Rounded intraplacental haematomas due to decidual vasculopathy have a distinctive morphology.

Within the placenta, most centrally placed intervillous thrombi are thought to form at sites of foetomaternal haemorrhage, while parabasally located intervillous thombi have been linked to maternal vascular disease. To determine whether parabasally located haemorrhagic lesions were morphologically heterogeneous, the authors performed a retrospective review of 25 placentas with thrombohaematomas occurring in the vicinity of the basal plate. Using morphological criteria, two lesions were distinguished: (1) the parabasally located intervillous thrombus, which had all the morphological features of more centrally located intervillous thrombi; and (2) the rounded intraplacental haematoma. Rounded intraplacental haematomas form as a result of disruption of vasculopathic decidual arterioles in a setting of maternal vascular underperfusion and are thus aetiologically distinct from classically described intervillous thrombi.