A Case of Right-Sided Direct Carotid Cavernous Fistula: A Diagnostic Challenge

Background

Carotid cavernous fistulas (CCF) are abnormal connections between the carotid artery and cavernous sinus, which can be either direct (high flow) or indirect (low flow) communication. It may occur spontaneously or due to secondary causes. We report a case of right-sided direct CCF that could be a diagnostic challenge for internists.

Case Report

An 83-year-old female with hypertension and dyslipidemia presented to emergency department (ED) with worsening pain and swelling over the right eye. A week ago, the patient visited the ED for the similar complaint without vision changes and she was discharged with a short course of oral prednisone for “allergic conjunctivitis”. Back then, she recalled having right eye itching shortly after eating shrimp. Then the next morning, she woke with a swollen right eye and inability to open it. She denied any known history of food or drug allergy. At the present visit, the patient complained of right-sided blurred vision. Her vital signs were stable and physical examination showed chemosis and tenderness over the right orbit (Figure 1). Both pupils were equal and reactive. Visual acuity was 20/30 for both eyes with corrective lens. Because of severe chemosis, ophthalmoplegia was difficult to assess for the right eye. Otherwise, the examination was normal. Workup showed normal white count without left shift, erythrocyte sedimentation rate, C reactive protein, ferritin and thyroid function test (TFT). Computed tomography (CT)-orbits-sella showed pre-septal cellulitis without evidence of abscess. She was empirically treated with antibiotics (vancomycin and piperacillintazobactam) and topical α2-adrenergic agonist (brimonidine). Ophthalmology was consulted.

Despite empiric antibiotics, the patient did not show improvement on the following day. There continued to be no evidence of infection (no fever, leukocytosis). So, further imaging was pursued. Magnetic resonance imaging (MRI) of the brain was unremarkable. Additionally, MR-orbits, face and neck, showed right pre- and post-septal orbital cellulitis and enlarged right superior ophthalmic vein with concern for non-occlusive venous thrombosis (Figure 2). However, MR venogram (MRV) of the head showed no evidence of intracranial venous sinus thrombosis. Additionally, MR angiogram (MRA) of the head showed normal circle of Willis. Further blood work including quantiferon test, treponemal antibody test, thyrotropin receptor antibody, thyroid stimulating immunoglobulin (TSI), rheumatoid factor (RF), anti-neutrophil cytoplasmic antibody (ANCA), and anti-nuclear antibody (ANA) were negative.

On repeat examination of the eye, a bruit with palpable thrill was noted over the right eyeball. Tonometry readings were 38 mm Hg and 22 mm Hg on right and left eyes respectively and visual acuity remained unchanged. Brominidine was stopped and topical brimonidine/timolol (combigan) was initiated. Given the orbital bruit/thrill and enlarged superior ophthalmic vein, CCF was suspected. Eventually, CTA of the head showed extensive arterial filling of the cavernous sinus and arterial opacification with bilateral superior ophthalmic veins, right greater than the left (Figure 3). Subsequently, carotid angiogram revealed early filling of the cavernous sinus and bilateral superior ophthalmic veins with more enlargement on the right than the left upon injection of the right internal carotid artery (ICA), confirming the diagnosis of right-sided direct CCF (Figure 4). No filling of the cavernous sinus was seen on the injection of the left ICA. So, antibiotics were discontinued and endovascular obliteration was planned. However, because of the temporary unavailability of neuro-interventionist at our facility, the patient was transferred to a tertiary facility for endovascular embolization of the right CCF. The patient tolerated the procedure and follow-up at our facility within four weeks showed normal eye examination with stable vision.

Discussion

Carotid cavernous fistulas (CCFs) are rare, abnormal connections between the carotid artery and cavernous sinus, which can be either direct (high flow) or indirect (low flow) communication. Barrow et al. reported a classification of CCFs as follows: direct (high-flow) communication of the carotid artery and cavernous sinus (Type A), indirect communications of the cavernous sinus with branches of the cavernous carotid artery (Type B), or dural branches of external carotid artery (Type C), or both the branches of external and internal carotid arteries (Type D) [1].

The CCFs may occur spontaneously or following secondary causes (trauma, vascular aneurysm or malformations and venous thrombosis). Direct CCFs are often caused by head trauma or rupture of intra-cavernous aneurysm or head surgery [2–5].

There is limited data regarding the incidence of CCFs, either primary or secondary types. However, through retrospective analysis, Liang et al. reported that the overall incidence of traumatic CCF was 3.8% among patients with basilar skull fractures [4]. Sudden increase in pressure within the internal carotid artery (ICA) may be the mechanism for the development of direct CCF [6]. Based on the different types, the presentation of CCFs is highly variable. Direct CCFs mostly present with orbital bruit (80%), proptosis (72%), chemosis (55%), abducens nerve palsy (49%), and conjunctival injection (44%) [7]. Vision loss is one of the most fearful complications of CCFs. Sight threatening complications may occur in direct CCF due to severe exposure keratopathy, corneal ulcerations, and possibly central retinal artery occlusion [8]. Currently, no data is available for incidence of vision loss if the direct CCF is not properly and timely treated.

Indirect CCFs often occur spontaneously and are more common in older women [1,9]. The cause of indirect CCFs is unknown and their presentations can vary widely by the patterns of venous drainage and the speed of blood flow. Indirect CCF especially of anterior drainage pattern may threaten the vision through increased intraocular pressure (due to venous congestion) [10].

The differential diagnoses of CCFs are cerebral aneurysms, vascular malformations of eyes, inflammation of orbits, retro-orbital cellulitis, thyroid exophthalmos, retrobulbar hemorrhage, tumor of lacrimal gland, cavernous sinus thrombosis, and vasculitis [11]. CCFs may be suggested by clinical evaluation and imaging studies, especially MR-orbits and CTA or MRA of the head. However, the gold standard test for CCFs remains carotid digital arteriography [5]. Treatment decision depends on the severity of clinical presentations [12]. Generally, treatment of CCFs is suggested if there are worsening visual function, severe proptosis, cranial nerve palsies, intractable bruit, intraocular pressure of more than 25 mm Hg, and increased filling of cortical veins on angiography [11,13]. The prognosis of CCFs is excellent after endovascular treatment [14,15].

Our patient was initially treated with empiric antibiotics for suspected peri-orbital cellulitis, as noted clinically and in CT orbits. However, lack of clinical improvement, physical finding of orbital bruit/thrill, normal leukocytes and inflammatory markers, and enlarged superior ophthalmic vein in MR-orbits suggest alternate diagnoses. Vascular malformations and venous thrombosis were unlikely given normal MRA and MRV respectively. Normal ANCA, ANA, RF, TFT, and TSI make vasculitis and thyroid ophthalmopathy unlikely. Eventually, CTA and carotid-arteriography confirmed the diagnosis of right-sided direct CCF, which was subsequently treated with endovascular embolization. It is likely that her direct CCF was related to a head trauma two years ago. The patient had no recurrent symptoms at regular follow-up at one and three months. Not only does this case highlight the importance of CCF, which could be a differential diagnosis of swollen red eye, it also addresses the vital importance of physical examination in modern medicine despite the seemingly promising technologies. We were able to provide the correct diagnosis and treatment for a potentially sight-threatening disease.

Conclusions

CCFs are rare potentially sight-threatening abnormal connections between carotid artery and cavernous sinus. Clinicians should have a low threshold for investigation of CCF in a patient with red swollen eyes in order to provide timely and proper management.