Thyroid volume and echostructure in children

TOPIC: Factors influencing thyroid volume in school-age children in an area with iodine sufficiency

Title: Thyroid volume and echo-structure in school children living in an iodine-replete area: relation to age, pubertal stage, and body mass index.

Authors: Kaloumenou I, Alevizaki M, Ladopoulos C, Antoniou A, Duntas LH, Mastorakos G, Chiotis D, Mengreli C, Livadas S, Xekouki P, & Dacou-Voutetakis C.

Reference: Thyroid 17: 875-881, 2007

Summary

Background

Thyroid volume (TV) is not uniform among geographical regions, mainly because of differences in iodine intake. Age, gender, developmental status, and perhaps unknown factors may affect thyroid size and anatomy as well. Thus, in regions with long-standing iodine sufficiency, standards for TV that are specific for a defined geographical region and its populations may be more accurate than a single international reference.

Purpose

The aim of the study was to determine TV and assess the prevalence of goiter and thyroid nodules in ethnically Greek school children aged 5-18 years living in Athens (Greece), an area considered to be iodine-sufficient.

Patients: Four hundred and forty apparently healthy schoolchildren (200 boys and 240 girls), aged 5 to 18 years (mean – SD: 10 – 2.9; median: 9.7 years) were selected from schools in Athens (Greece) and were examined. The selection process was designed to secure a -representative- sample of students who were of -Greek ethnic origin- from regional schools to achieve -homogeneity of the study population-. Four hundred and thirty-one of the children were born in the Athens area and lived in Athens until the date of the examination. Nine of the subjects lived in another iodine-replete region of the country for the first years of their life and moved to Athens before attending school.

Methods

All children included in the study had a questionnaire completed, underwent physical examination, and had ultrasonic examination of the thyroid. Vital statistics, body surface area (BSA), and body mass index (BMI) were recorded and urinary iodine excretion was measured. Pubertal status was defined using Tanner-s classification, in all cases by the same investigator. Children were classified as prepubertal if Tanner stage was I and pubertal if Tanner stage was II-V. The result of specific testing of thyroid function, antithyroid immunologic status, and profile of dietary intake were not reported. Thyroid Ultrasound examination: TV was determined by real-time ultrasonography with each child lying supine with the neck hyper-extended. The same experienced radiologist performed the measurements with a General Electric Pro Series (Milwaukee, Wisconsin, USA) scanner with a 7.5 MHz linear transducer. The length (l) , width (w), and depth (d) of each thyroid lobe (in cm) were measured on transverse and longitudinal scans. The volume (Vol) of each lobe (in mL) was estimated by the modified formula for an ellipsoid: Vol (mL) = (0.479 x d x w x l ). TV was defined as the sum of the volumes of both lobes. The presence of nodules and diffusely or irregularly reduced echogenicity were recorded. The 50 th and 97 th percentiles for TV were calculated (P50 and P97).

Urinary iodine: Urinary iodine was determined spectrophotometrically on a morning spot urine sample in all children and calculated as the ratio of -g iodine/g creatinine (-gI/g cr).

Statistical analysis: For statistical analysis the Statistical Package for Social Sciences (SPSS, version 10.00) program for Windows was used. Pearson correlation was performed for univariate analysis; Spearman-s correlation was used when the distribution was not normal. The chi-square test was employed followed by the Fisher-s exact test to compare categorical variables. One-factor analysis of variance (one-way ANOVA) was employed followed by the Scheffe post hoc test to compare quantitative variables. ANCOVA test was also used. All tests were two-sided. The limit of statistical significance was set at p < 0.05.

Results

The thyroid gland was palpable in 13/440 subjects (Pan American Health Organization [PAHO] Ia in 9; PAHO II in 4). Otherwise, none of the subjects included in the study had obvious clinical signs or symptoms of thyroid disease. A questionnaire about date of birth and family history for thyroid disorders as well as any underlying chronic disease was completed for each subject. None of the subjects had any evidence of acute or chronic disease, and no previous known thyroid disorder was reported. There were no thyroid function or antibody data. Concerning urinary iodine excretion , the median urinary iodine concentration was 307.83 -g I/g cr (range: 44 – 1.105). There was no significant difference between boys and girls. Ninety-seven percent of the subjects had an iodine concentration above 100 -g I/g cr, which is considered normal. Concerning thyroid volume , mean TV was 4.99 – 2.75 mL (boys: 4.94 – 2.76 mL, girls: 5.03 – 2.65 mL; P=0.797). The volume of the thyroid gland increased significantly with chronological age in both genders and TV was positively correlated to BSA in both genders. TV was weakly related to body mass index-standard deviation score in boys only (boys: P=0.023; girls: P=0.150). An inverse relationship was found between urinary iodine and TV (P < 0.0005). Mean TV increased significantly at puberty in both sexes. Mean TV in boys at Tanner stage I was 3.4 - 1.3 mL and at Tanner stages II-V 7.3 - 2.7 mL (P < 0.0005). In girls at Tanner stage I, mean TV was 3.7 - 1.7 mL and at Tanner stages II-V 5.9 - 2.8 mL (P < 0.0005). There was no significant difference in TV between boys and girls at Tanner stage I (3.4 - 1.3 mL vs 3.7 - 1.7 mL; P = 0.202), while mean TV at Tanner stages II-V was significantly greater in boys than in girls (7.3 - 2.7 mL vs 5.9 - 2.8 mL; P = 0.001). Concerning the prevalence of goiter , goiter was defined as a TV above the 97 th percentile of the study population. According to this criterion, 3.2% of the schoolchildren were goitrous. TV in these children ranged from 9.4 to 15.3 mL, with a mean TV of 12 – 2.7 mL. Subjects with a goiter had a mean urinary iodine concentration of 217 – 65 -g I/g cr, which did not differ significantly from that of children without a goiter. Finally concerning thyroid ultrasonographic characteristics , the echographic appearance of the thyroid lobes was altered from normal in 9.2% of the study group. In 5.1%, there were one or more nodules (sizes ranging from 5.4 x 4.5 x 3.2 mm to 13.5 x 10 x 9.5 mm). These children were treated with L- thyroxine and examined every six months with a new echography and thyroid function tests: during follow-up, the U/S findings remained stable in ten children and size of thyroid nodule(s) regressed in thirty children.

Conclusions

TV was assessed in 440 selected, healthy, Athenian, ethnically Greek children living in an iodine-replete area. The observed influential factors on TV in both boys and girls were the age, BSA, and pubertal stage. The prevalence of goiter was 3.2% and of an abnormal echo-structure of the thyroid gland was 9.2%.

Commentary

Ultrasonography (US) has been used effectively for epidemiologic studies even in rural and remote regions in under-developed areas and in field studies to evaluate anatomic thyroid features such as size, vascularity, and presence of nodules. The method is safe, inexpensive, reproducible, and easily learned. The equipment is effortlessly portable. Among the insights that have been gained in this way are:

  • Normative data about thyroid dimensions for neonates, children, and adults.
  • Correlations between goiter-size and iodine deficiency in endemic regions.
  • Objective assessment of nodules in populations that have been exposed to environmental irradiation, which is essential for early thyroid cancer detection.
  • Identifying certain diseases in remote populations based on echo-patterns and glandular or nodular blood flow.

In this study the authors reported that age, BSA, gender, and puberty are the major factors that impact on thyroid size and development in an ethnically homogeneous small population of children who live in an iodine-sufficient region. An interesting and intriguing observation relates to the significant boost in thyroid size that occurs at puberty, especially in boys. It will be exciting to know the correlation of thyroid growth, height spurt, adrenarche, actual puberty, and hormonal concentrations as well as their precise sequence, particularly if thyroid growth acceleration antedates or presages puberty. The authors- contention that standards for TV for a particular geographical region and its unique population may be more accurate than a single international reference has not been tested critically but may be valid. This question should be addressed more fully.

A limitation of the present study is the absence of thyroid function tests. When epidemiologic studies are done in a remote, under-developed area, sophisticated laboratory studies that validate or expand observations may understandably be unavailable. However, in Athens (Greece), one would have expected data like TSH and thyroid antibodies to be available, in order to amplify the information about thyroid development, size, and nodules, particularly in the 3.2% of the children who had a goiter and in the 9.2% who presented thyroid nodules. The latter forty children received thyroxine and ultrasonographic findings were stable in ten and the size of thyroid nodule(s) reduced in thirty children. Observations that employ TSH suppressive therapy do not allow one to exclude thyroid cancer and the medication may potentially carry well-known risks.

Summary and commentary prepared by Manfred Blum (related to Chapters 6c & 15 of TDM)













Word count: 1452 Last edited by Vicente Cano on June 18, 2011 at 9:10 pm