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Leiomyomatosis refers to diffuse or multifocal proliferation of benign smooth muscle tissue, most often arising from the uterus but may extend beyond.

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Unlike a solitary leiomyoma (“fibroid”), leiomyomatosis denotes a diffuse/multinodular pattern.

Classification

Variants	Key features
Uterine Leiomyomatosis	• Multiple leiomyomas in the uterus (common).
• Often seen in premenopausal women, associated with menorrhagia, dysmenorrhea, infertility.
Diffuse Peritoneal Leiomyomatosis (DPL)	• Rare. Multiple smooth muscle nodules studding the peritoneal cavity.
• Usually in women of reproductive age, strongly associated with exogenous estrogen exposure (oral contraceptives, pregnancy).
• Radiologically can mimic peritoneal carcinomatosis or metastases.
Intravenous Leiomyomatosis (IVL)	• Benign uterine smooth muscle tumor that extends into venous channels (uterine veins → IVC → right atrium).
• Can cause cardiac symptoms if tumor thrombus reaches heart.

Pathogenesis

Hormonal (estrogen-dependent).
Seeding of myometrial cells after surgery (e.g., hysterectomy, morcellation).
Metaplastic transformation of mesothelial cells (in peritoneal form).

Clinical Features

Uterine leiomyomatosis: menorrhagia, infertility, mass effect.
DPL: often asymptomatic, may present with abdominal pain, mass.
IVL: pelvic pain, abdominal mass, cardiac symptoms (syncope, right heart obstruction) if intracardiac extension.

Radiology

Variant	Imaging features
Uterine leiomyomatosis	Multiple, well-defined, hypointense (T2) masses within uterus ± degeneration (cystic, calcific)
Diffuse peritoneal leiomyomatosis	Multiple peritoneal nodules, isodense/isointense to uterine muscle, enhance with contrast. Mimics peritoneal carcinomatosis but lacks ascites/omental caking.
Intravenous leiomyomatosis	• Worm-like intraluminal filling defects in pelvic/abdominal veins.
• Extends into IVC ± right atrium.
• Isointense to myometrium on MRI.
• May be mistaken for bland thrombus, but it enhances.

Differentials