Role of Imaging Modalities in Obstetric Emergencies

FIGURE 16.1 Endovaginal image of an early intrauterine pregnancy demonstrating gestational sac.

FIGURE 16.2 Endovaginal image of an intrauterine gestational sac with a yolk sac visualized within it.

suggest that the cutoff should be lowered to 3mm (12). Correlation of serum levels and endovaginal ultrasound findings are key when patients are being evaluated for pain or bleeding (13). It is important to keep in mind that these parameters depend largely on the operator’s experience and the instrumenta­tion used.

VAGINAL bleeding in pregnancy

Vaginal bleeding occurs in about 20% to 30% of all confirmed pregnancies in the first 20 weeks; about 50% of these end in spontaneous abortions (14). Disorders that commonly cause abnormal bleeding include ectopic (ruptured/unruptured) pregnancy, spontaneous abortion (to include complete, missed, inevitable, incomplete, blighted ovum, and threatened abortion), gestational trophoblastic disease, placenta previa/vasa previa, and placental abruption. Readers may also wish to consult Chapter 8.

First Trimester Bleeding

Implantation bleeding: This term refers to a transient spotting associated with the normal implantation of the embryo into the uterine wall. Bleeding is usually minimal and is no cause for concern.

Threatenedmiscarriage/abortion: This diagnosis refers to early pregnan­cies complicated by bleeding and/or cramping, while with endovaginal ultra­sound, the fetal pole is visualized and fetal cardiac activity is present (Fig. 16.3). Contributing factors may include abnormal karyotype, infection, dehydration,

FIGURE 16.3 Endovaginal image of a first trimester fetus. Measurement of the crown-rump length (CRL; calipers).

FIGURE 16.4 Endovaginal image of a retroplacental hematoma (the hypoechoic region measured).

physical trauma, or use of drugs or medications. In many cases of threatened miscarriage, no contributing factors are identified. Occasionally, a retroplacen­tal hematoma is seen (Fig. 16.4), and 25% of these pregnancies will miscarry, while without a hematoma, the risk of loss is 7% (15).

Spontaneous (Complete)Abortion', This term refers to heavy bleeding and cramping (in women with previously documented intrauterine pregnancy), and endovaginal ultrasound shows an empty endometrial cavity.

Incomplete Abortion: Partial expulsion of products of conception from the uterus with some retained products, usually clots and placental tissue. Sometimes the cervix appears to be open when inspected by speculum exami­nation. Ultrasound may reveal the presence of tissue within the endometrial cav it y.

Blighted ovum (anembryonic): This terminology refers to pregnancies in the embryo that have failed to develop appropriately. The discriminatory crite­rion for anembryonic pregnancy by endovaginal ultrasound is a mean gesta­tional sac diameter (MGSD) of >10mm without a yolk sac or a MGSD >18mm without a fetal pole. By transabdominal ultrasound, MGSD cutoffs of 20 mm without a yolk sac and 25 mm without embryo fetal pole are used (13).

Ectopic pregnancy: An ectopic pregnancy occurs when a fertilized ovum implants at a site other than the endometrial lining of the uterus. Diagnosis is often made by a pelvic examination and a combination of serum BhCG and endovaginal ultrasound. The sonographic identification of an intrauterine gestational sac with yolk sac essentially excludes an ectopic pregnancy. An intrauterine pregnancy should always be visualized at a BhCG level of 2,000 IU/L by endovaginal ultrasound and at a 6,500 IU/L by transabdominal ultrasound. An adnexal mass, in a patient with a BhCG level the cervical length (CL) is obtained by measuring the endocervical canal from the internal cervical os to the external os (Fig. 16.8). Endovaginal approach is a more accurate method since it does not have the distortion associated with the transabdominal approach. Because of the dynamic nature of the cervical canal and lower uterine segment throughout pregnancy, the normal length of a competent cer­vix falls within a wide range (0.5 to 5 cm) (17). Consequently, the sonographic assess­ment of the cervix requires attention to the temporal changes of the CL during every examination. Furthermore, the Valsalva maneuver or manual compression of the uterine fundus may corroborate the sonographic diagnosis of cervical incompe­tence. The sonographic determination of the residual closed length of the cervix may be used as a prognostic indicator of the risk of preterm labor progressing into pre­term delivery. A cervical cerclage is a surgical procedure performed before 24 weeks that presents an option for women with cervical incompetence (18).

Placenta previa: This term refers to implantation of the placenta over or near the internal cervical os. It can be termed complete, partial, marginal or low- lying depending on its location relative to the internal os. Bleeding is usually bright red and painless.

FIGURE 16.7 Endovaginal ultrasound image of an incompetent cervix. Funneling indicates that the internal cervical os is dilated, allowing the amniotic sac to enter into the endocervical canal. Residual CL is measured with calipers.

FIGURE 16.8 Sagittal view of the maternal cervix with endovaginal ultrasound showing a normal endocervical canal. CL is measured from the internal os to the external os (calipers).

lower uterine segment, even at full term; therefore, it is used to improve the accuracy of diagnosis of placenta previa (Fig. 16.9).

Vasa Previa: This term refers to an obstetric complication when fetal vessels traverse the fetal membranes over the internal cervical os. These vessels may be from either a velamentous insertion of the umbilical cord or may be joining an accessory placental lobe (succenturiate) to the main lobe of the placenta. If these fetal vessels rupture, the bleeding is from the fetoplacental circulation, and fetal exsanguination will rapidly occur, leading to fetal death. Vasa previa must be ruled out in all cases of bilobed, succenturiate, and low-lying placentas; pregnancies resulting from in vitro fertilization; and multiple pregnancies. Endovaginal ultra­sound in combination with color Doppler is the most effective tool in antenatal diagnosis of vasa previa (20).

Placental abruption: Abruption describes the condition which occurs when the placenta separates from the wall of the uterus prematurely and blood collects in that space between the two. On ultrasound examination, one may see a fluid collection of varying echogenicity based on the age of the hemorrhage with or without a connection to the placenta.

Uterine Rupture: Uterine rupture may be associated with acute, potentially catastrophic complication which may result in maternal and perinatal mortal­ity. It is defined as a full-thickness separation of the uterine wall and the overlying serosa. Uterine rupture is associated with clinically significant uterine bleeding; fetal distress; expulsion or protrusion of the fetus, placenta, or both into the abdominal cavity; and the need for prompt surgical intervention for delivery, uterine repair, or hysterectomy. Prior cesarean delivery is the most common risk factor. With complete wall disruption, protrusion of the amniotic sac beyond the uterus may be seen, as well as intraperitoneal or extraperitoneal hemorrhage.

FIGURE 16.9 Endovaginal image of the uterine cervix demonstrating a complete placenta previa (the placenta completely covers the internal os).

TRAUMA IN PREGNANCY

Trauma and accidental injuries complicate 6% to 7% of all pregnancies (21) and are usually due to motor vehicle accidents, domestic abuse or assaults, and falls. Once fetal heart tones are confirmed, two patients exist and both require assessment and treatment. The anatomic and the physiologic changes of pregnancy make the trauma assessment more difficult. Readers may also wish to consult Chapter 4.

The cardinal principle in the management of trauma in pregnancy is that there can be no fetal survival without maternal survival, with the rare exception of the gravely injured mother late in pregnancy where urgent cesarean delivery may allow for fetal survival. With pregnancy, there is an increased risk of internal hem­orrhage, and identification of bleeding is more difficult. Common adverse conse­quences to abdominal trauma in pregnancy include uterine contractions, preterm labor or delivery, and placental abruption. In many cases, external fetal monitor­ing and ultrasound may be adequate for assessment of the placenta, uterus, and fetal well-being. Obstetric and emergency department clinicians should recognize that even minor trauma in the pregnant woman can cause fetal demise (22).

From an imaging perspective, ultrasound is an excellent tool for initial evaluation of the trauma pregnant patient, but CT is the preferred modality when clinical or ultrasound findings suggest visceral injuries unaccompanied by intraperitoneal hemorrhage or injuries of the bones, chest, mediastinum, aorta, spine, retroperitoneum, bladder, and bowel. MRI is not a practical option for rapid evaluation of all these body parts in an unstable patient after trauma. Placental abruption typically appears on CT as a single avascular area of varying size that extends from the placental base to the placental surface. High attenua­tion in the nonplacental portion of the uterus indicates contusion, tear, or par­tial uterine disruption. Loss of amniotic fluid into the maternal peritoneum or free fetal parts in the maternal abdomen may indicate uterine rupture. But it may be difficult to determine if free intraperitoneal fluid is amniotic fluid or hemorrhage from a maternal visceral injury. In general, ultrasound may be suf­ficient for the initial imaging evaluation of a pregnant patient who has sustained trauma, but CT should be performed if a serious injury is suspected.

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