|Year : 2012 | Volume
| Issue : 3 | Page : 96-98
Incidental diagnosis of primary intrathoracic goiter on radionuclide 99m-tc pertechnetate radioisotope thyroid scan
Madhuri Shimpi Mahajan, Digamber S Negi, Rajkumar Sharma
Department of Nuclear Medicine, Saral Diagnositics, E-1073, Saraswati Vihar, Pitampura, Delhi, India
|Date of Web Publication||11-Aug-2012|
Madhuri Shimpi Mahajan
Department of Nuclear Medicine, Saral Diagnositics, E-1073, Saraswati Vihar, Pitampura, Delhi - 110034
Source of Support: None, Conflict of Interest: None
Retrosternal goiters are classified into two groups. One is the truly primary intrathoracic or aberrant goiter. Presence of accessory thyroid tissue in the mediastinum of these patients group is congenital, with the blood supply derived entirely from intrathoracic vessels and it has no direct connection to the cervical thyroid gland. This primary intrathoracic goiter group represents less than 1% of surgically removed goiters. The much more common second group represents the acquired retrosternal goiter. It arises in the cervical thyroid gland and while growing it descends along a fascial plane, through the thoracic inlet into the mediastinum. Intrathoracic goiters usually present with clinical symptoms due to pressure on adjacent structures as the goiter enlarges within the rigid thoracic inlet. Asymptomatic large retrosternal, especially primary intrathoracic goiters are very uncommon. Here, we report a case of large retrosternal primary intrathoracic goiter found serendipitously on Technetium-99m (99mTc) pertechnetate radioisotope thyroid scan, which was missed on ultrasonogralhy (USG) neck in an asymptomatic patient presented with neck heaviness. Thus, here we emphasize the role of radioisotope thyroid scan over USG neck to diagnose retrosternal goiter.
Keywords: Intrathoracic goiter, radioisotope thyroid scan, retrosternal goiter
|How to cite this article:|
Mahajan MS, Negi DS, Sharma R. Incidental diagnosis of primary intrathoracic goiter on radionuclide 99m-tc pertechnetate radioisotope thyroid scan. Thyroid Res Pract 2012;9:96-8
|How to cite this URL:|
Mahajan MS, Negi DS, Sharma R. Incidental diagnosis of primary intrathoracic goiter on radionuclide 99m-tc pertechnetate radioisotope thyroid scan. Thyroid Res Pract [serial online] 2012 [cited 2020 Apr 2];9:96-8. Available from: http://www.thetrp.net/text.asp?2012/9/3/96/99655
| Introduction|| |
Thyroid disorders are commonly encountered in general surgical practice. The prevalence of a palpable thyroid nodule is approximately 5% in women and 1% in men  Goiter is a nonspecific term, which describes any swelling of the thyroid. It does not imply any particular pathological change so it is important that every goiter is properly assessed and the diagnosis carried beyond that of goiter. It is also important that surgeon develops a consistently reliable technique of examination by which he can properly assess the whole gland, its extent and functioning status of gland. Apart from thyroid function tests, thyroid ultrasonography, fine needle aspiration cytology and radioisotope scans are important investigations used in the work-up of various thyroid disorders. However, their order of preference and indications differs from case to case. Here, we report a case of large retrosternal primary intrathoracic goiter found serendipitously on Technetium-99m (99mTc) pertechnetate radioisotope thyroid scan which was missed on USG neck in an asymptomatic patient presented with neck heaviness. Here, we emphasize the role of radioisotope thyroid scan over USG neck to know retrosternal extent of thyroid.
| Case Report|| |
A 42-year-old female was presented with complaints of neck heaviness since one last week on lying down. Further interrogation revealed that the neck swelling was present for 10-15 years. There was no evidence of hypothyroidism or hyperthyroidism. She was asymptomatic without any history of dysphagia, hoarseness or stridor. On examination, vital signs were stable. Physical examination revealed a moderate size thyroid swelling in the anterior part of the neck which was asymmetric, non-tender, non-pulsatile with nodular surface and palpable lower pole of thyroid. No bruit was audible over the thyroid swelling. No cervical lymph node was palpable. Laboratory investigations confirmed euthyroid status. USG of neck was performed, which showed enlarged thyroid with heterogeneous echotexture suggestive of multinodular goiter without any definitive evince of retrosternal extension.
Radionuclide thyroid scan was obtained 20 mins after i.v. administration of 5 mCi of 99mTc on a dual head gamma camera equipped with low energy general purpose parallel hole collimator. Image showed moderately enlarged thyroid gland with overall reduced and patchy uptake and multiple areas of further reduced tracer uptake within [Figure 1] and [Figure 2]. In addition, large area of low grade tracer uptake seen in the mediastinum without any obvious path of continuous tracer uptake between mediastinal mass and thyroid gland [Figure 1] and [Figure 2]. A diagnosis of multinodular goiter with a functioning primary intrathoracic goiter was made. Computerized tomography scan of the neck and chest confirmed the radioisotope thyroid scan findings. It did not show obvious tracheal compression, nor any pressure symptoms [Figure 3]. Mediastinal biopsy confirmed it to be benign colloid goiter. Sternotomy was performed to excise the retrosternal goiter. She had an uneventful post-operative recovery.
|Figure 1: Technetium-99m pertechnetate thyroid scan: Moderately enlarged thyroid gland with overall reduced and patchy uptake and multiple areas of further reduced tracer uptake within (arrow). Large area of low grade tracer uptake seen in the mediastinum without any obvious path of continuous tracer uptake between mediastinal mass and thyroid gland (arrow head)|
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|Figure 2: Technetium-99m pertechnetate thyroid scan: Large area of low grade tracer uptake seen in the mediastinum without any obvious path of continuous tracer uptake between mediastinal mass and thyroid gland (arrow head)|
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|Figure 3: (a) Saggital and (b) Coronal sections of computer tomography thorax: Large mediastinal mass without any continuity between mass and cervical thyroid gland|
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| Discussion|| |
Retrosternal goiter is usually referred to as enlarged thyroid gland with greater than 50% of its mass below the thoracic inlet. They are classified into two groups. One is the truly primary intrathoracic or aberrant goiter. Presence of accessory thyroid tissue in the mediastinum of these patients group is congenital, with the blood supply derived entirely from intrathoracic vessels and it has no direct connection to the cervical thyroid gland. This primary intrathoracic goiter group represents less than 1% of surgically removed goiters.  The much more common second group represents the acquired retrosternal goiter (Substernal and partial intrathoracic goiters). It arises in the cervical thyroid gland and while growing it descends along a fascial plane, through the thoracic inlet into the mediastinum.  Retrosternal goiter has a clinical importance because its compressive symptoms may cause diagnostic problems and the selection of surgical approach is sometimes difficult.
Intrathoracic goiter is one of the major considerations in the evaluation of superior mediastinal masses. The retrosternal goiter, most commonly seen in the fifth decade of life with a female predilection of 3 to 4: 1.  Majority of patients present with shortness of breath or asthma like symptoms, neck mass, hoarseness, dysphagia, stridor or SVC obstruction.  Asymptomatic large retrosternal goiters are very uncommon. The diagnostic procedures currently in use for evaluation of intrathoracic goiter include chest radiography,  radionuclide scintigraphy;  computed tomography,  angiography and mediastinoscopic biopsy. The routine chest X-ray is a valuable initial study for compartmental localization of a mediastinal mass, also demonstrates tracheal displacement or compression and areas of calcification. Computerized tomography can note continuity of the mediastinal mass with the cervical gland, borders, focal calcifications, high contrast attenuation values of the goiter and postcontrast enhancement.
Radionuclide scintigraphy is capable of detecting most intrathoracic goiters  and provides an excellent estimate of the functional status of a mediastinal goiter, its nature and extent. It is considered a best preoperative investigation as it can be performed quickly, reliably and with very low radiation exposure. Though the 131-I scan is preferred over other radioisotopes for demonstration of intrathoracic goiter due to its low background activity, we currently prefer 99m-Tc to 131-I /123-I for the following reasons: 99mTc is much more readily available than 131/123-I. The imaging procedure can begin only 20-30 mins after the dose of 99mTc, whereas a less convenient 4-24 h must elapse for a 123/131-I study. 99mTc is currently much less expensive than 123/131-I thyroid imaging, however, is preferred to 99mTc as the investigation of patients with retrosternal thyroid tissue with unsatisfactory Tc images due to poor radionuclide concentration.
Prognosis of retrosternal goiter is very good if diagnosed and treated in the proper time. Most authors agree that compression of the adjacent organs is an absolute indication for operation. , When obvious signs of compression are not present, resection is indicated for prevention of their possible appearance in the future. Establishing the diagnosis provides another important indication for resection because needle biopsy of intrathoracic goiters is frequently unsuccessful.  In addition; tissue diagnosis obtained from any part of the goiter is not necessarily representative of the entire gland. Any suspicion of malignancy is also an absolute indication for surgery.
A useful investigation is one in which the result will alter the management or add confidence to clinical diagnosis. As these cases are rare, it has been suggested that all patients with either a diffuse or multi-nodular goiter can be presumed to have retrosternal goiter. In such cases a radionuclide scanning should be done as first line of investigation followed by chest roentgenogram or USG to explore the possibility of an intrathoracic goiter and routine use of thyroid Scintigraphy in all goiter patients should be encouraged.
| Acknowledgement|| |
I would like to thank Dr Ravi Gupta, CEO, Saral diagnostics, Delhi, India and Dr. Chandrashekhar Debnath, anaesthetist, Saral diagnostics, Delhi, India for their continuous encouragement.
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[Figure 1], [Figure 2], [Figure 3]