# Uterine Leiomyoma Pathology > Leiomyoma pathology for MBBS Pathology: oestrogen dependence, site classification, degeneration types, glassy whorled histology and red degeneration. - Canonical URL: https://prepelephant.com/topics/mbbs/pathology/leiomyoma-pathology - Exam / course: MBBS · Subject: Pathology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Uterine Leiomyoma Pathology", PrepElephant, https://prepelephant.com/topics/mbbs/pathology/leiomyoma-pathology ## Direct answer Leiomyoma (fibroid) is the commonest tumour in women — a benign, oestrogen-dependent neoplasm of smooth muscle whose cut surface is whorled, grey-white and sharply circumscribed, whose cells in bundles run in intersecting fascicles with blunt-ended cigar-shaped nuclei, and whose behaviour follows its site: submucous fibroids bleed heavily and distort the cavity, intramural ones enlarge the uterus asymptomatically, subserous ones pedunculate or press on bladder and rectum, and cervical ones threaten the ureters. Size tracks reproductive hormones — growing in pregnancy, shrinking after menopause — and degeneration (hyaline, cystic, red, fatty, calcific) is the tumour's response to outgrowing its blood supply, with sarcomatous transformation a rare event a pathology answer must always qualify. ## What you must remember - **Site classification and clinical logic:** submucosal (menorrhagia, infertility, miscarriage — closest to endometrium), intramural (commonest), subserosal (mass effect, pedunculated, rarely parasitic when it draws omental blood supply), intraligamentous and cervical; a submucosal fibroid prolapsing through the cervix mimics a uterine inversion or polyp. - **Histology that names the tumour:** interlacing fascicles of smooth-muscle cells with eosinophilic cytoplasm, blunt-ended "cigar" nuclei, minimal atypia and no mitoses to speak of; the gross whorled, bulging, rubbery white surface with a false capsule of compressed surrounding myometrium is the spot-diagnosis. - **Degeneration ladder:** hyaline (commonest, homogeneous eosinophilic collagen), cystic (liquefaction), red or carneal (haemorrhagic infarction in pregnancy, with pain and low-grade fever — a classic obstetric emergency), fatty, calcific (the radio-opaque fibroid of the postmenopausal), and hydropic. - **Hormonal signature:** oestrogen and progesterone receptor-rich, hence growth on oral contraceptive pills and pregnancy and shrinkage after menopause; GnRH agonists shrink them preoperatively at the price of bone loss. - **Malignant transformation is rare:** sarcomatous change occurs in well under 1% — the exam sentence must be quantified; leiomyosarcoma more often arises de novo than from a fibroid. - **Fibroid versus leiomyosarcoma on histology:** the triad of diffuse atypia, high mitotic count (more than 10 mitoses per 10 high-power fields for outright sarcoma) and coagulative tumour-cell necrosis; a smooth-muscle tumour with two of three features is STUMP (smooth-muscle tumour of uncertain malignant potential). - **Special variants worth naming:** cellular leiomyoma, lipoleiomyoma, epithelioid leiomyoma, symplastic (bizarre) leiomyoma with atypical nuclei but benign course; intravenous leiomyomatosis worms through veins, and benign metastasising leiomyoma seeds lungs postpartum — benign tissue, malignant geography. ## A bleeding uterus, worked through A 38-year-old multipara presents with years of worsening menorrhagia and a twelve-week-size irregularly enlarged uterus; her haemoglobin is 7.8 g/dL. Step one: confirm the anatomy — ultrasound or saline infusion sonography mapping the fibroids, because management follows site more than size; an intramural fundal fibroid in a woman nearing menopause may simply be watched, a submucosal one explains her anaemia and needs hysteroscopic resection. Step two: correct the iron deficiency, and consider tranexamic acid or hormonal modulation (levonorgestrel intrauterine system where cavity shape permits). Step three: choose the operation — myomectomy for the woman wanting fertility (with the classical warning about scarred uterus in future labour), hysterectomy for the completed family with severe symptoms, uterine artery embolisation for the unfit or those declining surgery. The pathologist's report afterwards reads "leiomyoma with hyaline degeneration" — a reminder that a rapidly growing "fibroid" in a perimenopausal woman is the situation where sarcoma must be excluded, ideally before the operation is planned as minimally invasive morcellation, which can upstage an unsuspected leiomyosarcoma. ## Where students slip Two slips dominate. First, the unquantified sentence "fibroids can turn malignant" — correct teaching is transformation in well under 1%, and leiomyosarcoma is usually de novo; the examiner is testing whether you know the order of magnitude. Second, calling every painful enlarged fibroid in pregnancy a "red degeneration" without the mechanism: pregnancy's high hormone levels enlarge a tumour whose blood supply lags, and venous obstruction produces infarct-like haemorrhagic necrosis with local peritonism and low-grade fever — treated supportively, because surgery in pregnancy risks rupture and preterm labour. The third, subtler slip: diagnosing sarcoma from size or rapid growth clinically; only the histological triad — atypia, mitotic count, coagulative necrosis — makes that call, which is why STUMP exists as a category at all. ## Frequently asked questions ### Which fibroid site causes menorrhagia most? Submucosal fibroids, which distort and enlarge the endometrial surface and cavity, causing heavy cyclical bleeding, dysmenorrhoea and sometimes infertility. ### What is red degeneration? Haemorrhagic infarction of a fibroid, typically in pregnancy or on oral contraceptives, presenting with acute pain, tenderness and low-grade fever, managed conservatively. ### How does a leiomyosarcoma differ histologically from a fibroid? Diffuse cytological atypia, coagulative tumour-cell necrosis and mitotic activity exceeding 10 per 10 high-power fields; tumours with ambiguous features are labelled STUMP. ### Why do fibroids shrink after menopause? Their cells are rich in oestrogen and progesterone receptors, so the hormonal withdrawal of menopause deprives them of growth stimulation, with hyaline and calcific degeneration following. ### What is intravenous leiomyomatosis? Benign smooth-muscle tumour growing within uterine and pelvic veins, sometimes reaching the heart via the inferior vena cava — histologically benign but surgically perilous.