Clinical overview
Uterine leiomyomas (fibroids) are the most common gynaecological tumour: by age 50, ~70% of white women and ~80% of Black women have at least one. In South Africa, the burden is therefore enormous. Most are asymptomatic; symptomatic disease arises from a combination of size, location, and number, producing the clinical phenotypes of heavy menstrual bleeding (Heavy menstrual bleeding management), bulk pressure symptoms, pain, infertility, and adverse obstetric outcomes. The registrar's task is to correlate location, size, and histology to symptoms — and to choose between expectant, medical, interventional, and surgical management.
Core knowledge
Pathology
Histology:
- Monoclonal benign smooth muscle tumour.
- Whorled bundles of spindle-shaped smooth muscle cells with abundant eosinophilic cytoplasm.
- Mitotically inactive; nuclear pleomorphism minimal.
- Pseudocapsule of compressed adjacent myometrium (key for surgical enucleation).
- Variable connective tissue stroma.
- Pseudo-vascular system: large peripheral feeding vessels, paucity of internal vasculature — explains susceptibility to ischaemic degeneration.
Genetic and molecular:
- Most have somatic mutations: MED12 (~70%), HMGA2 rearrangements, fumarate hydratase (FH) mutations.
- Steroid hormone-responsive: oestrogen and progesterone drive growth (regress at menopause unless on HRT).
- Familial clustering; hereditary leiomyomatosis and renal cell cancer (HLRCC) — FH mutations.
FIGO classification of fibroid location
This 0–8 system is essential for surgical planning and predicts symptoms:
- Type 0: pedunculated submucosal.
- Type 1: submucosal, <50% intramural.
- Type 2: submucosal, ≥50% intramural.
- Type 3: 100% intramural, contacts endometrium.
- Type 4: intramural.
- Type 5: subserosal, ≥50% intramural.
- Type 6: subserosal, <50% intramural.
- Type 7: pedunculated subserosal.
- Type 8: extrauterine (e.g., cervical, broad ligament, parasitic).
Types 0–2 dominate HMB symptoms; types 5–8 dominate bulk symptoms.
Degenerations
Hyaline, cystic, red and calcific degeneration have distinct appearances that explain symptoms and imaging findings.
- Hyaline degeneration — most common; homogeneous pink replacement of muscle on histology; usually asymptomatic.
- Cystic degeneration — cysts form from coalescent hyaline change; mimics ovarian cyst on imaging.
- Red degeneration — ischaemic infarction in pregnancy. Acute pain, low-grade fever, raised CRP, mildly raised WCC. Self-limiting; analgesia + reassurance. See Acute pelvic pain pathophysiology.
- Calcification — late degenerative change; "popcorn" calcifications on imaging.
- Sarcomatous change (leiomyosarcoma) — RARE (<0.5% of clinically diagnosed fibroids); typically presents with rapid growth, postmenopausal growth, MRI features (irregular margins, high T2 signal, restricted diffusion). Important consideration when choosing morcellation (avoid in suspected malignancy) and HRT use after fibroid history.