Ocular Prenatal Imaging

Chapter 14 Ocular Prenatal Imaging




Introduction


Ultrasonographic studies are routinely conducted during prenatal care in the United States. As of 2000, nearly two-thirds of pregnant women received at least one prenatal ultrasonogram.1 However, the optimal number and timing of ultrasonographic studies during pregnancy has not been established. Although it has been deemed a cost-effective tool safe for mother and fetus, several limitations, including operator experience variability, fetal position, gestational age, and tissue definition on ultrasonography, may negatively affect this prenatal screening technique.2


Additionally, there is no conclusive evidence that routine ultrasonographic screening of all pregnancies is effective. In 1984, the National Institute of Health organized the Consensus Development Conference on Diagnostic Imaging in Pregnancy.3 This conference concluded that prenatal ultrasonography improves patient management and outcome only when there is an accepted indication.3 The Routine Antenatal Diagnostic Imaging with Ultrasound study (RADIUS) later conducted a randomized trial comparing a group of women who underwent first and second-trimester screening to a group who underwent ultrasonography only for medical indications, and found that screening ultrasonograms did not reduce perinatal morbidity or mortality when compared with the selective use of ultrasonography based on clinical judgment.4,5 In contrast to these findings, the Helsinki Ultrasound Trial identified a lower perinatal mortality rate in the ultrasound-screening group secondary to a higher detection rate of anomalies and subsequent termination of affected pregnancies.6


Current recommendations from the American College of Obstetricians and Gynecologists do not recommend examination of the globe, orbit, or adnexal structures as part of the routine fetal anatomy screening evaluation.7 However, reports of prenatal ultrasonography for diagnosis of diseases involving the eye and ocular adnexae have been described since the 1980s. Herein, we summarize a literature review of relevant reports to date.




Imaging modalities


Using transvaginal ultrasonography, the eyes may be detected at 12 weeks gestation as hypoechogenic structures superolateral to the nasal bone. By 14 weeks gestation, the lens may be detected as an oval structure in the center of each orbit. It is characterized by a thin echogenic margin overlying an anechoic center. Additionally, the hyaloid artery can be detected in nearly all fetuses by 14 weeks gestation. This structure should disappear by approximately 29 weeks gestation (Figure 14.1). The eyelids may be identified at the beginning of the second trimester. The earliest reported gestational age at diagnosis of anomalies of the globe, orbit, and ocular adnexae by prenatal ultrasonography are given in Table 14.1.



Table 14.1 Earliest reported diagnoses of ocular anomalies by prenatal ultrasonography.












































Gestational age Ocular anomaly
11 weeks Cyclopia42
Microphthalmia31
14 weeks Anophthalmia14
Cataract14,50,51
17 weeks Orbital teratoma78
19 weeks Proptosis27,74
20 weeks Hypertelorism22
21 weeks Retinoblastoma64
22 weeks Hypotelorism15
23 weeks Orbital cyst75
Persistent hyperplastic primary vitreous46
27 weeks Dacryocystocele81,82
34 weeks Retinal detachment68
Orbital rhabdomyosarcoma77

Fetal magnetic resonance imaging (MRI) is currently accepted as a second line imaging modality in the examination of the normal and pathological fetal central nervous system and is also indicated when there is need to confirm or fully characterize a finding from fetal ultrasonography.11 Current software and hardware for fetal magnetic resonance imaging allow the acquisition of high-quality images of the globe and orbit (Figure 14.2). These images may be acquired in less than 1 second, thus permitting the performance of MRI without maternal or fetal sedation.2 However, while there is no evidence to suggest adverse effects of MRI on the fetus, the safety of MRI during pregnancy has not been proven. Therefore, the use of MRI during the first trimester of pregnancy is best avoided when possible.2



Computed tomography is not routinely used for prenatal diagnosis. Carcinogenesis in the fetus is a major concern, hence this imaging modality should be avoided in all trimesters of pregnancy unless absolutely necessary.12



Globe anomalies



Anophthalmia


True anophthalmia is the complete absence of the globe in the presence of ocular adnexae. However, the term “clinical anophthalmia” is sometimes used to reference extreme microphthalmia in which a small blind eye persists. Primary anophthalmia occurs when the eye never forms during gestation. This diagnosis is oftentimes associated with genetic syndromes or chromosomal anomalies. Secondary anophthalmia, on the other hand, is regression of the globe, usually by an insult during development. Potential etiologies of secondary anophthalmia include infectious, vascular, metabolic, or toxic events. In a review of 58 patients with congenital anophthalmia, Schittkowski and colleagues identified systemic findings in 50% of patients, predominantly Goldenhar’s syndrome, facial clefts, and cerebral anomalies.13 In this review, 18 of the 38 patients with unilateral anophthalmia had anomalies in the fellow eye, for the most part consisting of coloboma, dermoid, sclerocornea, and glaucoma.13


The gestational age at diagnosis in the reports ranged between 14 and 32 weeks (Chapter 19).1420 Characteristic findings on ultrasonography included an absent or small orbit, an absent globe, and an absent lens (Figure 14.3). Of the three cases that were unilateral,1618 two were associated with microphthalmia in the fellow eye.16,17 Systemic associations included anophthalmia-plus syndrome,19 Waardenburg-type ophthalmo-acromelic syndrome,20 otocephaly,16 limb body wall complex,17 and holoprosencephaly.15 A family history of anophthalmia was present in two cases14,19 and a maternal history of recurrent miscarriages was present in one case.18 Reported outcomes in pregnancies that were not terminated included stillbirth at 21 weeks gestation in the fetus with limb body wall complex,17 and death shortly after birth in the fetuses with ophthalmo-acromelic syndrome20 and otocephaly.16




Microphthalmia


Microphthalmia refers to an abnormally small eye. Causes of microphthalmia include chromosomal abnormalities, craniofacial disorders, intrauterine infections, teratogens, and syndromic processes.21 It also may be inherited as an autosomal dominant, autosomal recessive, or X-linked trait.


Nomograms for ocular biometric measurements based on ultrasonography have been reported.2225 Microphthalmia is considered when the ocular diameter is less than the 5th percentile for gestational age (Figure 14.4). However, Blazer has noted that normal ocular biometry in early pregnancy does not preclude the subsequent development of microphthalmia.26



Gestational age at diagnosis has ranged between 11 and 32 weeks. While most of the reported cases were bilateral, several unilateral cases have been reported.2629 Associated ocular findings include hypotelorism,27 hypertelorism,30 contralateral anophthalmia,31 and colobomatous cyst.28,31 Reported non-ocular associations include Fraser’s syndrome,29,30,32 limb body wall complex,33 trisomy 13,26 trisomy 18,26,34 Dandy Walker malformation,26 holoprosencephaly,26 hydrocephalus with phocomelia,27 and nasal vestibule stenosis.28 Of the 23 cases reporting outcome, 22 pregnancies were terminated.



Mar 5, 2016 | Posted by in ULTRASONOGRAPHY | Comments Off on Ocular Prenatal Imaging
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