What is the most common pelvic mass in pregnant women and how should it be managed?

Most Common Pelvic Mass in Pregnant Women

The most common pelvic mass requiring surgical management in pregnant women is the dermoid cyst (mature cystic teratoma), accounting for 32% of all adnexal masses removed during pregnancy. 1

Epidemiological Context

The overall landscape of adnexal masses in pregnancy shows that approximately three-quarters of incidentally identified masses are simple cysts <5 cm that typically resolve spontaneously. 1 However, when examining masses that persist and require surgical intervention or removal at cesarean delivery, the distribution is clear:

Frequency of Surgically Managed Masses in Pregnancy

• Dermoid cysts: 32% (range 18-50%) 1
• Endometriomas: 15% (range 0-24%) 1
• Functional cysts: 12% (range 3-41%) 1
• Serous cystadenomas: 11% (range 4-19%) 1
• Mucinous cystadenomas: 8% (range 3-15%) 1
• Hyperreactio luteinalis: 9% (range 0-14%) 1

Diagnostic Approach

Transvaginal ultrasound is the essential initial imaging modality for characterizing adnexal masses in pregnancy. 1 The American College of Radiology emphasizes that ultrasound is highly accurate, low cost, readily available, and safe throughout pregnancy. 1

Characteristic Ultrasound Features by Mass Type

• Dermoid cysts: Complex echo patterns with hyperechoic areas and distal shadowing due to fat, solid components, and calcifications 1, 2
• Endometriomas: Complex unilocular or multilocular cysts with diffuse low-level internal echoes 1
• Simple/functional cysts: Anechoic, unilocular with smooth thin walls 1
• Hemorrhagic cysts: Hypoechoic internal debris 1
• Cystadenomas: Simple cysts or thin septations; serous are anechoic, mucinous have low-level echoes 1

Ultrasound achieves 95% accuracy for dermoid tumors, 80% for endometriomas, and 71% for simple cysts in pregnancy. 1

Important Caveat

Gadolinium-enhanced MRI is contraindicated during pregnancy for adnexal mass assessment. 3 If ultrasound is indeterminate and additional imaging is needed, non-contrast MRI may be considered, though this is rarely necessary for typical dermoid cysts which have pathognomonic ultrasound features. 3

Management Algorithm

For Masses <5 cm with Benign Features

Expectant management with ultrasound surveillance is appropriate, as 68-72% of complex masses ≥2.5-5.0 cm spontaneously resolve by 6 weeks postpartum. 1 This applies particularly to functional cysts and simple cystadenomas. 1

For Masses ≥5 cm Persisting Beyond First Trimester

Surgical intervention should be considered, with the optimal timing being the second trimester when spontaneous resolution is unlikely and before the uterus becomes too large to impair visualization. 1 However, necessary surgery should not be delayed based solely on gestational age. 1

For Masses ≥10 cm

Surgical removal is mandatory due to substantially increased risk of torsion (mean size of torsed masses ≈10 cm), technical difficulty, and minimal likelihood of spontaneous resolution. 4 The overall torsion risk during pregnancy is 3-12%, with larger lesions carrying the highest risk. 4

Surgical Approach in Pregnancy

Laparoscopic cystectomy is the preferred approach over laparotomy, offering shorter hospital stays, less postoperative pain, lower blood loss, and reduced risks of fetal loss (1% vs 5%) and preterm birth (4% vs 12%). 4

Critical technical modifications for pregnancy include: 4

• Left lateral decubitus positioning to maintain placental perfusion
• Insufflation pressure ≤12-15 mm Hg
• Port placement adjusted for fundal height
• Intraoperative capnography monitoring
• Pre- and postoperative fetal heart rate monitoring

Management at Cesarean Delivery

A 10-cm incidental adnexal mass discovered at cesarean delivery should be removed during the same operation to avoid a second surgery, provide definitive histopathology, and eliminate postpartum torsion risk. 4 The standard low-transverse cesarean incision provides direct access to the adnexa without requiring additional ports. 4

Malignancy Risk

Approximately 2% of adnexal masses in pregnancy are malignant, with most (64-81%) being early stage (stage I) when diagnosed. 1 The most common malignancies are epithelial tumors (51%), followed by germ cell tumors (39%). 1

Red Flags Suggesting Malignancy

Ultrasound features warranting heightened concern include: 1

• Thick or irregular septations
• Mural nodules or papillary projections
• Solid components
• Diameter >5 cm
• Ascites

If these features are present, laparotomy rather than laparoscopy should be performed to allow for proper staging and oncologic principles. 4

Common Pitfalls to Avoid

Do not assume all masses require immediate surgery—most functional cysts and simple masses <5 cm in pregnancy are benign and resolve spontaneously. 5 Size alone does not determine malignancy risk; morphologic features on ultrasound are far more important. 5

Do not delay necessary surgery based solely on gestational age—when performed at facilities with appropriate obstetric, anesthetic, and neonatal support, adnexal surgery in pregnancy results in excellent outcomes. 1

Do not overlook the possibility of pregnancy-specific masses: Hyperreactio luteinalis presents as bilateral ovarian enlargement with multiple peripheral thin-walled cysts, typically in the third trimester, and spontaneously regresses postpartum. 1