What is the approach to diagnose and manage an 18-week abdominal lump arising from the pelvis in a 40-year-old woman?

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

Initial Clinical Assessment

Begin with transvaginal and transabdominal ultrasound with Doppler as the first-line imaging modality to characterize the mass and determine its origin. 1, 2, 3

Key Clinical Features to Elicit

• Symptom assessment: Persistent pelvic/abdominal pain, urinary urgency/frequency, increased abdominal size/bloating, difficulty eating, and abnormal vaginal bleeding 4
• Menstrual history: Cycle regularity, heavy menstrual bleeding, and intermenstrual bleeding 5
• Obstetric history: Parity status influences likelihood of certain diagnoses (nulliparous women have reduced odds of additional pathology) 5
• Surgical history: Previous cesarean sections or gynecologic procedures increase risk of abdominal wall endometrioma 6
• Physical examination: Assess for ascites (fluid wave or shifting dullness suggests malignancy), abdominal distension, and palpable mass characteristics 2

Differential Diagnoses and Diagnostic Approach

Gynecologic Masses

Ovarian Cystadenoma (Benign)

• Ultrasound findings: Unilocular or multilocular cystic mass with thin septations (<3mm), no solid components or papillary projections 2
• Management: If clearly benign on ultrasound, can be followed conservatively 1

Ovarian Malignancy

• Ultrasound features: Solid components with strong internal vascularity, thick irregular septations (>3mm), papillary projections (≥4 suggests malignancy), ascites, peritoneal nodules, omental thickening, size >10cm 2, 4
• Laboratory: CA-125 (though limited specificity in premenopausal women) 2, 4
• Advanced imaging: If malignancy highly suspected, proceed directly to CT abdomen and pelvis with IV contrast for staging 1, 2
• Management: Immediate referral to gynecologic oncologist without image-guided biopsy due to risk of malignant cell spillage and upstaging 2, 3

Uterine Leiomyoma (Fibroids)

• Ultrasound findings: Well-defined hypoechoic masses within uterine wall, may be multiple 5
• Clinical context: Heavy menstrual bleeding, pelvic pressure, bulk symptoms 5
• Additional imaging: MRI pelvis without and with contrast if ultrasound shows multiple fibroids, as 44% of women have additional findings (adenomyosis, endometriosis, partially endocavitary fibroids) that alter management 5

Adenomyosis

• Ultrasound findings: Heterogeneous myometrium, thickened junctional zone, myometrial cysts 7, 5
• Clinical context: Dysmenorrhea, heavy menstrual bleeding 5

Endometrioma

• Ultrasound findings: Low-level internal echoes, mural echogenic foci, nonvascular solid attenuating components 1
• Follow-up: Requires surveillance due to small risk (<1%) of malignant transformation 1

Abdominal Wall Endometrioma

• Clinical context: History of cesarean section or gynecologic surgery, cyclic pain at incision site 6
• Imaging: Ultrasound or MRI shows solid mass in abdominal wall 6
• Management: Wide local surgical excision 6

Non-Gynecologic Masses

Gastrointestinal Origin

• Imaging: CT abdomen and pelvis with IV contrast to characterize bowel-related masses 3

Urologic Origin

• Imaging: Ultrasound with Doppler can identify renal or bladder masses 3

Imaging Algorithm

First-Line: Ultrasound

Combined transvaginal and transabdominal ultrasound with Doppler should assess: 1, 2, 4

• Size and unilateral/bilateral location of mass
• Origin (look for "bridging vessel sign" to confirm uterine vs. ovarian origin) 2
• Internal architecture: solid vs. cystic components, septation thickness, papillary projections 2, 4
• Doppler evaluation for internal vascularity (differentiates solid tissue from debris/clot) 1, 2
• Presence of ascites 2, 4

Second-Line Imaging

MRI Pelvis Without and With IV Contrast

Indications: 1, 3, 5

• Indeterminate ultrasound findings requiring better characterization of solid components
• Multiple fibroids on ultrasound (reveals additional pathology in 44% of cases)
• Pelvic pain with poor quality of life scores
• Cannot tolerate transvaginal ultrasound

Advantages: Superior for characterizing complex adnexal masses and identifying coexisting adenomyosis or endometriosis 1, 3, 5

CT Abdomen and Pelvis With IV Contrast

Indications: 1, 2

• High suspicion of malignancy for staging
• Assessment for metastatic disease
• Characterization of non-gynecologic masses

Note: CT is not indicated for routine characterization of benign or indeterminate adnexal masses 1

Laboratory Investigations

• CA-125: For postmenopausal women or when malignancy suspected (limited specificity in premenopausal women) 2, 4
• AFP and hCG: Age-dependent, particularly for younger women with suspected germ cell tumors 3
• Complete blood count: Assess for anemia from chronic bleeding 5

Management Strategy

Benign-Appearing Masses

• Simple cysts: No follow-up needed regardless of size in premenopausal women (100% benign) 1
• Characteristic benign lesions (endometriomas, dermoids): Can be followed conservatively with ultrasound unless symptomatic 1

Indeterminate Masses

• Follow-up ultrasound in 6 weeks (scheduled for first half of menstrual cycle) to assess for resolution of functional cysts 1
• Alternative: MRI pelvis with contrast for definitive characterization 1

Highly Suspicious for Malignancy

• Immediate gynecologic oncology referral 2, 4
• CT abdomen and pelvis with IV contrast for staging 1
• Proceed directly to surgical excision without image-guided biopsy 2, 3

Critical Pitfalls to Avoid

• Do not perform image-guided biopsy of suspected ovarian masses due to risk of malignant cell spillage and upstaging 2, 3
• Do not delay gynecologic oncology referral for patients with high suspicion of malignancy, as they benefit from initial comprehensive staging by specialists 2, 4
• Do not rely solely on ultrasound in women with pelvic pain, multiple fibroids, or poor quality of life scores—MRI reveals additional pathology in >40% of cases 5
• Do not assume all pelvic masses in reproductive-age women are benign—always consider malignancy in any age group 4