Compressive Optic Neuropathy Due to Dolichoectatic Ophthalmic Artery

ABSTRACT

A 63-year-old man experienced progressive vision loss in his right eye over five years. Ophthalmologic examination showed right optic neuropathy with optic nerve pallor. Prior MRI findings of gadolinium enhancement near the prechiasmatic optic nerve had suggested acute optic neuritis. A repeat MRI revealed a dilated vascular structure compressing the optic nerve, confirmed by Time-of-Flight MRA as dolichoectatic ophthalmic artery. Compression-related optic neuropathy caused by a dolichoectatic ophthalmic artery can have similar appearance to acute optic neuritis on MRI. When the clinical history or course does not align with the initial diagnosis, it is important to reconsider the diagnosis.

Case presentation

A 63-year-old man presented to our clinic with progressive worsening of vision in his right eye. His medical history included hypertension, prediabetes, hyperlipidaemia, and low back pain. Regarding his ocular history, he had undergone cryopexy for retinal detachment, scleral buckle, pars plana vitrectomy (left eye), blunt trauma with a retinal tear, status post retinopexy (right eye), keratoconus and cataract surgery (both eyes) all many years prior to the episode of vision worsening for which he was seeking care. His post-surgical visual acuity was 20/50 in the right eye and 20/25 in the left eye.

Two years prior he was seen by an optometrist for evaluation of subacute vision loss and diagnosed with right optic neuropathy with right eye having baseline visual acuity of 20/50, but dyschromatopsia, severe depression on Humphrey Visual Field and relative afferent pupillary defect. At that time, an MRI of the orbits with and without gadolinium reported enhancement of the prechiasmatic optic nerve extending to the orbital apex with no signs of extrinsic compression, interpreted to represent acute optic neuritis, (Figure 1a,b). A neurology consultation and demyelinating disease workup were unrevealing, and further evaluation was recommended, but the patient was lost to follow-up. One year later, he was seen by an optometrist for evaluation of progressive vision loss which was attributed to optic neuropathy, and he was referred to our clinic.

Figure 1.

Post-contrast T1 MRI images from initial MRI orbit performed after onset of symptoms. There is enhancement of the prechiasmatic portion of the right optic nerve extending into the orbital apex, without extrinsic compression or mass. (a) Coronal view. (b) Transverse view.

During our initial evaluation, vision in the right eye was 20/50 and 20/25 in the left eye with right eye dyschromatopsia, relative afferent pupillary defect and right optic nerve head pallor. Optical coherence tomography (OCT) revealed superior and inferior retinal nerve fibre layer thinning in the right eye (average of 66 µm) compared to the left eye (average 79 µm). Visual field testing showed diffuse depression in the right eye and was normal in the left eye. Contrast sensitivity was not assessed. Due to his persistent vision loss not consistent with prior diagnosis of optic neuritis, a repeat MRI was ordered. At a follow-up visit 2 months later, visual acuity in the right eye had declined from 20/50 to 20/80. The MRI had not yet been completed, so it was rescheduled. At a follow-up appointment 3 months later, visual acuity and ophthalmologic evaluation remained stable. MRI of the orbits with and without gadolinium revealed a dilated vascular structure extending from the right supraclinoid internal carotid artery (ICA) through the right optic canal, compressing the right optic nerve (Figure 2a,b). A right dolichoectatic ophthalmic artery compressing the right optic nerve was suspected, and a Time-of-Flight (TOF) MRA confirmed the diagnosis (Figure 2c,d).

Figure 2.

T2-weighted MRI and 3D TOF MRA images performed 2 years after onset of symptoms. (a) coronal T2-weighted MRI view at 5-month follow-up, showing a dilated vascular structure compressing the right optic nerve at the optic canal, highlighted in white boxes. (b) Axial T2-weighted MRI view of the same structure. (c) 3D TOF MRA at 11-month follow-up, showing dolichoectasia of the right ophthalmic artery at its origin with 50% stenosis (white arrow). (d) Comparison image showing normal composition of the left internal carotid and ophthalmic artery (white arrow).

The patient was referred to Neurosurgery for consideration of decompression surgery. Unfortunately, in the interval, he experienced rapid visual decline in the right eye, and surgical decompression was not pursued due to potential complications and the low likelihood of vision improvement.

Explanation of findings

We present a case of progressive optic neuropathy caused by compression of the optic nerve by a dolichoectatic ophthalmic artery. Although dolichoectasia of the ophthalmic artery has been described before,¹ to our knowledge, this is only the second case reported as a cause of optic neuropathy. Dolichoectatic ICA compressive optic neuropathy has been reported more broadly.^2,3

Dolichoectasia of intracerebral vessels is a rare disorder that typically affects the large arteries at the base of the brain, with the vertebrobasilar system being more commonly affected than the internal carotid arteries. “Dolichos” means elongation, and “ectasia” means distension. It is characterised by weakness of the tunica intima and/or media, predisposing the vessel to elongation and distension. The risk increases with age and is associated with cardiovascular risk factors. Neuro-ophthalmic manifestations, often related to compression, as in our case, include cranial nerve palsies, optic neuropathy, chiasmal syndromes, nystagmus, hemifacial spasm, and ophthalmalgia.^1,4 Other neurological deficits may occur due to vasculopathy of the dolichoectatic artery, including downstream embolisation, thrombotic occlusion, or, rarely, rupture.⁴ Dolichoectasia of the ICA has been reported to cause an optic neuropathy that mimics glaucoma, with a pattern of vertical progression in the size of the optic disc cup and focal notching.⁵ Although surgery can lead to partial or complete recovery, it carries risks of complications such as subdural haematoma requiring evacuation and pulmonary embolism. Moreover, recovery is often limited in cases involving severe optic neuropathy.⁶ Because our case featured severe optic neuropathy, a decision to not pursue surgery was made.

Discussion

In this case the MRI findings of gadolinium enhancement in the region of the optic canal were initially interpreted as optic neuritis. Gadolinium enhancement is characteristic of blood vessel lumina and occurs where there is breakdown of the blood-brain barrier, typically in inflammatory, neoplastic, or infectious conditions, which allows gadolinium contrast to enter the extracellular space and generate enhancement signal on MRI. Optic neuritis is a common cause of gadolinium enhancement of the optic nerve, but any inflammatory, neoplastic, or infectious optic neuropathy can produce similar findings. Vascular enhancement in the region of the optic nerve can be difficult to distinguish from acute optic neuritis in the area of the optic canal due to the close proximity of the vessels to the optic nerve, as seen in this patient’s initial MRI. MRI findings must be interpreted in the context of the patient’s clinical history and disease course. In this case the initial MRI suggested demyelinating optic neuritis, but the patient did not have the expected course of optic neuropathy developing over days and improving over months which motivated additional testing to arrive at the final diagnosis. When the clinical history or course does not align with the initial diagnosis, it is important to reconsider the diagnosis. Further diagnostic studies can provide clarification and confirmation.

Funding Statement

[NIH P30 026877], unrestricted grant from Research to Prevent Blindness to the Stanford Department of Ophthalmology.

Disclosure statement

No potential conflict of interest was reported by the author(s).