Invasive treatment modalities for severe chronic twin-to-twin transfusion syndrome (TTTS), such as fetoscopic laser coagulation of communicating vessels, have revived the need for detailed studies of placental angioarchitecture. We describe a practical placental vascular injection technique using alcohol-resistant tissue-staining dyes. Injection of color-coded gelatin-dye mixtures effectively delineated the intertwin vasculature, and allowed unequivocal macroscopic classification of vascular communications as artery-to-artery, vein-to-vein, or deep artery-to-vein anastomoses. The existence of deep artery-to-vein anastomoses was further confirmed by light microscopic demonstration of venous dye of one twin and arterial dye of the opposite twin within the same stem villus. Furthermore, the injection technique allowed determination of the caliber of the anastomoses, the direction of the artery-to-vein anastomoses, and the relative vascular territory of each twin. Documenting the vascular communications in monochorionic twin placentas with and without TTTS may enhance our understanding of the pathogenesis of chronic TTTS. Correlating the anastomotic patterns and location of the laser coagulation scars with post-ablation outcome will aid in the design of rational therapeutic methods for this often lethal condition.

The transverse cerebellar diameter (TCD) is well established in the ultrasound literature as a reliable parameter for estimating the duration of gestation. In cases of growth restriction the cerebellum is usually spared, making TCD a reliable indicator of gestational age even when other parameters fall off the appropriate growth curve. The purpose of this study is to establish normal values for the transverse diameter of the cerebellum in pathology specimens, and to determine if these values correlate with those obtained by ultrasound. We examined 96 specimens ranging from 14 to 42 weeks gestational age and found that our values correlate well with those published in the ultrasound literature. Mean TCD with 2 standard deviations for each gestational week were determined as reference values.