Ophthalmic segment aneurysm

The ophthalmic segment aneurysms arise from the internal carotid artery (ICA) between the roof of the cavernous sinus and the origin of the posterior communicating artery.

The ophthalmic segment of the internal carotid artery (C6) extends from the distal dural ring to the origin of the posterior communicating artery.

The segment is known as the carotid ophthalmic segment.

Ophthalmic segment aneurysms (OSAs) OSAs include (NB: nomenclature varies among authors):

1. ophthalmic artery aneurysms:

2. superior hypophyseal artery aneurysms:

a) Paraclinoid internal carotid artery aneurysm: usually does not produce visual symptoms

b) suprasellar variant: when giant, may mimic pituitary tumor on CT.

1. ≈45% present as SAH

2. ≈ 45% present as visual field defect:

a) as the aneurysm enlarges it impinges on the lateral portion of the optic nerve →inferior temporal fiber compression →ipsilateral monocular superior nasal quadrantanopsia

b) continued enlargement →upward displacement of the nerve against the falciform ligament (or fold) →superior temporal fiber compression →monocular inferior nasal quadrantanopsia

c) in addition to near-complete loss of vision in the involved eye, compression of the optic nerve near the chiasm may also produce a superior temporal quadrant defect in the contralateral eye (junctional scotoma AKA“pie in the sky” defect) from injury to the anterior knee of Wilbrand (nasal retinal fibers that course anteriorly for a short distance after they decussate in the contralateral optic nerve).

3. ≈ 10% present as both