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British Journal of Radiology (2004) 77, 63-67
© 2004 British Institute of Radiology
doi: 10.1259/bjr/54722743
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Case report

Unusual uptake of radioiodine in the chest in a patient with thyroid carcinoma

N Nair, MD 1 S Basu, MBBS (Hons), DRM DNB 1 and H Pakhale, MBBS, DMRD 2

1 Radiation Medicine Centre and 2 Department of Radiodiagnosis, Tata Memorial Hospital, Jerbai Wadia Road, Parel, Bombay 400012, India

Correspondence: Dr Sandip Basu


   Abstract
Top
 Abstract
Introduction
 Case report
 Discussion
 References
 
A wide spectrum of potentially misleading artefacts can arise in 131I whole body scans from various anatomical variants and physiological processes as well as several unrelated non-thyroidal disease processes. A proper understanding of the causes of false positive 131I scans is essential for accurate interpretation of the images and to obviate diagnostic errors which may lead to administration of unnecessary therapy doses. The authors, in this article, present a case which had 131I uptake in the mediastinum persisting after surgical excision of mediastinal nodes, which was subsequently found to be due to accumulation of radioiodine in a hugely dilated oesophagus in secondary to achalasia. A comprehensive and rational classification of the various false positive 131I scintigraphic patterns based on the knowledge of the existing literature is reviewed.


   Introduction
Top
 Abstract
 Introduction
Case report
 Discussion
 References
 
Whole body 131I scintigraphy is a relatively inexpensive, simple yet highly accurate procedure that plays a pivotal role in clinical decision-making in the evaluation of post thyroidectomy cases of differentiated thyroid carcinoma. The presence of the unique sodium iodide symporter (NIS) in the basolateral surface of thyroid follicular cells resulting in sodium-dependent active transport of iodine, its organification and retention has been successfully exploited in investigation as well as targeted treatment of various thyroid disorders with 131I. The central indication for treating with 131I is the appearance of abnormal focal uptake in a diagnostic whole body scan. Though thought highly specific, there is growing evidence of false positive uptakes in several other organs and their associated disease processes. The present vignette is a classical example of it.


   Case report
Top
 Abstract
 Introduction
 Case report
Discussion
 References
 
A 50-year-old man presented with a nodule in the right lobe of the thyroid in 1993. Fine needle aspiraion cytology of the nodule suggested papillary carcinoma of the thyroid and a right hemithyroidectomy was carried out. Histopathology (HPR) confirmed a papillary carcinoma of the thyroid with capsular infiltration, vascular invasion and invasion into adjacent thyroid tissue. Completion thyroidectomy with right radical neck dissection was carried out in 1994. The HPR revealed metastatic lymph nodes.

A diagnostic 131I uptake scan was done 5 weeks after surgery, with 3.7 MBq administered orally. The scan revealed residual thyroid tissue in the thyroid bed with a 24 h neck uptake of 0.723% of dose.

In view of the age of the patient and the evidence of lymph node invasion, the patient was treated with 9250 MBq 131I and was subsequently put on thyroxin supplementation. Following this, the patient did not report back for follow up until 1998, when he came in with a large fungating nodal mass approximately 7.5 cm x 7.5 cm in the left half of his neck extending retrosternally.

Excision of the nodal mass and bilateral modified neck dissection was performed. The nodal mass was found to extend into the mediastinum and surgery was extended to include this. HPR revealed the fungating nodal mass to be a metastasis from papillary carcinoma of the thyroid.

Pre-surgery level of serum thyroglobulin was 1000 ng ml-1 (in our Institute, values are considered normal without thyroxin supplementation when below 20 ng ml-1 and while on thyroxin supplementation when below 10 ng ml-1), which declined to 301 ng ml-1 after surgery. A post-surgery whole body survey with 142.08 MBq of 131I showed a 4 cm x 3 cm intense uptake in the chest at the level of D4 vertebra with a 5 cm long, 1.5 cm broad trail in the midline upto the level of D10 vertebra (Figure 1Go). The initial suspicion was of residual mediastinal lymph nodes but the peculiar shape of 131I uptake area also raised the possibility of a benign cause.



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  		Figure 1. (a, b) Large dose 131I scan showing tracer concentration in the chest at the level of D4 vertebra with a 5 cm long, 1.5 cm broad trail in the midline upto the level of D10 vertebra.

 
The patient was instructed to drink plenty of water and a repeat scan was taken 1 day later which showed almost complete disappearance of the mediastinal concentration (Figure 2Go). Barium swallow examination revealed delayed passage of barium through a dilated thoracic oesophagus with multiple mobile filling defects intraluminally suggestive of food residue. The terminal oesophagus revealed smooth concentric narrowing with no evidence of shouldering (Figure 3Go). The barium emptied spurtingly in the stomach. A confirmatory CT scan of neck and upper chest was carried out. This did not reveal any pathology corresponding to the focal radioiodine concentration in the chest (Figure 4Go). It was concluded that concentration in the upper chest at the level of D4 in the diagnostic 131I scan was most probably due to accumulation of 131I above the accumulated food residue in the oesophagus or a transient peristaltic dilatation at that site, giving rise perhaps to a temporary "pouch-like" appearance. Thyroxine substitution was restarted and the patient was advised to return for follow up after a year.



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  		Figure 2. "Post-wash" repeat scan showing almost complete disappearance of mediastinal concentration.

 


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  		Figure 3. Chest radiograph with barium swallow study, (a) frontal and (b) right lateral view, showing dilated thoracic oesophagus with smooth narrowing of terminal oesophagus. No evidence of proximal shouldering noted. The filling defects seen intraluminally are due to food residue in the dilated oesophagus.

 


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  		Figure 4. CT scan chest revealing dilated oesophagus with intraluminal food residue. No evidence of mediastinal adenopathy seen.

 

   Discussion
Top
 Abstract
 Introduction
 Case report
 Discussion
References
 
Anecdotal case reports have contributed significantly to the continuously accruing literature of artefactual 131I scans [1–39]. In addition to these, there have also been some excellent articles addressing this issue [40]. The uptake in the 131I scans can be broadly categorized into the following groups according to the mechanism of localization.

Localization related to NIS function
Localization in the thyroid at unusual sites
Faulty descent from the base of the tongue to its normal adult position during embryogenesis may lead to lingual and other ectopic thyroid tissue along the course of the thyroglossal duct. This can also occur in the chest and may appear in the mediastinum [1–6]. 131I uptake in these ectopic thyroid can lead to misinterpretation of scan.

Struma ovarii is a rare but possible cause [7, 8].

Uptake in non-thyroidal tissues possessing NIS
Besides the thyroid, NIS function is active in some other tissues normally or overexpressed in their disease states.

Normal physiological uptake occurs in salivary gland, lacrimal gland, nasopharynx and lactating breast [3, 9–12].

Uptake in neoplastic sites; neoplasms arising from the abovementioned tissues do retain the iodide transport property and can show 131I uptake, e.g. gastric adenocarcinoma, Warthin's tumour, adenocarcinoma of lungs, several teratoma containing similar tissues [13–16]. There has also been a growing evidence of overexpression of NIS in breast malignancies [17, 18].

Uptake in abnormally located gastric mucosa; abnormally located gastric mucosa do retain the NIS function and can be misleading at times. Examples:

  1. developmental anomalies, e.g. Meckel's diverticulum [19] and duplication cysts
  2. metaplastic gastric mucosa, e.g. Barrett's oesophagus [20]
  3. displaced normal gastric mucosa, e.g. in hiatus hernia and gastric pull up surgeries [21, 22]

Localization unrelated to NIS function

Contamination artefacts by physiological secretions [23–25], e.g. by saliva, urine, vomitus, nasal secretions.

Artefacts due to urinary tract anomalies, e.g. diverticuli, fistulae, hydronephrosis etc. [26, 27].

False positive uptake in various gastrointestinal anomalies [28–30], e.g. in Zenker's diverticulum, oesophageal stricture, oesophageal motility disorders, asymmetrical salivary uptake owing to ductal pathology and tumour etc. is caused by radioiodine retention in the diseased site.

Intracavitary accumulation of 131I in pleural, peritoneal and pericardial effusions [31, 32].

Various inflammatory conditions shown to cause false positive scans may be related to their increased vascularity and capillary permeability [33–35], e.g. cholecystitis, sebaceous cyst, rheumatoid arthritis associated lung disease.

Uptake due to unknown mechanism
Uptake in thymus is frequently reported [35–39] and very often a cause of diagnostic dilemma. The mechanism is presently unexplained though iodine trapping by the Hassal's bodies is proposed to be responsible [36].

In our case, achalasia of the cardia was the cause of the dilated oesophagus which led to the demonstratable 131I retention in it. This disorder of unknown aetiology is characterized by absence of peristalsis throughout the oesophagus and failure of lower oesophageal sphincter (LES) to relax on swallowing [41]. There is marked reduction of ganglion cells in Auerbach's plexus in the LES and body of oesophagus on microscopic examination [41]. Chagas disease, caused by Trypanosoma cruzi, in its chronic phase produces the so-called "mega" disease affecting oesophagus in a way which is clinically indistinguishable from achalasia [41]. Dilatation by hydrostatic or pneumatic bag, cardiomyotomy, isosorbide dinitrate or nifedipine (in cases unfit for dilatation or surgery) are the recommended modalities of treatment [41].

Radioiodine accumulation in the oesophagus due to achalasia has been rarely reported. While it is true that the 131I uptake pattern of a broad area at D4 trailing off into a narrow tail by D10 suggested accumulation in dilated oesophagus, the history of recent mediastinal lymph node excision made it imperative to exclude the possibility that the uptake was due to persistence of metastatic disease in the mediastinum. Confounding the issue was the fact that serum thyroglobulin though having declined from >1000 ng ml-1 to 301 ng ml-1 after excision of the mass, was nonetheless, still elevated. Did this mean persistence of mediastinal adenopathy? Obviously strenuous efforts to clarify the situation were called for. The typical appearance on barium swallow, the absence of tumour mass on CT scan and the "washout" of the tracer following continued ingestion of water over several hours settled the issue.

To the best of our knowledge, only one such case has been reported previously [29]. The case, presented here, is a classical example of radioiodine accumulation in a greatly dilated oesophagus revealed in the diagnostic scan, which can be misinterpreted, particularly in a patient with a known mediastinal tumour mass. It illustrates the often overlooked fact that patients with carcinoma of the thyroid (or indeed any cancer) may have coexisting benign conditions that may masquerade as abnormalities related to the cancer itself. Awareness of this situation cannot be overemphasised nor can be the value of meticulous history taking.

Received for publication August 23, 2002. Revision received February 25, 2003. Accepted for publication April 24, 2003.


   References
Top
 Abstract
 Introduction
 Case report
 Discussion
 References
 

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