of two-dimensional water-filled cavities: The well-studied rectangular cavity with prescribed wall actuation, and a more generic elliptical cavity embedded in an externally actuated rectangular elastic glass block.

Thyroid fine-needle aspiration and The Bethesda Classification System.

INTRODUCTION: Fine-needle aspiration (FNA) is a cornerstone in diagnosing thyroid nodules. For decades, Danish FNA has been categorised into the groups: "FNA not performed", "Inadequate", "Cystic", "Inconclusive", "Benign", "Suspicious", "Malignant" and "Information missing". Internationally, The Bethesda Classification System (TBCS) is increasingly accepted, especially owing to a detailed specification of FNA suspicious for malignancy. The Danish "Suspicious" group is very broad and includes atypia, follicular neoplasia and FNA suspicious of other malignancies. The purpose of this study was to apply TBCS to the Danish "Suspicious" FNA group and to estimate the frequency of malignancy in the individual Bethesda groups (BG). METHODS: This descriptive study is based on a prospective cohort from the THYKIR database. It includes 479 patients with a "Suspicious" FNA and surgical treatment in The Region of Southern Denmark from 2001 to 2013. Based on pathology records, FNA was classified according to the TBCS. Malignancy was determined by the histological diagnosis from the THYKIR database. RESULTS: The Danish "Suspicious" group was allocated to the BG I, II, III, IV, V and VI with a malignancy risk of 36.4%, 13.3%, 17.2%, 16.1%, 55.3% and 88.2%, respectively. CONCLUSIONS: The Danish "Suspicious" group contains a broad spectrum of BG with varying malignancy risk. The results indicate a need for standardisation of the Danish FNA classification. A national introduction of the TBCS might secure an international and comparable standard. FUNDING: none. TRIAL REGISTRATION: not relevant.

Risk of malignancy in fine-needle aspiration biopsy in patients with thyroid nodules.

INTRODUCTION: Fine-needle aspiration biopsy (FNAB) is the cornerstone of thyroid nodule evaluation. In most cases, FNAB can discriminate between benign and malignant disease. In other cases, it is only indicative of malignancy and the results are considered "suspicious". In Denmark, thyroid FNAB results are categorised into six groups: "inadequate", "cystic", "inconclusive", "benign", "suspicious" and "malignant". The risk of malignancy in the Danish "suspicious" group is of interest for patients as well as doctors participating in the diagnosis and treatment. The Danish Thyroid Surgery Database (THYKIR) registers preoperative thyroid FNAB and final histology. The aim of this study was to assess the malignancy risk among patients with a suspicious thyroid FNAB according to the Danish criteria and to identify possible predictors of malignant histology. METHODS: A prospective cohort counting 483 patients with a "suspicious" thyroid FNAB who had been treated surgically in The Region of Southern Denmark in the 2001-2013 period was retrieved from the THYKIR database. RESULTS: The risk of malignancy in the Danish thyroid FNAB "suspicious" group is 22%. Serum thyroid-stimulating hormone outside the normal range and vocal cord palsy may be patient-related predictors of malignancy. CONCLUSION: Awaiting the introduction of reliable tools for preoperative evaluation, the current practice with histo-logical clarification of the "suspicious" thyroid FNAB seems justified. FUNDING: none. TRIAL REGISTRATION: not relevant.