Omental pregnancy is an uncommon variety of abdominal ectopic pregnancy that is prevalent in one in 10,000 deliveries.¹ The maternal mortality rate is 6%, which is seven times higher than tubal ectopic pregnancy, and the clinical presentation is extremely variable. It has become exceptional to see an advanced abdominal pregnancy. A review of the literature showed that only a few cases of omental pregnancies have been reported to date, and most were secondary omental pregnancies. The diagnosis of omental pregnancy is usually made at laparoscopy/laparotomy. This case report reveals a primary omental pregnancy that was diagnosed at laparoscopy. By presenting this case, the authors want to emphasise that in a patient suggesting ectopic pregnancy with clinical findings, if both adnexa are ‘normal’ during surgical exploration, the omentum may be the implantation site and should be carefully examined.

Case report

A woman in her late 20s presented with abdominal pain at six weeks gestation. The transvaginal scan revealed an empty uterus, free fluid 6cm depth with a cyst floating at the fluid margin. Serum human chorionic gonadotropin (hCG) was 4,650IU/L. The initial diagnosis was tubal ectopic pregnancy. Laparoscopy was performed and showed grossly normal uterus, tubes and ovaries, with minimal blood in the pouch of Douglas. There was a haemorrhagic mass adherent to the omentum. Laparoscopic omentectomy and dilatation and curettage was performed. The histology established the diagnosis of omental pregnancy.

Discussion

Omental pregnancy is the rarest form of abdominal pregnancy and its mortality is seven times higher than non-abdominal pregnancies. Early detection of rare ectopic sites is feasible with extensive use of serial serum hCG, transvaginal scan, MRI² and advanced skills in laparoscopy.³ The symptoms may vary from lower abdominal pain to haemorrhagic shock. Laparoscopic management is feasible once the ectopic site is identified. 

Although there has been no consensus for the diagnosis of primary omental pregnancy, Studdiford’s criteria are used to diagnose primary abdominal pregnancy, namely:

• Normal bilateral Fallopian tubes and ovaries with no recent or remote injury
• Absence of any uteroperitoneal fistula
• Presence of a pregnancy related exclusively to the peritoneal surface and early enough to eliminate the possibility of implantation following a primary nidation in the tube.²

Clinical, ultrasonographic, histopathological and surgical findings must be combined to diagnose a case as a primary omental pregnancy. Recent contraceptive usage such as progesterone-only pills and intrauterine devices can be accepted as a risk factor.⁴ This patient has not been using any contraceptive method. Symptoms show differences when compared with classical tubal pregnancy. The most common symptom is severe lower abdominal pain, as in this case. 

Mortality due to omental pregnancy is mostly related to haemorrhagic shock. In laparoscopic exploration, a gynaecologist must have high index of suspicion, otherwise an omental pregnancy can easily be missed. In this case, pre-operative diagnosis was tubal pregnancy during laparoscopic exploration, upper genital organs were completely normal and there was a haemorrhagic mass adherent to the omentum. Laparoscopic omentectomy and dilatation and curettage was performed. The success of the procedure can be checked by rapid decrement in hCG titres. In this case, there was a 90% decrease in five days. 

Usually, omental pregnancies are divided into two categories: primary and secondary. In primary omental pregnancy, histological evidence of neovascularisation or growth of trophoblast into the supporting tissue must be found. However, in the absence of histological evidence of neovascularisation or growth of trophoblast into the supporting tissue, all cases should be considered as secondary omental pregnancy.⁵ In these pathological sections, extensive villus formation and dense trophoblastic invasion deep into the omental tissues including blood vessels were seen. These histopathological findings proved this case to be a primary omental pregnancy. Although rarely seen, a primary omental pregnancy can present as a ruptured tubal pregnancy. During surgical exploration, with intact tubes and ovaries, omentum should be checked as a possible implantation site. 

References

1. Yildizhan R, Kurdoglu M, Kolusari A, Erten R. Primary omental pregnancy. Saudi Med J 2008; 29: 606-609
2. A Studdiford WE. Primary peritoneal pregnancy. Am J Obstet Gynecol 1942; 44: 487-491 
3. Yi KW, Yeo MK, Shin JH et al. Laparoscopic management of early omental pregnancy detected by magnetic resonance imaging. J Minim Invasive Gynecol 2008; 15(2): 231-234
4. Mousa HA, Thong J. Omental pregnancy in a woman taking the progestogen-only pill. Acta Obstet Gynecol Scand 2001; 80(12): 1139-1140
5. Berghella V, Wolf SC. Does primary omental pregnancy exist? Gynecol  Obstet Invest 1996; 42(2): 133-136