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Unruptured 32-week rudimentary horn pregnancy presenting as right upper quadrant pain.


Background: An unruptured third trimester rudimentary horn pregnancy is rare, life threatening, and can go undetected until the onset of symptoms. Given the high risk of uterine rupture, conservative management after viability is controversial.

Case: A 21 year-old with a 32-week rudimentary horn pregnancy, diagnosed via exploratory laparotomy five days earlier, presented with acute right upper quadrant pain. The patient underwent cesarean delivery. The rudimentary horn was noted to be intact, but so thin it was transparent.

Conclusion: Advanced ectopic pregnancy or rudimentary horn pregnancy should be considered in cases of unusual or undiagnosed abdominal pain in pregnancy. When surgical exploration is performed, an incision allowing optimal visualization and exposure is recommended.


Pregnancy in a noncommunicating rudimentary horn is a rare event with an estimated occurrence of 1 in 76,000-100,000 pregnancies. (1,2) These pregnancies carry a high rate of both maternal and fetal morbidity and mortality. Because the rudimentary horn is thinner and devoid of muscular tissue, 50% of the time these pregnancies end with uterine rupture. (1) Despite the availability of advanced imaging modalities, the diagnosis can be difficult to make and easily missed. Currently, there are no definitive management recommendations, but generally, these pregnancies are delivered shortly after diagnosis.


A 21 year-old G2P1 at 30 4/7 weeks gestational age was admitted secondary to persistent right upper quadrant pain of unknown etiology. The pain had started three days earlier and was associated with fevers, nausea, dysuria, and vaginal spotting. Otherwise, the pregnancy had been uncomplicated; second trimester multiple marker screening was declined. Her prior pregnancy resulted in a normal spontaneous vaginal delivery. Laboratory studies were all normal, fetal monitoring was reassuring, and no uterine contractions were detected. A CT scan demonstrated a pregnancy in the right horn of what was described as a bicornuate uterus. (Figure 1) MRI findings were consistent with the CT scan report. A fetal ultrasound revealed a gestational sac circumscribed by a very thin membrane which was suspicious for an advanced intra-abdominal ectopic pregnancy. The patient was transferred to a facility more experienced in the management of abdominal pregnancy. At the outside facility, the patient underwent surgical exploration via Pfannenstiel skin incision. The findings included a normal appearing unicornuate uterine horn in the left pelvis, hemoperitoneum that was evacuated, and a right rudimentary horn pregnancy. No pregnancy intervention was performed, the patient's abdomen was closed, and she was discharged to home three days later. Two days after discharge, at 32 1/7 weeks gestational age, the patient was again hospitalized due to worsening right upper quadrant pain. Exploratory laparotomy was performed with a vertical midline incision. The uterine wall of the rudimentary horn was transparently thin with large caliber, engorged vessels traversing the surface, but no gross disruption was noted. (Figures 2, 3) There was a thick septum separating the right horn from the left horn. A classical cesarean section and excision of the right non-communicating uterine horn and fallopian tube was performed. The patient delivered a viable, 32-week female neonate weighing 1680g. No communication between the horns could be identified after transcervical instillation of sterile milk into the left uterine cavity. The neonate did well and was discharged home 22 days after delivery.


Mullerian anomalies are estimated to affect 0.5-4.3% of the general population. (3, 4) A unicornuate uterus with or without a rudimentary horn is estimated to affect 5-10% of all women with a Mullerian anomaly.3, 4 There are four subtypes of rudimentary uterine horn uteri as defined by The American Society for Reproductive Medicine: A1a. Communicating rudimentary horn with endometrial cavity; A1b. Noncommunicating rudimentary horn with endometrial cavity; A2. Rudimentary horn without endometrial cavity; and B. No rudimentary horn. (5)

The uterus presented in this case was type A1b, or a unicornuate left uterus with a noncommunicating right rudimentary horn. A rudimentary horn arises when there is an arrested development of 1 of 2 Mullerian ducts. (6) Rudimentary horns are found in 74% of patients with a unicornuate uterus. (6) A noncommunicating horn is the most common subtype and is present in 75-85% of cases.1 When there is no communication between the two endometrial cavities, fertilization is facilitated by transperitoneal migration of the sperm and/or fertilized ova. These pregnancies are very high risk and can be life-threatening due to a 50% chance of uterine rupture. (1) The maternal mortality rate associated with this type of pregnancy has fallen from 6-23% in the early 19th century to approximately 0.5%, however, even with modern neonatal support, newborn survival is still only 13%. (1)




Twenty percent of rudimentary horn ruptures occur in the third trimester, with 67% occurring in the second trimester and only 13% occurring in the first trimester. (1) Even with modern imaging techniques, these pregnancies often go undiagnosed until the time of uterine rupture. These patients typically present with a number of symptoms ranging from pain to hypovolemic shock to death. This patient presented at 30 4/7 weeks gestation with complaints of right upper quadrant pain. Given the history of a prior normal delivery and the chief complaint of abdominal pain, primary investigations were geared toward abruption, infection, and gastrointestinal causes. Even with the question of a bicornuate uterus on a recent CT scan and MRI, the idea of an abdominal or rudimentary horn pregnancy was not immediately entertained. This highlights the importance of not only including uterine anomalies in the differential diagnosis of obstetric complaints,2 but considering abnormal pregnancy as the cause of any type of unusual or undiagnosed abdominal pain. Also, it is important to note that a prior normal pregnancy and/or delivery cannot rule out the possibility of a subsequent uterine horn pregnancy. (7)

On average, these pregnancies are diagnosed at 21 weeks gestation. (6) Previous studies have reported very low preclinical and preoperative detection rates (14% overall). (6) A large systematic review reported that ultrasound was only 26% sensitive in the detection of a rudimentary horn. (6) MRI has been shown to be useful for the diagnosis and preoperative management of these pregnancies. In our case, MRI imaging did reveal a uterine anomaly, however, the interpretation of the images were inconclusive regarding the specific anomaly. Although there are no definitive ultrasonographic markers for a rudimentary horn pregnancy, advanced gestation, a well-defined placenta, and the presence of a myometrial wall can differentiate a rudimentary horn from an ectopic abdominal pregnancy. (6) Findings of the sac being separate from the uterus, a large distance between the horns, or the endometrial lining not being contiguous with the internal cervical os are suggestive of a rudimentary horn pregnancy as opposed to a pregnancy in a bicornuate uterus. (6) Another clue that a pregnancy might be in a rudimentary horn is an elevated maternal serum alpha-fetal protein (MSAFP). Because the rudimentary horn wall is so thin, the AFP is able to easily diffuse into the maternal peritoneal cavity or bloodstream resulting in abnormal MSAFP levels. (6) Thus, a high MSAFP without any evidence of multiple gestation or structural abnormalities warrants careful evaluation of the uterine contour and wall thickness. (6) In this case, a MSAFP was not helpful because the patient declined second trimester multiple marker screening.

Several cases of third trimester rudimentary horn pregnancies have been reported, however, this is one of the first in which the diagnosis was confirmed surgically, yet conservative management was continued. After surgical evaluation at the outside facility, the patient's abdomen was closed and she was discharged to home for conservative management. When the patient returned to our facility with an acute increase in her pain, there was an obvious concern for uterine rupture and immediate intervention occurred. Complete evaluation of the myometrial thickness likely could not have been accomplished through a Pfannenstiel incision. Had the transparent myometrial wall and engorged vessels been visualized at the initial laparotomy, delivery would undoubtedly have been performed. This case illustrates the need to consider advanced ectopic pregnancy or rudimentary horn pregnancy in cases of unusual or undiagnosed abdominal pain. If surgical exploration is performed, it should be done through a vertical midline incision to maximize surgical exposure and visualization.


(1.) Nahum, GG. Rudimentary Uterine Horn Pregnancy: The 20th-Century Worldwide Experience of 588 Cases. J Reprod Med. 2002;47(2):151-163.

(2.) Kukreti, M, Singhal, VP, Kukreti, R, Prakash, A. Pregnancy in a rupturing noncommunicating rudimentary horn masquerading as epigastric pain. Australian and New Zealand Journal of Obstetrics and Gynecology. 2004;44:470-72.

(3.) Nahum, GG. Uterine anomalies. How common are they, and what is their distribution among subtypes? J Reprod Med. 1998;43(10):877-87.

(4.) Grimbizis, GF, Camus, M, Tarlatzis, BC, Bontis, JN, Devroey, P. Clinical implications of uterine malformations and hysteroscopic treatment results. Human Reproduction Update. 2001;7(1):161-174.

(5.) American Fertility Society. The American Fertility Society classifications of adnexal adhesions, distal tubal occlusion, tubal occlusion secondary to tubal ligation, tubal pregnancies, Mullerian anomalies and intrauterine adhesions. Fertil Steril. 1988;49(6):944-955.

(6.) Jayasinghe, Y, Rane, A, Stalewski, H, Grover, S. The presentation and early diagnosis of the rudimentary uterine horn. Obstet Gynecol. 2005;105(6):1456-1467.

(7.) Nishi, H, Hitoshi, F, Fukumine, N, Yagishita, M, Nohira, T, Suzuki, Y, et al. Rupture of pregnant noncommunicating rudimentary uterine horn with fetal salvage: a case report. Arch Gynecol Obstet. 2003;268:224-226.


This case report was a poster presentation at the 2008 ACOG District IV meeting in Orlando, Fl.

Courtney D. Cuppett, MD

Fellow, Magee-Womens Hospital Department of Obstetrics, Gynecology, and Reproductive Sciences, Division of Maternal-Fetal Medicine, Pittsburgh, PA

Michael L. Stitely, MD Associate Professor, West Virginia University Department of Obstetrics and Gynecology, Morgantown, WV

Roger C. Toffle, MD Professor, West Virginia University Department of Obtetrics and Gynecology, Morgantown, WV
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Title Annotation:Scientific Article
Author:Cuppett, Courtney D.; Stitely, Michael L.; Toffle, Roger C.
Publication:West Virginia Medical Journal
Article Type:Case study
Date:Jul 1, 2011
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