Review of Ultrasound Diagnosis of Ichthyosis in Fetuses

Congenital ichthyoses are inherited disorders in which the outer layer of the skin forms abnormally. Prenatal ultrasound can show a recognizable pattern in some affected fetuses, but most published evidence comes from case reports and small case series. This narrative review summarizes sonographic findings that have been reported, when they became visible, and how they should be interpreted in clinical practice. The strongest imaging literature concerns harlequin ichthyosis. Reported findings include ectropion, eclabium or persistent mouth opening, a flattened nasal contour, fixed flexion of the hands or feet, an abnormal skin surface, echogenic amniotic fluid, and polyhydramnios. However, these findings are not specific and may appear only in the second half of pregnancy. Therefore, an earlier normal scan does not exclude disease. Evidence for other congenital ichthyoses is more limited. A genotype-confirmed TGM1-related case showed facial findings similar to harlequin ichthyosis, whereas ichthyosis prematurity syndrome has a late-gestation pattern described in a small series. By contrast, X-linked ichthyosis is more often suspected from maternal serum or genetic findings than from a structural fetal ultrasound pattern. Three-dimensional ultrasound can improve display of surface anatomy when two-dimensional findings are suspicious, but its diagnostic accuracy has not been established. Fetal magnetic resonance imaging has only an adjunctive role. Overall, ultrasound is best used to recognize a phenotype, guide further assessment, and prompt genetic testing rather than to provide a stand-alone molecular diagnosis.