# Challenging diagnosis and treatment of rare paranasal sinus metastasis from thyroid cancer: a case report and literature review

## TL;DR

A rare case of thyroid cancer metastasizing to the sphenoid sinus is reported, highlighting the challenges in diagnosis and treatment.

## Contribution

This case report adds to the limited literature on rare thyroid cancer metastasis to the paranasal sinuses.

## Key findings

- The most common type of thyroid cancer in reported cases was follicular thyroid carcinoma.
- Patients with this condition often have a poor prognosis due to delayed diagnosis and widespread disease.
- Multidisciplinary approaches may improve treatment outcomes for these rare cases.

## Abstract

Metastasis of thyroid carcinoma to the paranasal sinuses is extremely rare. Herein, a case of clinically occult thyroid cancer arising from a long-standing thyroid nodule that metastasized to the sphenoid sinus is presented, accompanied by a literature review.

A 48-year-old woman visited to the otorhinolaryngology department with visual disturbance and partial nasal obstruction. Computed tomography imaging revealed a tumor in the right sphenoid sinus with adjacent bony destruction, suggestive of paranasal sinus cancer. Thyroid ultrasonography (US) was performed to identify the primary cancer, revealing a thyroid nodule previously diagnosed as a benign follicular nodule 11 years prior. Histopathological examination confirmed minimally invasive follicular thyroid carcinoma (FTC) and poorly differentiated thyroid carcinoma with sphenoid sinus metastasis. Lenvatinib therapy was initiated after total thyroidectomy and radioactive iodine (RAI) therapy, achieving stable disease for 29 months. The patient ultimately succumbed to newly developed brain metastasis with cerebral infarction, 31 months after the initial diagnosis. A literature review of 19 cases revealed that FTC was the most common type (68.5%), followed by papillary thyroid carcinoma (31.6%). Among the 12 cases with assessable clinical outcomes, three patients achieved remission, while nine had persistent disease, with four confirmed deaths.

Diagnosis of paranasal sinus metastasis from thyroid cancer is often delayed due to its rarity and is commonly associated with widespread disseminated disease, resulting in a poor prognosis. Careful follow-up of large thyroid nodules and clinical suspicion of unusual metastasis is essential for early detection of malignancy and metastasis. Multidisciplinary collaboration and various treatment approaches can improve treatment efficacy.