A 38-year-old woman from Bangalore presents with a 2-year history of progressive abdominal distension, early satiety, and constipation. She denies vaginal bleeding or dysmenorrhea. On examination, the abdomen is distended with a firm, irregular mass palpable suprapubically extending to the epigastrium. Transvaginal ultrasound shows a large intramural fibroid (8 cm) with significant mass effect on adjacent bowel. CA-125 is mildly elevated at 52 U/mL. What is the most likely explanation for her symptoms and the elevated CA-125?

Explanation

## Large Fibroids: Mass Effect and Biomarker Elevation **Key Point:** Large benign fibroids can cause significant mechanical symptoms and mild CA-125 elevation through pressure effects and peritoneal irritation, NOT malignancy. ### Pathophysiology of Symptoms in Large Fibroids This patient's symptoms (abdominal distension, early satiety, constipation) are classic **mass effect phenomena** from a large intramural fibroid: 1. **Mechanical compression** of adjacent organs: - Stomach → early satiety - Colon/rectum → constipation - Small bowel → bloating, distension 2. **Peritoneal irritation** from the fibroid mass: - Stretching of peritoneal surface - Reactive peritoneal inflammation - Mild elevation of peritoneal markers (CA-125) **High-Yield:** CA-125 is a peritoneal marker, NOT specific for malignancy. It is elevated in any condition causing peritoneal irritation: fibroids, adenomyosis, endometriosis, peritonitis, and malignancy. A single elevated CA-125 in the setting of imaging-confirmed benign fibroid does NOT indicate malignancy. ### CA-125 in Benign vs. Malignant Fibroids | Feature | Benign Fibroid | Leiomyosarcoma (LMS) | |---------|---|---| | **CA-125 level** | Mildly elevated (usually <100 U/mL) | Often markedly elevated (>100 U/mL) | | **Imaging appearance** | Homogeneous, well-demarcated, low signal on T2 MRI | Heterogeneous, ill-defined margins, high signal on T2, necrosis/hemorrhage | | **Growth rate** | Slow or stable over years | Rapid growth (>2 cm/year) | | **Symptoms** | Pressure effects (mass effect) | Pain, hemorrhage, systemic symptoms | | **Frequency** | ~99.5% of smooth muscle tumors | ~0.5% (rare) | **Clinical Pearl:** Leiomyosarcoma is extremely rare (0.1–0.5% of uterine smooth muscle tumors). Rapid growth, heterogeneous imaging, and marked CA-125 elevation (>100 U/mL) are red flags; this patient's stable 8 cm fibroid with mild CA-125 elevation is benign. ### Diagnostic Approach to Elevated CA-125 in Fibroids ```mermaid flowchart TD A["Large fibroid + elevated CA-125"]:::outcome A --> B{"Imaging features?"}:::decision B -->|"Homogeneous, well-demarcated, low T2 signal"|C["Benign fibroid"]:::action B -->|"Heterogeneous, ill-defined, high T2 signal, necrosis"|D["Suspect LMS"]:::urgent C --> E{"CA-125 <100 U/mL?"}:::decision E -->|"Yes"| F["Peritoneal irritation from mass effect"]:::outcome E -->|"No"| G["Consider concurrent pathology"]:::action D --> H["MRI staging + tumor markers"]:::action H --> I["Oncology referral for surgical planning"]:::urgent ``` **Tip:** Always correlate CA-125 with imaging. A benign-looking fibroid with mild CA-125 elevation requires reassurance and conservative management, NOT oncology referral.