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Chorionic hematoma (also chorionic hemorrhage) is the pooling of blood (hematoma) between the chorion, a membrane surrounding the embryo, and the uterine wall.〔Nagy, Sándor MD; Bush, Melissa MD; Stone, Joanne MD; Lapinski, Robert H. PhD; Gardó, Sándor MD, DSci. ''Clinical Significance of Subchorionic and Retroplacental Hematomas Detected in the First Trimester of Pregnancy'' (). Obstetrics & Gynecology: July 2003 - Volume 102 - Issue 1 - p 94-100〕 With an incidence of 3.1% of all pregnancies,〔 it is the most common sonographic abnormality and the most common cause of first trimester bleeding.〔Avneesh Chhabra, MD et al. "Subchorionic Hemorrhage" (), Medscape.〕 ==Cause and diagnosis== Chorionic hematomas can be caused by the separation of the chorion from the endometrium (inner membrane of the uterus). Hematomas are classified by their location between tissue layers:〔Trop, Isabelle and Levine, Deborah. ''Hemorrhage During Pregnancy: Sonography and MR Imaging'' (). Amer J Roentgenology 2001; 176:607-615.〕 * Subchorionic hematomas, the most common type, are between the chorion and endometrium. * Retroplacental hematomas are entirely behind the placenta and not touching the gestational sac. * Subamniotic or preplacental hematomas are contained within amnion and chorion. Rare. Most patients with a small subchorionic hematoma are asymptomatic.〔Trop I, Levine D. ''Hemorrhage during pregnancy: sonography and MR imaging.'' AJR Am J Roentgenol. Mar 2001;176(3):607-15.〕 Symptoms include vaginal bleeding, abdominal pain, premature labor and threatened abortion.〔Hodgson DT, Lotfipour S, Fox JC. ''Vaginal bleeding before 20 weeks gestation due to placental abruption leading to disseminated intravascular coagulation and fetal loss after appearing to satisfy criteria for routine threatened abortion: a case report and brief review of the literature.'' J Emerg Med. May 2007;32(4):387-92〕 Ultrasonography is the preferred method of diagnosis.〔Abu-Yousef MM, Bleicher JJ, Williamson RA, Weiner CP. ''Subchorionic hemorrhage: sonographic diagnosis and clinical significance.'' AJR Am J Roentgenol. Oct 1987;149(4):737-40.〕 A chorionic hematoma appears on ultrasound as a hypoechoic crescent adjacent to the gestational sac. The hematoma is considered small if it is under 20% of the size of the sac and large if it is over 50%.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chorionic hematoma」の詳細全文を読む スポンサード リンク
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