Keywords
Intracardiac - metastases - radioiodine-131 - thyroid cancer
Introduction
Follicular thyroid cancer (FTC) constitutes approximately 10%–15% of the total incidence
of well-differentiated thyroid cancers worldwide. FTC is generally divided into either
minimally invasive (MI-FTC) or widely invasive (WI-FTC) types. There are mixed reports
of the clinical outcome for MI-FTC with some reporting the benign clinical course
of the disease and the others reporting the more aggressive metastatic nature of the
disease.[1] We report a rare case of a female with MI-FTC with metastases to the superior vena
cava (SVC) and right atrium.
Case Report
A 57-year-old woman with underlying diabetes mellitus and hypertension initially presented
with thyrotoxicosis and anterior neck swelling in early 2013 and was treated for toxic
multinodular goiter. However, she had total thyroidectomy in April 2014 when the progressively
enlarging goiter caused dysphagia. The histopathology report revealed minimally invasive
follicular thyroid cancer with angioinvasion. The large 17 cm lesion in the right
thyroid gland extended to the left gland through the isthmus (pT3N0). She was started
on thyroxine suppression (150 mcg daily) and referred for radioiodine-131 (131I).
Her first post-131I remnant ablation scan in 2015 revealed iodine-avid lesions in
the neck and mediastinum[Figure 1]. Contrast-enhanced computed tomography (CECT) of the neck and thorax in March 2016
revealed no obvious lesion in the neck, but there was a filling defect in the SVC
extending into the right atrium suggesting intraluminal SVC thrombosis with intracardiac
extension or SVC tumor with intracardiac extension. Despite the extensive lesion,
there were no signs and symptoms of SVC obstruction. She was started on warfarin and
had repeated 131I therapies with cumulative doses of 25 GigaBecquerel (GBq).
Figure 1 Fused single photon emission computed tomography coronal, axial and sagittal (a-c)
images of postradioiodine-131 therapy (5.6GBq) in 2015 showing intense uptake in the
thyroid bed, superior vena cava and right atrium
Magnetic resonance imaging of the thorax in January 2017 revealed an SVC mass extending
into the right atrium. The mass measured approximately 8.6 cm × 3.9 cm × 3.9 cm with
clear demarcation of the lesion from the interatrial septum [Figure 2a]. A repeat CECT on March 10, 2017, showed extensive thrombus from the right brachiocephalic
vein confluence up to the right atrium with irregular filling defects signifying non-patent
part of the lesion [Figure 2b] and [Figure 2c].
Figure 2 Combo images showing the tumor thrombus in relation to the heart in axial T1-sequence
magnetic resonance imaging thorax (a), axial view of contrast-enhanced computed tomography
thorax (b), coronal view of contrast-enhanced computed tomography thorax (c) and transesophageal
echocardiogram (d)
The transesophageal echocardiography in June 2016 revealed a well-circumscribed mass
with regular margin in the right atrium arising from the SVC with neither dilatation
of the cardiac chambers nor regional wall motion abnormalities. There was only trivial
tricuspid regurgitation. No septal defects were noted. The left ventricular ejection
fraction was measured at 60% [Figure 2d].
The post-131I therapy (5.6 GBq) scan on February 27, 2017, revealed intense iodine
uptake in the mediastinum and faint uptake in the neck [Figure 3]. The uptake in the neck has reduced compared to the previous scans, but the uptake
in the mediastinum remained relatively intense. If the residual disease was due to
the uptake in the neck alone, the thyroglobulin (Tg) levels would have reduced in
tandem. However, the Tg levels remain persistently elevated (>300 ng/mL) with negative
anti-Tg levels. She remains well and is still adamant to continue treatment with 131I
rather than other forms of intervention. The definite diagnosis of the mediastinum
lesion remains unknown, but the likelihood of it being tumor thrombus is high due
to the persistently elevated Tg levels. Therefore, treatment with 131I remains the
best available treatment option for her.
Figure 3 Postradioiodine-131 therapy scan on February 27, 2017 (a) anterior view, (b) posterior
view showed intense uptake in the mediastinum and faint uptake in the neck. Physiological
uptake is seen elsewhere
Discussion
The classification of follicular thyroid cancer into widely invasive follicular thyroid
cancer (WI-FTC) and minimally-invasive follicular thyroid cancer (MI-FTC) is frequently
questioned due to the mixed reports of favorable and aggressive behaviors of MI-FTC.
Therefore, some clinicians would further classify these tumors by identifying the
presence of angioinvasion, for example, MI-FTC with angioinvasion and MI-FTC without
angioinvasion. The identification of MI-FTC without angioinvasion and the other FTC
with angioinvasion is useful in terms of prognostic and therapeutic purposes.
While MI-FTC without angioinvasion carries a relatively good prognosis, MI-FTC with
angioinvasion, and WI-FTC with or without angioinvasion carries higher potential of
metastatic disease. FTC is known to metastases hematogenously to involve the lungs
and bones, and it is rare for FTC to present with massive angioinvasion, and the prognosis
for such cases is grave.[2] With the extensive thrombus from the confluence of the right brachiocephalic vein
up to the right atrium seen in this case, the patient has a high risk of pulmonary
embolism and obstructed tricuspid valve.
The lesion seen in the SVC up to the right atrium is likely due to tumor thrombus.
The CT findings for this case are fairly similar to the findings described by Thomas
et al. For purely venous thrombus; the typical CECT findings include distended veins
with enhancing walls, low-attenuating intraluminal filling defects, and adjacent soft-tissue
swelling. On the contrary, tumor thrombus show enhancing heterogeneous intraluminal
tumor thrombi and low-density thrombi surrounded by a rim of contrast.[3] Nevertheless, it is occasionally difficult to distinguish venous thrombus and tumor
thrombus as both may occur concurrently. Therefore, the early initiation of anticoagulants
to prevent and dissolve the existing thrombus is essential.
Surgery remains the mainstay in the management of such cases, but there are no definite
management guidelines to date. Vascular resection and reconstruction is the preferred
choice in poorly differentiated and papillary thyroid cancers whereas thrombectomy
is more often performed for follicular tumors. Transcervical tumor thrombectomy has
been shown to be a safe surgical option in patients with positive “ring” sign, which
is a thin rim of contrast surrounding the thrombus on CECT.[4],[5] Thrombectomy is thus possible in this case as there was no adherence to the venous
wall.
Radiation therapy is possible in the event of the manifestation of SVC syndrome. In
fact, radiation therapy has been shown to be effective and safe as demonstrated by
Davenport et al. in 1976.[6] Nevertheless, radiotherapy is not without side effects and complications. The risk
of cardiac toxicity is high as the lesion, in this case, involves not only the SVC
but also the right atrium.
Nevertheless as forementioned, the patient had refused the options for either surgery
or radiotherapy, and preferred to be treated with 131I and anticoagulants. This case
illustrates the various imaging modalities and, treatment options, in managing well-differentiated
thyroid cancer with intraluminal SVC and right atrium metastasis.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
