Not Your Typical “Lipoma”; An Unusual Case of Thyroid Cancer Presenting With a Skull Lesion

Abstract

Abstract Background: Bone metastases from thyroid cancers tends to more commonly afflict the long bones, pelvis, ribs, vertebrae and sternum. Skull metastases are exceedingly rare being found in only ~2.5% of patients with thyroid cancer, more commonly in patients with Follicular thyroid carcinomas. We present an unusual case of thyroid cancer presenting with skull metastasis. Clinical Case: A 55 year- old male with a slowly growing skull lesion was referred to our center after an attempt to remove this scalp lesion was aborted as the lesion extended through a calvarial defect. This lesion was noted by the patient 1 year prior to presentation and was slowly growing in size. He opted for watchful monitoring as this was presumed to be a lipoma at the time. Imaging revealed a 6.4 x 4.6 x 6.3 cm lesion in the left parietal region with a large extra-axial and soft tissue components with intervening bone destruction as well as adjacent dural thickening. Differential for the lesion given the radiological appearance included meningioma, hemangiopericytoma, or an osseous/dural metastasis with an unclear primary malignancy. Excision of the extra-axial parietal lesion was consistent with metastatic thyroid carcinoma (follicular variant of papillary carcinoma). Further imaging revealed a multi nodular goiter with a prominent 6 cm left thyroid nodule. Patient had no obstructive symptoms. He underwent a total thyroidectomy with findings of a 6.8 cm minimally invasive follicular carcinoma with multifocal capsular invasion and a focus of vascular invasion. The right lobe revealed 1.5 cm classic PTC. Notably, margins were free of disease and cervical lymph nodes were negative for disease. Imaging revealed no other metastatic lesions. Patient received RAI after his total thyroidectomy and was started on suppressive doses of levothyroxine. He has been followed with annual MRI Brain, USG thyroid and Thyroglobulin levels and remains free of recurrence for the past 36 months. Conclusion: Thyroid cancer can present with skull metastasis without causing significant morbidity. This is a rare manifestation of disease and can be easily misdiagnosed. This case highlights the importance of keeping a broad differential when evaluating skull lesions.