Hydropic villi are abnormal, fluid-filled structures that develop within the placenta during pregnancy. They appear swollen due to fluid accumulation, indicating abnormal placental development.
What Are Hydropic Villi
The placenta, a temporary organ forming during pregnancy, contains structures known as chorionic villi. These are tiny, finger-like projections that extend from the chorion, which is the outermost membrane surrounding the embryo. Chorionic villi are designed to maximize the surface area for the exchange of oxygen, nutrients, and waste products between the mother and the developing fetus.
Normally, these villi contain blood vessels that connect to the baby’s bloodstream through the umbilical cord. When villi become “hydropic,” they are swollen due to excessive fluid accumulation within their stromal core. Microscopically, hydropic villi often appear poorly vascularized or avascular. This fluid accumulation can lead to central, empty-looking areas called cisterns within the villous stroma. These changes contribute to an enlarged, often translucent appearance, sometimes resembling a “bunch of grapes” in advanced cases.
Conditions Linked to Hydropic Villi
Hydropic villi are a hallmark feature of gestational trophoblastic diseases (GTD), a group of rare pregnancy-related conditions involving abnormal growth of placental trophoblast cells. The most common form of GTD associated with hydropic villi is a hydatidiform mole, often referred to as a molar pregnancy. Molar pregnancies are classified into two main types: complete hydatidiform moles and partial hydatidiform moles.
In a complete hydatidiform mole, all or most villous tissue shows generalized hydropic swelling and significant trophoblastic overgrowth. This condition results from the fertilization of an “empty” egg (lacking maternal chromosomes) by one or two sperm, leading to an entirely paternal genome. Complete moles lack any embryonic or fetal tissue.
Partial hydatidiform moles, in contrast, involve only a fraction of the villi, exhibiting variable hydropic changes and less extensive trophoblastic proliferation compared to complete moles. Partial moles result from a viable egg being fertilized by two sperm, leading to a triploid genome (containing both maternal and paternal DNA). They may include some embryonic or fetal development, though these are abnormal.
While molar pregnancies are the primary association, hydropic villi can also be present in other, less common non-molar conditions. These include spontaneous miscarriages, particularly those involving a blighted ovum or missed abortion, where the villi may show edematous changes. In these non-molar cases, the villi are only slightly enlarged and do not exhibit the extensive dimensions or marked trophoblastic hyperplasia seen in complete or partial moles. Another rare condition, placental mesenchymal dysplasia, can also present with hydropic villi; it is distinct from molar pregnancies and has a diploid karyotype. Differentiating these conditions from molar pregnancies is important for proper diagnosis and management.
How Hydropic Villi Are Diagnosed
The detection of hydropic villi and the conditions they indicate involves a combination of diagnostic tools. Ultrasound imaging is a primary method used to assess the pregnancy. For a complete molar pregnancy, ultrasound reveals a characteristic “snowstorm” appearance within the uterus, corresponding to the swollen, fluid-filled villi. Anechoic cystic clusters, described as “grape clusters,” are also seen. In partial moles, ultrasound shows fetal parts alongside areas of abnormal placental tissue.
While ultrasound provides strong indicators, a definitive diagnosis relies on the pathological examination of placental tissue. This tissue is obtained after a procedure like a dilation and curettage (D&C) following a suspected miscarriage or abnormal pregnancy. A pathologist examines the tissue microscopically to identify the characteristic features of hydropic villi, such as edematous stroma, poorly vascularized villi, and the presence and degree of trophoblastic proliferation. Blood tests, particularly those measuring human chorionic gonadotropin (hCG) levels, also play a role. Abnormally high hCG levels can suggest a molar pregnancy, but tissue examination remains necessary for confirmation.
Outlook and Management
The management of conditions involving hydropic villi, particularly molar pregnancies, begins with the evacuation of the uterine contents. This procedure, a suction dilation and curettage, aims to remove the abnormal placental tissue from the uterus. Following evacuation, close follow-up care is necessary to monitor for any remaining trophoblastic tissue or potential complications.
Monitoring involves regular blood tests to track human chorionic gonadotropin (hCG) levels. These levels should decline steadily after evacuation, indicating successful removal of the abnormal cells. Persistent elevation or rising hCG levels can suggest persistent gestational trophoblastic disease (GTD), which may require further treatment. This can include additional surgical intervention or chemotherapy. For non-molar conditions that present with hydropic villi, such as miscarriage, management focuses on complete evacuation of the pregnancy and subsequent monitoring as appropriate.