Atypical Appearance on Radioiodine Scintigraphy Due to Achalasia Cardia – A Potential Diagnostic Pitfall

Introduction

Theranostics with radioiodine (RAI) is integral to the management of differentiated thyroid cancer (DTC).[1] RAI diagnostic whole-body scintigraphy (DxWBS) serves as a useful tool for postoperative metastatic evaluation and may alter the decision to treat or the activity of therapeutic RAI to be administered.[2] While RAI DxWBS is a highly sensitive modality, there have been several reports of non-DTC-related, false-positive uptake.[3] We present a rare finding of atypical, diffusely increased esophageal uptake on RAI DxWBS caused by achalasia cardia.

Case Report

A 36-year-old woman had presented with complaints of progressive, anterior neck swelling for 6-month duration. On initial evaluation, neck ultrasound (USG) revealed a solid, predominantly hypoechoic right thyroid nodule (~3.0 cm × 1.8 cm size) with microcalcifications. The rest of the thyroid gland was normal with no significant cervical lymphadenopathy. Fine-needle aspiration cytology (FNAC) of the right thyroid nodule was reported as follicular neoplasm (Bethesda category IV).[4] The patient underwent a right hemithyroidectomy. Postoperative histopathology revealed papillary thyroid cancer (PTC) with focal hobnail changes and few foci of lymphovascular invasion. No capsular invasion or extra-thyroidal extension was identified. A neck USG done 3 months later revealed a rounded, hypervascular, level VI cervical lymph node (~11 mm × 10 mm in size) with a normal intact left lobe and isthmus of the thyroid gland. FNAC from the level VI cervical lymph node was inconclusive. Based on multi-disciplinary consensus and patient preference, completion thyroidectomy, and central compartment, lymph nodal dissection was subsequently performed. Postoperative histology revealed lymphocytic thyroiditis in the left lobe and isthmus of the thyroid gland with two out of four central compartment lymph nodes positive for metastatic PTC deposits. Levothyroxine was withheld and iodine-131 (I-131) DxWBS was planned 4 weeks after surgery. Just before the DxWBS, serum thyroid-stimulating hormone (TSH) was 106 µIU/ml, thyroglobulin (Tg) was 2.43 ng/mL, and Anti-Tg antibody was elevated at 20.1 IU/mL (reference range, <4.5 IU/mL). The initial RAI DxWBS [Figure 1a-c] suggested the presence of thyroid remnant and lymph nodal metastases. In addition, diffusely increased, band-like tracer uptake was also noted in the thoracic region consistent with the esophageal contour. Corresponding noncontrast computed tomography (CT) images [Figure 1d-f] showed paratracheal (~9 mm × 8 mm) and pretracheal (~11 mm × 8 mm) lymph nodes and a diffusely dilated esophagus with fluid retention. On retrospective inquiry, the patient revealed that she had long-standing, gradually progressive dysphagia to solid food for the past 2 years with episodes of regurgitation (more pronounced when supine). However, she was able to tolerate semi-solid and liquid diet. Subsequently, a timed barium swallow study was done, which revealed a diffusely dilated thoracic esophagus with significant hold-up of contrast and smooth tapering in the lower esophagus just above the esophagogastric junction (EGJ) suggestive of achalasia cardia. High-resolution esophageal manometry done using the Chicago protocol (with supine 5 mL swallows) showed elevated baseline EGJ pressure. On wet swallows, there was incomplete relaxation of the lower esophageal sphincter with raised integrated relaxation pressure of ~ 27.8 mmHg and evidence of pan-esophageal pressurization in few of the swallows suggestive of EGJ outflow obstruction likely due to type II achalasia cardia.

Close

Figure 1 A 36-year-old lady with papillary thyroid cancer underwent thyroidectomy and nodal dissection surgery. Planar images (a) anterior whole-body, (b) posterior whole-body, (c) anterior regional of the initial postoperative iodine-131 diagnostic whole-body scintigraphy (DxWBS) demonstrated three foci of intense tracer uptake in the neck and upper thorax suggestive of thyroid remnant and lymph nodal metastases (black arrows). Diffusely increased, tubular tracer uptake was also noted in the thoracic region consistent with esophageal contour (red arrows). Corresponding noncontrast computed tomography images (d) coronal, (e and f) transaxial revealed a diffusely dilated esophagus with air-fluid level (red arrows) and few rounded, paratracheal and pre-tracheal lymph nodes (yellow arrows). Follow-up DxWBS (g) anterior, (h) posterior planar images performed 6 months after high-dose radioiodine therapy and laparoscopic cardiomyotomy surgery (for achalasia cardia) showed no abnormal radiotracer uptake

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She underwent high-dose RAI therapy with 100 mCi (I-131) NaI given orally under medical supervision. Three months later, she also underwent laparoscopic cardiomyotomy with angle of his accentuation surgery. Overall, she had an excellent response to therapy with undetectable TSH-stimulated serum Tg, normalization of serum anti-Tg levels (2.0 IU/mL), and a negative DxWBS [Figure 1g and h] after 6 months. The abnormal esophageal uptake had also resolved on the follow-up DxWBS. The patient reported significant subjective improvement in dysphagia and was now able to comfortably tolerate a solid diet. The patient was advised a suppressive dose of levothyroxine (137 µg once daily) and regular annual follow-up visits with the department of nuclear medicine.

Discussion

RAI has successfully been used as a theranostic agent in thyroid cancer for over eight decades.[1] This is due to the preserved expression and function of NaI-symporter (NIS) on tumor cells in DTC.[5] RAI DxWBS is a valuable functional imaging tool for evaluating postoperative disease burden.[2] Despite its high sensitivity, several case reports have documented nonthyroidal, false-positive uptake. Common causes include disorders of organs with functional NIS expression (e.g., salivary glands, gastrointestinal tract, and breast), excretion of RAI in body-fluids/mucosal secretions, inflammation of varying etiology (e.g., infection, posttraumatic, nonspecific), and external contamination.[3]

Here, we present an atypical finding of diffusely increased esophageal uptake on RAI DxWBS caused by achalasia cardia, which has very rarely been reported.[6] Such abnormal tracer uptake can be explained by the retention of saliva and/or refluxed gastric secretions containing RAI. Other causes of esophageal uptake on RAI scintigraphy in published literature include ectopic gastric mucosa in the esophagus, postsurgical gastroesophageal outlet stricture, postradiation scarring, Zenker’s diverticulum, and epiphrenic diverticulum.[7891011] Ectopic gastric mucosa, Zenker’s diverticulum, and postradiation scarring typically demonstrate a focal area of abnormally increased tracer uptake whereas postsurgical gastroesophageal outlet stricture would result in diffuse tracer activity along the length of the esophagus as seen in our case. Such abnormal uptake can mimic or obscure metastasis and should, therefore, be interpreted with caution. In our patient, the nodal uptake was intense, appearing as distinct foci on planar images. However, smaller nodes or those with less intense uptake may be obscured by the pronounced esophageal activity. In addition, vertebral lesions may also be masked, given that the tubular esophageal uptake runs along the cervicothoracic vertebral column. Nevertheless, no definite lytic or sclerotic skeletal lesions were observed in the corresponding CT images in our case.

Achalasia cardia is a rare primary motility disorder of the esophagus with an estimated global prevalence of ~10.8 cases per 100,000 person-years.[12] The underlying pathophysiology is aperistalsis in the tubular esophagus and incomplete relaxation of the lower esophageal sphincter due to loss of inhibitory innervation of the esophageal myenteric plexus.[13] CT imaging, timed barium esophagogram, and endoscopy are useful diagnostic tools. However, the current gold standard investigation for diagnostic confirmation is high-resolution esophageal manometry, which was also used in our patient.[14] Pneumatic dilation, peroral endoscopic myotomy, and surgical myotomy are the only definitive therapeutic options for achalasia while pharmacotherapy is less effective.[15]

Conclusion

We aim to familiarize nuclear medicine physicians with the appearance of achalasia cardia on RAI scintigraphy, which may obscure the presence of surrounding lymph nodal or vertebral metastases. This case report also reiterates the importance of careful clinical and imaging correlation of atypical patterns of uptake on DxWBS. Accurate interpretation of DxWBS is critical to the judicious use of high-dose RAI therapy, ensuring optimal management of thyroid cancer, as well as other nonthyroidal conditions, as demonstrated in the present case.