Thyroid Isthmus Agenesis Diagnosed During Total Laryngectomy

Ismi O¹, Vayisoglu Y¹*, Ozcan C¹, Erdogan O¹, Gen R² and Gorur K¹

¹Department of Otorhinolaryngology, University of Mersin, Turkey

²Department of Endocrinology and Metabolism, University of Mersin, Turkey

*Corresponding author: Yusuf Vayisoglu, Department of Otorhinolaryngology, University of Mersin, Kulak Burun Boğaz A.D Çiftlikköy Kampüsü, Çiftlikköy/ Yenisehir-Mersin, Turkey

Received: November 10, 2015; Accepted: December 22, 2015; Published: December 28, 2015

Abstract

Although thyroid gland is a well-known endocrine organ both surgically and medically; it has multiple congenital anomalies seen from rare to common. Various anomalies reported and of these anomalies thyroid isthmus agenesis is very rarely seen. In this article we presented a case of thyroid isthmus agenesis diagnosed during surgery for a total laryngectomy in 52 years of male patient. We discussed the case with associated current literature emphasizing importance of knowing anomalies preoperatively to avoid complications during thyroid surgery.

Introduction

Thyroid gland is the endocrine organ responsible for production of thyroid hormones located in the lower neck between fifth cervical to first thoracic vertebrae ensheathed by pretracheal layer of deep cervical fascia. It has right and left lobes connected by a narrow median isthmus [1]. In 50 percent of cases thyroid gland has a pyramidal lobe extending from isthmus superiorly [2].

Wide spectrum of congenital anomalies and anatomic variations can occur regarding thyroid gland. Common anomalies include thyroglossal ductus cyst and persistent pyramidal lobe and rare anomalies such as agenesis, hemiagenesis of thyroid gland, aberrant thyroid glands can also be seen [3]. Of these anomalies the incidence of agenesis of isthmus (AGEIS) rare and very few cases have been reported. We presented the first case of AGEIS diagnosed during total laryngectomy for surgical treatment of laryngeal cancer in a 52 years old male patient.

Case Presentation

Squamous cell carcinoma of larynx was diagnosed in a 52 years old male patient. Tumor was transglottic with a subglottic extension of nearly 1,5 cm. He had no history of thyroid gland diseases. Preoperative thyroid hormone levels were in normal limits. During surgery for total laryngectomy; when strap muscles were retracted to skeletonize larynx, thyroid gland was seen. The thyroid gland had separate right and left lobes without interconnecting isthmus (Figure 1). Pyramidal lobe was not seen. There were no palpable nodules in thyroid lobes or nearby ectopic thyroid tissue. Total laryngectomy was done without complication and postoperative period was uneventful. Patient was discharged from hospital on postoperative eleventh day.

Figure 1: Thyroid isthmus agenesis during laryngectomy was shown. (R: Right Thyroid Lobe; L: Left Thyroid Lobe; I: Thyroid Isthmus Agenesis).

    
    
    Figure 1:  Thyroid isthmus agenesis during laryngectomy was shown. (R:
Right Thyroid Lobe; L: Left Thyroid Lobe; I: Thyroid Isthmus Agenesis).

Discussion

Thyroid gland has left and right lobes connected by midline isthmus. Each lobe is approximately 5 cm in long axis. Isthmus connects the lower part of lobes and is 1,25 cm long transversely and vertically located anterior to second and third tracheal cartilages. Surgical proximity of isthmus to vascular structures is important to avoid major complications during thyroid surgery. Superior thyroid arteries anastomose along its upper border and at its lower border inferior thyroid veins leave the gland [1,4]. Near surgical proximity; thyroid isthmus is also important for deciding the type of thyroid surgery. It is resected with one of the lobes for unilateral thyroid nodules (unilateral lobectomy with isthmusectomy), and thyroid isthmusectomy without lobectomy can be done for nodules confined to isthmus. Isthmus preserving total bilobectomy may be an alternative surgery for C-cell hyperplasia of thyroid gland [5].

During embryological development some anomalies of thyroid gland such as hypoplasia, ectopy, hemiagenesis and agenesis of the gland can occur [4]. Among these AGEIS can be rarely seen with an average incidence of 5-10% [6]. For some species birds, amphibians, many mammals have separate thyroid lobes without isthmus. In rhesus monkeys, thyroid glands are normal in position without an isthmus [7]. For human beings; embryologically thyroglossal ductus arises from the endodermic epithelium at level of second and third pharyngeal arch. During descending from foramen caecum, its caudal end bifurcates and gives origin to thyroid lobes and isthmus. Cephalic end of the duct degenerates. Rarely, a higher separation of the ductus can result in separate right and left lobes without interconnecting thyroid isthmus [3]. Since thyroid isthmus formation is a late stage during embryogenesis, an insult affecting development prior to, can cause AGEIS [7,8]. Although AGEIS can be alone, it can be with additional anomalies such as absence of either lobe or presence of ectopic thyroid tissue at nearby cervical region, can also be seen with levator glandula thyroidea [3]. AGEIS can also accompany some benign and malignant thyroid diseases such as nodular goiter, Graves basedow disease with solitary nodule, thyroid papillary carcinoma, thyroiditis, neoplastic metastases and amyloidosis deposition [1,4,9,10]. For our case; there was no an additional anomaly or diseases about thyroid gland. The only known disease was laryngeal cancer.

Diagnosis of AGEIS is difficult since most cases are euthyroid [9] like in our case. Most of the patients are diagnosed incidentally during evaluation of a thyroid disease [9]. There is no known predisposing factor, but trisomy of chromosome 22 was supposed to be a possible related factor [11]. Diagnosis of AGEIS can be achieved by ultrasonography, computerized tomography, magnetic resonance imaging, and scintigraphy or during a thyroid related surgery [4] like in our case.

True incidence of AGEIS is hard to determine since most of the patients are euthyroid and most are diagnosed incidentally [9]. Although average incidence can be accepted as 5-10% [6] there are great variations among authors [2,7,12-15]. Braun et al. found a 6,8% incidence [12], whereas Dixit et al. found 14,6% [13] in cadaver studies. Marshall investigated thyroid anomalies in 60 children less than 10 years of age. AGEIS was detected in 10 % of cases [14]. Prakash et al. found 8,5 % of AGEIS in totally 70 cadavers [7]. Joshi et al. diagnosed a slightly higher percentage (16,6%) among 90 cadavers [15]. For Ranade et al. incidence was much higher (33%) comparing other authors [2]. AGEIS can also be seen with different percentages among different races. Among korean adults Won and Chung published a 3 % incidence [16] whereas Harjeet et al. found 7,9% incidence [17] among northwest Indians.

Head and neck surgeon dealing with thyroid gland must be aware of anomalies and variations to avoid serious complications such as recurrent laryngeal nerve and major vascular damage. Thyroid isthmus has proximity with superior thyroid arteries and inferior thyroid veins. Since most of the cases are diagnosed incidentally; thyroid isthmus agenesis must also be kept in mind during dissection to prevent hazardous complications.

References

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Citation: Ismi O, Vayisoglu Y, Ozcan C, Erdogan O, Gen R and Gorur K. Thyroid Isthmus Agenesis Diagnosed During Total Laryngectomy. Austin J Otolaryngol. 2015; 2(9): 1066. ISSN :2473-0645

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