HYALOID VESSELS OF THE FETAL EYE

The hyaloid artery is a transient fetal vessel that may be observed in the second and early third trimester of pregnancy.

ANATOMY

• Originate from the ophthalmic artery and provide a transitory path
• way for nourishment of the fetal eye.
• It invades the optic cup at the 5mm stage and gives rise to branches that increase in complexity that almost fills the interior of the optic cup at the 40mm-60mm stage.
• Begins to atrophy soon after reaching full maturity (1).
• Regresses into its transparent membrane (canal of Cloquet) near the start of the third trimester (2).

ULTRASOUND

• Usually seen before 20 weeks and spontaneously regressed by about 25 weeks gestational age.
• Linear structure within the vitreous.
• It is a thin horizontal echogenic structure that traverses the fetal globe from the posterior part of the eye and the posterior part of the lens capsule (3).
• Reported to be detectable in 90% of fetuses by 14th week of gestation using a 6.5 MHz endovaginal transducer (4).
• Canal of Cloquet has not been visualized antenatally.
• <1% is seen in healthy fetuses in the mid third trimester.
• Delayed regression may occur in trisomy 21 and other forms of abnormal brain development (2).

REFERENCES

1. Strek W, Strek P, Nowogrodzka-Zagorska M et.al. Hyaloid vessels of the human fetal eye: A scanning electron microscopic study of corrosion casts. Arch Ophthalmol 1993;111:1573-1577.
2. Birnholz JC, Farrell EE. Fetal hyaloid artery: Timing of regression with US. Radiology 1988;166:781-783.
3. Winderl LM. Transvaginal sonographic demonstration of the hyaloid artery in an anencephalic fetus. JDMS 1997;13:84-86.
4. Bronshtein M, Zimmer E, Gershoni-Baruch R et.al. First and second trimester diagnosis of fetal ocular defects and associated anomalies: Report of eight cases. Obstet Gynecol 1991;77:443-449.