In spina bifida (Fig. 68.4), both posterior ossification centers are splayed laterally and the spinal canal is dorsally open Measuring the maternal serum a-fetoprotein identifies only spina bifida aperta, but not the covered form.

spina bifida occulta. The indirect sonographic signs of spina bifida ("banana" and "lemon" signs) have already been illustrated on page 67 (refer to Figs. 67.2, 67.3).

Facial bones and neck: Transverse and coronal sections of the face are usually evaluated for decreased (hypotelorism) or increased (hypertelorism) interorbital distance, and the sagittal sections for an atypical profile. A lip-palate cleft generally is lateral and can best be appreciated as a gap in the echogenic upper lip on the coronal section. The normal upper lip (-> , \ ) appears as continuous structure (Fig. 69.1).

Nuchal translucency (NT): After the 1st trimester, edema of the facial soft tissues or cervical subcutaneous tissue (hygroma colli) that exceeds 3 mm in width indicates imparied lymphatic drainage and in one third of cases it is associated with chromosomal abnormalities, such as monosomy X (Turner syndrome), trisomy 21 (Down syndrome), and trisomy 18. To distinguish a prominent nuchal membrane from an amniotic membrane along the posterior cervical area, the finding should be re-evaluated after fetal movements have been observed. Furthermore, a tangen-tially visualized cervical skin can mimic a double contour (i) (Fig. 69.2), which is invariably less than 3 mm in width. The more severe the elevation of the posterior cervical skin and the older the mother, the more likely a chromosomal abnormality (Fig. 69.2 c).

Risk for fetal trisomies 100T [ % ] (Ref': Pandya et al>


Fig. 69.1

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