Central nervous system in twin reversed arterial perfusion sequence with special reference to examination of the brain in acardius anceps

The twin-reversed arterial perfusion (TRAP) sequence, or acardia, is the mo st severe complication in monozygotic twinning. Although more than 400 case s with TRAP sequence were reported since 1533, thorough investigations of t he brain in those cases with a rudimentary head remained infrequent. We rep ort a TRAP sequence with microcephaly and a severely rudimentary brain anla ge. Neuropathologic examination clearly demonstrated two types of change: ( 1) developmental arrest of brain at the prosencephalic stage (holoprosencep haly), and (2) hypoxic damage to the holospheric brain mantle with cystic c hange (hydranencephaly). With reference to previous studies in experimental animals showing that lack of oxygen during early embryogenesis can induce severe disruptions of head-brain and heart formation, it is concluded that oxygen deficiency due to TRAP may be responsible not only for the encephalo clastic changes in the acardius anceps, but for the developmental arrest of the brain cases as well. This would make it unnecessary to postulate addit ional primary causes such as asymmetric zygote cleavage (Schwalbe, '07) for the maldevelopment. (C) 2000 Wiley-Liss, Inc.