MON-447 Schwannoma Masquerading as Metastatic Papillary Thyroid Carcinoma in a Cervical Lymph Node

Background: Schwannomas originate from peripheral nerve sheath Schwann cells and develop in various locations, commonly seen in the head and neck in up to 45% of cases. On ultrasound, they appear hypoechoic, lack a hilum, and can resemble a metastatic lymph node in patients with thyroid cancer. We describe a case of a schwannoma masquerading as metastatic papillary thyroid carcinoma. Clinical Case: A 59-year-old woman presented to our clinic with a history of Graves’ disease and papillary thyroid cancer (PTC) for which she underwent surgery over fifteen years ago at an outside institution. Pathology revealed two microfoci of PTC (0.5 and 0.4 cm) and 0 of 3 positive lymph nodes, with no other concerning features. She underwent radioactive iodine therapy (RAI) with 100 mCi postoperatively. There was no evidence of metastasis on her post-treatment scan. She had surveillance including neck ultrasounds with no evidence of recurrence. Five years later, neck ultrasound revealed a 5 mm nodule in the right neck posterior to the jugular vein. This nodule remained stable a year later and was not mentioned on subsequent ultrasounds. Two years ago upon presentation to our institution, she was found to have a suspicious hypoechoic solid mass on neck ultrasound. It was located in the lateral neck deep to the internal jugular vein and immediately adjacent and lateral to the common carotid and measured 8 x 7 x 7 mm enlarging to 13 x 9 x 10 mm in the next year. On one of the ultrasounds, the mass was noted to be inseparable from the surrounding nerve fibers and the possibility of nerve sheath tumor was suggested although a metastatic lymph node could not be excluded. This nodule enlarged to 13 x 9 x 10 mm in the next year. Due to the location, biopsy was deemed difficult and she underwent surgical resection of the mass. Intraoperatively, the lesion was noted to be very firm and intimately involved with the vagus nerve, which had to be sacrificed as it could not be dissected off. Pathology revealed a schwannoma, which was confirmed by immunohistochemical staining. Conclusion: This case highlights the importance of recognizing subtle but important ultrasonographic features of a schwannoma in the neck as it can resemble a metastatic lymph node, especially in a patient with history of thyroid cancer. Clinicians should consider this in the differential diagnosis when there are appropriate imaging findings that may be consistent with a schwannoma, including homogeneous hypoechogeneity and nerve continuity.