A case report and literature review of rare isolated metastatic papillary thyroid carcinoma in the orbit

Abstract

Purpose

Orbital metastasis secondary to thyroid carcinoma is an exceedingly rare occurrence. In this case report, we present a rare isolated orbital metastasis of papillary thyroid carcinoma (PTC).

Methods

A case report and literature review study.

Result

A 55-year-old female, who presented with right-sided exophthalmos persisting for seven months and a week-long history of decreased visual acuity. Orbital computed tomography (CT) revealed a solid, isolated, well-circumscribed mass confined to the right intra-conal orbital cavity. Surgical excision via lateral orbitotomy confirmed the diagnosis of metastatic PTC.

Conclusion

Most cases reported in the literature have identified orbital masses concurrently with the initial diagnosis of thyroid carcinoma. In contrast, our patient exhibited ocular symptoms following a prolonged interval after normal post ablative iodine imaging, highlighting a significant delay in metastatic presentation. Moreover, the solid and well-defined nature of the metastatic orbital mass, confined solely to the orbital cavity without evidence of bony destruction, muscle involvement or intracranial extension in this patient, constitutes a distinctive clinical feature rarely documented in existing case reports.

Introduction

According to the Iranian National Population-based Cancer Registry (INPCR), thyroid cancer is projected to experience the most significant rise in incidence compared to other cancer types in Iran by the year 2025 [1]. Papillary thyroid carcinoma (PTC), accounts for the most common type of thyroid malignancy, accounts for 85% of primary thyroid cancers. The prognosis for papillary thyroid carcinoma is excellent, with an overall 5-year survival rate of 98%, and nearly 100% for localized tumors [2]. However, distant metastasis, which significantly worsens patient outcomes, is rare, occurring in only 3–5% of cases [2, 3] PTC most commonly invades lungs and bones. It rarely metastasizes to orbit [4].

In previous case reports concerning metastatic orbital lesions secondary to PTC, patients often presented with additional distant metastases [5]. Moreover, involvement of other orbital structures, such as the medial rectus muscle, bony erosion, and concurrent sinus involvement, has been documented [5,6,7].

We present a compelling case with a history of treated PTC, who developed proptosis and a acute decline in visual acuity. To the best of our knowledge, this case represents the first instance of an isolated metastatic lesion stemming from PTC, notable for its absence of concurrent distant metastases or involvement of other orbital structures. The manuscript adhered to the tenets of the Declaration of Helsinki.

Case presentation

A 55-year-old woman was referred to the oculoplastic clinic with a seven-month history of progressive right-sided proptosis, and visual acuity decline. Her medical history revealed a diagnosis of PTC four years prior. At the time of diagnosis, the thyroid stimulating hormone (TSH) was 45 mlU/L, thyroglobulin (TG) was 1.5 ng/mL and anti-TG antibodies (Ab-TG) was 30 IU/mL. Neck ultrasound findings indicated no extrathyroidal extension. In February 2019, she underwent a total thyroidectomy, followed by radioactive iodine therapy with one single ablation session (dose of 100 mCi) with preparation of thyroid hormones withdrawal, to eliminate any remaining tumor tissue. Histopathology was showed PTC with TNM staging of T1N0M0 as defined in the 7th edition of the American Joint Commission on Cancer (AJCC, Springer, 2010). Post ablative neck ultrasound, blood tests like TSH, TG, and Ab-TG levels, and iodine imaging were checked by oncologist during follow-up visits, and showed no sign of metastasis until six months before the onset of gradual orbital proptosis. At the time of referral to our ophthalmology clinic, her Snellen chart best-corrected visual acuity (BCVA) was no light perception in the right eye and 20/25 in the left eye. A relative afferent pupillary defect (RAPD) was present in the right eye. Ocular motility tests revealed severe restriction of movement in all directions in the right eye. Exophthalmometry using a Hertel exophthalmometer revealed values of 18 mm in the left eye and 28 mm in the right eye, demonstrating an abnormal 10 mm proptosis in the right eye compared to the left eye (the maximum normal eye protrusion value is 20.1 mm in Iranian population) [8]. The intraocular pressure measured with goldmann applanation tonometry (GAT) was elevated to 26 mmHg in the right eye, while it was 14mmHg in the left. Other examination was done with slit lamp microscope, and anterior segment examination of the right eye showed conjunctival injection and chemosis. “Fig. 1(a,b)” Posterior segment evaluation revealed a cherry red spot of macula and optic disc swelling due to external pressure effect of orbital mass on central retinal artery and optic nerve. The examination of the left eye retina was unremarkable.

Fig. 1

Right eye severe proptosis, frontal view (a), Worms eye view (b), Six months post orbitotomy surgery and mass exision (c)

Orbital computed tomography (CT) and magnetic resonance imaging (MRI) revealed an isolated ovoid, heterogeneous intraconal lesion with sharp margins, extending from the orbital apex to the area behind the globe without any evidence of muscle involvement. “Fig. 2(a-c)” This mass caused indentation of the globe and exerted pressure on the optic nerve, resulting in decreased vision to no light perception (NLP) in the affected eye. A clear line was seen radiologically at the cleavage area between the mass and the eyeball. Notably, there was no evidence of bone destruction, any sinus involvement or intracranial extension.

Fig. 2

Coronal view of T1 sequence of orbital MRI showed intraconal medial site well defined mass without any extention to sinus (a), Axial view of T1 sequence of orbital MRI fat saturated without contrast enhancement showed well defined solid ovale shaped mass exerts pressure on globe (b), Axial view of T1 sequence of orbital MRI fat saturated with contrast, showed ring enhancement of mass (c)

Thyroid examination was unremarkable due to the previous thyroidectomy. The thyroid function test was indicative of severe iatrogenic hyperthyroidism and TG level was raised to 25 ng/mL. Right lateral orbitotomy with bone window, followed by mass excision, was conducted for the patient under general anesthesia. A well-circumscribed solid mass measuring 30 × 20 × 20 mm was excised. Orbital tumor histopathology confirming the diagnosis of metastatic PTC. At her three-month follow-up examination, the TG level was 0.1 ng/mL, and further investigations in search of other metastases, including whole-body PET/CT scan, demonstrating no abnormal findings or any other metastatic lesion or remaining tumor in the orbit. The chest radiograph was normal, as well.

The same ophthalmologist observed regression of right eye proptosis (The 10 mm proptosis, when compared to the left eye, had resolved) and improvement in eye movements. “Fig. 1(c)” Her vision had improved to hand motion in the right eye. An orbital CT scan confirmed the complete elimination of the tumor mass in the orbital cavity. The patient has continued to take therapeutic doses of levothyroxine and calcium supplements, and repeated the blood test and follow up imaging. she has remained asymptomatic for 1.5 years since tumor excision, up to the present time.

Discussion

Thyroid carcinoma metastasizing to the orbit is a rare occurrence, with limited cases reported in the literature. Among orbital tumors, only approximately 3–5% stem from differentiated thyroid carcinoma (DTC) [2]. However, the exact prevalence of orbital and choroidal metastases is hard to determine. This is due to the fact that the orbital metastases occur late in the course of patients’ disease, and some of the patients with orbital metastasis do not develop ocular symptoms at all [9]. The thyroid is not a common site as the origin of orbital metastases. To our knowledge, the literature review revealed that there have been nine documented cases of PTC with orbital invasion. The mean age of reported cases was 58.62 ± 16.11. The majority of the cases were female [6, 7, 10,11,12,13].

In a review study published in 2013, a total of twenty-two well-documented cases of thyroid metastasis to the eye were reviewed, of which 7 were PTC orbital metastasis [14]. Orbital metastasis involved bone, muscle, and lacrimal gland in the reported patients who also had another distant metastasis simultaneously. In contrast, our case involved no other distant metastases, such as those to the bone or lungs, concurrent with the orbital metastasis, highlighting a unique presentation of isolated orbital involvement [5,6,7, 10].

Previous case reports of PTC with orbital metastasis, often involve orbital roof or sphenoid bone, cause destruction, and intracranial extension, our case exhibited none of these features [7, 11, 12, 15]. Our patient exhibited a well-defined, isolated metastatic mass confined solely to the orbital cavity, with no evidence of bone destruction or intracranial involvement [15]. The distinct characteristics of the mass allowed for complete excision with no residual orbital tumor, obviating the need for adjuvant radiotherapy or chemotherapy post-surgery, which contrasts with the management required in previous cases [7, 16].

Most previously reported cases of orbital metastasis from PTC involve the supratemporal part of the orbit, a common site for such metastases [6, 16, 17]. Present case, the orbital metastasis involved the medial side of the orbital cavity without medial rectus muscle invasion, which is a rare feature, comparing to previous report [13].

The majority of orbital metastases were found after confirmation of the primary carcinomas [5,6,7, 10]. Proptosis and decreased visual acuity were observed in 55% of cases [18, 19]. Our patient presented with these two common signs, emphasizing their significance as indicators of orbital involvement in metastatic lesions.

Most orbital metastases are unilateral [19]. By extension, all of the reported cases of orbital metastasis with the origin of PTC till now were unilateral. There was only one case of orbital metastasis involvement bilaterally with follicular type of thyroid carcinoma [20].

Among the previously reported cases, several patients presented with an orbital tumor at the time of their initial diagnosis of PTC [15]. Notably, one case exhibited the development of right-sided proptosis four decades following thyroidectomy [14]. Our patient manifested orbital metastasis at a later stage in the disease course. Ocular symptoms in this case emerged six months subsequent to a normal post ablative iodine imaging. This observation underscores the critical importance of long-term follow-up in monitoring patients with PTC. Additionally, the emergence of a growing tumor in the orbit six months following a normal whole-body scan underscores the rapid growth characteristic of this metastatic lesion.

According to the American Thyroid Association Management Guidelines, Contrast-enhanced CT scan is the preferred imaging modality for detecting distant metastases or disease recurrence in differentiated thyroid carcinoma. Also, it is the modality of choice for detecting orbital metastasis [21]. Specific patterns, including intramuscular focal masses and diffuse intraconal lesions along with the prior history of systemic malignancies, place orbital metastases at the top of the differential diagnoses list. Fine needle aspiration (FNA) biopsy can be helpful to find out the origin of the orbital mass [22]. Open biopsy also can help in establishing the diagnosis in case of focal masses. If debulking surgery is needed regardless of the histology of orbital masses, open biopsy is indicated. Presence of the TG in metastatic cells is the most reliable finding confirming the diagnosis [9]. Positive radioactive iodine uptake is specific for thyroid metastasis [14]. Biopsy was not performed for our patient, and the diagnosis was confirmed by histopathology examination of the completely excised tumor.

From a therapeutic perspective, external beam radiation can relieve symptoms in case of solitary orbital, that is diffuse or involves important structures. Surgical debulking can help patients suffering from decreased vision due to optic nerve compression and can improve vision. If the tumor is focal, excision may be beneficial [23]. There is previous report that revealed radioactive iodine therapy and chemotherapy were helpful for the treatment of patient with PTC metastatic orbital mass [6]. In the case of the patient presented above, the tumor was totally resected, and no adjuvant therapy was needed.

In conclusion, given the rising incidence of thyroid cancer, the unique presentation observed in our case, characterized by a well-defined isolated mass located in the medial aspect of the orbital cavity, enabled complete excision of the tumor, and improve vision without the necessity for adjuvant chemotherapy or radiotherapy.