LAUSR

We read ‘Extravasating uterine pseudoaneurysm: A rare cause of postpartum haemorrhage’ by Yi (2017) with great interest. The uterine artery is usually a parent artery of uterine pseudoaneurysm, and, thus, this disorder is referred to as uterine artery pseudoaneurysm (UAP), which will be used here. Traditionally, UAP was considered to occur after ‘traumatic exogenous preceding events’ (such as caesarean section or dilatation & evacuation), which injure the uterine artery wall, leading to UAP occurrence. Yi proposed a novel concept regarding UAP occurrence: ‘it (UAP) is thought to arise from abnormal vascular regression and a recurrent vascular healing state, vascular stricture and relaxation with thrombin deposits after placenta expulsion’. Yi et al. previously reported three patients with ‘fundal’ UAP, where ‘trauma’ is less likely to occur. Solely based on these cases, Yi sates: ‘the placenta plays a definitive role’ and ‘a vascular wall lesion may have developed due to disruption of the arterial wall by the placenta rather than as a result of trauma’. These statements can be interpreted as: placenta (possibly its separation) disrupted the arterial wall and arteries abnormally regressed. In short, placenta-associated regression abnormalities of the placental-site-arteries without traumatic exogenous preceding events may account for some UAP formation. The previous belief that UAP occurs after traumatic exogenous preceding events is no longer held. Our study on 50 consecutive UAP cases revealed that 40% occurred after ‘uneventful’ delivery/miscarriage (Baba et al. 2016). Our previous studies attempted to associate rapid-delivery-related shear forces (Matsubara and Baba 2015) or some underlying vascular disorders (Matsubara et al. 2014a) with the occurrence of some UAP without evident preceding events; however, they did not explain, or only partly explained, the mechanism. Septic-abortion-related UAP may represent a specific category of ‘UAP without preceding events’: the arterial wall at the site may be eroded from the outside, with UAP eventually occurring (Matsubara et al. 2014b). However, this may explain the UAP mechanism of very rare types, not accounting for the mechanism of UAP in general. Thus, the mechanism of ‘less/no trauma-related UAP’ has yet to be determined. Yi’s concept/theory is attractive, suggesting that circumstances surrounding the placenta or arterial mal-regression may cause UAP; however, this concept is not based on evidence. UAP is referred to as a ‘chameleon of obstetric practice’: markedly changing its clinical features (colours) in a patient-by-patient manner (Matsubara 2011). Behind this clinical heterogeneity, aetiological heterogeneity may be hidden, necessitating further studies.