AJR 2005; 184:1600-1601
© American Roentgen Ray Society
Retroperitoneal Ectopic Pregnancy
Jung Whee Lee1,
Kyung Myung Sohn and
Hyun Seok Jung
1 All authors: Department of Radiology, Our Lady of Mercy Hospital, The Catholic
University of Korea, 665 Bupyeong-dong, Bupyeong-gu, Incheon 403-720, South
Korea.
Received April 23, 2004;
accepted after revision July 22, 2004.
Address correspondence to J. W. Lee.
Introduction
The terms "ectopic pregnancy" and "extrauterine
pregnancy" refer to a gestation anywhere outside the endometrial cavity
of the uterus. The fallopian tubes are by far the most common sites of such
pregnancy, whereas the ovary and abdominal cavity are less frequently involved
[1]. The retroperitoneal space
is an exceptional location. We describe a rare case of retroperitoneal
pregnancy.
Case Report
A 21-year-old woman, gravida 0, para 0–0–0–0, was
admitted via the emergency department with the main complaint of left flank
pain. The patient's medical and gynecologic history was unremarkable. Physical
examination showed mild tenderness on the left flank area. The patient had a
6-week history of amenorrhea, and the results of the urine test were positive
for pregnancy. Abdominal sonography revealed a large mass below the left
kidney with mild dilatation of the left renal pelvis and proximal ureter
(Fig. 1A). The mass contained a
gestational sac and embryo (Fig.
1B). Cardiac activity and gross motion of the embryo were also
noted on real-time gray-scale sonography. There was neither an intrauterine
gestational sac nor an adnexal mass.
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Fig. 1A. —21-year-old woman with retroperitoneal pregnancy. LK = left
kidney. Abdominal sonogram of left flank area shows echogenic mass (M)
compressing left proximal ureter (arrow) and causing mild dilatation
of left renal pelvis.
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The patient was brought to the operating room with the diagnosis of
retroperitoneal ectopic pregnancy. Careful inspection in the field of
operation revealed that the uterus, fallopian tubes, and other pelvic organs
were normal with no evidence of pelvic adhesion. The posterior peritoneum was
also intact. There was no free fluid in the peritoneum and retroperitoneum. A
retroperitoneal mass of approximately 5 cm was found in the left paraaortic
region below the left kidney. The base of the gestational sac was not
completely removed because of the adhesion around this mass lesion. Grossly,
products of conception together with a placenta were noted, and an embryo with
gestational sac and chorionic villi was identified histologically. The embryo
was grossly normal without abnormal development. The patient did well after
surgery.
Discussion
Ectopic pregnancy occurs when the fertilized ovum becomes implanted in
tissue other than the endometrium. Most ectopic pregnancies are located in the
ampullary segment of the fallopian tube. However, they may also occur within
the interstitial portion of the fallopian tube, in the uterine cervical canal,
between the leaves of the broad ligament, within the ovarian cortex, or on the
peritoneal surface (abdominal pregnancy)
[1]. In very rare cases, the
abdominal pregnancy may be retroperitoneal. The incidence of abdominal
pregnancy has been variously reported as between one per 3,372 births and one
per 7,931 births [2]. Abdominal
pregnancies are classified as either primary or secondary. Most abdominal
pregnancies probably originate as tubal or ovarian pregnancies that rupture
into the peritoneal cavity, where they implant for a second time (hence, the
term "secondary abdominal pregnancy")
[2]. Only a very small fraction
of the reported cases meet the three criteria for primary abdominal pregnancy
established in 1942 by Studdiford: normal tubes and ovaries, absence of
uteroperitoneal fistula, and pregnancy related exclusively to the peritoneal
surface and diagnosed early enough to exclude the possibility of secondary
implantation after primary nidation elsewhere
[3]. Our case meets these
criteria apart from the fact that implantation occurred in the retroperitoneal
space rather than in the peritoneal surface.
Reported sites of primary abdominal pregnancy are the pouch of Douglas,
posterior uterine wall, uterine fundus, liver, spleen, lesser sac, and
diaphragm [2]. Ectopic
pregnancy, a known complication of in vitro fertilization–embryo
transfer (IVF–ET), has increased in frequency due to the nationwide
proliferation of IVF–ET programs. As ectopic pregnancies become more
common, so too do reports of unusual implantation sites including the
retroperitoneum [4]. Two
mechanisms may account for the retroperitoneal location of an ectopic
pregnancy in IVF–ET patients: spontaneous retrograde migration of the
embryo after intrauterine transfer and uterine perforation with unintended
retroperitoneal or intraabdominal embryo placement at the time of transfer
[4]. However, our patient had
not undergone IVF–ET, and there was no evidence of tubal rupture or
uterine perforation found at surgery.
There have been very few reports of retroperitoneal ectopic pregnancy in
the absence of IVF–ET
[5–7],
and it is difficult to explain how these rare implantations occur. However,
several theories have been proposed. Dissemination of cells or tissue
fragments through vascular channels, as in the case of trophoblastic diseases,
typically terminates in pulmonary tissue, whereas dissemination of endometrial
cancers through lymphatic channels leads to metastases in the periaortic and
portal hepatic nodes [8]. Hall
et al. [9] suggested that the
fertilized ovum reaches the retroperitoneal space via the lymphatic system
because they found lymphatic tissue together with the ectopic mass. Another
explanation is that the embryo implants on the posterior peritoneal surface in
the first instance and reaches a retroperitoneal position by subsequent
trophoblastic invasion through the peritoneum
[4].
In summary, we have presented a rare case of retroperitoneal pregnancy.
Retroperitoneal location probably involved trophoblastic invasion after
primary abdominal pregnancy or a lymphatic route.
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Introduction
Case Report
