Indications for CT Scan in Obstetrics and Gynecology
CT scans in obstetrics and gynecology should be used selectively when ultrasound is inconclusive or for specific indications, with careful consideration of radiation exposure, especially during pregnancy. 1
General Principles
- Transvaginal/transabdominal ultrasound is the first-line imaging modality for all suspected gynecologic or obstetric conditions 1
- MRI without gadolinium is preferred over CT when additional imaging is needed, especially during pregnancy 1
- CT with IV contrast is recommended for most urgent indications when required 1
Specific Indications for CT in Gynecology
Acute Pelvic Pain
- Poorly localized pain with suspected gynecologic and non-gynecologic etiologies
- Nonspecific clinical presentation with broad differential diagnosis
- Equivocal or nondiagnostic ultrasound evaluation, particularly with concern for appendicitis 1
Adnexal Conditions
- Adnexal torsion when ultrasound is inconclusive (sensitivity 74-95%, specificity 80-90%)
- Characteristic findings: enlarged, featureless, hypoenhancing ovary with swirling vascular pedicle 1
- Tubo-ovarian abscess (appears as complex cystic mass with thick enhancing walls)
- Ovarian vein thrombosis 1
Uterine Conditions
- Degenerating or torsed uterine fibroids (shows diminished contrast enhancement with 86% sensitivity)
- Pelvic inflammatory disease with suspected complications 1
Hemorrhage and Vascular Complications
- Suspected intra-abdominal hemorrhage
- Unstable pelvic fractures
- Persistent hemorrhage after empiric embolization
- Mesenteric ischemia (CT angiography preferred) 1
Specific Indications for CT in Obstetrics
Postpartum Complications
- Failed conventional medical treatment for postpartum hemorrhage
- Suspected vascular complications
- Suspected uterine dehiscence or rupture
- Subfascial or perivaginal space hematomas
- Parametrial abscess or infected hematoma 1
Trauma in Pregnancy
- Polytrauma assessment in pregnant patients with high-velocity trauma 1
- Placental abruption evaluation after trauma (86% sensitivity, 98% specificity) 2
CT Techniques and Advantages
- Contrast-enhanced CT has higher sensitivity (89% vs 70%) than ultrasound for urgent diagnoses 1
- Multiphasic CT has excellent accuracy (97%) for detection of active extravasation in hemorrhage 1
- CT provides 88% overall accuracy compared with surgical diagnosis 1
Radiation Safety Considerations
During Pregnancy
- Avoid CT scans whenever possible, using ultrasound and MRI as alternatives
- Cumulative ionizing radiation exposure should be less than 50 mGy to minimize risks to the fetus
- Use proper abdominal shielding to minimize fetal exposure 1
- Fetal radiation exposure >50mGy is associated with doubled risk of childhood cancer
- Exposure >100mGy increases risk of mental retardation
- Exposure >150mGy increases risk of malformations 1
Contrast Considerations
- Iodinated contrast should be used only when absolutely necessary during pregnancy
- Gadolinium-based contrast agents should be avoided during pregnancy as they cross the placenta
- Breastfeeding after iodinated contrast is considered safe (less than 0.01% of CT contrast present in breast milk) 1
Limitations of CT in Obstetrics and Gynecology
- Cannot reliably distinguish vascular uterine abnormalities from normal postpartum changes
- Hypodense edema at cesarean incision site can be misinterpreted as dehiscence in first postpartum week
- Limited accuracy for adnexal mass characterization compared to ultrasound or MRI
- Retained products of conception can be difficult to differentiate from blood products
- Poor sensitivity for detecting myometrial invasion in endometrial cancer (58-61% accuracy vs 88-89% for MRI) 1