What is the differential diagnosis for a 24-year-old female patient with a gradually enlarging abdominal mass over 9 months?

Differential Diagnosis for Gradually Enlarging Abdominal Mass in a 24-Year-Old Female

In a 24-year-old woman with a 9-month history of gradually enlarging abdominal mass, the most likely diagnoses are ovarian neoplasms (particularly benign cystadenomas or mature cystic teratomas), followed by uterine leiomyomas, and less commonly gastrointestinal stromal tumors or other soft tissue masses. 1, 2

Key Clinical Context

The 9-month duration is critical—ascites typically presents over weeks, not months to years, making a slowly enlarging abdomen over this timeframe most consistent with a solid or cystic mass rather than fluid accumulation. 1 This timeline strongly favors neoplastic processes over inflammatory conditions. 1

Primary Differential Diagnoses

Gynecologic Masses (Most Likely)

Ovarian cystadenomas are the leading consideration, as they are common benign ovarian neoplasms that can present as large abdominal masses in young women and may reach enormous sizes over months. 1, 3 These masses:

• Can be serous or mucinous in type 3
• May be bilateral 3
• Are often asymptomatic until reaching substantial size 1

Mature cystic teratomas (dermoid cysts) represent the most common persistent ovarian mass in this age group and should be high on the differential. 1 Up to 70% of adnexal lesions in young women are functional cysts that resolve spontaneously, but persistent masses over 9 months are more likely dermoids or cystadenomas. 1

Uterine leiomyomas can occur in the abdominal wall or arise from the uterus itself, though abdominal wall location is rare. 4 These smooth muscle tumors should be considered even without prior uterine surgery. 4

Non-Gynecologic Solid Masses

Gastrointestinal stromal tumors (GIST) can present as slowly enlarging upper abdominal masses with nonspecific symptoms including abdominal pain, discomfort, and palpable mass. 1, 5 Small bowel GISTs may remain silent for extended periods before presenting. 1

Soft tissue sarcomas including retroperitoneal sarcomas often present as large masses before symptoms develop and should be considered in the differential. 6

Abdominal wall leiomyomas can occur at any location with smooth muscle and may develop without prior surgical history. 4

Less Common Considerations

Chronic expanding hematoma (CEH) should be considered if there is history of abdominal trauma, as these can slowly enlarge over months to years and mimic malignancy on imaging. 7

Paragangliomas rarely present as large intra-abdominal masses and may be non-functional, making diagnosis challenging. 8

Diagnostic Approach

Initial Imaging Strategy

Begin with combined transabdominal and transvaginal ultrasound with Doppler evaluation, as this is the first-line imaging modality for all abdominal masses in women of reproductive age. 1, 2 This approach:

• Determines if the mass is solid or cystic 2
• Assesses vascularity and relationship to surrounding structures 2
• Identifies the organ of origin (ovarian, uterine, or other) 1
• Utilizes O-RADS or IOTA classification systems for risk stratification 1

Laboratory Evaluation

Obtain age-appropriate tumor markers including:

• CA-125 for epithelial ovarian neoplasms 1, 9
• AFP (alpha-fetoprotein) and hCG (human chorionic gonadotropin) given age <35 years, as germ cell tumors are more common in this demographic 2, 9
• Complete blood count and comprehensive metabolic panel for baseline assessment 9

Advanced Imaging When Indicated

If ultrasound findings are indeterminate, proceed to MRI pelvis with and without IV contrast, which is superior to CT for characterizing complex adnexal masses. 1, 2 MRI provides:

• 91% overall accuracy for diagnosing malignancy 1
• Superior characterization of endometriomas, dermoids, and fibromas 1
• Better identification of vascular vegetations and solid components 1
• Higher specificity than CT or Doppler ultrasound alone 1

CT abdomen/pelvis with IV contrast is reserved for suspected malignancy with need for staging or when MRI is contraindicated. 2, 9

Critical Clinical Pearls

Risk Stratification Factors

The incidence of malignancy in adnexal masses in reproductive-age women is low (approximately 3.6-10.7% for indeterminate lesions), making benign diagnoses far more likely. 1 However, certain features warrant heightened concern:

• Solid components with internal vascularity 1
• Papillary projections 1
• Ascites 1
• Rapid growth 1

Common Diagnostic Pitfalls

Do not assume all pelvic masses are gynecologic in origin—always consider gastrointestinal and soft tissue sources, particularly with upper abdominal location. 1, 5, 8

Avoid fine-needle aspiration for suspected ovarian masses due to risk of malignant cell spillage; core needle biopsy under image guidance is preferred if tissue diagnosis is needed. 2, 9

Do not rely solely on clinical examination, as studies show only 85% accuracy for physical examination alone in identifying soft tissue masses. 9

When to Obtain Tissue Diagnosis

Pre-operative histologic diagnosis is essential for:

• Large masses requiring potentially morbid surgery (e.g., total gastrectomy, multi-visceral resection) 1
• Masses with features suspicious for malignancy requiring neoadjuvant therapy 1
• Suspected non-gynecologic masses where diagnosis would alter management 1, 9

Plan biopsy tracts so they can be removed during definitive surgery if malignancy is confirmed. 2, 9