Caso Clínico

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Lingual thyroid: a new surgical approach
Tiroides lingual: un nuevo abordaje quirúrgico

 

I. Zubillaga Rodríguez¹, G. Sánchez Aniceto², I. García Recuero², J.J. Montalvo Moreno³

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Abstract: Lingual thyroid is an uncommon congenital disorder of thyroid gland development, resulting in a lack of descend of the gland from the foramen caecum to his normal prelaringeal location. In this paper we present a case of a postmenopausic patient presenting with a big size lingual thyroid deeply located in the base of the tongue, suffering increasing disphagia and respiratory impairment. For tumor resection, we chose a surgical approach combining a cervical submental incision, lingual pull- through and midline glossotomy. We discuss the different image studies recommended for proper diagnosis also reviewing the most common surgical techniques used for treatment, as compared with the approach we have described in this case. Key words: Lingual thyroid; Lingual pull-through; Glossotomy; Transcervical approaches.

Resumen: El tiroides lingual es una rara anomalía congénita del desarrollo tiroideo resultante de la ausencia de descenso del mismo desde el foramen caecum hasta la localización prelaríngea habitual. Presentamos el caso de una paciente en edad postmenopáusica con diagnóstico anatomopatológico de tiroides lingual de gran tamaño y localización profunda en la base de la lengua que producía disfagia y dificultad respiratoria crecientes. Asimismo, planteamos un nuevo abordaje quirúrgico para la resección combinando cervicotomía media, pull-through lingual y glosotomía media. Se discuten las distintas pruebas complementarias para llegar a su diagnóstico y se revisan las diferentes técnicas quirúrgicas habitualmente empleadas en su tratamiento concluyendo con las ventajas del abordaje empleado en este caso. Palabras clave: Tiroides lingual; Pull- through lingual; Glosotomía; Abordajes cervicales.

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1 Médico Residente
2 Médico Adjunto
3 Jefe de Servicio
Servicio de Cirugía Oral y Maxilofacial
Hospital Universitario "12 de Octubre", Madrid, España.

Correspondencia:
>Ignacio Zubillaga Rodríguez
Servicio de Cirugía Oral y Maxilofacial. Hospital Universitario "12 de Octubre"
Avda. de Córdoba s/n
28041 Madrid, España.
E-mail: ignaciozubillaga@yahoo.es

 

Introduction

Embryologically, the thyroid is derived from three primary sources.¹ An endodermic diverticulum in the area of the foramen caecum in the midline on the base of the tongue appears during the third week of gestation, between the first and second pharyngeal pouches, migrating later to the neck until it reaches its definitive position. This will turn into the greater part of the functional thyroid tissue. In the seventh week, now in its prelaryngeal position, the fusion of two lateral masses of cells derived from the four pharyngeal pouches is attached, being an inconsistent process.² Parafollicular C cells arise representing 1-30% of the total weight of the thyroid.³ At this point the thyroglossal duct becomes atrophied. Remains of the thyroid tissue along the migratory route taken by the principal diverticulum give rise to the formation of cysts in the thyroglossal duct that can be present in any area from the foramen caecum to the prelaryngeal area passing through the hyoid bone.⁴

Total failure of embryonic migration gives rise to a lingual thyroid which clinically does not have, in the majority of cases, functional thyroid tissue in its normal cervical position. The presence of ectopic thyroid tissue (90% of cases involving the tongue) has also been described in other locations such as in the midline of the neck near the hyoid bone, trachea, esophagus and even in distant locations such as in the porta hepatis, heart and diaphragm.

The pathogeny remains unknown5. Maternal antithyroid immunoglobulins have been claimed as stopping the descent of the gland and predisposing patients to a poorly functioning thyroid gland through out their lifetime.

Even though lingual thyroid is a benign mass most commonly found at the junction of the anterior two thirds and the posterior third, between the epiglottis and the circumvallate papillae, clinically it is a rare entity.⁶ Postmortem studies have showed an incidence of 10% of lingual thyroid.⁴ Clinical incidence varies. However, between 1:3000 and 1:10000⁷ lingual thyroid is the only functioning thyroid tissue in 70% of cases.⁸ The presence of ectopic thyroid tissue is 3 or 4 times more frequent in women than in men even though some authors estimate that the proportion can be 7:1.⁹

Its size varies from a few millimeters to various centimeters and symptoms and signs are directly related to its size. Most patients are asymptomatic and discovery is made during routine oral examination. Symptomatic lesions may appear at any moment from birth until adulthood. It is probable in the cases present at birth that all the thyroid tissue, or nearly all of it, is found in the tongue. This is the most common area for finding totally ectopic thyroids. Most symptomatic cases of lingual thyroid appear during puberty, pregnancy or menstruation. The average age for clinical manifestation is 40, with two peaks of greater incidence at 12 and 40.³ As we have seen, signs and symptoms are directly related to lesion size and these consist in dysphagia, dysphonia, dyspnea, foreign body sensation and occasionally hemorrhaging. 10% of young patients present juvenile myxedema or cretinism. ¹⁰ Approximately 70% of patients present hypothyroidism and between two thirds and three quarters of symptomatic patients do not have any other functional thyroid tissue. A greater frequency of thyroid pathology has been reported in the family members of patients with lingual thyroid.

This can be limited but in the majority of cases thyroid tissue had been found interdigitated with skeletal muscles and in minor salivary glands at the base of the tongue. Generally embryonic thyroid tissue is presented, mature thyroid tissue or a combination of both. Ectopic thyroid tissue does not represent a greater risk of malignant degeneration compared with the thyroid gland. The presence of carcinoma in ectopic thyroid tissue is extremely rare, representing approximately 1%.¹¹ The majority of cases described are follicular carcinomas, which are presented more frequently in the third decade of life.³ Lingual thyroid is not associated with the parathyroid glands, which are normally positioned in the posterior area, as these originate from the dorsal part of the third and fourth pharyngeal pouches (having a different embryologic origin).

Clinical Case

A 56-year-old Caucasian female was sent to the Maxillofacial Surgery and presented with a six-month history of progressive dysphagia. She complained of a foreign body sensation that was more accentuated on swallowing. Her personal history included psychomotor retardation and borderline intellectual functioning. Her right leg had functional limitation. She was short and had hypothyroidism that had never been evaluated. During the intraoral examination a purplish vascularized tumor was vaguely distinguished which was hard, not painful on palpation and in the midline of the tongue after the foramen caecum (Fig. 1). The tumor surface, which was visible, did not show ulceration. Palpation did not reveal cervical adenopathies. An MR test was requested (Fig. 2) in which a uniform mass at the base of the tongue was visible measuring approximately 5 x 4 cm. It was compatible with lingual thyroid with severe airway obstruction. The study was completed with an isotopic gammagraphy with Tc⁹⁹ that showed significant enhancement at the base of the tongue with no contrast enhancement in the normal prelaryngeal position of the hyoid. This was sent to the endocrinologist for thyroid function control, and with the diagnosis of a probable lingual thyroid, surgical intervention was decided upon given the progressive obstruction due to dysphagia.

First a tracheotomy was performed under general anesthesia in order to ensure airway protection given the considerable size and posterior location of the tumor at the base of the tongue. A suprahyoid midline cervicotomy was carried out (Fig. 3) together with periosteum removal of the mandibular lingual plate, followed by a lingual pull-through (Fig. 4) which was enlarged for surgical control during the resection.

A blood free midline glossotomy was performed given the posterior location and the depth of the tumor (Fig. 5), which permitted complete tumor excision (Fig. 6) under direct control with no associated lesion to adjacent vital structures (Fig. 7). Finally the approach sites were closed in layers (Fig. 8 and 9).

The patient made an excellent recovery and all tubes were removed during the immediate postoperative period.

Pathological anatomy confirmed the diagnosis of lingual thyroid. The MR control (Fig. 10) showed an absence of lingual thyroid tissue.

She underwent periodic checkups by us and by the endocrinologist controlling her basal hypothyroidism.

Discussion

Lingual thyroid is a rare congenital anomaly of thyroid development as a result of it not descending from the foramen caecum to its prelaryngeal location. It usually appears as a submucous nodule at the base of the tongue.

Hickman¹² in 1869 was the first to make its discovery in a case of a neonatal female that died of suffocation as a result of a lingual thyroid 16 hours after birth. In 70% of patients with lingual thyroid the gland is completely contained in the tongue and nearly 70% of cases are associated with different grades of hypothyroidism, a condition commonly brought on by increases in the physiological demand of thyroid hormones. In any event, many patients are asymptomatic during most of their lives or may not even require medical attention.

The initial evaluation of lingual thyroid is based on clinical symptoms: dysphagia, dysphonia, dyspnea, hemorrhage. The stridor can appear at any time but it is more common in neonatal infants.

Lingual thyroid is generally presented within one of the following clinical descriptions: children or young adults with lingual thyroid detected during routine screening. These patients often have retarded growth and mental development. In the second group, the start of symptoms coincides with situations in which there is an increase in metabolic demand of thyroid hormones (puberty, pregnancy or menopause). The increase in TSH levels leads to an increase in the size of the gland.⁶

Intraoral clinical examination reveals the presence of a smooth, irregular and well vascularized mass in the midline of the tongue after the circumvallated papillae. On occasions this is ulcerated giving rise to frequent hemorrhages. Exploration with a rigid or flexible endoscope of the upper airway establishes the size of the gland and air permeation. Careful pretracheal cervical palpation in the usually normal position of the gland is imperative.

The first laboratory studies that are precise are thyroid function tests. These often shown euthyroidism or hypothyroidism conditions with normal or low levels of T3 and T4 and high TSH and thyroglobulin levels. Hyperthyroidism although less frequent has been described. The most specific study for the diagnosis of lingual thyroid in the gammagraphy with Tc⁹⁹ or I¹³¹.

It shows activity or radionucleotide uptake at the base of the tongue and no apparent activity in the normal position of the gland in the neck. This method avoids the need for performing a diagnostic biopsy, which carries the risk of an unstoppable hemorrhage or acute thyrotoxicosis.

With regard to imaging tests CT scans are useful for determining the size of the gland. However, the best non-invasive technique is RMI which permits multiplane imaging and an excellent definition of soft-tissues. The size and location of the lesion are shown with precision. Signal intensity of normal thyroid tissue is greater than that of muscular tissue in T1 and T2 [weighted sequences]. Calcifications and intraglandular cysts are appreciated better in T2 [weighted sequences]. Currently echographic studies have lost importance with regard to the techniques described. A selective angiography of the external carotid [artery] may detect an aberrant vascularization pattern. The superior thyroid artery is sometimes absent and the lingual thyroid receives vascularization from the lingual and facial artery.⁶ Embolization of the nutrient vessels prior to surgery is the most secure method from the surgical point of view.

The differential diagnosis should include cysts of the thyroglossal duct, teratomas, dermoid cysts, lymphadenitis, lymphangiomas, lipomas, fibromas, squamous cell carcinomas, tumors of minor salivary glands and lymphomas.

There is no real consensus in the literature as to the adequate management of lingual thyroid due to the rarity of this condition and to the series that have been published being both scarce and short. However, it appears to be clear that the basic objectives to be met are complete excision, thus eliminating the presence of obstructive symptoms that may sometimes endanger the life of the patient, and thyroid function control.

Treatment depends on a series of factors: severity of the symptoms, size of the lesion, sex and age of the patient and thyroid function. Euthyroid patients with asymptomatic lingual thyroids should be regularly followed, with treatment being unnecessary.¹³ If a lingual thyroid does not cause symptoms of obstruction due to size, in principle there is no need for surgical treatment, and if hypothyroid symptoms are presented, thyroid hormone supplements can be used on their own. Likewise suppressive therapy with thyroid hormones becomes the key factor in the medical management of the condition. The objective is to suppress the levels of TSH and to eliminate the growth stimulus of the gland. However, not always can the size of the lesion be reduced and on occasions prolonged therapy is involved before significant changes in thyroid reduction can be appreciated. It is indicated for patients with moderate symptoms and for asymptomatic patients with high levels of TSH. Thyroid function should be monitored at regular intervals, ideally every 3 months.

Ablation with therapeutic doses of radioactive I¹³¹ is an alternative method of treatment which implies the exogenous supplement of thyroid hormones for life. This is particularly contraindicated in women of a fertile age, and should be reserved for patients who have rejected surgical treatment. Disadvantages include fibrosis and the development of tardive myxedema.¹³

Surgical treatment should be considered for those cases in which symptoms of obstruction and/or hemorrhages are produced because of size, when malignancy is suspected, and in cases in which the initial symptoms worsen after suppressive therapy. However, in symptomatic patients, conservative treatment with thyroid hormones should be administered before surgical treatment with the aim of reducing the size of the tumor. Intubation of patients with lingual thyroid can have serious complications from the point of view of hemorrhaging. In addition, postoperative edema can cause airway compromise, and a tracheotomy should therefore be considered as the initial surgical procedure. Prophylactic tracheostomies have as a result been defended by certain authors¹⁴ while some others prefer to perform these on those patient showing early airway compromise during the immediate postoperative period.

With regard to surgical tr eatment, we should never forget that our objective is complete exeresis of the lesion. When lingual thyroid is associated with functioning thyroid tissue in its habitual position, total excision is curative; in the opposite case, reimplantation of the ectopic thyroid tissue that has been removed is the most adequate form of treatment in order to avoid the development of a hypothyroid state that would require life-long thyroid hormone treatment.

Surgical excision of lingual thyroid can be carried out transorally or through a midline cervicotomy or lateral pharyngotomy.

Most of the cases described in the literature have been resolved using a transoral approach. Different modifications have been introduced with the object of improving exposure such as incising the full thickness of the cheek, midline lipsplit, midline mandibulotomy with lip split, and/or midline glossotomy.⁴ It offers an adequate aesthetic result and the risk of infection and of postoperative orocervical fistulas is reduced. However, exposure of larger lesion masses is worse being conducive to inadequate control of possible intraoperative hemorrhages. Kamat et al¹⁵ describe bilateral ligation of lingual arteries at the level of the horn of hyoid using cervical incisions separated before the median glossotomy. On occasions this has led to massive lingual necrosis. Atiyeh4 introduces a median glossotomy only in the posterior two thirds of the tongue thus minimizing the risk of damaging vital structures.

The cervical approach offers a better global visualization of the lesion, and is especially useful for large size cases with a posterior location. There are less possibilities of intraoperative hemorrhaging and, should it occur, control is easier. Among the disadvantages are cervical scarring and postoperative orocervical fistulas. This can be done using a midline pharyngotomy that is either transhyoid, suprahyoid or infrahyoid or through a lateral pharyngotomy.

Some authors¹⁶ combine transoral and transcervical techniques in the management of lingual thyroid, obtaining the benefits of each method. Moving the posterior portion of the gland by means of a pharyngotomy allows the control of areas with a high risk of hemorrhaging. This permits the mass to then be displaced anteriorly so that complete resection is facilitated. A new approach is presented in this clinical case that combines an initial extraoral technique using a midline cervicotomy followed by a pull-through and a final midline glossotomy. In this way clear exposure of the lesion is assured which allows for total excision with adequate control of vital cervical structures while not morbility is not added to the classical procedures.

Autotransplantation of lingual thyroid following excision is indicated in patients lacking normally functioning thyroid tissue which is not situated in the midline of the tongue. The tissue is implanted as a free graft under the fascia of the anterior rectus abdominis muscle or into the submandibular region following sectioning into layers with a 4-5 mm thickness.¹⁷ Treatment with thyroxin is not administered during the immediate postoperative [period] in order to prevent the graft from being suppressed. Some 30% of the patients remain euthyroid with no thyroxin therapy.⁶

An alternative to autotransplantation consists in the transposition of the lingual thyroid from the base of the tongue to the submandibular region through a lateral suprahyoid pharyngotomy.¹⁸ A pedicled flap is made, with random lingual muscle, which acts as a vehicle for the lingual thyroid. According to the authors, this offers a better result regarding thyroid function when compared with excision and autotransplantation. They defend that its new location is more accessible with regard to possible exploration in the event of hypertrophy or malignancy.

The use of laser has been described in the surgical management of lingual thyroid in a six-year-old boy.¹⁹

Conclusions

Even though the transoral techniques are simple and satisfactory for managing small lesions, the cervical approach is essential for the management of large lingual thyroids which are deep into the muscle. The combination of techniques increases tumor exposure, ensuring complete resection and minimizing intraoperative morbility derived from the control of vital cervical structures.

 

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