In a pregnant patient experiencing severe 30‑minute nighttime pain episodes, what can a non‑contrast magnetic resonance imaging (MRI) demonstrate?

MRI Findings in Pregnancy for Severe Nightly Pain

Non-contrast MRI of the abdomen and pelvis is the preferred imaging modality after inconclusive ultrasound in pregnant patients with severe pain, and can accurately identify gastrointestinal, genitourinary, gynecologic, and vascular pathologies without fetal radiation exposure. 1

What MRI Can Demonstrate

Gastrointestinal Causes

Appendicitis is the most common surgical emergency in pregnancy, and MRI demonstrates:

• Appendiceal diameter >7mm with periappendiceal fluid or edema 1
• Sensitivity of 100% and specificity of 93.6-98% for appendicitis diagnosis 1
• The T1 bright appendix sign (high-intensity signal filling >50% of appendix length on T1-weighted imaging) indicates a normal appendix with 95.5% specificity 1
• Even when the appendix is not visualized (occurs in 30-50% of cases), absence of ancillary inflammatory signs indicates low risk for appendicitis 1

Other gastrointestinal pathology MRI can identify:

• Inflammatory bowel disease exacerbations (Crohn's disease, ulcerative colitis) 1, 2
• Bowel obstruction or intussusception 2
• Pancreatitis 2
• Intraabdominal abscesses 2

Genitourinary Causes

Urolithiasis and obstruction are distinguished from physiologic hydronephrosis by:

• Static-fluid MR urography showing the "double kink sign" (constriction at pelvic brim and vesicoureteral junction with standing column of urine) indicates pathologic obstruction 1
• Renal edema, perirenal fluid, or periureteral fluid suggests true obstruction rather than physiologic pregnancy-related hydronephrosis 1
• High-resolution T2-weighted sequences can identify small calculi 1
• Sensitivity of 95% and specificity of 100% for detecting hydronephrosis 1

Pyelonephritis demonstrates:

• Renal parenchymal edema and inflammatory changes 2, 3

Gynecologic Causes

Adnexal pathology MRI can characterize:

• Ovarian torsion with enlarged edematous ovary and twisted vascular pedicle 2
• Complex ovarian cysts or masses, with 88% overall accuracy using structured scoring systems 1
• Uterine fibroid degeneration or torsion of pedunculated fibroids 2, 3
• Non-contrast MRI achieves 85% sensitivity and 96% specificity for detecting malignancy in adnexal masses 1

Hepatobiliary Causes

MRI can identify:

• Cholecystitis and choledocholithiasis 3
• Hepatic pathology unique to or exacerbated by pregnancy 3

Vascular Causes

MRI demonstrates:

• Adrenal hemorrhage 2
• Deep vein thrombosis in pelvic vessels 1

Critical Safety Considerations

Gadolinium contrast must be avoided in pregnancy except for life-threatening maternal conditions:

• Gadolinium crosses the placenta and accumulates in amniotic fluid with unknown duration of fetal exposure 1, 4
• Associated with increased stillbirth/neonatal death (17.6 per 1,000 exposed vs 6.9 per 1,000 unexposed) 1, 4
• Increased risk of childhood rheumatologic and inflammatory skin conditions 1, 4
• FDA Category C classification 1, 4

Non-contrast MRI is safe at any gestational age on 1.5T or 3.0T systems with no known deleterious fetal effects 4

Diagnostic Performance

Non-contrast MRI in pregnancy achieves:

• Overall accuracy of 94-96% for acute abdominal pain evaluation 1, 4
• Correctly identified disease entities in 28 of 29 pregnant patients in one series 2
• Prevented unnecessary surgery in 88% of patients with suspected appendicitis after inconclusive ultrasound 1
• Identified alternative diagnoses in 10-14% of cases initially suspected to be appendicitis 1, 5

Clinical Algorithm

Step 1: Ultrasound remains first-line imaging for pregnant patients with acute pain 1, 4

Step 2: When ultrasound is nondiagnostic or inconclusive, proceed directly to non-contrast MRI abdomen and pelvis 1, 4

Step 3: Include MR urography sequences if urinary tract pathology is suspected 1

Step 4: Reserve gadolinium contrast only for life-threatening maternal conditions where diagnosis cannot be established otherwise and immediate management depends on contrast-enhanced findings 1, 4

Common Pitfalls to Avoid

• Do not interpret non-visualization of the appendix as indeterminate—if MRI quality is adequate and no ancillary inflammatory signs are present, report as "low risk for appendicitis" 1
• Do not mistake physiologic hydronephrosis for obstruction—look for the double kink sign and perirenal fluid to distinguish pathologic obstruction 1
• Do not delay MRI in late pregnancy—appendix visualization rates are actually lower on ultrasound (7%) compared to MRI (80%) in pregnant patients 1
• Do not position patients supine—use left lateral decubitus or left pelvic tilt to avoid aortocaval compression 4

MRI provides comprehensive evaluation of multiple organ systems in a single examination, making it invaluable for pregnant patients with severe pain of unclear etiology after initial ultrasound 5, 2, 3.