PubMed · 5718696
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J S McLaughlin, C Suddhimondala, K F Mech, R L Llacer, J Houston, S M Attar, R A Cowley. 1968. Pulmonary function in human shock.. https://pubmed.ncbi.nlm.nih.gov/5718696/
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Although placental vascular anastomoses between the fetoplacental circulations are ubiquitous in monochorionic twin pregnancies, the factors regulating their formation and maintenance are not understood. Increasing evidence implicates asymmetric anastomotic patterns in the aetiology of severe twin-to-twin transfusion syndrome (TTTS). The authors propose that anastomoses between placental circulations in monochorionic twins occur in a random manner at the embryological stage of connection of embryonic and extra-embryonic circulations. Placental expansion is then associated with random disruption of anastomoses and regression of their associated villus districts. TTTS develops as discordant loss of anastomoses results in asymmetrical flow resistance. Pregnancies with fetal growth concordance but discordant nuchal translucency at 10-14 weeks are at increased risk of developing subsequent severe TTTS because these clinical features indicate significant pressure differentials in the presence of a placentoplacental circulation, consistent with the presence of numerous, asymmetric anastomoses. However, since the anastomotic pattern is dynamic in the first half of pregnancy this hypothesis predicts that it will not be possible to devise a clinical test at 12 weeks that will predict with certainty the outcome of monochorionic twin pregnancies in relation to TTTS because this depends on random subsequent events.
In 1985, the International Study of Extracranial-to-Intracranial Arterial Anastomosis demonstrated no benefit from extracranial-to-intracranial arterial bypass operations in treatment of patients with extensive cerebrovascular disease including those with occlusions of the internal carotid artery. Interest in the potential use of extracranial-to-intracranial arterial bypass operations, however, has been rekindled by evidence that some patients with occlusion of the internal carotid artery have a poor collateral circulation and a high risk for recurrent ischemic events. Other patients with adequate perfusion after occlusion have a low likelihood for recurrent stroke. Restricting surgical treatment to only those patients judged to have a high risk for recurrent stroke might improve the usefulness of the bypass operation. A new clinical trial is proposed, testing the potential usefulness of extracranial-to-intracranial arterial bypass operations for treatment of carefully selected patients with occlusion of the internal carotid artery. Several issues that are being addressed in this new trial are described in this article.
OBJECTIVE: We sought to correlate placental vasculature with fetal growth and outcome in monochorionic twins. STUDY DESIGN: Eighty-two patients with consecutive monochorionic pregnancies underwent biweekly ultrasonography for determination of fetal growth and well-being. After delivery, blinded placental injection studies delineated vascular anastomoses and territory share. Degree of balance in arteriovenous anastomoses equaled the number of arteriovenous anastomoses in one direction minus the number in the other. RESULTS: Pregnancies affected by fetofetal transfusion syndrome (n = 21) had numbers of arteriovenous and venovenous anastomoses that were similar to those in pregnancies without fetofetal transfusion syndrome but fewer arterioarterial anastomoses (P <.0001). Fetofetal transfusion syndrome occurred in 78% of pregnancies with >/=1 arteriovenous and no arterioarterial anastomoses. Birth weight discordancy correlated with placental territory discordancy (P <.0001) and the degree of balance in arteriovenous anastomoses (P =.004). The larger placental share twin had a greater growth velocity than its smaller placental share co-twin (P =.008) for all but one anastomotic pattern. Where arteriovenous anastomoses were aligned with the net venous outflow to the fetus with the smaller territory, co-twins had similar birth weights and growth velocities irrespective of placental share. Fetal survival was higher in pregnancies with an arterioarterial anastomosis (P =.01) but lower with a venovenous anastomosis (P =. 01). Survival of both fetuses was inversely associated with birth weight discordancy (P <.0001). CONCLUSION: Although interrelationships among the various types of anastomoses are complex, our data suggest that the placental territory share and the pattern of arteriovenous anastomoses influence fetal growth, that arterioarterial anastomoses protect against fetofetal transfusion syndrome, and that venovenous anastomoses reduce perinatal survival.