Leiomyoma

Definition

Leiomyoma (fibroid) is the most common benign tumour of the uterus, arising from smooth muscle of the myometrium. Histologically it consists of intersecting fascicles of bland spindle-shaped smooth muscle cells with cigar-shaped nuclei, eosinophilic cytoplasm, and low mitotic activity.

General / Essential Features

• Intersecting fascicles of spindle-shaped smooth muscle cells
• Elongated cigar-shaped (blunt-ended) nuclei — no significant atypia
• Abundant eosinophilic cytoplasm
• Variable collagen between muscle bundles
• No significant nuclear pleomorphism or hyperchromasia
• Low mitotic activity (<5 mitoses per 10 HPF)

Sites

• Intramural: within myometrial wall — most common (70%)
• Subserosal: projecting from outer uterine surface — can become pedunculated
• Submucosal: bulging into endometrial cavity — causes heavy bleeding
• Cervical fibroids: rare
• Broad ligament fibroids: may compress ureter

Pathophysiology

Oestrogen and progesterone drive growth; leiomyomas have increased oestrogen receptor expression. Somatic mutations in MED12 (>70% of cases) drive clonal expansion. Growth is slow; menopause causes regression. Secondary degenerative changes: hyaline (commonest), cystic, red (carneous — in pregnancy), calcific.

Etiology

• Hormonal: oestrogen-dependent — increases in reproductive years, regresses post-menopause
• MED12 mutation: most common somatic driver
• Genetic predisposition: Black women have 3–5× higher incidence
• Obesity, nulliparity, early menarche — risk factors

Clinical Features

• Heavy menstrual bleeding (HMB) — leading to iron-deficiency anaemia
• Dysmenorrhoea and pelvic pain
• Urinary frequency or retention (pressure on bladder)
• Subfertility: submucosal fibroids distort endometrial cavity
• Abdominal mass in large fibroids
• Many are asymptomatic — incidental finding on ultrasound

Diagnosis

• Pelvic ultrasound: hypoechoic, well-defined myometrial masses
• MRI pelvis: gold standard for mapping fibroid location pre-surgery
• Hysteroscopy: for submucosal fibroids
• Histopathology: spindle cells, cigar nuclei, low mitoses

Treatment

• Conservative: GnRH analogues (leuprolide) to shrink fibroids pre-surgery
• Mifepristone or ulipristal acetate: SPRM for medical management
• Myomectomy: surgical removal preserving fertility
• Hysterectomy: definitive — for completed family or severe symptoms
• Uterine artery embolisation (UAE): minimally invasive alternative