Cesarean scar ectopic pregnancy- MRI

History – 28 yrs age gravid female with history of past LSCS delivery. USG done about 1 month back suggesting relative low intrauterine pregnancy (images not available).  Patient did not want to continue the pregnancy due to unknown reasons & hence MTP was attempted following which minimal PV bleed occurred without any definite expulsion of products.

Patient was referred for MRI pelvis  to assess the present status of the gestation sac & to look for the status of uterine scar from previous LSCS.

-          T2 images ( sag , cor & axial) – show mixed signal fairly well defined oval shaped lesion in the low anterior uterine segment extending into the cervix causing dilatation of the cervix along with inferior bulge of the lower cervical lips causing effacement of the posterior fornix of vagina with possible endocervical canal extension. Superiorly thin extension of the T2 hypointense signal from the lesion into the endometrial cavity was also seen. Lesion appears iso to hyperintense in T1 with marked blooming areas within the lesion in GRE extending into the endometrial cavity suggesting hemorrhagic contents in the lesion.

-          Focal grossly thinned out anterior myometrium seen in the low uterine seg

-          ment ( LUS) showing broad contact with the above mentioned lesion in LUS & cervix.  No defect or any rupture was seen in the uterine scar. No collection or any free fluid was seen in the parametrium.

-          Thick  adhesion bands with T2 hypointense  signal were seen between the anterior wall of uterus & adjacent abdominal wall .

These MR imaging findings suggest lesion with hemorrhagic contents in LUS with extension into the cervix causing its dilatation along with hemorrhage within  the endometrial cavity – likely   retained products of conception ( in view of previous USG findings) & broad contact of lesion with anterior LUS scar suspicious for cesarean scar ectopic pregnancy.

—  Intra op findings - Crumpled sac like structure with hemorrhages & with dense adherence to the thinned out uterine scar which was cleared & myometrium was resutured.Uterus was preserved in the surgery & diagnosis of Cesarean scar ectopic pregnancy along with RPOC was made.

Discussion –

—  Cesarean scar ectopic pregnancy (CSEP) or Cesarean scar pregnancy (CSP) is a rare form of ectopic pregnancy resulting from implantation of a blastocyst within myometrial scar tissue (old uterine scars) in the anterior lower uterine segment (LUS) at the site of prior Cesarean section.

—  It is considered amongst the rarest type of ectopic pregnancy, although some do not include it in the category of ectopic pregnancy as implantation occurs within the uterus itself.

—  Incidence is on rise due to increasing numbers of elective Cesarean sections as well as improved detection with transvaginal ultrasound (TVUS). 

—  Estimated incidence is  about 1 per 1,800-2,226 pregnancies, exceeding than that of cervical ectopic pregnancies.

Clinical presentation -

—  Vaginal bleeding and abdominal pain.

—   Severe acute abdominal pain or heavy vaginal bleeding are concerning for impending rupture.

—  Hemodynamic instability may indicate rupture of CSP through the myometrium.

—  Up to 40 percent of patients may remain asymptomatic.

—  CSP can present at any time during gestation.

PATHOLOGY-  

—  Myometrial defects result from prior Cesarean section or after other uterine interventions like, dilatation and curettage ( D & C), myomectomy, hysteroscopy, and metroplasty.

—  Poor vascularity in the LUS impairs healing of scar and contributes to the formation of small myometrial defects in which the trophoblast may implant.

—  Poor healing can result in a focal thinning of the scar, which may be more susceptible to implantation of the gestational sac at this point rather than in the endometrial cavity.

—  Women who undergo multiple Cesarean sections are at increased risk of scar implantation due to increased scar surface area.

DIAGNOSIS -

TVUS -  modality of choice for diagnosis of CSP in the first trimester.  A sagittal view along the long axis of the uterus through the plane of the gestational sac allows accurate localization within the anterior LUS.

The following sonographic criteria have been proposed for diagnosis of CSP:

—  empty uterine cavity with clearly visualized endometrium;

—  empty cervical canal;

—  gestational sac in the anterior Low uterine segment and

—  absent or deficient intervening myometrium between the gestational sac and bladder wall, typically <5mm .="" o:p="">

—  High velocity (>20cm/sec), low-impedence peritrophoblastic color Doppler flow (pulsatility index <1 0.5="" 3.1="" also="" and="" been="" cases="" described="" flow="" have="" implantation.="" in="" index="" o:p="" of="" peak="" ratio="" resistive="" scar="" systolic:diastolic="">

Noncontrast MRI

—  Better demonstrate involvement of adjacent organs such as the urinary bladder and in orienting the surgeon.

—  In more advanced pregnancies, MR optimally demonstrates findings of placenta accreta spectrum, which may include thinning or absence of the subplacental myometrium, aberrant vessels, focal bulging of the uterine contour, and invasion of the urinary bladder or anterior abdominal wall. The presence of T2 hypointense, irregular intraplacental bands analogous to the vascularized lacuna seen on ultrasound, is strongly associated with abnormalities of placentation.

DDs-

—  Cervical ectopic pregnancies - located within cervical stroma, adjacent to the cervical canal. 

—  Normal low intrauterine pregnancies  - seen above the internal os and should have normal-thickness  of overlying myometrium.

—  Spontaneous abortion - gestational sac will often appear collapsed or irregular, lack normal surrounding color Doppler flow.

Management  -

—  Management decisions depend on gestational age and size, severity of implantation anomaly, clinical stability, and patient desire for future fertility.

—  Ultrasound-guided methotrexate injection has emerged as the treatment of choice.

—  Isolated dilatation and curettage is generally contraindicated due high risk of incomplete evacuation, uterine rupture and injury to the bladder.

—  Termination of pregnancy in the first trimester is generally recommended due to the high rate of complications  which later require hysterectomy .

—  Patients who do not respond to conservative measures may require laparoscopic or open excision, which allows for concurrent revision of the Cesarean scar to minimize risk of recurrence.