Cavernous sinus and abducens nerve in human fetuses near term

Area of Science:

• Neuroanatomy
• Developmental Biology
• Surgical Anatomy

Background:

• The adult course of the abducens nerve (ABN) through the cavernous sinus is tortuous and clinically significant for neurosurgery.
• The developmental trajectory of the ABN's unique course from fetal to adult anatomy remains largely uncharacterized.

Purpose of the Study:

• To investigate the embryonic and fetal development of the abducens nerve's course within the cavernous sinus.
• To determine when the characteristic angulations of the ABN are established relative to the internal carotid artery and surrounding structures.

Main Methods:

• Histological examination of 18 near-term fetal specimens, including frontal and sagittal sections.
• Analysis of the spatial relationship between the abducens nerve, internal carotid artery, sympathetic nerves, parasellar veins, and oculomotor nerve.

Main Results:

• In near-term fetuses, the ABN follows a straight path alongside a nearly straight intracavernous carotid artery.
• The ABN's straight course is maintained with the addition of sympathetic nerves and minimal separation by developing parasellar veins.
• The ABN exhibits a lateral bend near the developing tendinous annulus, likely to accommodate the oculomotor nerve.

Conclusions:

• The characteristic tortuosity and angulation of the abducens nerve in the cavernous sinus appear to develop significantly after birth, during childhood.
• This postnatal development highlights the abducens nerve as a potential example of substantial course alteration postnatally.
• Knowledge of the ABN's developmental anatomy is vital for preventing neurovascular injury during pediatric endovascular and skull base interventions.