Keywords
endovascular treatment - orbital arteriovenous fistula - superior ophthalmic vein
- transvenous embolization - visual impairment
Introduction
Orbital arteriovenous fistula (AVF) is extremely rare, with approximately 20 cases
reported so far.[1]
[2] The natural course of this disease is not known in detail, and the treatment method
is controversial. While proptosis and chemosis are the most common symptoms,[2] only 4 cases of visual impairment have been reported in the past.[3]
[4]
[5]
[6] In addition, they also have other symptoms such as proptosis or chemosis. Herein,
we report a case of an orbital AVF that develops only with visual impairment without
proptosis or chemosis which is rare in that no similar reports have been reported
in the past.
Case Description
History
A 70-year-old man with no history of trauma was aware of the deterioration of his
visual acuity 6 months before his visit. A close examination by an ophthalmologist
revealed a decrease in his left visual acuity of 0.3, visual field impairment ([Fig. 1A]), and no increase in intraocular pressure nor capillary dilation of the ocular conjunctiva.
Also, there was no difference between left and right in the central retinal arteries
and veins. The neurological findings at the time of admission to our hospital showed
left visual impairment, but no chemosis, proptosis, or eye movement disorder were
observed. Magnetic resonance (MR) angiography demonstrated flow void anterior to the
left ophthalmic artery ([Fig. 2A]) and T2-weighted image of MR imaging (T2WI) showed dilation of the left superior
ophthalmic vein (SOV, [Fig. 2B]), suggesting an arteriovenous shunt and cerebral angiography was performed for further
examination. Left internal carotid angiography revealed a shunt between the ophthalmic
artery and SOV ([Fig. 2C]) while there was no feeding from the external carotid artery system. Furthermore,
after the SOV meandered markedly (arrowhead) according to the three-dimensional digital subtraction angiography (3D-DSA), it
flowed out to the angular vein and facial vein ([Fig. 2D]). No obvious cortical reflux or venous stasis was observed in the venous phase of
cerebrovascular angiography ([Fig. 2E]). Based on the above findings, a diagnosis of orbital AVF was made, and the cause
of the visual impairment was considered to be compression of the optic nerve by dilated
SOV rather than increased venous pressure. After admission, visual impairment gradually
progressed, so transarterial embolization was performed for the purpose of improvement
of visual impairment.
Fig. 1 Pre- and postoperative visual field examination of the left eye. The preoperative
examination showed left side hemianopsia (A), which had significantly improved in the postoperative examination (B).
Fig. 2 Preoperative imaging. (A) Flow void in the orbit (arrowheads) is visualized in magnetic resonance (MR) angiography. (B) Axial T2-weighted MR image showing marked dilation of the left superior ophthalmic
vein (SOV) (arrowheads). (C) Left internal carotid angiography revealed an arteriovenous shunt between the ophthalmic
artery and SOV, which flowed out to the angular and facial veins (arrowheads). (D) Three-dimensional digital subtraction angiography (3D-DSA) showed significant meandering
of the SOV (arrowheads) distal to the shunt point (arrow). (E) No obvious cortical reflux or venous stasis was observed in the venous phase of
cerebrovascular angiography.
Endovascular procedure was performed under local anesthesia. A 4-French diagnostic
catheter (Medikit co. ltd., Tokyo, Japan) was guided through the left femoral artery
to the left internal carotid artery and roadmap images and control runs were obtained
during the procedure. A 7-French guide catheter (Asahi Intec co. ltd., Aichi, Japan)
was navigated through the right femoral vein to the left internal jugular vein. The
microcatheter (Terumo MicroVention, Tustin, California, United States) was set up
coaxially with the 3.4-Fr distal access catheter (Technocrat co., Aichi, Japan) and
was guided to the immediate distal to the shunt point through the internal jugular
vein, facial vein, angular vein, and SOV ([Fig. 3A]). The outflow side of the shunt was obliterated by placing a total of six removable
coils ([Fig. 3B,C]) and the shunt blood flow had disappeared after embolization ([Fig. 3D]).
Fig. 3 Intra- and postoperative imaging. (A–D) Lateral (A,D) and right anterior oblique view (B,C) of the intraoperative cerebral angiography. A microcatheter was placed just distal
to the shunt point via the facial, angular, and superior ophthalmic veins (SOV) (A). Coil embolization was started just distal to the shunt point (B), and a total of six coils was deployed (C). The shunt blood flow had disappeared after embolization (D). (E,F) Postoperative imaging at 3 months after the procedure. The flow void had disappeared
on magnetic resonance (MR) angiography (E), and the SOV was thin on the coronal T2-weighted MR image (F).
Visual acuity did not change soon after the operation, but a marked improvement in
visual acuity, from 0.3 to 0.9, was observed on the seventh postoperative day. The
SOV was thin on the T2WI, and the flow void disappeared on MR angiography 3 months
after the procedure ([Fig. 3E,F]). The visual field at 5 months after the operation also significantly improved compared
to the preoperative examination ([Fig. 1A,B]).
Discussion
Orbital AVF is a very rare disease, and only about 20 cases have been reported in
the past.[1]
[2]
[3]
[4]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19] Asymptomatic patients are often just followed up conservatively because it is a
disease that may disappear spontaneously.[9]
[20] On the other hand, some patients have symptoms such as chemosis, proptosis, double
vision, and visual impairment. Visual impairment is a rare symptom and only a few
cases have been reported in the past, and all of them have other ocular symptoms simultaneously.[3]
[4]
[5]
[6] In the above cases, visual impairment was improved by endovascular or surgical intervention.
This case is an orbital AVF that develops only with visual impairment and is rare
in that no similar reports have been reported in the past.
In general, the symptoms of orbital AVF are presumed to differ depending on the pattern
of venous drainage. Increased pressure of ophthalmic veins causes conjunctival hyperemia,
chemosis, exophthalmos, and secondary glaucoma due to increased intraocular pressure.
On the other hand, increased pressure of cavernous sinus causes extraocular muscle
paralysis, ptosis, and anisocoria. In past case reports, symptoms corresponding to
the pattern of venous return have appeared. In contrast to previous reports, this
case is extremely rare in that it causes only visual impairment. In this case, the
intraocular pressure was normal and there was no difference between left and right
in the central retinal arteries and veins. These findings indicate there was no abnormality
in venous reflux which is possibly due to significant development of drainage to the
facial vein via the angular vein. On the other hand, markedly meandering SOV physically
pressed the optic nerve, causing visual impairment. In other words, symptoms appear
not due to increased venous pressure but due to the mechanical compression to the
optic nerve.
Treatment strategies for orbital AVF include surgical treatment, transarterial embolization,
and TVE when the patient experiences progressive symptoms. Surgical treatment that
exposes and treats the SOV is extremely invasive as is reported in the past.[5]
[12] Transarterial embolization from the ophthalmic artery, which is the most common
feeder, proximal to the origin of central retinal artery may cause loss of vision.[21] Transarterial embolization is a treatment that can overcome the weaknesses of the
above treatment policy, although it may be difficult to guide the catheter due to
meandering of the vein. In fact, most of the past reports have been treated by transarterial
embolization only, which followed good outcomes.[1]
[2]
[4]
[6]
[7]
[10]
[14]
[16]
[17] The most important risk of transarterial embolization is a hemorrhage associated
with venous congestion by blocking the outflow. Originally, the SOV has blood flow
from the orbit toward the cavernous sinus in normal condition. Therefore, embolization
of the SOV may cause venous congestion of the central retinal vein and its branches,
resulting in fundal hemorrhage. Preoperative fundus examination revealed no dilation
of the central retinal vein or its branches so it was presumed that these veins flow
into the cavernous sinus by a route unrelated to the SOV. Embryologically, orbital
venous drainage and cavernous sinus form one continuous channel, but gradually differentiate
into multiple channels.[17] In other words, even if the SOV is not involved in orbital venous drainage, the
return from other veins is maintained. In this case, 3D-DSA revealed meandering of
the proximal part of SOV which compressed the optic nerve from above. The treatment
strategy was to reduce the pressure of the SOV and release the pressure on the optic
nerve by embolizing the fistula. In order to achieve this goal, it is essential to
embolize the coil at the appropriate site. In detail, the proximal portion of the
lesion is the optic canal, which runs optic nerve, arteries, and veins in a very narrow
space and the distal portion is the part where the SOV squeezes the optic nerve. By
packing coils in those areas, the optic nerve is unintentionally compressed, which
may worsen the symptoms. By performing necessary and sufficient embolization on the
planned site via the facial vein, we succeeded in improving the symptoms ([Fig. 4]).
Fig. 4 Schema of this case. It was essential to embolize the coil at an appropriate site
just distal to the shunt point (A, black arrowhead). In this case, the proximal portion of the lesion is the optic canal, in which runs
a number of important nerves, arteries, and veins in a very narrow space, and the
distal portion is the part where the superior ophthalmic vein (SOV) squeezes the optic
nerve (A, white arrowhead). The coil was deployed in the SOV, just distal to the shunt point (B, arrow). The meandering SOV shrank, and the pressure on the optic nerve was released.
Conclusion
Orbital AVF is a very rare disease and which causes only visual impairment has not
been reported in the past. The etiology of this case is nerve compression by dilated
meandering SOV. There are various nerves and blood vessels around the shunt point,
and it is necessary to evaluate the pathological condition in detail before treatment.
In the case of this mechanism, coil embolization for proper position and reduction
of venous pressure which relieves compression on the optic nerve may be useful in
improving visual impairment.
