A tricky case of unilateral orbital inflammation: carotid cavernous fistula in Graves-Basedow disease

Purpose: To describe a rare clinical case of Carotid Cavernous Fistula (CCF) in Graves-Basedow disease (GBD). Method: A 62-year-old female with history of GBD and inactive Graves’ ophthalmopathy (GO) was admitted with progressive exophthalmos in her right eye (RE) and diagnosed with GO reactivation the previous month. Results: On examination, dilated and tortuous conjunctival blood vessels, chemosis and exophthalmos were observed in the RE. There was an asymmetry in the intraocular pressures of 20 mmHg in the RE and 10 mmHg in the LE. Laboratory results showed normal thyroid function and positivity of some of the antibodies related to immune thyroid disorders. Neuroimaging showed an early and abnormal filling of the cavernous sinus (CS) and an enlarged superior ophthalmic vein. Consequently, the diagnosis of CCF was established. Interventional treatment was performed with good clinical outcome and no recurrence after 6 months of follow-up. Conclusions: CCFs are abnormal arteriovenous connections between the carotid arteries and CS. CCF picture can mimic the GO’s manifestations. Thus, CCF should be considered in the differential diagnosis of GO, especially in unilateral, asymmetric, and atypical cases. We reported herein a case of CCF in a patient diagnosed with GBD, having a previous history of inactive GO, a diagnostic challenge, since the first presumed diagnosis in patients with GBD is always GO. To the best of our knowledge, there are only three previous reports in the medical literature in which the CCF was diagnosed in a GBD patient with a history of GO. Abbreviations: CCF = Carotid Cavernous Fistula, GBD = Graves-Basedow disease, GO = Graves’ ophthalmopathy, CS = cavernous sinus, SOV = superior ophthalmic vein, ICA = internal carotid artery, IOP = intraocular pressure


Introduction
Graves-Basedow disease (GBD) is an autoimmune disorder characterized by diffuse goiter, thyrotoxicosis, sometimes associated with other manifestations, such as ophthalmopathy and dermopathy. Graves' ophthalmopathy (GO) appears in up to 50% of Graves patients. GO's clinical picture varies in severity and number of manifestations, but it usually appears as a bilateral, often asymmetric orbital inflammation, with a characteristic upper lid retraction.
Carotid Cavernous Fistulas (CCFs) are abnormal arteriovenous connections between the carotid arteries and cavernous sinus (CS). Clinical findings of CCF include orbital manifestations secondary to the venous congestion, it may be unilateral or bilateral. The symptoms often reported are orbital discomfort, pulsatile proptosis, orbital congestion, conjunctival chemosis, periorbital edema, and ophthalmoplegia, among others. CCF picture can mimic the GO's manifestations. Thus, CCF should be considered in the differential diagnosis of GO, especially in unilateral, asymmetric, and atypical cases [1,2].
We reported herein a case of CCF in a patient diagnosed with GBD, having a previous history of inactive GO, being a diagnostic challenge.

Case Report
A 62-year-old female with history of GBD and inactive GO was admitted in the ophthalmology department with progressive exophthalmos in her right eye (RE) for the last two months. One month before, she attended the Emergency Department and was diagnosed with GO reactivation.
On examination, the visual acuity (VA) was 20/ 20 in each eye. Dilated and tortuous conjunctival blood vessels (corkscrew hyperaemia), chemosis and exophthalmos were observed in the RE (Fig. 1 A).

A B
There was an asymmetry in the intraocular pressures (IOP) of 20 mmHg in the RE and 10 mmHg in the LE, both not increasing in up gaze (Bradley maneuver). Extraocular motility and funduscopy were normal. There was no previous history of trauma or high blood pressure. Laboratory results showed normal thyroid function, and positivity of some of the antibodies related to immune thyroid disorders (anti-thyroglobulin and anti-peroxidase). Due to the great asymmetry in the manifestations, which is not common in GO, vascular pathology was included in the differential diagnosis.
Angio-CT scan was performed and showed an early and abnormal filling of the CS and an enlarged superior ophthalmic vein (SOV) (Fig. 2 A, B). Brain arteriography confirmed the abnormal filling of the CS from both internal carotid arteries; diagnosis of CCF was established (Fig. 2 C, D). Interventional treatment was performed by the neuro-radiologists with good clinical outcome and no recurrence after 6 months of follow-up.

Discussion
GBD is an autoimmune disorder that mainly affects women, being more frequent between 20 and 50 years of age. GO is the most frequent extra thyroidal manifestation of GBD. Proptosis, orbital congestion, periorbital edema, eyelid retraction, conjunctival chemosis, ocular motility impairment and diplopia are the most common manifestations of GO [1,2]. Neuroimaging studies have revealed a high number of GBD patients who, despite not having GO symptoms, showed radiological changes such as extraocular muscle involvement [2]. Although the most usual cause of orbital inflammation in GBD patients is GO, the physician should take into consideration other possible diagnoses especially in unilateral affectation or very acute onset. Idiopathic orbital inflammation, orbital cellulitis, metastatic tumors, orbital haemorrhage and CCF should be considered in the differential diagnosis of an asymmetric or unilateral eye involvement, even in GBD patients [1].
CCF is an abnormal vascular connection between the carotid system and the CS. It can be classified by