Carotid-cavernous fistula masquerading as thyroid associated orbitopathy: a diagnostic challenge

Purpose: To report a case of indirect carotid-cavernous fistula (CCF) in a patient who presented as a case of thyroid-associated orbitopathy (TAO). Case presentation: A 60-year-old female, known case of hypothyroidism, presented with left-sided headache associated with pain, protrusion and redness of left eye, the examination revealing vision of 20/ 80, proptosis, chemosis and severe ophthalmoplegia. All routine investigations were normal, including thyroid hormone levels. MRI brain & orbits showed increase in bulk of all extraocular muscles with tendon sparing. In view of suspicion of TAO, she was initially misdiagnosed and treated with parenteral and oral steroids, which resulted in further worsening of vision. Optical coherence tomography macula of the left eye revealed acute central serous chorioretinopathy that compelled the stoppage of steroids. While reviewing the patient again, dilated cork-screw tortuous episcleral vessels were found in the left eye. Thus, advised Digital subtraction angiography, confirmed as a case of low-flow left Indirect CCF, managed with endovascular embolization therapy improved her ocular symptoms completely in three days. Conclusion: CCF may mimic TAO due to overlapping features. In-view of different treatment protocols for both, it is critically important to look for atypical features in thyroid eye disease and keep CCF as one of the differential diagnoses for accurate management. Abbreviations: CCF = carotid-cavernous fistula, ICA = internal carotid artery, ECA = external carotid artery, TAO = thyroid-associated ophthalmopathy, BCVA = best corrected visual acuity, MRI = magnetic resonance imaging, IVMP = intravenous methylprednisolone, OCT = Optical coherence tomography, CSCR = central serous chorioretinopathy, DSA = digital subtraction angiography, IOP = intraocular pressure, CT = computed tomography