Asian Cardiovasc Thorac Ann 1999;7:228-232
© 1999 Asia Publishing EXchange Pte Ltd
Posterior Mediastinal Goiters: Literature Review and Report of Three Cases
Rajinder Singh Dhaliwal, MCh,
Deepak Puri, MCh,
Sandeep Singh Rana, MCh,
Gurpreet Singh, MS,1
Department of Cardiovascular and Thoracic Surgery
1 Department of General Surgery
Postgraduate Institute of Medical Education and Research
Chandigarh, India
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For reprint information contact: Rajinder Singh Dhaliwal, MCh Tel: 91 172 74 7585 Ext. 400 Fax: 91 172 74 4401 P.O. Box 1515 (PGI-Campus), Chandigarh 160012, India.
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Abstract
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Posterior mediastinal goiters are very rare and occur mostly due to descent of a posterolaterally enlarging inferior pole of the thyroid gland, or very infrequently to failure of fusion of the ultimobranchial bodies with the isthmus in the 7th embryonic week. Most patients present with a cervical mass and symptoms due to compression or distortion of the trachea, esophagus, or superior vena cava. The diagnosis is established by chest skiagram, computed tomography scan, and barium esophagogram. Progressive enlargement, risk of sudden hemorrhage within the gland causing respiratory impairment, and the possibility of associated malignancy, make excision of the goiter mandatory. A combined cervicothoracic approach is the procedure of choice as it provides easy access and visualization, better control of blood vessels, and avoids the risk of perioperative tumor seeding. We present our experience of 3 such cases successfully managed at our institute. All 3 patients presented with a cervical mass and symptoms of posterior mediastinal compression; one had thyrotoxicosis. A combined cervicothoracic approach was used for surgical excision with excellent results.
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Introduction
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Substernal goiter, usually in the anterior mediastinum, is generally due to massive enlargement of a cervical goiter and is seen in 1% to 10% of all thyroidectomies.1–3 Less than 10% of substernal goiters are located in the posterior mediastinum between the trachea and esophagus or even behind the esophagus, cephalad or caudal to the body of the 4th thoracic vertebra, behind the subclavian, innominate vessels, and azygos vein.3 It is most frequently seen in otherwise asymptomatic female patients presenting with a palpable cervical goiter. However, symptoms due to compression or distortion of the trachea, esophagus, and superior vena cava manifest later, making surgical excision necessary.
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Case Reports
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A combined cervicothoracic approach was successfully used to excise 3 posterior mediastinal goiters at our institute over the last 15 years.
Case 1
A 38-year-old female presented with a cervical swelling that had gradually increased in size over the previous 10 years and with grade-I dysphagia of one-year duration. Physical examination revealed a cervical thyroid swelling of variable consistency, moving up on deglutition, and with substernal extension. She was clinically euthyroid, there was no tracheal deviation, and bilateral air entry into the chest was adequate. Thyroid function tests were normal. A chest skiagram revealed a homogenous round shadow approximately 8 cm in diameter in the right posterosuperior mediastinum (Figure 1
). Anterior displacement of the esophagus by the mass was seen on a barium esophagogram (Figure 2). The inferior thyroid pedicle was ligated through a classical cervical incision preserving the recurrent laryngeal nerve and a subtotal thyroidectomy was performed. A 10 x 6 x 6-cm well-encapsulated mass posterior to the superior vena cava and the arch of azygos, extending into the neck, was excised by a right posterolateral thoracotomy. The patient had an uneventful recovery and is doing well 12 years after the surgery with no recurrence. The histopathology report was consistent with multinodular goiter with focal areas of calcification, hemorrhage, and hemosiderin deposition.
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Figure 1. Chest skiagram (posteroanterior view) showing a homogeneous round right paratracheal mass with smooth margins, compressing the trachea.
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Figure 2. Barium esophagogram showing displacement of the esophagus anteriorly and to the left by a right posterior mediastinal goiter.
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Case 2
A 50-year-old female with a cervical goiter for more than 30 years, developed breathlessness, dry cough, stridor, right upper limb swelling, and hoarseness of voice 2 months prior to presentation. Physical examination revealed exophthalmos, fine tremors, and a positive Pamberton sign. The right midarm circumference was 3.5 cm more than the left and there was a multinodular cervical goiter involving predominantly the right lobe, with substernal extension. Thyroid function tests were suggestive of hyperthyroidism with triiodothyronine 2.8 µg•L–1 (normal, 0.7 to 1.90 µg•L–1), thyroxine 200 µg•L–1 (50 to 120 µg•L–1), and thyroid stimulating hormone 5 mUnits•L–1 (0.45 mUnits•L–1). Her electrocardiogram showed sinus tachycardia and pulmonary function tests revealed moderate obstructive pathology. A homogenous round radiopaque shadow approximately 10 cm in diameter was seen in the right posterosuperior mediastinum on a chest skiagram. A contrast-enhanced computed tomo-graphy scan revealed a well-defined nonhomogeneous posterior mediastinal mass in continuity with the cervical mass with amorphous calcification. The trachea was compressed and displaced anteriorly (Figure 3). The patient was given a 6-week course of carbimazole (2 x 10 mg per day) and propranolol (3 x 20 mg per day) until she became euthyroid. A 10 x 8 x 8-cm mass, weighing 140 g (Figure 4) and compressing the superior vena cava and trachea, was excised by a combined cervicothoracic approach without any complication. The patient had an uneventful postoperative recovery and has been asympto-matic and euthyroid over a 3-year follow-up. The histopathology report confirmed multinodular goiter with areas of hyalinization, hemorrhage, necrosis, calcification, cystic degeneration, cholesterol clefts, and hemosiderin-laden macrophages.
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Figure 3. Contrast-enhanced computed tomography scan of the chest showing a huge nonhomogenous posterior mediastinal mass on the right side with well-defined margins, compressing the trachea and displacing it anteriorly.
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Figure 4. A 10 x 8 x 8-cm multinodular posterior mediastinal goiter with its cervical components after subtotal thyroidectomy.
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Case 3
A 43-year-old male who had an asymptomatic cervical goitre for more than 10 years, developed dyspnea over the last 3 years. On physical examination, there was a large cervical goiter with substernal extension on the right side, moving up on deglutition. The patient was clinically euthyroid and thyroid function tests were normal. A chest skiagram showed a homogenous paratracheal mass about 10 cm in diameter in the right posterosuperior mediastinum. A posterior mediastinal mass in continuity with the cervical goiter, compressing the trachea and displacing it anteriorly, was seen on a contrast-enhanced computed tomography scan of the chest. Pulmonary function tests revealed mild obstruction. A combined cervicothoracic approach was used to excise the 10 x 6 x 6-cm mass (Figure 5) without complication and the postoperative course was uneventful. He has been symptom-free during follow-up of more than 2 years. The histopathology report was consistent with multinodular goiter.
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Figure 5. Combined cervicothoracic approach for the excision of a posterior mediastinal goiter on the right side.
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Discussion
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The main bulk of a mediastinal goiter is located below the thoracic inlet.4 A posterior mediastinal goiter descends into the posterior part of the superior mediastinum below a transverse line between the lower end of manubrium sterni and the body of the 4th thoracic vertebra and the plane of the azygos vein, with part of it within the true posterior mediastinum. A goiter completely confined to the true posterior mediastinum is an extremely rare occurrence.5 The clarity of this definition is most important as the position of the adjacent vessels determines the choice of surgical approach. In all 3 of our cases, the goiter extended into the posterior mediastinum. In 2 cases, it was lying between the trachea and the esophagus, compressing and deviating the trachea anteriorly. In the 3rd case, it was lying behind the esophagus, compressing it anteriorly and causing dysphagia.
There are two theories to explain the origin of posterior mediastinal goiters. The majority arise from descent of the enlarging posterolateral part of the inferior pole of the thyroid within its investing fascia along the path of least resistance (plunging goiter), as described by Sweet.6 Crohn and Kobak5 described the origin of the aberrant thyroid as due to failure of fusion of the ultimobranchial bodies with the isthmus near the posterior pericardium in the 7th embryonic week, leaving thyroid tissue in the developing posterior mediastinum.
Isolated mediastinal goiters may be aberrant or follow progressive attenuation of their cervical component.7 Posterior mediastinal goiters are usually ipsilateral to their cervical origin but contralateral descent has been reported rarely when the goiter passes between the trachea and esophagus or behind the esophagus to the opposite side.3,8 They are more frequently found on the right side because the aortic arch on the left side obstructs the path of descent.3,9 However, the observations of Bressler and Thomson10 and Sweet6 were to the contrary. The blood supply to posterior mediastinal goiters is usually from the inferior thyroid vessels but mediastinal branches from the arch of aorta and venous drainage into the innominate vein or superior vena cava have also been reported. Falor and colleagues11 reported 7 cases of intrathoracic goiters with a completely intrathoracic vascular supply.
Most patients are women in their 6th decade; female predominance is 4:1.3 Although most patients are initially asymptomatic, later symptoms and signs due to com-pression or distortion of the trachea, esophagus or superior vena cava may develop.1,12 Patients usually present with a neck swelling, while dyspnea, cough, stridor, dysphagia, dysphonia as a result of recurrent laryngeal nerve compression, facial flushing, and choking on recumbency are other common symptoms.3,4,8 The duration of symptoms may range from 6 months to over 3 decades.4 As seen in case no. 2, the onset of stridor may be acute and it has also been reported following hemorrhage within the goiter due to trauma.13,14 Collaterals between the obstructed superior vena cava and azygos vein or even the portal circulation (downhill varices) may cause gastrointestinal bleeding in the absence of signs of portal hypertension.15 Rarely, chylothorax as a result of thoracic duct occlusion and abscess formation within the intrathoracic goiter may occur.16,17 On physical exami-nation, in addition to a cervical mass with relatively decreased mobility on deglutition and substernal extension, tracheal deviation may be present. Nearly half of the patients are obese with short necks and wide chests.1 Substernal growth in these patients is facilitated by their body habitus and neck musculature.18 The Pamberton sign may be positive, recurrent laryngeal nerve palsy and thyrotoxicosis may be present, as seen in one of our patients, and features of tracheal compression and Horner's syndrome have also been reported.19,20 The incidence of hyperthyroidism ranges from 0% to nearly 50%.18,21,22
Posterior mediastinal goiters can be differentiated from other posterior mediastinal masses including neurogenic tumours and aneurysms of the aorta or innominate artery, by radiological investigations. McCort1 described the following radiological findings on chest skiagram: tracheal displacement beginning at larynx; tracheal compression; smooth or slightly nodular outline of the mediastinal paratracheal mass; reflection of mediastinal pleura below the goiter; a nonpulsatile nature and movement on swallowing usually seen on fluoroscopy; and calcification in 25% of cases. Contralateral retroesophageal or retro-tracheal goiters usually produce deviation of the trachea and esophagus to the same side on which the mass is present.9 Contrast-enhanced computed tomography scans of the chest are helpful in the diagnosis by showing the following features: clear continuity with the cervical thyroid gland; well-defined borders; punctate, coarse, or ring like calcifications; nonhomogeneity with discrete nonenhancing low-density areas reflecting hemorrhages or cyst formation; pre-contrast attenuation values at least 15H greater then adjacent muscles and more than 25H after contrast enhancement; and characteristic patterns of goiter extension into the mediastinum.23 A barium esophagogram is useful for anatomical localization by the pattern of compression or displacement of the esophagus.4,8,9 Pulmonary function tests may reveal obstructive pathology.13
Posterior mediastinal goiters may not function sufficiently to concentrate detectable amounts of radioactive iodine.4,5 Function may be complicated further by interference from the chest wall, mediastinum, and blood pool.8 Thus, the role of radioisotope thyroid scans is insignificant. Fine-needle aspiration cytology may not yield a positive diagnosis due to the relative inaccessibility of the posterior mediastinal mass and the role of this technique is less significant compared to that in cervical goiter.24 On histopathological examination, most mediastinal goiters are either multinodular or follicular adenomas with areas of old hemorrhages, calcification, cyst formation, fibrosis or focal thyroiditis, and a small but definite incidence of associated malignancy.18
Most surgeons now adopt a selective approach for excision of posterior mediastinal goiters. De Andrade3 emphasized that excision should always be initiated through the conventional cervical approach but if the attempt to completely mobilize the mediastinal part of goiter is unsuccessful, recourse to a supplementary thoracic approach may be sought. The combined cervicothoracic approach, first suggested by Sweet,6 prevents tumor seeding in unsuspected malignancy and avoids the risk of severe hemorrhage due to injury to an intimately adherent azygos vein or superior vena cava by blind dissection from above. It has been advocated for larger goiters with a predominantly intrathoracic component and for contralateral retrotracheal or retroesophageal posterior mediastinal goiters.8,25
We used the classical Kocher's cervical thyroidectomy incision, mobilized the cervical part of the goiter, and identified and preserved the parathyroid glands and recurrent laryngeal nerve. Then the superior and inferior thyroid pedicles were ligated and divided. Subsequently, a right posterolateral thoracotomy was carried out through the 5th rib bed and adequate exposure for visualization of the mediastinal structures (the aortic arch and the innominate vessels) was obtained before mobilizing the posterior mediastinal component of the goiter and performing a subtotal thyroidectomy. In our opinion, the combined cervicothoracic approach is the procedure of choice for excision of posterior mediastinal goiters because it combines the advantages of the cervical approach with those of a thoracotomy and at the same time overcomes the disadvantages of either of the two approaches when used alone. The cervical approach provides adequate control of the inferior thyroid pedicles that form the major blood supply of a posterior mediastinal goiter. Serious perioperative hemorrhage and injury to the recurrent laryngeal nerve is prevented. This is combined with a thoracotomy that provides easy access and visualization of important mediastinal structures, particularly blood vessels, which is not possible by the cervical approach alone or in combination with a transsternal mediastinotomy as described by Lelienthal.26 The risk of tumour seeding in an unsuspected malignancy associated with Lahey's technique of morcellation (piecemeal removal) is also avoided.2 In our experience, complete excision of the goiter by this approach is safe with no significant morbidity or mortality and it is associated with a negligible chance of recurrence.
Presented at The 44th Annual Conference of the Indian Association of Cardiovascular and Thoracic Surgeons, Jaipur, India, March 22–25, 1998.
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References
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Abstract
Introduction
