What is the approach for a 40-year-old woman presenting with an 18-week abdominal lump arising from the pelvis?

Approach to an 18-Week Abdominal-Pelvic Mass in a 40-Year-Old Woman

Begin with combined transabdominal and transvaginal ultrasound with Doppler as the initial imaging modality, as this provides the highest diagnostic yield for characterizing pelvic masses and determining their origin. 1

Initial Clinical Assessment

Key History Elements

• Menstrual history: Determine if premenopausal or perimenopausal, as this significantly impacts differential diagnosis 2
• Pain characteristics: Assess for cyclic versus non-cyclic pain, which may suggest endometriosis or functional cysts 3
• Obstetric history: Prior cesarean sections or uterine surgeries raise suspicion for abdominal wall endometrioma 3
• Constitutional symptoms: Weight loss, early satiety, increased abdominal girth, urinary urgency/frequency suggest possible malignancy 2
• Duration and growth rate: An 18-week history suggests a persistent rather than functional lesion 2

Physical Examination Specifics

• Mass characteristics: Determine if the mass is mobile versus fixed, smooth versus irregular, and whether it moves separately from the uterus 2
• Ascites assessment: Fluid wave or shifting dullness suggests advanced malignancy 1
• Scar examination: Palpate any surgical scars for tenderness or nodularity if abdominal wall endometrioma is suspected 3

Initial Imaging Protocol

Perform transabdominal ultrasound, transvaginal ultrasound, and duplex Doppler pelvis as complementary studies—all three should be done together. 1, 4

Ultrasound Assessment Criteria

• Size and laterality: Document maximum diameter and whether unilateral or bilateral 2
• Internal architecture: Distinguish solid versus cystic components, septation thickness, presence of papillary projections or excrescences 1, 2
• Doppler evaluation: Assess for internal vascularity, which helps differentiate solid tissue from debris or clot 1
• Ascites: Presence suggests malignancy 1
• Origin determination: Look for "bridging vessel sign" to confirm uterine versus ovarian origin 1

Differential Diagnoses with Specific Investigations

1. Uterine Leiomyoma (Fibroid)

Clinical clues: Most common pelvic mass in this age group; may be pedunculated and mimic adnexal mass 5

Ultrasound findings to confirm:

• Hypoechoic solid mass with whorled appearance
• Bridging vessels connecting mass to uterus 1
• May show cystic degeneration mimicking ovarian malignancy 5

Additional testing: None required if typical appearance; MRI pelvis without and with contrast if ultrasound indeterminate 1

Management:

• Observation if asymptomatic
• Myomectomy or hysterectomy if symptomatic or rapidly enlarging

2. Ovarian Cystadenoma (Benign)

Clinical clues: Typically asymptomatic; may cause pressure symptoms

Ultrasound findings to confirm:

• Unilocular or multilocular cystic mass with thin septations (<3mm)
• No solid components or papillary projections
• Minimal or absent internal vascularity 1

Additional testing:

• CA-125 level (though limited specificity in premenopausal women) 1, 2
• MRI pelvis without and with contrast if ultrasound indeterminate 1

Management:

• Observation with repeat ultrasound in 6-12 weeks if simple and <10cm
• Surgical excision if persistent, enlarging, or concerning features

3. Ovarian Malignancy

Clinical clues: Persistent pelvic/abdominal pain, bloating, urinary symptoms, early satiety, weight loss 2

Ultrasound findings to confirm:

• Solid components with strong internal vascularity 1
• Thick irregular septations (>3mm)
• Papillary projections (≥4 suggests malignancy) 1
• Ascites, peritoneal nodules, omental thickening 1
• Size >10cm 1

Additional testing:

• CA-125: Elevated levels (>35 U/mL) increase suspicion, though can be elevated in benign conditions 1, 2
• MRI pelvis without and with contrast: For indeterminate masses to better characterize solid components 1
• CT abdomen and pelvis with IV contrast: If malignancy highly suspected, to assess for metastatic disease 1, 4

Management: Immediate referral to gynecologic oncologist for comprehensive surgical staging 2

4. Endometrioma

Clinical clues: Cyclic pelvic pain, dysmenorrhea, dyspareunia, history of endometriosis 3

Ultrasound findings to confirm:

• Homogeneous low-level internal echoes ("ground glass" appearance)
• Thick walls
• No internal vascularity 1

Additional testing: MRI pelvis if ultrasound indeterminate—shows T1 hyperintensity with T2 "shading" 6

Management:

• Medical management with hormonal suppression
• Surgical excision if symptomatic or enlarging

5. Abdominal Wall Endometrioma

Clinical clues: Mass within or adjacent to cesarean section or hysterectomy scar; cyclic or non-cyclic pain 3

Ultrasound findings to confirm:

• Solid or complex mass within abdominal wall musculature
• Located at or near surgical scar 3

Additional testing: MRI pelvis if diagnosis uncertain 6

Management: Wide surgical excision with clear margins 3

6. Mature Cystic Teratoma (Dermoid)

Clinical clues: Often asymptomatic; most common germ cell tumor in reproductive age

Ultrasound findings to confirm:

• Echogenic sebaceous material with posterior acoustic shadowing
• "Dermoid plug" or "Rokitansky nodule"
• Fat-fluid levels 1

Additional testing: None typically required if classic appearance

Management: Surgical excision (risk of torsion and rare malignant transformation)

7. Tubo-Ovarian Abscess

Clinical clues: Fever, pelvic pain, elevated white blood cell count, history of pelvic inflammatory disease 1

Ultrasound findings to confirm:

• Complex cystic mass with thick irregular walls
• Internal debris and septations
• Surrounding free fluid 1

Additional testing:

• Complete blood count, inflammatory markers (ESR, CRP)
• Cervical cultures

Management:

• Broad-spectrum IV antibiotics
• Drainage if no response to antibiotics
• Surgery if ruptured

Algorithm for Further Imaging Based on Initial Ultrasound

If Ultrasound Shows Likely Benign Features

• Premenopausal: Repeat ultrasound in 6-12 weeks 1
• Postmenopausal: Lower threshold for MRI or surgical evaluation 1

If Ultrasound Shows Indeterminate Features

Obtain MRI pelvis without and with contrast for better tissue characterization 1, 4

If Ultrasound Shows Features Highly Suspicious for Malignancy

Obtain CT abdomen and pelvis with IV contrast for staging AND MRI pelvis without and with contrast for local assessment 1, 4

• Refer immediately to gynecologic oncologist 2

Common Pitfalls to Avoid

• Do not assume all pelvic masses are ovarian: Pedunculated fibroids commonly mimic adnexal masses 5
• Do not rely solely on CA-125 in premenopausal women: Limited specificity due to elevation in benign conditions (endometriosis, fibroids, pregnancy) 1
• Do not perform image-guided biopsy of suspected ovarian masses: Risk of malignant cell spillage and upstaging; proceed directly to surgical excision 4
• Do not overlook abdominal wall endometrioma: Always examine surgical scars in patients with prior uterine surgery 3
• Do not delay gynecologic oncology referral: Patients with high suspicion for malignancy benefit from initial comprehensive staging by specialists 2

Risk Stratification

Calculate Risk of Malignancy Index (RMI) if ovarian origin suspected:

• RMI = Ultrasound score × Menopausal status × CA-125 level
• RMI >200 warrants gynecologic oncology referral 2