Prenatal, Congenital, and Neonatal Abnormalities

Chapter 5

Prenatal, Congenital, and Neonatal Abnormalities

Assessment of the orbits is part of a detailed fetal sonographic or magnetic resonance imaging (MRI) scan, particularly in the setting of suspected central nervous system malformation. When further assessment is performed by fetal MRI, quite obvious ocular pathologies can be missed, particularly if they are bilateral and symmetrical. Diagnoses can be further honed or even altered completely when a coexisting ocular pathology is found.

Ocular evaluation comprises assessment for the presence or absence of eyes, the morphology of the lens and vitreous, and ocular biometry.1

Presence or Absence of the Eyes

Anophthalmia and Microphthalmia

The only way that anophthalmia and microphthalmia truly can be differentiated is pathologically, with anophthalmia being complete absence of the globe but the presence of the ocular adnexa (i.e., eyelids, conjunctiva, and lacrimal apparatus).

Secondary Anophthalmia

Loss of ocular tissue caused by an insult during development results in secondary anophthalmia. Etiologies include infection (e.g., rubella), a vascular event (e.g., Goldenhar syndrome), or a toxic or metabolic event (e.g., low or high vitamin A levels). The ocular diameter is below the fifth percentile.8

Matthew-Wood syndrome (also known as Spear syndrome, PMD, or PDAC syndrome) is composed of pulmonary hypoplasia/agenesis, diaphragmatic hernia/eventration, anophthalmia/microphthalmia, and cardiac defect.9 In a case of congenital diaphragmatic hernia, associated abnormal orbital morphology and biometry and cardiac anomalies can allow this diagnosis to be made antenatally (Fig. 5-1).

Walker-Warburg syndrome, a type of congenital muscular dystrophy, also can be diagnosed antenatally through the association of Dandy-Walker spectrum, along with a Z-shaped brainstem on midline sagittal MRI views, an occipital cephalocele, and ocular asymmetry (Fig. 5-2 and e-Fig. 5-3).

Aicardi syndrome is a rare genetic malformation syndrome that can be diagnosed antenatally by the association of partial or complete absence of the corpus callosum, ocular abnormalities, and a posterior fossa cyst. Aicardi syndrome is thought to be caused by a defect on the X chromosome because it has only been seen in girls and in boys with Klinefelter syndrome (Fig. 5-4 and e-Fig. 5-5).

Morphology of the Lens and Vitreous

On ultrasound examination, the lens and vitreous are equally hypoechoic; however, the outline of the lens can be seen as a thin hyperechoic ovoid anteriorly within the globe. Typically, however, the only reflection from the lens is from the surfaces perpendicular to the insonating beam, and it can be difficult to see (Fig. 5-6).

On MRI, the entire lens has a low signal compared with the high signal of the vitreous (Fig. 5-7). By endovaginal ultrasound, the lens is visible by 14 weeks as a thin echogenic rim with an anechoic center. The hyaloid artery can be seen as an echogenic line bisecting the vitreous, which, during conversion of the primary vitreous to mature secondary vitreous, gradually becomes beaded as it involutes, a process that should be completed by 30 weeks menstrual age.10,11 The remnant channel through the vitreous is known as the Cloquet canal.

Persistent Hyperplastic Primary Vitreous

Failure of involution of the hyaloid artery results in a spectrum of abnormalities known as persistent hyperplastic primary vitreous, which is seen frequently with trisomy syndromes and other forms of abnormal brain development.12,13 It is usually unilateral. Clinically the presentation is variable and includes leukokoria, vitreous hemorrhage, retinal detachment, microphthalmos, and lens opacification.

The diagnosis can be made antenatally or by ultrasound, computed tomography (CT), or MRI postnatally. Ultrasound can detect the hyaloid vessel. A cone-shaped retrolental density is the characteristic finding on CT and MRI. Findings described on CT include a small irregular lens with a shallow anterior chamber; intravitreal densities of variable shape, suggesting the persistence of fetal tissue in the Cloquet canal; and enhancement of abnormal intravitreal tissue after intravenous administration of contrast media. On MRI the appearance is that of low-signal intensity linear plaques extending from the posterior part of the lens to the optic nerve head. Calcification is unusual (Fig. 5-8 and e-Fig. 5-9).

Optic Nerve Hypoplasia

Optic nerve hypoplasia is usually sporadic and difficult to detect prenatally; however, it has a number of associations that potentially can be diagnosed prenatally because of associated structural abnormalities, several of which are discussed in this chapter (Box 5-1 and Fig. 5-11).

Dec 20, 2015 | Posted by in PEDIATRIC IMAGING | Comments Off on Prenatal, Congenital, and Neonatal Abnormalities
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