Clinical Images: Temporalis muscle and temporal bone metastasis: giant cell arteritis mimicker

Giant cell arteritis (GCA), a form of large vessel vasculitis, is typically characterized by headaches localized to the temporal or occipital regions, although the pain may sometimes be less well-defined.1 The clinical presentation of GCA can sometimes be mimicked by other conditions, leading to a potential misdiagnosis. The patient, a 70-year-old woman with a past medical history of estrogen receptor positive endometrial carcinoma stage T3 initially treated with total abdominal hysterectomy and chemotherapy, presented for evaluation of sharp right-sided headaches radiating to the ear and throat. She also reported right temporal tenderness, but no vision changes or jaw claudication. On physical examination, temporal artery pulses were present bilaterally. Tenderness was noted on palpation of the right temporal area. Initial gadolinium-enhanced magnetic resonance imaging (MRI) brain and soft tissue neck, performed soon after headache onset, did not show definite metastasis or structural pathology. Initial evaluation revealed elevated markers of inflammation, raising suspicion for GCA. She was started on high-dose prednisone; however, her symptoms did not improve despite glucocorticoid therapy. To investigate further, a temporal artery ultrasound was performed, revealing mild circumferential wall thickening. This prompted a right temporal artery biopsy, which was negative for findings of GCA. As symptoms progressively worsened over the course of a month, a repeat MRI of the brain with and without intravenous contrast revealed concerning findings (Panel A). There was an enhancing process adjacent to the anterior inferior right hemisphere with progressive dural thickening and involvement of the right sphenoid bone, right temporalis muscle, and right periorbita. A biopsy of the right temporal skull bone showed metastatic adenocarcinoma, and the immunostains were consistent with metastatic endometrioid adenocarcinoma (Panels B and C). Panel B shows the bone involved by metastatic endometrioid adenocarcinoma. Histologic section from the right temporal skull bone demonstrates malignant glands and trabecular bone. Immunostain for Estrogen Receptor is positive. Panel C shows soft tissue retroperitoneal mass showing metastatic endometrioid adenocarcinoma. Malignant glands with villoglandular architecture, composed of columnar cells with pseudostratified nuclei. Immunostain need for Pax 8 is positive. Metastasis to the temporal bone has rarely been documented as a mimic of GCA.2 There are no previous reports of temporalis muscle metastasis mimicking GCA. Therefore, it is important to consider the clinical history, especially a history of malignancy, when evaluating patients for possible GCA. Disclosure form. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.