Thyroid dysgenesis in monozygotic twins: variants identified by scintigraphy

Hemiagenesis of the thyroid gland detected by coincidence-what is the clinical relevance? : Case report and review of the literature

Hemiagenesis of the thyroid gland (THA) represents a rare congenital anomaly. It is characterized by the absence of one thyroid lobe, and sometimes the isthmus as well. It can occur with all kinds of other thyroid pathologies that may be present in the remaining thyroid lobe. A case of a 21-year-old male patient is presented; he sought a thyroid consultation because of hair loss, fatigue, and problems concentrating, thus raising the suspicion of hypothyroidism. Thyroid function was normal, but sonography of the thyroid gland revealed THA of the left lobe and the isthmus. The current knowledge concerning the genesis and the clinical consequences of THA are discussed based on the current literature.

Thyroid hemiagenesis: a case report

Thyroid hemiagenesis is a rare entity in the literature. Developmental hemi-thyroid anomalies can result from either an abnormal descent or an agenesis of one lobe of the thyroid gland. This study aimed at presenting a thyroid hemiagenesis case incidentally diagnosed by neck ultrasonography (USG), who had complaints of pain and swelling in the neck. USG examination revealed lack of left thyroid lobe and multiple nodules in the right lobe. Fine Needle Aspiration Biopsy (FNAB) showed follicular neoplasia, and right subtotal thyroidectomy was performed. We report the rarity of the condition and emphasize the role of imaging techniques in preoperative diagnosis and subsequent management.

Molecular defects in thyroid dysgenesis

Congenital hypothyroidism (CH) is a neonatal endocrine disorder that might occur as itself or be associated to congenital extra-thyroidal defects. About 85% of affected subjects experience thyroid dysgenesis (TD), characterized by defect in thyroid gland development. In vivo experiments on null mice paved the way for the identification of genes involved thyroid morphogenesis and development, whose mutation has been strongly associated to TD. Most of them are thyroid-specific transcription factors expressed during early thyroid development. Despite the arduous effort in unraveling the genetics of TD in animal models, up to now these data have been discontinuously confirmed in humans and only 5% of TD have associated with known null mice-related mutations (mainly PAX8 and TSHR). Notwithstanding, the advance in genetic testing represented by the next-generation sequencing (NGS) approach is steadily increasing the list of genes whose highly penetrant mutation predisposes to TD. In this review we intend to outline the molecular bases of TD, summarizing the current knowledge on thyroid development in both mice and humans and delineating the genetic features of its monogenetic forms. We will also highlight current strategies to enhance the insight into the non-Mendelian mechanisms of abnormal thyroid development.

A case report of 131I therapy for Graves' disease patient with hemiagenesis

RATIONALE

Thyroid hemiagenesis is a rare congenital dysplasia, whereas a variety of pathological changes may occur in residual thyroid lobe. The most frequently described pathology in residual thyroid lobe is Graves' hyperthyroidism. Although I therapy has been generally recommended as the preferred treatment for Graves' disease (GD), subjects relating to hemiagenesis are very limited, especially in China.

PATIENT CONCERNS

A 43-year-old female patient presented to our hospital on November 2014, with a 1-year history of palpitation, fatigue, and hand tremor. Her situation was getting worse within 2 months.

DIAGNOSIS

The thyroid function tests were suggestive of thyrotoxicosis. The technetium thyroid scintigraphy only showed an enlarged right lobe with increased tracer uptake. Then, the agenesis of left lobe and isthmus was confirmed by ultrasound and magnetic resonance imaging (MRI). Thus, a diagnosis of GD with hemiageneis of the left lobe and isthmus of thyroid was made.

INTERVENTIONS

Thiamazole was discontinued because of drug-induced hepatic injury. According to our procedures, the patient was treated by I.

OUTCOMES

Hypothyroidism was observed 3 months after I therapy. After replacement therapy with L-thyroxine (LT4), the state of euthyroid maintained.

LESSONS

Once hypothyroidism occurs, regular application of LT4 and review of thyroid function is very important. Thus, patients' compliance needs to be strengthened. Besides, we could not convince the family members of our patient to undergo ultrasonographic examination. The genetic factor of the agenesis could not be proved in this case.

Mutations in BOREALIN cause thyroid dysgenesis

Congenital hypothyroidism is the most common neonatal endocrine disorder and is primarily caused by developmental abnormalities otherwise known as thyroid dysgenesis (TD). We performed whole exome sequencing (WES) in a consanguineous family with TD and subsequently sequenced a cohort of 134 probands with TD to identify genetic factors predisposing to the disease. We identified the novel missense mutations p.S148F, p.R114Q and p.L177W in the BOREALIN gene in TD-affected families. Borealin is a major component of the Chromosomal Passenger Complex (CPC) with well-known functions in mitosis. Further analysis of the missense mutations showed no apparent effects on mitosis. In contrast, expression of the mutants in human thyrocytes resulted in defects in adhesion and migration with corresponding changes in gene expression suggesting others functions for this mitotic protein. These results were well correlated with the same gene expression pattern analysed in the thyroid tissue of the patient with BOREALIN-p.R114W. These studies open new avenues in the genetics of TD in humans.

Thyroid Hemiagenesis: Incidence, Clinical Significance, and Genetic Background

CONTEXT

Thyroid hemiagenesis (THA) constitutes a rare, congenital disorder that is characterized by an absence of one thyroid lobe. Because the pathogenesis and clinical significance of this malformation remain undefined, specific clinical recommendations are lacking, especially for asymptomatic cases.

EVIDENCE ACQUISITION

The PubMed database was searched (years 1970 to 2017), and the following terms were used to retrieve the results: "thyroid hemiagenesis," "thyroid hemiaplasia," "one thyroid lobe agenesis," and "one thyroid lobe aplasia." Subsequently, reference sections of the retrieved articles were searched.

EVIDENCE SYNTHESIS

There is a noticeable susceptibility of subjects with THA to develop additional thyroid and nonthyroidal pathologies. In pathogenesis of concomitant thyroid pathologies, a chronic elevation in thyroid-stimulating hormone values may play an important role. Thus far, genetic studies failed to find a common genetic background of the anomaly, and the potential underlying cause was identified in a minority of the cases.

CONCLUSIONS

Patients with THA are prone to develop additional thyroid pathologies and theoretically might benefit from l-thyroxine treatment to lower the thyrotropin levels to those observed in the normal population. However, further research should be done to ascertain whether such intervention early in life would prevent development of associated thyroid conditions. At least, increased vigilance should be maintained to reveal all of the concomitant disorders as soon as possible during follow-up examinations. Application of high-throughput technologies enabling a genome-wide search for novel factors involved in thyroid embryogenesis might be the next step to expand the knowledge on THA pathogenesis.

Pictorial essay of developmental thyroid anomalies identified by Technetium thyroid scintigraphy

Developmental anomalies and anatomic variations of the thyroid gland in the general population with no known thyroid dysfunction usually goes unnoticed. Only those patients with neck swellings, incidentally detected hypo or hyperthyroidism, and those with a maternal history of hypothyroidism undergo screening for the thyroid gland. Neck ultrasound and scintigraphic techniques are the imaging tools routinely used to identify these anomalies. We present interesting technetium (Pertechnetate and sestaMIBI) scintigraphic images of adults and children who presented to our department with thyroid dysfunction showing developmental anomalies of the thyroid.

Sublingual thyroid ectopy: similarities and differences with Kallmann syndrome

Permanent primary congenital hypothyroidism (CH), the commonest cause of preventable intellectual disability, is due to defects in the embryonic development of the thyroid in the vast majority of cases. These defects are collectively called thyroid dysgenesis. The thyroid may be absent (athyreosis) but, more commonly, a sublingual thyroid ectopy without lateral lobes, is the only thyroid tissue present. Such an ectopy presumably results from an arrest in the downward migration of the median anlage. Thyroid ectopy almost always occurs in a sporadic fashion. However, first-degree relatives are affected more often than chance alone would predict. On the other hand, almost all reported monozygotic twin pairs are discordant for thyroid ectopy. Current research is aimed at reconciling these contradictory epidemiological data. We propose a two-hit mechanism associating a germline predisposing factor with another genetic or epigenetic alteration within the ectopic thyroid tissue itself or, as in some forms of Kallmann syndrome, in the structures surrounding the thyroid during embryogenesis. Thyroid ectopy, a model for sporadic congenital malformations in humans, is also associated with congenital heart disease, and molecular mechanisms common to thyroid and heart development are being unraveled.

Congenital thyroid hemiagenesis with multinodular goiter

Thyroid hemiagenesis is a rare form of thyroid dysgenesis characterized by an absence of half of the thyroid gland. Developmental hemi-thyroid anomalies can result from either an abnormal descent or an agenesis of one lobe of the thyroid gland. We report a case of a 40-year-old woman with history of a longstanding gradually progressive thyroid swelling without any complication. An ultrasonographic examination diagnosed the absence of the left thyroid lobe and enlargement of the right lobe, which was confirmed on a computed tomography (CT) angiogram and a radionuclide scan of the neck. A cytological examination showed nodular goiter with cystic degeneration. Right subtotal thyroidectomy was performed and histopathological examination confirmed adenomatous goiter with degenerative changes. We report the rarity of the condition and emphasize the role of a comprehensive radiological, cytological, and radionuclide algorithm for an accurate preoperative diagnosis and subsequent management.

Surgical strategy for primary hyperparathyreoidism with thyroid hemiagenesis

BACKGROUND

Thyroid hemiagenesis is a rare congenital anomaly, and still more rarely associated with primary hyperparathyroidism (pHPT). Due to the embryologic pathways of the thyroid and parathyroid glands, it remains unclear whether or not thyroid hemiagenesis may be linked to ipsilateral parathyroid agenesis, and consequently, surgical strategy for thyroid hemiagenesis associated pHPT (THAP) does not only depend on preoperative localization but also on the thyroid anomaly.

METHODS

Including the present case report, a total of nine cases with THAP retrieved from the literature were reviewed. Seven of nine cases had thyroid hemiagenesis on the left side, three out of nine showed a parathyroid adenoma on the contralateral side to the thyroid hemiagenesis.

CONCLUSIONS

Based on these cases, it can be concluded that the embryologic pathways of the thyroid and parathyroid glands are different, and in cases of THAP, parathyroid exploration should follow standard recommendations for pHPT surgery.

Left thyroid hemiagenesis in a patient with primary hyperparathyroidism

The case of a patient with primary hyperparathyroidism with the incidental finding of left thyroid hemiagenesis with isthmus involvement is presented. Thyroid hemiagenesis is a rare congenital abnormality. There have been approximately 310 cases reported in the literature to date. It has been reported as an incidental finding with a wide range of associated pathological conditions. It is important to consider this in patients being prepared for thyroid lobectomy due to the inevitability of postoperative hypothyroidsm. Due to the female predominance of thyroid disease, hemiagenesis was first thought to be more common in women. Left lobe cases accounts for the majority of instances and isthmus is absent in half the cases. Ultrasonography is the diagnostic tool of choice.

Thyroid hemiagenesis and Graves' disease in a child

Hemiagenesis of the thyroid is a rare malformation and Graves' disease with ophthalmopathy is reported quite rarely in adult patients but is not seen in children. This is a report of an 8-year-old girl with congenital absence of the left thyroid lobe, or hemiagenesis.

Unusual thyroid constellation in Down syndrome: congenital hypothyroidism, Graves' disease, and hemiagenesis in the same child

We report a girl with Down syndrome who was diagnosed with congenital hypothyroidism in the newborn period due to left thyroid hemiagenesis. Unexpectedly, her hypothyroidism resolved at the age of 3 years. After being off thyroid hormone replacement for 7 years and having normal thyroid function, she developed Graves' disease. Although Graves' disease in association with thyroid hemiagenesis has previously been reported, this represents the youngest patient in whom this scenario has been described. Issues pertaining to thyroid hemiagenesis, autoimmune hyperthyroidism, and thyroid disease in children with Down's syndrome are discussed.

Papillary carcinoma of a thyroglossal duct cyst in a patient with thyroid hemiagenesis: effectiveness of conservative surgical treatment

OBJECTIVE

To describe a case of thyroglossal duct cyst carcinoma that arose in a patient with right thyroid lobe hemiagenesis.

METHODS

We present the imaging, physical examination findings, treatment, and clinical course of the study patient.

RESULTS

A 35-year-old woman was evaluated for a neck mass that had been present for 6 months and was slowly growing. She reported a previous diagnosis of right hemithyroid agenesis. The patient's preoperative workup included ultrasonography of the neck and head and neck T1- and T2-weighted magnetic resonance imaging, which showed right hemithyroid agenesis and a cystic lesion in the median region of the neck below the hyoid bone. Findings from chest x-rays and thyroid function tests were normal. The patient underwent a modified Sistrunk procedure that included removal of the median portion of the hyoid bone. Histologic findings showed a 2.5-cm thyroglossal duct cyst with a 0.6-cm focus of follicular variant of papillary carcinoma with invasion of the cyst wall. Total thyroidectomy was not performed because of the absence of tumoral invasion of the parenchyma around the thyroglossal duct cyst and because the patient was at low risk for aggressive disease. Cervical ultrasonography examinations were performed 6, 12, and 24 months after treatment, and all findings were normal. Presently, the patient is symptom-free after 4 years of follow-up and has no evidence of disease.

CONCLUSION

Incidentally discovered, well-differentiated thyroid cancer that is confined to a thyroglossal duct cyst in a patient at low risk for aggressive disease can be adequately treated by a modified Sistrunk procedure that includes the median portion of the hyoid bone.

Thyroid hemiagenesis with Graves' disease, Graves' ophthalmopathy and multinodular goiter

Thyroid hemiagenesis is a rare congenital anomaly in which one of the thyroid lobes with or without isthmus fails to develop. Here we present a woman patient with thyroid hemiagenesis, Graves' disease and ophthalmopathy with nodular goiter. Fine needle aspiration biopsy of the dominant nodule was suspicious of malignancy. The patient was referred for surgery for total thyroidectomy. Histopathological examination of the surgical material revealed benign features. The present case confirms that, although rare, a number of concomitant thyroid disorders can exist in a single patient with thyroid hemiagenesis just as it is seen for a normally developed thyroid gland.

Prevalence of thyroid hemiagenesis in an asymptomatic schoolchildren population

BACKGROUND

Thyroid hemiagenesis is a rare congenital anomaly in which one lobe of thyroid gland fails to develop. Because variations of the prevalence of this anomaly have been reported, the aim of this study was to evaluate the prevalence rate of thyroid hemiagenesis in an apparently normal population from Northern Poland.

METHODS

Ultrasound examination of the thyroid gland was performed in 4004 unselected 7-15-year-old school-children from the seaside zone of Northern Poland.

RESULTS

Two cases of thyroid hemiagenesis were found, both being absence of the left lobe in two girls. Thyroid volumes, adjusted to body surface area, were within normal range; serum thyrotropin, free thyroxine, and free triiodothyronine were within normal limits. Physical examination, abdominal ultrasound, and echocardiography did not show extrathyroidal malformations. Thyroid ultrasound was normal in the girls, parents, and siblings.

CONCLUSIONS

The study showed a 0.05% prevalence of thyroid hemiagenesis in asymptomatic schoolchildren population from iodine-sufficient area of Northern Poland.

Primary Hyperparathyroidism with Thyroid Hemiagenesis

Thyroid hemiagenesis is a very rare anomaly. We herein report a case with right thyroid lobe agenesis, which was incidentally found during the assessment of primary hyperparathyroidism. A 42-year-old male presenting with urinary lithiasis was suspected of having primary hyperparathyroidism, and had elevated levels of both serum calcium and intact parathyroid hormone. Both computed tomography and ultrasonography demonstrated the absence of right thyroid lobe and a mass of 1 cm in diameter at the left lower pole of the thyroid. The patient underwent lower left parathyroidectomy, which confirmed the right thyroid hemiagenesis, as well as the absence of both upper and lower right parathyroid glands. The resected left lower parathyroid gland was pathologically diagnosed as adenoma. The postoperative course was favourable and he was discharged on the 2nd day after surgery, without complications.

A mouse model demonstrates a multigenic origin of congenital hypothyroidism

Congenital hypothyroidism with thyroid dysgenesis (TD) is a frequent human condition characterized by elevated levels of TSH in response to reduced thyroid hormone levels. Congenital hypothyroidism is a genetically heterogeneous disease. In the majority of cases studied, no causative mutations have been identified and very often the disease does not show a Mendelian transmission. However, in approximately 5% of cases, it can be a consequence of mutations in genes encoding the TSH receptor or the transcription factors TITF1, FOXE1, or PAX8. We report here that in mouse models, the combination of partial deficiencies in the Titf1 and Pax8 genes results in an overt TD phenotype that is absent in either of the singly deficient, heterozygous mice. The disease is characterized by a small thyroid gland, elevated levels of TSH, reduced thyroglobulin biosynthesis, and high occurrence of hemiagenesis. The observed phenotype is strain specific, and the pattern of transmission indicates that at least two other genes, in addition to Titf1 and Pax8, are necessary to generate the condition. These results show that TD can be of multigenic origin in mice and strongly suggest that a similar pathogenic mechanism may be observed in humans.

Thyroid hemiagenesis is a rare variant of thyroid dysgenesis with a familial component but without Pax8 mutations in a cohort of 22 cases

Thyroid hemiagenesis is a rare form of thyroid dysgenesis of which some familial cases have been reported, including one associated with a heterozygous mutation in the Pax8 gene. However, the physiopathology remains not well known. The objectives of this study were 1) to describe the clinical features, 2) to look for familial clustering, and 3) to search for Pax8 mutations in a relatively large cohort of affected patients. A family history of thyroid dysgenesis was found in nine patients (40%), whose affected relatives had ectopic thyroid (n = 4), athyreosis (n = 1), thyroid hemiagenesis (n = 2), or thyroglossal duct cysts (n = 2). Screening for Pax8 mutations identified abnormal migration profiles by SSCP analysis in 3 patients, but direct sequencing did not show coding region mutations in any of the 22 patients. In conclusion, this study provides the first evidence that thyroid hemiagenesis can occur as a familial disorder associated with any form of thyroid dysgenesis. This finding supports both a common underlying mechanism to the various abnormalities in thyroid development and a role for genetic factors; however, our results from Pax8 analysis suggest that this gene may not be a key factor.

A singular case of Graves' disease in congenital thyroid hemiagenesis

We report the observation of an unusual case of Graves' disease associated with thyroid hemiagenesis. A 41-year-old woman who presented with symptoms and clinical signs of hyperthyroidism was discovered to have thyroid hemiagenesia of the left lobe. Thyroid ultrasound scan showed enlargement of the right lobe with a single nodule, and absence of the left lobe; isotope scan showed homogeneous uptake in the single lobe and nodule. Ophthalmopathy, which was absent at presentation, developed after two years; after a further 2 years the patient developed decompensated hypothyroidism requiring thyroxine replacement. This is the first case of Graves' disease in thyroid hemiagenesis evolved to hypothyroidism, and a rare case of thyroid ophthalmopathy accompanying this condition.

Thyroid hemiagenesis and incidentally discovered papillary thyroid cancer: case report and review of the literature

Thyroid hemiagenesis (TH) is a rare congenital abnormality in which one thyroid lobe fails to develop. Its prevalence is uncertain, because the absence of one thyroid lobe does not usually cause clinical symptoms. The detection of TH is usually incidental when the evaluation of other thyroid disorders is requested. It is more frequently found in female than in male patients (3:1 ratio) and in the left lobe compared to the right lobe. We report the case of a 54-yr-old man, presenting with a large multinodular right-sided goiter, with mediastinal extension and dysphagia. Thyroid scan and ultrasound study showed the absence of the left lobe. The patient underwent surgery for compressive symptoms, and the operation confirmed the absence of the left lobe. Histological examination demonstrated a multi-nodular goiter with papillary carcinoma. To our knowledge, this case represents the first reported case of association between TH and papillary thyroid carcinoma in a male patient, and the second in which the tumor arose in the right lobe.

Genetic deletion of sonic hedgehog causes hemiagenesis and ectopic development of the thyroid in mouse

Thyroid dysgenesis encountered in 85% of patients with congenital hypothyroidism is a morphologically heterogeneous condition with primarily unknown pathogenesis. Here we identify sonic hedgehog (Shh) as a novel regulator of thyroid development. In Shh knockout mice the thyroid primordium is correctly specified in the pharyngeal endoderm, but budding and dislocation are slightly delayed. In late development the thyroid fails to form a bilobed gland. Instead a single thyroid mass is found unilaterally and mostly to the left of the midline. Thyroid-specific transcription factors (TTF-1 and TTF-2) and thyroglobulin are expressed indicating terminal differentiation. Strikingly, TTF-1- and TTF-2-positive cells aberrantly develop in the presumptive trachea of Shh-/- embryos. The ectopic tissue buds ventrolaterally into the adjacent mesenchyme, and less extensively into the tracheal lumen, forming follicle-like structures that accumulate thyroglobulin. Shh mRNA is not expressed in the thyroid precursor cells at any developmental stage. The results indicate that Shh signaling indirectly governs the symmetric bilobation of the thyroid during late organogenesis. Shh also seems to repress inappropriate thyroid differentiation in nonthyroid embryonic tissues. This study provides clues to the molecular mechanisms that might be dysregulated in thyroid hemiagenesis and development of ectopic thyroid tissue outside the thyroglossal duct.

Thyroid hemiagenesis associated with Graves' disease and Graves' ophthalmopathy: case report

Failure of embryologic development of a lobe of the thyroid gland is a rare anomaly. Usually, this condition is diagnosed when there are some other pathologic conditions in the gland and is often found when a patient presents with a thyroid nodule, which in reality is compensatory hypertrophy of the side that is present, therefore appearing as a nodule. A variety of pathological conditions occur in the remaining thyroid tissue in association with this rare anomaly such as adenoma, carcinoma, subacute thyroiditis, colloid nodule, Graves' disease, simple goiter, and Hashimoto thyroiditis. Association of Graves' disease with ophthalmopathy and thyroid hemiagenesis is quite rare and very few cases are reported in the literature. We report a 29-year-old female presented as Graves' disease and Graves' ophthalmopathy with left lobe hemiagenesis of the thyroid gland.

Development of the thyroid gland: lessons from congenitally hypothyroid mice and men

Congenital hypothyroidism is the most common congenital endocrine disorder (one newborn in 3000) and represents the most common cause of preventable mental retardation. In 10-20% of cases, it is due to autosomal recessive functional disorders leading to goiter formation (thyroid dyshormonogenesis). In the remainder, it is due to thyroid dysgenesis, which comprises usually isolated defects in: (1) migration of the median thyroid anlage, leading to a round cluster of ectopic cells (usually in a sublingual position) with no other thyroid tissue present; (2) differentiation or survival of the thyroid follicular cells leading to athyreosis; and (3) growth of a thyroid with the normal bilobed shape and in the normal cervical position (orthotopic hypoplasia). Mouse knock-outs have demonstrated that thyroid transcription factor-1 (TTF-1) and PAX8 are required for the survival and proliferation of thyroid follicular cell precursors, TTF-2 for their downward migration and the thyrotropin receptor (TSHR) for post-natal thyroid growth. In humans, thyroid dysgenesis is generally a sporadic malformation but an affected relative is found in 2% of cases, a figure 15-fold higher than by chance alone. Pedigree analysis is most compatible with dominant inheritance with variable penetrance. However, mutations in TTF-1, TTF-2, PAX8 and TSHR are found in <10% of patients with congenital hypothyroidism and these predominantly have orthotopic thyroid hypoplasia, often associated with other malformations. This low yield and the discordance of >90% of monozygotic twin pairs suggests that isolated thyroid ectopy or athyreosis most often results from early somatic mutations, epigenetic modifications or stochastic developmental events.

Thyroid hemiagenesis in an endemic goiter area diagnosed by ultrasonography: report of sixteen patients

During a period of 9 years, 71,500 patients underwent thyroid investigations at our department. Sixteen patients with thyroid hemiagenesis, 13 women and 3 men, were seen during this period. Fifteen had no left lobe and only 1 had no right lobe, the isthmus was present in 5 patients. Associated thyroid diseases of the lobe that was present could be observed in 11 patients (9 diffuse or nodular goiters, 2 thyroid autoimmune diseases). One patient was hyperthyroid and 7 were hypothyroid. Hypothyroidism associated with hemiagenesis has rarely been reported in the literature. In our survey, the high percentage of hypothyroidism may be explained by coexisting iodine deficiency, which could be verified in 4 hypothyroid patients. Ultrasonography is the key investigation to diagnose thyroid hemiagenesis. Fine-needle aspiration biopsies, laboratory tests, and scintigraphies are useful to diagnose other diseases within the remaining lobe or to visualize ectopic thyroid tissue. Review of the literature, including our cases, presented a total of 256 patients with thyroid hemiagenesis. Its prevalence can be estimated between 1:1900 and 1:2675. Left to right ratio of thyroid hemiagenesis is 3.6:1 with an isthmus present in 44%. The female-to-male ratio is 3:1; however, the larger number of females is probably based on a bias due to a female predominance of the populations investigated. On the basis of an equal distribution of both sexes, the female-to-male ratio of thyroid hemiagenesis would be only 1.3:1 in our survey.

Thyroid hemiagenesis and elevated thyrotropin levels in a child with Williams syndrome

A girl with Williams syndrome (WS) presented with elevated thyrotropin (TSH) levels (7.0 microU/ml), normal free thyroid hormone concentrations, and absent antithyroid autoantibodies. Thyroid ultrasonography and scintigraphy showed hemiagenesis of the left lobe and no evidence of ectopic tissue. TSH response to thyrotropin-releasing hormone (TRH) injection (200 microg/mq, i.v.) was exaggerated and prolonged, suggesting subclinical hypothyroidism. The biological activity of circulating TSH was slightly below the normal range [TSH bioactivity (B) to immunoreactivity (I) ratio (TSH B/I) = 0.4, normal: 0.6-2.2]. These abnormalities are similar to those seen in patients with hypothalamic hypothyroidism. Thyroid function is not a recognized manifestation of WS and is not routinely investigated. However, abnormalities of the hypothalamic-pituitary-thyroid (HPT) axis and thyroid dysgenesis have been found in other WS cases. Genes mapping at 7q11.23, contiguous to the chromosomal region deleted in most WS patients, may be involved in the development of the thyroid gland, contributing to the complex phenotype of WS.

Development of Graves' hyperthyroidism from primary hypothyroidism in a case of thyroid hemiagenesis

We report a 42-year-old female with right thyroid hemiagenesis who initially presented with hypothyroidism and then developed hyperthyroidism. The serum titer of thyroid-stimulating antibody was weakly positive in the initial hypothyroid state, and then markedly increased along with the development of hyperthyroidism, while thyroid stimulation-blocking antibody was continuously negative throughout the observation period. Thyroid histology of biopsied specimens during the hypothyroid state demonstrated diffuse thyroiditis with mononuclear cell infiltrations; however, the histology during the hyperthyroid state showed hyperplasia in follicular epithelial cells accompanied by partial lymphocyte infiltration. This is the first case of thyroid hemiagenesis associated with a conversion from primary hypothyroidism due to Hashimoto's thyroiditis to hyperthyroidism due to Graves' disease.

Thyroid hemiagenesis with subacute thyroiditis

A 58-year-old woman with thyroid hemiagenesis associated with subacute thyroiditis is described. Physical examinations revealed a firm nodule with spontaneous pain and tenderness in the left thyroid lobe. A serum thyroid hormone levels were elevated and thyroid scintiscan with 99mTc pertechnetate showed an extremely low uptake, we made a diagnosis of subacute thyroiditis. A 201Tl thyroid scan demonstrated an enlarged left lobe and absence of the right lobe. Ultrasonography of the thyroid gland revealed an enlarged left lobe occupied mostly with a hypoechoic region. An incidental finding was absence of the right lobe. Two months later thyroid function returned to normal. A follow-up thyroid scintiscan revealed a normal left lobe but absent right lobe. The diagnosis of hemiagenesis was confirmed by CT scan. This appears to be the first case report of thyroid hemiagenesis associated with subacute thyroiditis.

Thyroid hemiagenesis associated with the right aortic arch

The case of a 38-year-old woman with left thyroid hemiagenesis associated with the right aortic arch is presented. The diagnosis of hemiagenesis was established by isotopic and ultrasonic imaging, and also by angiographically defined absence of the left thyroid arteries. The aortogram revealed a right aortic arch with isolation of the left subclavian artery from the aorta. Although the significance and mechanism of the concomitant development of these anomalies is unknown, this case may be the first report in the literature.