Case Report: A 25-year-old woman G7P2A4L1 with two previous Cesarean sections presented with a history of amenorrhea of three months' duration with mild, dull-aching pain in the lower abdomen of one week's duration and per-vaginal blood-stained sticky discharge for the past few days. On examination, vitals were stable. Per-vaginal examination revealed an uterus of eight weeks size and a closed cervical os.

INVESTIGATIONS: The urine pregnancy test was positive. The beta HCG level was 3000 IU/L The Hb: was10 gm %

RADIOLOGICAL FINDINGS:

The patient was admitted and a USG was performed. This showed a mixed echogenic lesion with a central cystic area in the lower uterine segment separate from the endometrial canal displacing the endometrium posteriorly. On Doppler examination, pericystic vascularity was detected. The ovaries were normal bilaterally . No free fluid was detected in the pelvis.

MRI: T2WI revealed a 6.8 x 6.7 x 6.1 cm, well circumscribed lesion in the myometrium of the lower uterine segment which showed marked T2 shortening along the periphery with a central cystic area showing hyperintense signal. The lesion was separate from the urinary bladder and endometrial canal. Healthy myometrium was not seen between the mass and the bladder.

In view of the history of previous Cesarean section and the location of the gestational sac and elevated beta HCG levels above the discriminatory cut off value of 1,500-2,500IU/L, a final diagnosis of ectopic gestation in a Cesarean section scar was made

The patient was treated with IV Methotrexate 66mg% (50 mg/sq.m). Follow up beta HCG levels had dropped to 1700 at one week and 400 at 15 days. The patient was discharged. Currently she is on follow up.

DISCUSSION:

Cesarean scar pregnancy is the rarest form of ectopic pregnancy. Less than a 100 cases have been reported so far.

A uterine scar pregnancy is a gestation separate from the endometrial cavity and completely surrounded by the myometrium and the fibrous tissue of the scar. The most probable mechanism for its occurrence is the invasion of the myometrium by a microscopic tract. In 60% to 70% of Cesarean scar pregnancies, there is clear evidence of the trophoblast penetrating the endometrial-myometrial junction. It has been postulated that first trimester cesarean scar pregnancies that invade the myometrium may develop into placenta previa/accreta if the pregnancy is allowed to progress.

ETIOLOGY:
The tract is believed to develop from trauma from previous uterine surgeries like dilatation and curettage, myomectomy, metroplasty and caesarean section.

CLINICAL FEATURES:
Amenorrhoea of 2 to 3 months followed by vaginal bleed. History of previous operative procedure as mentioned above.

COMPLICATIONS:
Hemorrhage and uterine rupture are dreaded complications often occurring in the first trimester.

USG: Transvaginal ultrasonography (TVUS) combined with Doppler is a reliable tool for the diagnosis. TVUS, is the most useful imaging tool in the diagnosis of ectopic pregnancy. It is non-invasive, readily available and accurate.

Ultrasound imaging criteria to diagnose Cesarean scar pregnancy are as follows:

1) Empty uterine cavity and cervical canal;
2) Development of the gestational sac in the anterior uterine wall at the isthmus (presumed site of the previous lower segment caesarean section scar);
3) Evidence of functional trophoblastic circulation on Doppler examination, defined by the presence of an area of increased peritrophoblastic vascularity on colour Doppler examination
4) The absence of healthy myometrium between the bladder and sac, allowing differentiation from cervico-isthmic implantation.

This entity is to be should be distinguished from two conditions, cervical pregnancy and miscarriage-in-progress.

In cervical pregnancy, the endocervical canal can be seen bulging with gestational products In miscarriage-in-progress, there is no functional peri-trophoblastic circulation on Doppler examination, and probe pressure on the cervix will show that the sac can be displaced.

The combination of non diagnostic sonographic findings and a serum HCG level above the discriminatory zone are highly specific for a diagnosis of ectopic pregnancy .When the serum human chorionic gonadotrophin level is above the discriminatory cutoff value of 1,500-2,500IU/L, a normal intrauterine pregnancy should always be detected by TVUS

MRI
An irregularly-marginated mass with very heterogeneous signal intensity on T2-weighted images, irregular internal high-signal intensities on T1-weighted images, a partial or circumferential rim of low-signal intensity, dense irregular peripheral enhancement and enhancing papillary solid components with accompanying tubular signal voids, and variably increased parametrial vascularities. This heterogeneous hemorrhagic mass with densely enhancing solid papillary components may be the typical MR finding .

Treatment: Most other case reports involving conservative management have used methotrexate either systemically or by direct injection into the pregnancy sac or a combination, There are also different regimens of medical treatment-single and multiple dosage. Due to the rarity of scar pregnancy, it is impossible to conclude whether systemic or local methotrexate administration is safer or more effective. Local administration of methotrexate avoids the systemic side-effects and maybe more effective if the initial HCG level is higher than 10 000 IU/L. Systemic administration of methotrexate may be used for an early scar pregnancy with an HCG of <10 000 IU/L. In all other cases, and those where expectant or systemic methotrexate treatment fails, the choice should be surgery or ultrasound-guided local medical treatment with or without UAE, depending on local expertise and practice and experience. Surgical treatment is necessary for clinically unstable patients and where there is large amount of fluid in the pelvic cavity on the ultrasound scan. Beta HCG usually takes 6 to 10 weeks to reach undetectable level, but it may take upto six months.