Although hemoperitoneum in the pouch of Douglas in a pregnant lady has a 93 positive predictive value for ectopic pregnancy other causes of hemoperitoneum include ruptured ovarian cysts or corpus luteum placenta accreta and spontaneous abortion must be borne in mind The corpus luteum of pregnancy may sometimes be confused with the gestational sac It is situated in the ovary unlike a tubal ectopic and typically has high T1 signal intensity in its wall whereas it is homogenously hypointense in an unruptured gestational sac It is not associated with acute haemorrhage and resolves spontaneously regressed by the end of the second trimester Post contrast fat suppressed images after an intrauterine pregnancy has been excluded can help better delineate the gestational sac when there is difficulty in identification of the sac within a tubal hematoma or hemoperitoneum these are usually well enhancing thick sac like structures the middle layer of the trilamellar sac enhances and clearly visualized even in the background of hematoma Tubal enhancement related to increased vascularity post implantation and enhancing papillary projections of placental tissue may be identified within the tube reported in 81 of the cases
Ruptured tubal ectopic pregnancy is a clinical and surgical emergency accounting for most first trimester maternal deaths Clinically patients present with acute pain abdomen heavy vaginal bleeding rebound tenderness dropping haematocrit and hypovolemic shock Ruptured ectopic pregnancies usually result in more laparotomies compared with laparoscopy and salpingectomy rather than a salpingostomy thus affecting future fertility Imaging findings are usually characteristic on TVUS alone with a heterogenous adnexal mass identified in the clinical setting of a positive pregnancy test Although large amounts of pelvic fluid with mobile internal echoes are suggestive these can also sometimes be seen in unruptured ectopics 70 or normal pregnancy 30 hence it is not very specific MRI should not be performed in hemodynamically unstable cases however a deformed sac like structure within an ill defined complex hematoma lateral to the uterus disruption of tubal wall enhancement and the presence of large amounts of T2 low signal are usually noted Unilateral twin tubal ectopic pregnancy with implantation of two blastocysts in a single tube is very rare with a reported incidence of 0 5 of ectopic pregnancies however it is worthwhile to be aware of this specially in women who have undergone assisted reproductive techniques in whom multiple embryo transfers have been performed SUMMARY OF MRI FEATURES OF CTOPIC PREGNANCY Absence of intrauternine pregnancy Hemoperitoneum Tubal mass Hematosalpinx
INTERSTITIAL PREGNANCY Interstitial pregnancy is one in which implantation of the blastocyst occurs in the intramural or interstitial segment of the Fallopian tube just as it takes off from the cornu or lateral angle It comprises 2 of all ectopic pregnancies with a mortality rate of 2 5 It may sometimes present as late as 16 weeks Prior tubal surgeries like ipsilateral salpingectomy uterine anomalies use of assisted reproductive technologies and pelvic inflammatory disease have been shown to increase the risk of interstitial ectopic pregnancy The interstitial segment of the tube is completely surrounded by myometrium and allows greater distensibilty of the sac with the result that rupture is late and complicated by more severe haemorrhage given the proximity to the uterine ovarian arteries and the intramyometrial arcuate vasculature and uterine perforation in some cases Maternal mortality is up to 15 times higher than non interstitial tubal ectopic pregnancy On ultrasound one may observe the interstitial line sign which is an echogenic line extending from the endometrium of the lateral angle of uterus coursing through the myometrium and up to the centre of the gestational sac
This is seen best in the transverse plane at the level of the fundus The echogenic lines represent the opposed tubal lining which is normally seen albeit with difficulty in the interstitial segment This is interrupted in and seen to end at in cases of interstitial gestational sac This sign however requires significant operator expertise and diagnosis may be missed or delayed on TVUS Another sonographic sign is the myometrial mantle sign which represents the myometrium surrounding the sac completely and the bulging sign which represents a focal outer contouring of the uterus seen in the sagittal or transverse plane caused by the eccentric gestational sac These signs may be subtle and heavily dependent on operator experience Three dimensional ultrasonography or experience with the same may not be available in all centres Thus MRI is of definite clinical utility in doubtful cases Studies have shown that the presence of an intact junctional zone between the gestational sac surrounded by myometrium and the uterine cavity enables distinguishing suggestive of interstitial pregnancy The thickness of the myometrium surrounding the ectopic sac is typically 5 mm Given the relatively late presentation a foetus may also be visualized within the sac The closest and most difficult differential diagnosis would be an angular pregnancy in which case the gestational sac implants in the lateral angle of the uterine cavity TVUS may falsely misdiagnose one for the other in which case MRI plays an important role The former is implanted medial to the uterotubal junction and not associated with myometrium or junctional zone medial to the sac A normal eccentric intrauterine pregnancy is surrounded by 5 mm of myometrium on all sides Angular pregnancy also typically demonstrates a wide angle of contact with uterine cavity
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