Читать книгу Genetic Disorders and the Fetus - Группа авторов - Страница 159

A rarer, but important, placental phenotype recognizable prenatally, is that of PMD (Figure 4.1e, f). This can be misdiagnosed on ultrasound as a PHM and has been referred to as a “pseudo partial mole.”^142–146 Placentas with PMD may appear on ultrasound as unusually large and thick with multiple echo‐poor regions representing edematous stem villi and possibly enlarged blood vessels. Remarkably, PMD can often coexist with a completely normal fetus; however, there is increased risk of FGR and fetal or neonatal death. PMD can be distinguished from a partial or complete mole on pathology examination as there is no trophoblast hyperplasia. PMD shows abnormal vessels in enlarged and myxomatous appearing stem villi. There may be some edematous chorionic villi but this is not usually a prominent feature. Whereas partial moles are triploid, PMD generally have a normal diploid karyotype, but molecularly can be shown to have a chimeric mix of androgenetic and biparental cells.^147–149 In some cases, a CHM can grow closely adjacent to a twin placenta that is normal diploid and mimic the appearance of PMD on ultrasound.

Diagnosis of PMD has been associated with fetuses exhibiting features of BWS, including omphalocele, macroglossia, and visceromegaly.^{143, 145, 146} PMD associated with BWS generally results from mosaicism for maternal deletion, paternal duplication, or paternal UPD of chromosome 11p15.5, but appears to be a relatively rare finding among BWS cases as a whole.¹⁵⁰ Additionally, androgenetic chimerism (often reported as mosaic “complete paternal uniparental disomy”) has been associated with BWS.^{151, 152} In such cases, phenotype can be variable and there may be features of multiple imprinting disorders.¹⁵³

A frequent feature in the fetus from pregnancies affected by PMD, even in the absence of other fetal involvement, is the presence of hemangiomas. These may be benign skin hemangiomas, but in some cases hepatic hemangiomas are identified, as are hepatic mesenchymal hamartomas. These have been observed to be present in utero and may grow to an extent as to be life‐threatening to the fetus.^{148, 154, 155} Androgenetic chimerism can be found in some cases of liver hemangioma or hepatic mesenchymal hamartoma even in the absence of overt signs of PMD.¹⁵⁶ Other cases of PMD have been reported to involve rearrangements of chromosome 19, which contains the C19MC imprinted, placenta‐specific microRNA cluster.¹⁵⁷ Infantile hemangiomas may derive from placental mesenchymal cells that have invaded the fetus through the vascular system.^158–160