Size and location of thyroid gland in the fetal period

Iodine and Thyroid Maternal and Fetal Metabolism during Pregnancy

Thyroid hormones and iodine are required to increase basal metabolic rate and to regulate protein synthesis, long bone growth and neuronal maturation. They are also essential for protein, fat and carbohydrate metabolism regulation. Imbalances in thyroid and iodine metabolism can negatively affect these vital functions. Pregnant women are at risk of hypo or hyperthyroidism, in relation to or regardless of their medical history, with potential dramatic outcomes. Fetal development highly relies on thyroid and iodine metabolism and can be compromised if they malfunction. As the interface between the fetus and the mother, the placenta plays a crucial role in thyroid and iodine metabolism during pregnancy. This narrative review aims to provide an update on current knowledge of thyroid and iodine metabolism in normal and pathological pregnancies. After a brief description of general thyroid and iodine metabolism, their main modifications during normal pregnancies and the placental molecular actors are described. We then discuss the most frequent pathologies to illustrate the upmost importance of iodine and thyroid for both the mother and the fetus.

Developmental Trends in Postnatal Thyroid Hormones and Thyroid Dysfunction in Preterm Infants Born at less than 34 weeks Gestation

OBJECTIVES

To analyse the trends in thyroid function tests (TFT) in preterm infants, evaluate the frequency of thyroid dysfunction, and identify the factors that influence thyroid function.

METHODS

The TFT results and risk factors for thyroid dysfunction in preterm infants with gestational ages (GA) between 25 and 34 weeks were analysed.

RESULTS

In total, 535 infants were enrolled in this study. Thyroid hormone levels vary with gestational and postnatal age, and the total frequency of thyroid dysfunction is 50.3%. Thirty-one infants (5.8%) had delayed TSH elevation. Transient hypothyroxinaemia of prematurity remained significantly associated with both lower birth weight and GA. Congenital hypothyroidism was significantly associated with lower birth weight, 5 min Apgar score, and dopamine use.

CONCLUSIONS

Thyroid hormone levels in preterm infants are related to gestation and postnatal age, the frequency of thyroid dysfunction in premature infants is high, and is negatively correlated with GA and birth weight.

Fetal Physiologically Based Pharmacokinetic Models: Systems Information on the Growth and Composition of Fetal Organs

BACKGROUND

The growth of fetal organs is a dynamic process involving considerable changes in the anatomical and physiological parameters that can alter fetal exposure to xenobiotics in utero. Physiologically based pharmacokinetic models can be used to predict the fetal exposure as time-varying parameters can easily be incorporated.

OBJECTIVE

The objective of this study was to collate, analyse and integrate the available time-varying parameters needed for the physiologically based pharmacokinetic modelling of xenobiotic kinetics in a fetal population.

METHODS

We performed a comprehensive literature search on the physiological development of fetal organs. Data were carefully assessed, integrated and a meta-analysis was performed to establish growth trends with fetal age and weight. Algorithms and models were generated to describe the growth of these parameter values as functions of age and/or weight.

RESULTS

Fetal physiologically based pharmacokinetic parameters, including the size of the heart, liver, brain, kidneys, lungs, spleen, muscles, pancreas, skin, bones, adrenal and thyroid glands, thymus, gut and gonads were quantified as a function of fetal age and weight. Variability around the means of these parameters at different fetal ages was also reported. The growth of the investigated parameters was not consistent (with respect to direction and monotonicity).

CONCLUSION

Despite the limitations identified in the availability of some values, the data presented in this article provide a unique resource for age-dependent organ size and composition parameters needed for fetal physiologically based pharmacokinetic modelling. This will facilitate the application of physiologically based pharmacokinetic models during drug development and in the risk assessment of environmental chemicals and following maternally administered drugs or unintended exposure to environmental toxicants in this population.

Ultrasound Measurements of Fetal Thyroid: Reference Ranges from a Cohort of Low-Risk Pregnant Women

Background

Adequate thyroid function is essential for normal growth and development of the fetus. Sonographic recognition of alterations in fetal thyroid dimensions may be the first sign of thyroid dysfunction, permitting early diagnosis and intervention. The main goal of this study was to build curves with reference values for ultrasound measurements of the fetal thyroid from 14 to 40 weeks of gestation.

Methods

This is a prospective longitudinal study of 90 Brazilian pregnant women, complementary to a cohort multicentre study named “WHO multicentre study for the development of growth standards from fetal life to childhood: the fetal component.” Pregnant women without any pre-existing conditions that might affect fetal growth received antenatal care from the first trimester until childbirth, undergoing serial ultrasound evaluations of the fetus, including the thyroid. Longitudinal, anteroposterior, and transverse diameters of both thyroid lobes were measured in the fetus. Fetal thyroid lobe volume was also estimated. By quantile regression analysis, reference curves of measurements were fitted according to the gestational age.

Results

A reference standard of thyroid growth was defined during pregnancy by fitting curves of its measurements. Reference values for the 10^th, 50^th, and 90^th centiles of fetal thyroid measurements (longitudinal, anteroposterior, transverse diameters, and lobe volume) were defined, from 14 to 40 weeks of gestation.

Conclusion

We provided a reference curve of optimal thyroid development in a low-risk population that can be used as a standard of comparison to diagnose deviations from the norm. In addition, we demonstrated an alternative and simplified method for early recognition of thyroid morphological alterations by an individualized technique to evaluate the thyroid lobes.

Iodine-Induced Fetal Hypothyroidism: Diagnosis and Treatment with Intra-Amniotic Levothyroxine

BACKGROUND

Iodine is necessary for fetal thyroid development. Excess maternal intake of iodine can cause fetal hypothyroidism due to the inability to escape from the Wolff-Chaikoff effect in utero.

CASE REPORT

We report a case of fetal hypothyroid goiter secondary to inadvertent excess maternal iodine ingestion from infertility supplements. The fetus was successfully treated with intra-amniotic levothyroxine injections. Serial fetal blood sampling confirmed fetal escape from the Wolff-Chaikoff effect in the mid third trimester. Early hearing test and neurodevelopmental milestones were normal.

CONCLUSION

Intra-amniotic treatment of fetal hypothyroidism may decrease the rate of impaired neurodevelopment and sensorineural hearing loss.

Normal radiological anatomy of thyroid cartilage in 600 Chinese individuals: implications for anterior cervical spine surgery

Background

Thyroid cartilage is an important barrier in anterior cervical approach surgery. The objective of this study is to establish normative values for thyroid cartilage at three planes and to determine their significance on preoperative positioning and intraoperative traction in surgery via the anterior cervical approach.

Methods

Neck CT scans were collected from 600 healthy adults who did not meet any of the exclusion criteria. Transverse diameters (D1, D2, and D3) of the superior border of the thyroid cartilage (SBTC), inferior border of the thyroid cartilage (IBTC), and the trachea transverse diameters of the inferior border of the cricoid cartilage (IBCC) were measured on a horizontal plane.

Results

All measured variables had intra-class correlation coefficients (ICCs) of ≥ 0.7. The differences in transverse diameters on the same plane between males and females were significantly different (all p < 0.001). The SBTC is most often at C4 in women (59.5%) and C4/5 in men (36.4%), the IBTC is most often at C5 in women (48.1%) and men (46.2%), and the IBCC is primarily located at C6 in women (45.2%) and C6 or C6/7 in men (34.4%) (all p < 0.001).

Conclusion

We present normative values for thyroid cartilage at three planes of SBTC, IBTC, and IBCC in Chinese individuals. The individual and gender differences in the location of the thyroid cartilage and the size of the thyroid cartilage and the cricoid cartilage provide an anatomical basis to localize the skin incision, to predict the difficulty of intraoperative exposure and retractor pulling, and to identify that the thyroid cartilage protected the pharyngoesophageal wall.

Activation of the Nrf2-Keap 1 Pathway in Short-Term Iodide Excess in Thyroid in Rats

Wistar rats were randomly divided into groups of varying iodide intake: normal iodide; 10 times high iodide; and 100 times high iodide on Days 7, 14, and 28. Insignificant changes were observed in thyroid hormone levels (p > 0.05). Urinary iodine concentration and iodine content in the thyroid glands increased after high consumption of iodide from NI to 100 HI (p < 0.05). The urinary iodine concentration of the 100 HI group on Days 7, 14, and 28 was 60–80 times that of the NI group. The mitochondrial superoxide production and expressions of Nrf2, Srx, and Prx 3 all significantly increased, while Keap 1 significantly decreased in the 100 HI group when compared to the NI or 10 HI group on Days 7, 14, and 28 (p < 0.05). Immunofluorescence staining results showed that Nrf2 was localized in the cytoplasm in NI group. Although Nrf2 was detected in both cytoplasm and nucleus in 10 HI and 100 HI groups, a stronger positive staining was found in the nucleus. We conclude that the activation of the Nrf2-Keap 1 antioxidative defense mechanism may play a crucial role in protecting thyroid function from short-term iodide excess in rats.

An Overview of the Thyroid Gland and Thyroid-Related Deaths for the Forensic Pathologist

The thyroid gland is a butterfly-shaped organ situated in the anterior neck whose functions have system-wide effects. Thyroid diseases represent some of the most commonly encountered endocrine disorders and therefore are commonly encountered at the time of autopsy. Knowing how the gland functions and the effects it may have on vital organs is important when determining the cause of death and significant contributory conditions. Endocrine-related deaths may be anatomically subtle, therefore histologic examination, review of medical records, and selected postmortem testing must be performed to correctly identify and document their presence. For this reason, it is recommended that pathologists consider regularly examining the thyroid gland histologically, particularly on decedents where no apparent anatomic cause of death is identified after the autopsy. This article provides an in-depth review of the thyroid gland, thyroid hormones, and thyroid diseases, including potential thyroid-related deaths and incidental autopsy findings.