| Abstract|| |
A rare case of placental mesenchymal dysplasia (PMD) in a 26-year-old patient is reported. Ultrasound scan at 17 weeks of gestation showed placenta with multiple cystic spaces and a normal appearing fetus. Following delivery of a term live baby, histological examination of the placenta was suggestive of PMD. The early recognition of this rare condition by characteristic ultrasonographic findings is herein emphasized and hence that PMD is distinguished from molar pregnancy.
Keywords: Beckwith-Wiedemann syndrome, complete molar pregnancy, partial molar pregnancy, placental mesenchymal dysplasia
|How to cite this article:|
Balachandran Nair KG, Srinish M, Balan P, Sadasivan S. Mesenchymal dysplasia of placenta. Indian J Pathol Microbiol 2015;58:371-3
| Introduction|| |
Placental mesenchymal dysplasia (PMD) is a recently described vascular anomaly of the placenta. This uncommon anomaly presents with enlarged placenta with grape-like vesicles both on Ultrasonography and gross examination that may resemble a partial molar pregnancy.  Moscoso et al.  described this first, as stem villous hyperplasia with elevated maternal serum alpha proteins and enlarged placenta with sonographic features suggestive of partial mole and that this has to be distinguished from partial mole histologically by the absence of trophoblastic proliferation. 
The incidence of PMD is reported to be 0.02%,  however, the true incidence is unknown because this remains as an unfamiliar arena for many pathologists, and may be undiagnosed or under-reported. It is essential to distinguish PMD from other cystic lesions of placenta like partial hydatidiform mole, complete molar pregnancy with co-twin, normal pregnancy with chorangioma because, in most cases of PMD, fetus is normal. However, PMD may be associated with intrauterine growth restriction, intrauterine death and Beckwith-Wiedemann syndrome More Details (25% cases).  Herein, we report a case of PMD with normal fetus with special emphasis on sonographic findings.
| Case Report|| |
A 26-year-old female, gravida 2, para 1, live birth 1 (with a normal appearing fetus and cystic placenta) presented with bleeding per vaginum at 2 months of gestation. Ultrasound at 17 weeks revealed a normal fetus with numerous cystic areas in anterior half of placenta showing no vascularity. Dilated chorionic vessels were also noted. A presumptive diagnosis of PMD was made. Patient elected to continue the pregnancy and accepted the complications like increased risk of pre-eclampsia (27%), a persistent gestational trophoblastic disease (45%), and fetal loss (62%). The other screening tests including chest x-ray, liver enzyme levels, renal parameters, and thyroid profile were normal. She delivered a term live baby of weight 2.25 kg. Post natal followup was normal up to 12 weeks. Placenta with cord and membranes was subjected to histopathological study.
On gross examination, placenta weighed 600 g, with multiple grape-like vesicles and tortuous, dilated blood vessels, noted on the surface of placenta [Figure 1].
|Figure 1: Gross specimen of placenta showing dilated and tortuous vessels and multiple grape-like vesicles|
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Microscopically, villi with hydropic swelling and cistern formation were observed, admixed with unaffected terminal villi. Central thick walled blood vessels and peripherally placed small capillaries were also noted. However, there was no trophoblastic proliferation [Figure 2]a.
|Figure 2: (a) Normal terminal villi (low power). (b) Periphery showing dilated blood vessels walls of which are thickened (low power)|
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| Discussion|| |
Mesenchymal dysplasia of the placenta is a relatively rare disorder. We herein report one such case of a young female in whom an ultrasound diagnosis of PMD was subsequently confirmed by histopathological examination. Although the exact etiology for the development of PMD remains unknown, the presence of acid mucopolysaccharides in the enlarged stem villi and association with other mesenchymal proliferative disorders such as chorangiomas and chorionic vessel dilatation, support the theory that PMD might be a congenital mesodermal malformation. 
Fibroblast proliferation and vascular endothelial growth factor production leading to angiogenesis in response to hypoxia and hypoperfusion may also contribute to the phenotypic findings in PMD. 
The recently suggested etiology is androgenic/bi-parental mosaicism as suggested by Kaiser-Rogers et al.  Such mosaicism arise as a result of failure in replication of maternal genome prior to first cleavage, with paternal genome undergoing normal segregation and replication resulting in two types of daughter cells. One with normal, bi-parental genes and the other with only paternal genes. Such failed division produces a diploid or haploid mosaic embryo, and the haploid paternal only daughter cell undergoes endoreduplication to produce diploid androgenetic lineage, while the other normal haploid components would merge to form daughter cells with bi-parental inheritance. This accounts for the preponderance of females in PMD. 
Clinically, there is no specific symptomatology associated with PMD.  Most cases are diagnosed by prenatal ultrasound and confirmed by subsequent histopathological examination. Most common laboratory abnormality includes increased maternal serum alpha feto protein. The beta Human Chorionic Gonadotropin level is normal or slightly increased, but may return to normal levels postdelivery.  Many cases may be asymptomatic and may be diagnosed by abnormally large placenta postdelivery. In the case that we report here, the patient had an episode of bleeding per vaginum at 2 months of gestation. The remaining gestational period until delivery was largely uneventful with normal beta HCG levels.
Grossly, placenta is large for gestational age.  In the third trimester PMD placenta, the chorionic plate vessels are aneurysmally dilated and tortuous with abnormal branching. Luminal thrombosis or rupture may be seen in these dilated vessels.  Vesicle formation is usually seen and in rare cases, this may be minimal or absent.  The placenta in the present case, on examination was slightly heavier for the gestational age. The surface was characteristic with grape-like vesicles and tortuous, dilated vessels [Figure 1].
Microscopically, placenta shows large stem villi with hydropic swelling and cistern formation, with admixed, unaffected terminal villi. However, trophoblastic stromal inclusions and proliferations are absent in PMD, which are characteristic of vesicular mole. Similarly, chorangiosis and fetal thrombotic vasculopathy are associated with PMD and not with molar pregnancies.  Central thick walled blood vessels with constricted lumen and scattered peripherally placed small capillaries are also noted. Myofibroblastic proliferation of spindle and stellate mesenchymal cells without cytologic atypia or mitotic figures are also observed.  Histological examination of our specimen revealed villi with hydropic swelling and cistern formation admixed with unaffected terminal villi without trophoblastic proliferation [Figure 2]a, [Figure 3]a and b. The sections also revealed central thick-walled blood vessels with peripheral small capillaries [Figure 2]b. The gross and histological examination findings in our case were found to be largely consistent with descriptions of PMD in literature and thus a pathological diagnosis of PMD was offered.
|Figure 3: (a) Cystically dilated villi (low power). (b) Cystically dilated villi without trophoblastic proliferation (high power)|
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Immunohistochemically, stromal cells in large stem villi of PMD placentas are positive for desmin and vimentin and negative for alpha smooth muscle actin, whereas, stromal cells in normal appearing villi are positive for all three.  In PMD, the stromal cells fail to differentiate beyond the fibroblast stage.  The ground substance shows alcian blue positivity.  Antibodies against paternal imprinting genes such as antibody against p57kip2 are useful markers for distinguishing PMD from molar pregnancy.  Detection of androgenic/bi-parental mosaicism also suggests a diagnosis of PMD.  Di-chorionic twin placentas with a normal fetus and a complete mole need to be distinguished from PMD, but vascular anomalies associated with PMD are absent in their placenta and are completely androgenic. Spontaneous abortion with hydropic change may have vesicle formation, but their vesicles are usually small, and placenta may show usually degenerative changes. 
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Dr. Minu Srinish
CB Apartments, TC 2/3393/14, KRA 77, Kedaramnagar, Pattom, Trivandrum - 695 004, Kerala
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3]