A leiomyoma is a benign, non-cancerous tumor composed of smooth muscle tissue. These are the most common tumors found in the human body, especially within the uterus, where they are known as uterine fibroids. Leiomyomas can range in size from nearly microscopic to large masses that can fill the abdominal cavity. They can affect women of all ages but are most frequently diagnosed in those between 40 and 50 years old.
Uterine Leiomyomas by Location
Uterine leiomyomas are categorized based on where they develop within the uterus. The most common type is the intramural leiomyoma, which develops within the muscular wall of the uterus, known as the myometrium. These growths can range from very small to quite large, capable of distorting the natural shape and size of the uterus as they expand.
Submucosal leiomyomas grow just beneath the inner lining of the uterus, protruding into the uterine cavity. In contrast, subserosal leiomyomas develop on the outer surface of the uterus, projecting away from the organ and into the pelvic cavity.
A variation of these is the pedunculated leiomyoma. These growths are attached to the uterus by a stalk-like structure called a peduncle. A pedunculated submucosal fibroid hangs into the uterine cavity, while a pedunculated subserosal fibroid extends into the pelvic or abdominal area.
Leiomyomas in Other Body Locations
While the uterus is the most common site, leiomyomas can form in other areas of the body with smooth muscle tissue. These non-uterine leiomyomas are much less common.
One type is the cutaneous leiomyoma, or piloleiomyoma, which originates from the small arrector pili muscles attached to hair follicles, the same muscles responsible for causing “goosebumps.” They appear as small, firm bumps on the skin’s surface and can be sensitive or painful to the touch.
Another type is the angioleiomyoma, or vascular leiomyoma, which arises from the smooth muscle in the walls of blood vessels. These are most commonly found in the lower extremities, such as the legs and feet, and can be associated with sharp, localized pain.
Leiomyomas can also develop in other parts of the genital tract, including the vulva, vagina, and ovaries. In these locations, they present as firm masses and may be discovered during a gynecological exam. Any symptoms depend on their size and position.
Associated Symptoms and Complications
Many leiomyomas, especially small ones, do not produce noticeable symptoms. When symptoms do arise, they are linked to the size, quantity, and location of the growths.
Submucosal leiomyomas are directly linked to changes in menstrual bleeding. By disrupting the endometrial lining, they can cause heavy, prolonged periods (menorrhagia), which can lead to anemia. Their position can also interfere with fertility by affecting embryo implantation or contributing to miscarriages.
Large intramural and subserosal leiomyomas are associated with “bulk” symptoms. As they enlarge the uterus, they can press on nearby organs. A fibroid pressing on the bladder may lead to frequent urination, while one pressing on the bowel can cause constipation or low back pain. This enlargement can also create a persistent feeling of pelvic pressure or abdominal fullness.
A specific complication of pedunculated leiomyomas is torsion. If the stalk these fibroids are attached by twists, it cuts off their blood supply. This event causes a sudden onset of severe pelvic pain, often with nausea and fever, and requires prompt medical attention.
Distinguishing Benign from Malignant Growths
While leiomyomas are benign, a rare cancer called leiomyosarcoma can arise from the same smooth muscle tissue. It is a common misconception that benign leiomyomas can become cancerous over time. Current medical understanding is that leiomyomas do not transform into leiomyosarcomas; a leiomyosarcoma is a distinct type of tumor from its beginning. The chance of a tumor initially thought to be a fibroid actually being a sarcoma is very low.
Differentiating between a benign leiomyoma and a malignant leiomyosarcoma before surgery is challenging. Imaging like ultrasound and MRI can identify features that raise suspicion, but they cannot provide a definitive diagnosis. Final confirmation is made through a microscopic examination of the tissue after it has been surgically removed.
Certain clinical signs may increase suspicion for a leiomyosarcoma. The rapid growth of a uterine mass, particularly in a person who has gone through menopause, is a red flag. Postmenopausal bleeding associated with a new or growing uterine mass is another sign that warrants further investigation to rule out malignancy.