Placental lakes or placental lacunae are well-demarcated, mainly sonolucent avillous spaces of diverse size and shape, surrounded by placental tissue with normal echogenicity /subchorionic location. Their etiology is varied, so the contents of the lacunae can vary, with many containing venous maternal blood.

Abstract: Placental lakes or placental lacunae are well-demarcated, mainly sonolucent avillous spaces of diverse size and shape, surrounded by placental tissue with normal echogenicity /subchorionic location. Their etiology is varied, so the contents of the lacunae can vary, with many containing venous maternal blood. Frequently they are found as a sign of intraplacental hemorrhage or premature maturation of the placenta. They can also occur as a compound sign in patients with the suspicion of abnormal invasive placenta (AIP) and placenta previa. In general, and depending on their cause, the presence of placental lakes entails clinical risks including the occurrence of intrauterine growth restriction or massive maternal blood loss at delivery.  

Key words: placental lakes/lacunae, intraplacental hematomas/hemorrhage, subchorionic hematoma/hemorrhage, intraplacental infarction, abnormal invasive placenta (AIP), intrauterine growth restriction (IUGR). 

Authors: Dr. Petra Pateisky1,  Dr. Kinga Chalubinski.1

  1. Medical University of Vienna, Department of Obstetrics and Gynaecology, Division of Obstetrics and Feto-maternal Medicine.

Reviewer: Alexander Weichert

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Definition

Placental lakes (intra-placental lacunae) are defined as well-demarcated, mainly homogenous, hypoechoic, sonolucent intervillous or avillous vascular spaces surrounded by placental tissue with normal echogencity.1, 2 They can be different sizes and shapes. The term “placental lakes” is used variously and often very differently throughout the literature, comprising in its broadest form all sorts of sonolucent areas irrespective of echogenicity, location or pathogenic cause.3, 4, 5, 6, 7 The authors think it is essential to use distinct and homogenous definitions in order to correctly link pathogenic and ultrasound findings to clinically relevant outcomes. Therefore, in this chapter, the term placental lakes will be used to refer to intraplacental and subchorionic lesions  (hematomas, intraplacental hemorrhage, placental lacunae with flow and feeder vessels), based on the frequently-used definition of a low vascular flow in placental lakes in the literature. Other types will be handled as differential diagnoses to these lesions. 

The term “placental lakes” refers to sonolucencies displaying a sometimes turbulent, swirling, non-pulsatile low velocity flow on 2D gray-scale or colour Doppler examination, or low-resistance pulsatile intervillous flow velocity.1, 4, 8 Many contain blood flow, mainly from maternal origin.9, 10 Based on the referenced literature, the authors believe that the term placental lacunae should only be used for sonolucent, numerous, large and irregular intraplacental spaces suggestive of abnormally invasive placenta (AIP) to differentiate them from other lakes.11,12 This should provide a clear categorization of the different ultrasonographic findings/appearance and facilitate categorisation of the associated clinical entities. In accordance with the recent use in literature, this approach should allow clearer differentiation between the different sub-entities and support clinical usefulness. 

ICD code

O43.9 Placental disorder, unspecified
O43.8 Other placental disorders; placental dysfunction/infarction
 

Incidence/recurrence risk

Reports on the frequency of detection of placental lakes vary due to the heterogeneity and inconsistency of categorization (e.g. different definitions of the minimum size, different sonolucencies grouped together.) 4, 7, 13  Historically, the prevalence has been estimated to be as high as 42% in a general obstetric population.14 
In more recent literature, the prevalence of placental lakes varies between 11.9%5 and 17.8% in unselected obstetric patients.7 Other current studies report this condition to be present in about 2.2% of pregnancies13 between 15 and 34 weeks of gestation and up to 22% in the 1st trimester.15 
The latest data suggests that at least one placental lake can be found in about 8.7% of pregnant women at the time of the routine 2nd trimester ultrasonography scan.4 This seems to be the most relevant time interval for the detection of clinically significant placental lakes.5, 16
The recurrence risk for placental lakes or lacunae depends on the specific underlying clinical condition. There is currently no reliable data available on the isolated risk for recurrence. 

Etiology/pathogenesis

The mechanisms for the development of placental lakes or lacunae are numerous, and some are still under investigation. It is evident that the pathogenesis depends on the specific type of sonolucency referred to as “placental lake”7 Some authors suggest that they result from a suboptimal decidual response of the lower uterine segment to the vascular alterations in early pregnancy or underlying abnormalities.17 It is suggested that intraparenchymal lakes regulate the equalization of different placental intervillous blood flow pressures.2 They are thought to mainly contain maternal blood. Centro-cotyledonary spaces develop based on the dissemination of terminal villi by maternal blood arterial jets entering the intervillous space with increasing pressure as pregnancy advances.18 It has also been proposed that placental lakes form secondary to trauma from normal fetal movements at the feto-placental interface.19 Further, loss of fetal vascular integrity with small fetomaternal hemorrhage into the intervillous space triggering a maternal coagulation system reaction is one of the underlying factors.17 Intervillous thrombi/hemorrhages (fetomaternal hemorrhage into the intervillous space due to rupture of villous capillaries) can also create large intervillous hematomas10 still predominantly composed of coagulating maternal blood. 
Small hypoechoic spaces are routinely found in the center of the cotyledons in normal third trimester mature placentas.20 Larger intraplacental sonolucencies have been observed on ultrasound from the second trimester until term pregnancy.5 Multiple, large maternal lakes possibly interfering with the normal placental architecture are probably due to abnormal hemodynamic flow in the intervillous space.21 Incomplete transformation/invasion of the spiral arteries and other implantation abnormalities result in a disturbed and possibly turbulent intervillous flow causing focal overpressure within the above cotyledon with maternofetal hemorrhage.2 The blood flow volume to the placental lobule may be increased by involving blood flow form a larger than average spiral artery.22 Maternal blood then coagulates within the lakes causing obliteration of the intervillous circulation in this placental area leading to intervillous thrombosis.21, 10 Taken together, the interruption of the maternofetal circulatory exchange by thrombi/vascular narrowing affecting vessels between the uterine arteries and the fetal umbilical vascular branchings carries the risk of reduced placental function with impact on fetal growth and supply.9  
The mechanical disruption of the placenta due to a large amount of blood flow seems to be a crucial factor in the development of placental lakes associated with abnormally invasive placenta-disorders (AIP). Further, inappropriate placentation with pathological recruitment of the deep arterial system may be a causal factor for the development of placental lacunae in cases of abnormally invasive placenta.23, 24 The lacunae develop based on the distortion of one or more cotyledons due to high velocity maternal blood flow from a radial or arcuate artery.25 
 

Risk factors

Placental lakes by themselves, if not very numerous or large5, 16, 13, 7, do not seem to adversely impact obstetric and/or perinatal outcome.7 Therefore, risk factors for the appearance of intraparenchymal/subchorionic vascular spacesrefer to the most common associated clinical conditions:

  • History of previous caesarean sections or other surgery impacting the uterine wall as well as decidual/endometrial integrity (eg. dilatation and curettage, myomectomy) resulting in an intrauterine scarring with localized perfusion defects
  • Presence of abnormally invasive placenta (AIP) 
  • Presence of a thick placenta (i.e. maximum placental diameter > 3.5 – 4cm)
  • Vaginal bleeding episodes in first and second trimester (5%-22.4%)26, 27
  • Placental inflammation/maturation
  • Early poor placentation

Associated anomalies

Abnormally invasive placenta (AIP) (abnormal placental adherence to or invasion of trophoblast tissue into the myometrium) is significantly associated with the appearance of multiple, large and irregularly-shaped placental lacunae11, 12 in combination with myometrial thinning and irregularity of the hypoechoic plane between myometrium and placenta (‘clear zone’) (Collins et al: https://doi.org/10.1002/uog.14952.) The incidence of AIP varies between 1:588 to 1:2500 and carries significant risks for maternal morbidity, particularly causing massive maternal hemorrhage.28 The detection of abnormal placental lacunae - numerous lacunae with some large and irregular in shape (Finberg Grade 3) frequently displaying turbulent flow on grayscale examination11 is highly suggestive of AIP. It is the most common ultrasound sign visible in about 80% of cases in the 2nd trimester and should prompt further investigation.12 The patient group with the highest likelihood of AIP are patients with a placenta previa/low-lying placenta in the second trimester and a history of at least one cesarean delivery29 with an incidence of 4.1%. However, the risk for AIP increases with the number of cesarean deliveries. In a study by Silver et al. placenta accreta was present in 15 (0.24%), 49 (0.31%), 36 (0.57%), 31 (2.13%), 6 (2.33%), and 6 (6.74%) women undergoing their first, second, third, fourth, fifth, and sixth or more cesarean deliveries, respectively.51 

Beyond that, some studies suggest that especially large placental lakes are correlated with growth restricted fetuses4, overall significantly lower birth weight and even intrauterine death.21, 30, 31 Several studies have shown that hematomas early and late diagnosed in pregnancy are associated with a higher rate of adverse events such as early delivery, IUGR, miscarriage and pregnancy induced hypertension.32, 33, 34, 35 Still, some of the results need to be considered with precaution due to the varied terminology. 
Increased placental thickness was reported to be associated with the presence of placental lakes in one large prospective study with 1198 pregnancies analyzed at the time of the 18-22 weeks ultrasound scan. The finding of placental lakes was six times more likely with a placental thickness > 3cm at 20 weeks’ gestation and increased placental thickness was mildly associated with severe preeclampsia.

The finding of unexplained elevated maternal serum alpha-fetoprotein (AFP) levels seems to be associated to a certain degree with the occurrence of placental lakes.2, 36 It is believed that the high maternal serum AFP-levels are a consequence of the disruption of the normal placental barrier due to vascular damage, therefore indicating a breakdown of the maternal barrier. According to those studies, pregnancies with higher maternal AFP-levels and an abnormal placental sonographic appearance may be indicative of subsequent perinatal complications such as suboptimal intrauterine growth or preterm delivery. 
 

Diagnosis

The diagnosis of placental lakes and placental lacunae should initially be performed on a routine 2-D grey-scale ultrasound image. Ultrasound findings usually comprise an anechoic or hypoechoic space surrounded by echogenic placental tissue or subchorionic location. It is possible to visualize swirling vascular flow with real-time colour Doppler assessment by reducing the Pulse repetition frequency (PRF) and increasing the colour gain of the scanner.2, 7, 8 The optimal time for initial detection of placental lakes based on the herein reviewed literature and the authors’ experiences appears to be the 2nd trimester scan, optimally performed at 18-22 weeks of gestation.7, 8, 16 Intraplacental lakes (hematomas) and larger subchorionic hematomas (lakes) can be diagnosed sonographically as typically hypoechoic spaces with almost no sign of blood flow, located in the intervillous cavity of the placenta.8, 9, 32 The application of 2D colour-Doppler is an important tool in distinguishing placental lacunae typical for AIP from other placental lakes (intraplacental or subchorionic hematomas) based on the flow characteristics.11, 12 Hypoechoic areas, especially thiose at the outer parts of the placenta (suspicion of retroplacental location) or close to the cervical inner os, should be reviewed in terms of potentially exposed vessels (e.g. vasa previa.)8, 37 

Closer evaluation of the lesions on 2D colour Doppler is essential for diagnosis of a possible abnormal high vascularity and the venous flow characteristics.38, 12 Differences between placental lacunae and placental lakes are not completely clear but relate to number, shape, location and the velocity of blood flow inside the sonolucent space.12 The presence of so-called placental lacunae feeder vessels - vessels with high-velocity blood flow leading from myometrium into placental lacunae causing turbulence upon entry seen on colour Doppler examination39, 40 should prompt further investigation regarding AIP. In contrast, placental lakes usually present with a low velocity venous-type swirling flow.1 From our clinical experience sometimes the SMI-Doppler mode (Superb Micro-Vascular Ultrasound Imaging) may be used to better visualise low velocity flows in these lesions (available in the latest ultrasound machines.) The concomitant presence of subplacental hypervascularity as sign of AIP has to be ruled out. Hypervascularity is defined as a striking amount of colour Doppler signal seen in the placental bed indicating numerous contorted vessels with multidirectional flow and aliasing.11

More recently, the use of fetal MRI has been introduced into the clinical work-up of patients with suspicion of several conditions associated with the presence of placental lakes or placental lacunae, especially in conjunction with AIP in posterior placentas.40 Fetal MRI seems to have a certain value in the evaluation of placental vascular pathologies such as hemorrhages or ischemic lesions in the placenta with correlation to histopathologic results.41 It might serve as a second line imaging technique for more precise antenatal information of the fetus and the placental structure in selected high-risk pregnancies with T2-weighted images identifying most pathological changes (such as placental infarction, retroplacental hematoma and intervillous thrombi/hemorrhages.) There is evidence that vascular lesions with clinical relevance in terms of IUGR or intrauterine fetal demise are detected by MRI earlier than by umbilical artery doppler changes (villous occlusive disease before the detection threshold of umbilical artery doppler.)41, 42
 

Differential diagnosis

It essential to differentiate between placental lakes and other hypoechoic intraplacental/placental lesions for correct further management. The following placental lesions have to be distinguished from placental lakes/placental lacunae:

  • Placental infarction
  • Placental cyst
  • Retroplacental hematoma/chronic abruption
  • Jelly like placenta

Table 1. Differentiation of other placental lesions from placental lakes (intraplacental/subchorionic lesions).

 

Placental Lesion

 

 

Placental infarction

 

 

Placental cyst

 

Jelly like placenta

 

Retroplacental

hematoma  - chronic abruption

 

 

 

Definition

Intraplacental area of ischemic villous necrosis,

Result of occlusion or reduced fetal flow through spiral arteries in the placental floor, collapse of the intervillous space and degeneration of villous tissue; villi with intermittent fibrin/red blood cell deposits between them9

 

 

Cytotrophoblastic cysts isolated from the placental circulation2

Enlarged placenta with patchy hypo-echogenicity, moving like “jelly” in answer to a lateral push on the maternal abdominal wall2

Hypoechoic area between the basal plate & myometrium, lifting the placental parenchyma toward the amniotic cavity, consisting largely of uterine veins9,16

 

 

 

Location

 

Occlusion/underperfusion of maternal blood flow to the uterine spiral ateries

hyperechogenic halo surrounding the lesion representing fibrin deposits9

 

Septal cysts: within the placental tissue

Subchorionic cysts: on the fetal surface beneath the chorionic vessels

 

Intraplacental,

spread across the whole placental area

 

Located between the basal plate and the decidua of the myometrium

 

Prevalence

Small infarcts - 25% of pregnancies

Large and/or multiple infarcts in late onset preeclamptic pregnancies 2

 

 

20% of placentas at term

 

 

 

0.6 – 7.6 %7, 5

 

 

Large variation of detection rates

Sonographic appearance

Intraplacental, areas hypoechoic with an echogenic halo surrounding the lesion,

then hyperdense due to fibrin deposition

Single, round or oval cavity (gelatinous material), sonolucent areas showing no blood flow on real-time imaging

Patchy hypo-echogenicity throughout the placental tissue

Enhanced placental thickness (above the 95th centile - > 3 -3.5cm)

Acute haemorrhage: hypoechoic to placental tissue, resolving hematomas: mostly inhomogeneous hyper- and hypoechoic

 

Clinical impact

Association with preeclampsia, placental insufficiency, IUGR, coagulopathy, neurological impairment3, 10, 43

No relevant clinical impact, if found in chorion may be indicative of inflammation/infection

 

Adverse pregnancy outcome such as hypertensive disorders, IUGR, placental abruption, genetic syndromes44

Preterm vaginal bleeding, preterm delivery,

IUFD (intrauterine fetal demise)8, 9

 

For other placental abnormalities to be considered as differential diagnosis such as placental chorangiomas and related conditions, please see the VISUOG chapter “placental angiomas.”

Implications for sonographic diagnosis

The finding of single subchorionic lakes  between two cotyledons or at the placental margin larger than 2cm in diameter corresponds to a non-pathologic variant of normal placental anatomy and is not associated with an increase in perinatal complications.5, 45, 3 Appearance on scan of a thick placenta seems to be mildly associated with the occurrence of placental lakes.7 Placental thickness has been described using different cut-offs, with 4cm maximumused at any gestational age and 3.5 cm between the 18th and 24th weeks.46 A cut-off of 3cm corresponds to the 95th centile at 18-20 weeks.5 As this is the time point at which placental lakes – if at all – display some impact on/correlate to some extent with obstetric outcome, this cut-off for placental thickness is a reasonable choice. In general, the clinical significance seems to depend on time of appearance, and number and size of placental lakes, so these need to be assessed. It is supposed that relevant lesions which may impact obstetric adverse outcome will be present before 20-25 weeks of gestation.16 Further, they should be numerous (> 2 placental lakes) or of a certain size (> 2cm in largest diameter.)16,5 Earlier definitions referred to a minimum size of 1cm - 1.5 cm.46, 47 Placental lakes of a largest diameter > 5cm are considered to be large placental lakes.4, 8 

Placental lakes seem to be more common in later pregnancy (after 25 weeks of gestation), and their appearance earlier in pregnancy (between 20-23 weeks of gestation) may be warning sign for fetal adverse outcome.3,7 After confirming the presence of such placental lakes or placental lacunae, they should be classified into four grades from Grade 0 to Grade 3 according to Finberg`s criteria.48 Intraplacental lakes/lacunaeare graded as:

  • Grade 0 – no placental lesion seen.
  • Grade 1+ when one to three generally small lacunae were present (at least one within the placental parenchyma.)
  • Grade 2+ when four to six larger or more irregular lacunae were present.
  • Grade 3+ when there were many placental lesions throughout the placenta, some appearing large and irregular in shape.48

There is a strong tendency for placental lesions to be numerous, larger and more irregular in their appearance when they are present in conjunction with AIP.48 Therefore, the finding of multiple, prominent and irregular shaped lacunae (Finberg Grade 3, slightly lesser extend Finberg Grade 2) is highly suggestive of AIP, especially placenta percreta and increta (sensitivity 100% and specificity 97.2%, positive predictive value 93.8%.)38,12 Additional evaluation using 2D colour Doppler should be performed for closer evaluation of the present placental lake, so that appropropriate follow-up and management can be decided  according to the suspected associated clinical condition (see Diagnosis.) 
 

Implications for sonographic screening

So far, there exist no general recommendations for a special screening protocol for placental lakes. The routine 2nd trimester fetal anomaly scan (between 18 and 22 weeks of gestation) seems to serve as a good time point to look specifically for any abnormal placental findings as this investigation is routinely done in a large proportion of pregnancies. Furthermore, in cases of vaginal bleeding or other symptoms suspicious of threatened miscarriage earlier in pregnancy, an ultrasound is recommended, and presence of placental lakes should be documented. 
The presence of large, numerous and irregular placental lacunae at any gestational age must be considered a strong indicator for the presence of AIP.11, 12 
Careful examination for placental lacunae in patients with a history of one or more caesarean sections and/or a present low-lying placenta or placenta previa is of high importance to detect a presence of abnormal invasive placenta. At the routine 2nd trimester anomaly scan women with these risk factors should be carefully examined for placental lacunae and if present this should prompt further investigation at a specialized center.
 

Prognosis

Over the course of pregnancy there might be slight dynamic changes in the presence and appearance of placental lakes.4, 8, 12 Some placental lakes might decrease in size over pregnancy; however large placental lakes (> 5cm) persist until the 3rd trimester, with their appearances becoming increasingly inhomogeneous.8 Overall, placental lakes (and placental lacunae) seem to become more prominent from the 1st trimester onwards with the establishment of the intervillous circulation, and may change in shape and size.12, 22 

Where placental lakes are present, pregnancy outcome depends mainly on the examined risk  and the (underlying or) associated clinical condition. In general, placental lakes which are not numerous or  conspicuously irregular in appearance (i.e. irregular in shape, numerous and/or medium-sized – greatest diameter > 2cm and under < 5cm) found in an unselected patient group (routine ultrasound evaluation around the time of the 2nd trimester anomaly scan), do not seem to be associated with uteroplacental complications or adverse outcomes i.e. placental abruption,  IUGR with birth weight below the 5th or 10th percentile, the development of hypertensive pregnancy disorders or pre-eclampsia.7, 13

Placental lakes can be found  in only 2.2% of low risk pregnancies without additional maternal or fetal disease.13 The finding of placental lakes is six times more likely in thick placentas7 with only a mild increased risk for preterm preeclampsia (Odds Ratio 3.46) in patients with thick placentas as compared to controls.  Nevertheless, there seems to be a difference in the obstetrical outcome according to the size and number of intraplacental lakes.16, 4, 47, 8 Placental lakes with a diameter of less than 1cm do not seem to indicate an adverse obstetric outcome.15, 47 In pregnancies with large placental lakes (longest linear diameter 5cm or more) the risk for fetal growth restriction (IUGR) and NICU-admissions seems to be increased with a mean birthweight of fetuses of 2.69-2.75 mean kilograms in cases with placental lakes versus 3.19-3.24 in cases with disappearing or smaller placental lakes.4 

Regarding the time of detection of placental lakes in relation to their prognostic value, smaller subchorionic lesions detected in the first trimester do not seem to carry a higher obstetrical risk. Subchorionic placental lakes/hematomas detected in the second trimester tend to be larger and carry a risk of preterm delivery.32  In one retrospective study, intraplacental lakes detected in the 2nd trimester seem to be associated with significantly higher rates of placental insufficiency (31% versus 0.9% in controls), IUGR (27% versus 8.8% in controls) preterm labour (27.6% versus 5.3%) and early preterm delivery 31.3% versus 2.7%.)8 These findings are in accordance with previous data concerning IUGR (21, 2) and preterm delivery.36 Moreover, intraplacental lakes were also described as independent risk factors for the development of placental insufficiency and IUGR.8 This is possibly due to an overall reduction of the feto-maternal exchange area.  Placental lakes detected in the second-trimester further indicate a risk for 2nd trimester miscarriage with an incidence of 9.4%8 and threatened 1st trimester miscarriage.26 There is an increased risk for vaginal bleeding in the 1sr trimester4 and vaginal bleeding at least once during the course of pregnancy of 31.3%.It is important to note that it might not be the size of the placental lesion but rather the overall extent of placental mass involved in the lesions which is primarly important to their clinical relevance. Data concerning the clinical relevance of placental lakes reflects the need for a distinct categorization of placental lesions; possibly more precisely considering time of appearance, size of the lesions and exact location.7, 6, 8 Nevertheless, there is data that in some pregnancies the presence of placental lakes is associated with a poor pregnancy outcome, which has to be considered in clinical management. 

The prognostic and clinical value of placental lesions is completely different in the preselected patient group with a placenta previa/low-lying placenta and a history of cesarean delivery, based on several studies.38, 11, 29, 12 In these cases, the presence of placental lacunae (Finberg Grade 2+ and especially Grade 3+) is strongly correlated with the clinical outcome of those patients and can be used to predict obstetric complications. More serious variants of AIP (a major cause of severe obstetric bleeding) are seen in patients with Grade 2+ and Grade 3+ placental lacunae.38 During the second and third trimesters the finding of intraplacental lacunae is the most reliable predictor for an AIP with 93% sensitivity and 93% positive predictive value for this diagnosis.49, 50 They are even very useful in the early diagnosis of AIP between 15-20 weeks of gestation with a sensitivity of 79% and a positive predictive value of 92%.50 The presence of intraplacental lacunae is significantly associated with a higher rate of obstetrical complications such as need for massive transfusion (88.5 %), admission to intensive care unit (46.2%) and Cesarean hysterectomy (69.2 %.)38

Management

2D grey-scale ultrasound is the established technique for initial placental evaluation and screening for any abnormalities. If a placental lake/multiple placental lakes are detected at a routine fetal ultrasound examination without other pathologic conditions, there are no current specific recommendations on how frequently and if at all they should be followed-up. 
Performing a thorough growth scan and measuring the uterine and umbilical artery Doppler indices seems to be reasonable in order to check for signs suggestive of the further risk based on the reviewed data. The uterine artery PI or the presence of an end systolic/early diastolic notch suggests a probability for the development of  early onset preeclampsia and/or for development of IUGR. The umbilical artery Doppler with an abnormal pulsatility index (PI) and/or end-diastolic absent or reversed flow and signs of brain sparing in middle cerebral artery (MCA) would suggest fetal compromise. 

Although there is little data, detection of a large placental lake (> 5cm) in the second trimester scan seems to warrant the consideration of a growth scan in the early 3rd trimester4 in order to detect growth restricted fetuses with further regular monitoring. In patients with intraplacental lakes (> 2cm, more than 2 lakes present) diagnosed in the 2nd trimester, a growth scan in the early 3rd trimester assessing possible clinical effects is recommended.16, 8 In the larger studies on placental lakes4,13 regular follow-ups every 4 weeks until delivery (or more often depending on the initial findings – 8) were carried out for optimal fetal surveillance. 

In conclusion, the authors recommend, once placental lakes have been diagnosed, to schedule the patient for a growth scan and Doppler sonography (uterine arteries, umbilical artery and MCA) follow-up 2-4 weeks after the initial the scan. Further monitoring and management needs to be carried out based on the recommendations for the underlying/associated conditions and the appearance, size and development of the placental lesions. A clear differentiation of placental lakes from other placental lucencies such as placental infarction and placental abruption is essential for proper management bearing in mind the different associated clinical risks.Table 1, 7 

Presumptive sonographic diagnosis of one of the associated special clinical conditions outlined in the above sections should prompt appropriate and detailed patient counselling and the assignment of the patient to the proper follow-up. In cases of placental lacunae in patients with placenta previa, low-lying placenta after previous caesarean section or uterine surgery and suspicion of AIP, timely referral to a specialized center is essential in establishing optimal antenatal and perinatal management. 

The optimal mode of delivery in case of placental lakes should be determined based on the local standard obstetric care program in place, on the basis of the generally good prognosis.7, 4 Rarely, cases have been described in which a cesarean delivery was performed due to the presence of large placental lakes and the concern they woyld rupture during spontaneous delivery with massive bleeding after placental separation.6 The mode of delivery will mostly depend upon the associated clinical condition. The final decision on the delivery mode should remain with the managing center and take into consideration the clinical situation/associated conditions in accordance with local treatment protocols and national/international guidelines. 

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This article should be cited as: Chalubinski, K., Pateisky, P.: Placental Lakes, Visual Encyclopedia of Ultrasound in Obstetrics and Gynecology, www.isuog.org, February 2019.


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