Abdominal pain in pregnancy protocol (MRI)

The abdominal pain in pregnancy MRI protocol encompasses a set of MRI sequences for assessment of causes of non-traumatic abdominal pain in pregnancy.

Note: This article aims to frame a general concept of an MRI protocol for the assessment of the abdomen in pregnancy. Protocol specifics will vary depending on MRI scanner type, specific hardware and software, radiologist and perhaps referrer preference, patient factors e.g. implants, specific indications and time constraints.

Indications

Acute non-traumatic abdominal pain in a pregnant woman, either as a primary imaging modality or following indeterminate or abnormal ultrasound findings.

1.5 vs 3 Tesla

Due to considerations around fetal heating, 1.5 tesla is recommended for this type of study.

Patient preparation 

No specific preparation is required.

Patient positioning

The study can be conducted with the patient in the supine position, but with increasing gestational age, patients may be more comfortable lying in the left lateral position to reduce pressure on the IVC by the gravid uterus.

Technical parameters

Coil

• phased-array surface body coil

Planning

Due to pain often not being localized to one region, and due to the anatomic changes encountered during pregnancy, images are acquired from the diaphragm to the pubic symphysis, provide complete anatomic coverage.

Sequences

The set of sequences used must allow for adequate interrogation of the altered anatomy of the pregnant abdomen, yet also minimize the specific absorption rate (SAR) and minimize the time spent in the scanner.

Standard sequences

• T2-weighted
  • purpose: to identify bowel including appendix, solid upper abdominal organs and uterus
  • technique: single-shot fast spin-echo (SSFSE)
  • planes: axial, coronal and sagittal
• T2-weighted with fat saturation
  • purpose: to identify edema and free fluid
  • technique: single-shot fast spin-echo (SSFSE) with fat saturation
  • planes: axial, coronal and sagittal
• Gradient echo (+/- fat saturation)
  • purpose: to identify blooming artifact in the appendix confirming luminal gas and therefore patency; to identify retroperitoneal structures such as dilated ureter and ovarian vein
  • technique: gradient-echo +/- fat saturation
  • planes: axial (optional: coronal and sagittal)
• T1-weighted
  • purpose: to identify blood products, such as in degenerating fibroids
  • technique: dual-echo or T1W spin-echo (SE)
  • planes: axial (optional: coronal and sagittal)
• Diffusion-weighted imaging
  • purpose: to identify edema and inflammatory changes
  • technique: diffusion-weighted imaging, b0-50, b400, b800
  • planes: axial or coronal

Practical points

• the use of MRI in all trimesters of pregnancy is considered to be safe by the American College of Radiology's Manual of MRI Safety, but patients should be consented about the as-yet-unknown long term effects of MRI on the fetus
• the use of gadolinium contrast is relatively contraindicated in pregnancy due to gadolinium crossing the placental barrier and the unknown effects on the fetus
• the appendix may be difficult to identify on MRI, particularly in the latter stages of pregnancy, due to movement outside of the usual position in the right iliac fossa and compression of bowel loops
• the presence of restricted diffusion in the region of the cecal pole helps to diagnose acute appendicitis
• physiologic hydronephrosis is commonly seen in pregnancy, more frequently on the right side, with gradual tapering of the ureter as it is compressed between the uterus and psoas muscle
• a dilated ovarian vein is another tubular retroperitoneal structure that may be mistaken for an appendix but can be followed caudally from the ovary to its cranial drainage to the IVC on the right and left renal vein on the left
• if fetal assessment isn't carried out, a statement explicitly stating this should be added to the report