Ectopic Intratracheal Thyroid: A Rare Cause of Airway Obstruction

Ectopic intratracheal thyroid tissue (EITT) is a rare abnormality with only limited cases reported so far. The presenting symptoms can be very similar to those of bronchial asthma. We discuss the case of a 29-year-old man with subglottic ectopic thyroid, with a history of thyroid surgery for goiter, which has been managed with laser-assisted endoscopic approach. We have also included presenting symptoms, pathophysiology, diagnosis, and management of EITT. We aim to include EITT in the differentials of airway obstruction, particularly in those patients who have goiter or previous thyroid surgeries.


Introduction
Ectopic thyroid tissue (ETT) is a rare entity, which can be seen anywhere in the midline from the base of the tongue to mediastinum. Among them, the laryngotracheal region has the rarest occurrence that can cause upper airway obstruction. Since ectopic intratracheal thyroid tissue (EITT) is a rare condition, its symptoms can easily be mistaken for those of asthma. An associated hypothyroid level can lead to enlargement of EITT and worsening of symptoms. We are discussing EITT-causing stridor in a young man with a history of thyroid surgery who missed thyroxine therapy.

Case Report
A 29-year-old male, nonsmoker, presented to the emergency department with breathing di culty. He had increasing dyspnea since few months, for which his general practitioner had treated him for asthma. Five years earlier, the patient had undergone thyroid surgery for goiter with subsequent thyroxine replacement therapy. But the patient missed the course and follow-up.
During the current presentation, ber optic endoscopy showed bilateral mobile vocal cords and narrow infraglottic trachea with a right-sided subglottic mass.
CT showed subglottic soft tissue mass of about 4 × 4.7 × 2.4 cm in the craniocaudal, anteroposterior, and transverse dimensions, respectively, extending at the level of C4, C5, C6, and C7 vertebrae, and it causes marked narrowing of the airways (Figures 1(a) and 1(b)).
On admission, TSH was 7.82 mIU/L (normal range 0.5-5.0 mIU/L) and free T4 was 13.31 mcg/dl (normal range 7.0-14.0 mcg/dl). e patient underwent emergency tracheobronchoscopy which showed subglottic mass ( Figure 2). Biopsy of mass done and the patient was tracheostomised. e histopathology and immunostain study result con rmed multinodular goiter associated with hyperplastic nodules with no evidence of malignancy.
We have done microlaryngoscopic excision of the subglottic mass utilizing CO 2 laser. e histopathology con rmed ectopic thyroid tissue (Figures 3-5). e patient weaned from tracheostomy tube and discharged on thyroxin supplement, and regular follow-up with ENT and endocrinology was given.
e percentage of ETT in trachea contributes 6-7% of all primary endotracheal tumors [13]. e rst case was described in 1875 by Ziemssen [14][15][16]. e majority of the cases were reported from endemic goiter regions of the world [17].
ough EITT has been found anywhere from glottis to tracheal bifurcation, its most common appearance is as a submucosal mass on the lateral subglottic and upper tracheal wall [17][18][19].
e origin of EITT is explained by two theories. " e malformation theory" by Ziemssen in 1875 postulates that tracheal cartilage which develops later splits the thyroid gland, creating a small ectopic nest in the tracheal cavity [15,16]. " e ingrowth theory" by Paltauf in 1892 states that the improper development of the mesenchymal tissue between the thyroid and trachea results in adherence of the former to the latter thus permitting the ingrowth [20].
Usually, patients are symptomless until a change in their hormonal status happen. Stimulatory factors including TSH, epidermal growth factor, and human chorionic gonadotropin could stimulate thyroid growth [21]. Symptomatic EITT causes di culty in breathing, cough, stridor, and dysphagia. On physical examination, di erentiating stridor of EITT from wheezing of asthma is not easy. e ndings suggestive of malignancy of EITT include multiple nodules, ulceration, and bleeding. 11% of EITT has been reported to undergo malignant transformation [16]. e most common malignancy found is papillary thyroid carcinoma [22,23].
In a symptomatic patient, complete ENT examination should be carried out. Laboratory studies including thyroid assessment should also be conducted. Indirect laryngoscopy, exible laryngoscopy, and CT and MR studies must be included. Radionuclide studies are highly sensitive and speci c in detecting functional EITT [24]. Tc-99m pertechnetate scans high value in assessing the size, distribution, and activity of EITT. Fusion imaging techniques like single photon emission tomography-computed tomography (SPECT-CT) is valuable in diagnosis of EITT.

Case Reports in Otolaryngology
If associated with multinodular goiter, FNAC can be done. Direct laryngobronchoscopy will help in proper visualization of mass and performing biopsy. Since there is a chance of severe hemorrhage, a biopsy should be carried carefully [16]. e factors determining management of EITT include the size of lesion, the patient's age, the presence of local symptoms, the status of thyroid function, and histological ndings. Surgical excision, radioiodine ablation, and thyroid suppression therapy are the main treatment options adapted. e complete surgical excision is indicated in symptomatic cases and in cases of histological malignancy. e two common surgical methods are removal via an endoscopic laser-assisted approach as in the present case and removal of the tumor via an open cricoid procedure [25]. Postoperative thyroid suppression therapy is performed to prevent hypertrophy of residual tissue. Radioiodine ablation with hormonal suppression has only limited success [25]. e risks associated with ablation therapy include radiation thyroiditis and tracheitis. It can be useful in patients who refuse or are un t for surgery. While considering all the management options, surgical removal should be counted as the best option for the long-term outcomes [26][27][28].

Conclusion
Even though EITT is a rare abnormality with few case reported in the literature, it must be included in the di erentials in patients presenting with airway obstruction, particularly in those who have goiters or previous thyroid surgeries.

Conflicts of Interest
e authors declare that there are no con icts of interest.