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.