It is essential to confirm the presence of trophoblastic tissue as rapidly as possible so that therapy may be instituted. After tissue is obtained by curettage, it can be added to saline, in which it will ﬂoat (Fig. 20.4). Decidual tissue does not ﬂoat. Chorionic villi are usually identified by their characteristic lacy frond appearance. The sensitivity and specificity of this technique are 95% when the tissue is examined with the aid of a dissecting microscope. Because ﬂotation of curettage sample tissue is not 100% accurate in differentiating an intrauterine from extrauterine gestation, histologic confirmation or serial β-hCG level measurement is required. The presence of chorionic villi may be assessed rapidly with frozen section analysis, which avoids the waiting period of at least 48 hours for permanent histologic evaluation. Immunocytochemical staining techniques are used to identify intermediate trophoblasts that are not normally identified by light microscopy (169).
When frozen section analysis is not available, serial assessment of hCG levels permits rapid diagnosis. After evacuation of an abnormal intrauterine pregnancy, the hCG level decreases by greater than 15% within 12 to 24 hours. A borderline fall may represent interassay variability. A repeat level should be obtained in 24 to 48 hours to confirm the decline. If the uterus is evacuated and the pregnancy is extrauterine, the hCG level will plateau or continue to increase, indicating the presence of extrauterine trophoblastic tissue.
Figure 20.4 When ﬂoated in saline, chorionic villi are often readily distinguishable as lacy fronds of tissue. (From Stovall TG, Ling FW. Extrauterine pregnancy: clinical diagnosis and management. New York: McGraw-Hill, 1993:186, with permission.)
Culdocentesis Culdocentesis was used widely as a diagnostic technique for ectopic pregnancy. With the use of hCG testing and transvaginal ultrasonography, culdocentesis is rarely indicated. The purpose of the procedure is to determine the presence of nonclotting blood, which increases the likelihood of ruptured ectopic pregnancy. After exposing the posterior vaginal fornix with a bivalve vaginal speculum, the posterior lip of the cervix is grasped with a tenaculum. The cul-de-sac is entered through the posterior vaginal wall with an 18-to 20-gauge spinal needle with a syringe attached. As the cul-de-sac is entered, suction is applied, and the intraperitoneal contents are aspirated. If nonclotting blood is obtained, the results are positive. If serous ﬂuid is present, results are negative. A lack of ﬂuid return or clotted blood is nondiagnostic.
Historically, if the culdocentesis results were positive, laparotomy was performed for a presumed diagnosis of ruptured tubal pregnancy. The results of culdocentesis do not always correlate with the status of the pregnancy. Although about 70% to 90% of patients with ectopic pregnancy have a hemoperitoneum demonstrated by culdocentesis, only 50% of patients have a ruptured tube (170). About 6% of women with positive culdocentesis results do not have an ectopic gestation at the time of laparotomy. Nondiagnostic taps occur in 10% to 20% of patients with ectopic pregnancy and are not definitive of the diagnosis. A study concludes that culdocentesis is an obsolete tool in the diagnosis of suspected ectopic pregnancy (171).