The Cerebral Vascular System
The CNs can be affected by the surrounding cerebrovascular system, which includes both arterial and venous components. CN palsies can be harbingers of life-threatening conditions. Thus, it is imperative to understand the CNs’ anatomical relationships with adjacent structures. For further discussion of the cerebral vasculature and the various resultant syndromes of the CNs, see BCSC Section 5, Neuro-Ophthalmology.
The cavernous sinus is an interconnected series of venous channels located just posterior to the orbital apex and lateral to the sphenoid sinus and pituitary fossa. The following structures are located within the venous cavity:
Figure 3-23 Lacrimal reflex arc (after Kurihashi). The afferent pathway is provided by the first and second divisions of CN V. The efferent pathway proceeds from the lacrimal nucleus (close to the superior salivatory nucleus) via CN VII (nervus intermedius), through the geniculate ganglion, the greater superficial petrosal nerve, and the nerve of the pterygoid canal (vidian nerve) (where it is joined by sympathetic fibers from the deep petrosal nerve). The fibers then pass to the pterygopalatine ganglion, where they synapse with postganglionic fibers. These fibers reach the lacrimal gland directly, via the retro-orbital plexus of nerves (particularly CN V1). The fibers carry cholinergic and vasoactive intestinal polypeptide (VIP)-ergic fibers to the gland.
(Modified with permission from Spalton D, Hitchings R, Hunter P. Atlas of Clinical Ophthalmology. 3rd ed. New York: Elsevier/Mosby; 2005:642.)
Figure 3-24 shows the entry of CNs III–VI into the cavernous sinus from the midbrain. Figure 3-25 depicts the relative location of these structures in different parts of the cavernous sinus.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.