Thyroid hemiagenesis

Thyroid hemiagenesis (TH), characterized by the total absence of one lobe, is a very rare congenital anomaly of the thyroid gland. The remaining lobe generally has normal function, such that patients with TH are usually asymptomatic. The pathogenesis and clinical significance of this malformation remain undefined, and specific clinical recommendations are lacking, especially for asymptomatic cases. Therefore, discovering TH in asymptomatic cases is only possible using a screening program with various imaging modalities (1). In clinical practice, TH is usually established during evaluation of patients with symptomatic thyroid pathology (2,3). It is difficult to establish the true prevalence of TH in the normal population due to the normal functioning nature of the remaining lobe of the thyroid gland. Establishing this prevalence would require a screening program on a very large population. Suzuki et al. (4) performed a cross-sectional study of 3.5 years of duration on approximately 300,000 children and young adults to screen for congenital anatomic abnormalities of the thyroid and establish the prevalence of structural changes such as hemiagenesis and agenesis. They reported the prevalence of TH as 0.02% and of agenesis as 0.004% (4). This was the largest study reported in the literature for asymptomatic cases of TH. Some previous studies using ultrasound screening reported a prevalence of TH between 0.025% and 0.5% in the asymptomatic population (1,5-7). The incidence of TH is different in patients presenting with thyroid disorders. Gursoy et al. (5) reported an incidence of 0.25% in 4,833 patients evaluated for thyroidal pathologies. Berker et al. (8) identified ten cases (0.16%) of hemiagenesis in 6,242 patients with thyroid disorders. These results indicate an increase in the incidence of TH in patients with thyroid disorders when compared with the asymptomatic normal population. In our patients who underwent primary thyroid surgery for the treatment of various disorders in the last 4 years, the incidence of TH was 1% (4/405). This finding suggests an increase in the TH incidence among patients with thyroid diseases treated by surgical procedures when compared with both the asymptomatic normal population and patients with medical disorders. The prevalence of TH is up to 5.7% in children with congenital hypothyroidism (1).

Previous reports have shown that in TH, left lobe absence significantly outnumbers right lobe absence. Suzuki et al. (4) determined left lobe absence in 55 of 67 (82.1%) TH patients. Previous manuscripts have also reported the incidence of left hemiagenesis to be between 70% and 87.5% of all TH cases (1,8-11). All of our four identified TH patients had left-sided agenesis.

Gender was found to have a significant effect in TH cases with right lobe absence in that 10 of 12 (83.3%) patients were female (4). On the other hand, gender does not appear to affect left hemiagenesis; Suzuki et al. (4) have reported that 56.4% (31/55) of patients with left hemiagenesis were female; comparable to our finding of half of the cases of left hemiagenesis (50%; 2/4) being female.

An interesting and important finding of the study of Suzuki et al. is the increasing volume of the remaining lobe in cases of hemiagenesis. The volumes of the intact thyroid lobes in subjects with TH were significantly larger than those of ipsilateral lobes in normal subjects (4). This suggests significant compensatory voluminous changes occur in TH. TH without glandular disorders is generally asymptomatic due to production and secretion of thyroid hormones that is comparable to that of a bilobar thyroid gland. Therefore, enlargement of unilobate gland may be the result of expected compensatory growth aimed at maintaining physiological status and normal serum levels of thyroid hormones. Average thyroid stimulating hormone (TSH) and free triiodothyronine (FT3) serum concentrations were significantly higher in unilobate groups than in bilobate glands. In most cases, a compensatory hypertrophy of the remaining lobe was described that was relative to half the normal total thyroid volume (1).

In their screening study of thyroid structure on a young population, Suzuki et al. (4) established 67 cases of TH using ultrasound examination. Noninvasive imaging of the anterior cervical region can successfully identify structural anomalies of the thyroid gland. A combination of ultrasound examination and isotope scintigraphy is sufficient to establish and confirm the diagnosis of TH (1). Ultrasound is the imaging modality of choice to assess structural features of the gland. Beside lobe absence, ultrasound can reveal the structural changes in the remaining lobe, and demonstrate underlying pathology. Nuclear scan is the modality that establishes functional anatomy of the thyroid. This modality can confirm the absence of one lobe detected by ultrasound. Nuclear scan has also established functional status of the remaining lobe. These two imaging modalities are complementary tools to assess structural and functional features of the thyroid and to establish any anatomic abnormality. Many previous reports have also shown that ultrasound is the first tool for evaluation of thyroid anatomy (5,8,12). Previous studies have also emphasized the importance of nuclear scan to assess functional status and to establish functional abnormality of the gland (8,12-14).

Suzuki et al. (4) incidentally diagnosed TH during a screening program in an asymptomatic normal population. TH has no specific symptoms and signs leading to its diagnosis. The remaining lobe of the gland generally has normal function. Usually, patients with TH are biochemically euthyroid and clinically asymptomatic (10). The remaining lobe is usually capable of sufficient hormonal synthesis and secretion to sustain clinical euthyroidism. The abnormality is much more likely to be discovered incidentally during the course of imaging examinations of concomitant cervical pathologies. Most of the cases of TH are diagnosed when the patients present a lesion in the functioning lobe. The remaining lobe of the thyroid gland can be a site of pathological changes similar to a normally developed gland and may present with a spectrum of diseases (11). TH is generally established during the clinical workup of symptomatic patients with thyroid disorders. Several thyroid diseases are associated with TH, including: benign or malignant, hyper-, normal-, hypo-functioning disorders, and autoimmune diseases (2,3,8,10,15-18). A higher incidence of associated functional, morphological, and autoimmune thyroid disorders in patients with TH was observed when compared to subjects with bilobate thyroid (10).

The unique lobe of the unilobate gland generally has normal activity and continues to produce and secrete thyroid hormones to sustain euthyroidism. Therefore, TH itself does not require specific treatment. Indications for medical treatment and surgical procedures in TH are not different from those for normal bilobate glands. The remaining lobe may harbor a variety of lesions, and present with disorders indicating surgical intervention (2,3,10,16,17). Thyroid surgery for TH cases involves total excision of the remaining lobe, that is, total excision of thyroidal tissue. Total lobectomy in a bilobate thyroid does not generally require postoperative replacement therapy, because the proper function of the remaining lobe maintains normal serum level of thyroid hormones. In TH, total excision of the remaining lobe is performed. Hemithyroidectomy in TH cases technically becomes a total thyroidectomy with a need for postoperative replacement therapy.

In conclusion, TH is a very rare congenital anatomical anomaly of the thyroid gland with a reported prevalence between 0.02% and 1%. This rate has shown some variation across screening studies performed on asymptomatic populations, imaging studies of patients with thyroid disorders, and preoperative imaging and/or operative findings in patients with surgical thyroidal diseases. TH can be successfully diagnosed using noninvasive imaging methods such as ultrasound and nuclear scan. Left lobe absence is significantly more predominant than right lobe absence. Usually, TH patients without glandular disorders are biochemically euthyroid and clinically asymptomatic, as the remaining lobe is capable of sufficient hormone synthesis and secretion to sustain normal physiology. TH itself does not require specific treatment. However, in some cases, the unique lobe may have medical disorders and harbor surgical diseases. Unilateral exploration and total excision of the remaining tissue achieves definitive treatment of various disorders. Total lobectomy in TH cases technically becomes a total thyroidectomy with a need for postoperative thyroid replacement therapy.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This is an invited Editorial commissioned by Editor-in-Chief Dr. Wen Tian (Department of General Surgery, Chinese People’s Liberation Army General Hospital, Beijing, China). The article did not undergo external peer review.

Conflicts of Interest: The author has completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/aot.2018.01.03). The author has no conflicts of interest to declare.

Ethical Statement: The author is accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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References

1. Szczepanek-Parulska E, Zybek-Kocik A, Wartofsky L, et al. Thyroid Hemiagenesis: Incidence, Clinical Significance, and Genetic Background. J Clin Endocrinol Metab 2017;102:3124-37. [Crossref] [PubMed]
2. Gurleyik E, Dogan S, Cetin F, et al. Toxic Adenoma in a Patient with Thyroid Hemiagenesis. Cureus 2017;9:e1695. [PubMed]
3. Gurleyik G, Gurleyik E. Thyroid Hemiagenesis Associated with Hyperthyroidism. Case Rep Otolaryngol 2015;2015:829712.
4. Suzuki S, Midorikawa S, Matsuzuka T, et al. Prevalence and Characterization of Thyroid Hemiagenesis in Japan: The Fukushima Health Management Survey. Thyroid 2017;27:1011-6. [Crossref] [PubMed]
5. Gursoy A, Anil C, Unal AD, et al. Clinical and epidemiological characteristics of thyroid hemiagenesis: ultrasound screening in patients with thyroid disease and normal population. Endocrine 2008;33:338-41. [Crossref] [PubMed]
6. Korpal-Szczyrska M, Kosiak W, Swieton D. Prevalence of thyroid hemiagenesis in an asymptomatic schoolchildren population. Thyroid 2008;18:637-9. [Crossref] [PubMed]
7. Shabana W, Delange F, Freson M, et al. Prevalence of thyroid hemiagenesis: ultrasound screening in normal children. Eur J Pediatr 2000;159:456-8. [Crossref] [PubMed]
8. Berker D, Ozuguz U, Isik S, et al. A report of ten patients with thyroid hemiagenesis: ultrasound screening in patients with thyroid disease. Swiss Med Wkly 2010;140:118-21. [PubMed]
9. Melnick JC, Stemkowski PE. Thyroid hemiagenesis (hockey stick sign): a review of the world literature and a report of four cases. J Clin Endocrinol Metab 1981;52:247-51. [Crossref] [PubMed]
10. Ruchala M, Szczepanek E, Szaflarski W, et al. Increased risk of thyroid pathology in patients with thyroid hemiagenesis: results of a large cohort case-control study. Eur J Endocrinol 2010;162:153-60. [Crossref] [PubMed]
11. De Sanctis V, Soliman AT, Di Maio S, et al. Thyroid Hemiagenesis from Childhood to Adulthood: Review of Literature and Personal Experience. Pediatr Endocrinol Rev 2016;13:612-9. [PubMed]
12. Garel C, Léger J. Thyroid imaging in children. Endocr Dev 2007;10:43-61. [Crossref] [PubMed]
13. Pizzini AM, Papi G, Corrado S, et al. Thyroid hemiagenesis and incidentally discovered papillary thyroid cancer: case report and review of the literature. J Endocrinol Invest 2005;28:66-71. [Crossref] [PubMed]
14. Sari O, Ciftçi I, Törü M, et al. Thyroid hemiagenesis. Clin Nucl Med 2000;25:766-8. [Crossref] [PubMed]
15. Nsame D, Chadli A, Hallab L, et al. Thyroid Hemiagenesis Associated with Hashimoto's Thyroiditis. Case Rep Endocrinol 2013;2013:414506.
16. Wu YH, Wein RO, Carter B. Thyroid hemiagenesis: a case series and review of the literature. Am J Otolaryngol 2012;33:299-302. [Crossref] [PubMed]
17. Wang J, Gao L, Song C. Thyroid hemiagenesis associated with medullary or papillary carcinoma: report of cases. Head Neck 2014;36:E106-11. [Crossref] [PubMed]
18. Wang M, Hou L, Chen M, et al. Thyroid hemiagenesis and Hashimoto's thyroditis-diagnostic and treatment pitfalls. World J Surg Oncol 2017;15:182. [Crossref] [PubMed]