Uterine fibroids, also known as leiomyomas, are non-cancerous muscular growths that develop within the uterus. These growths are extremely common, affecting a significant percentage of women during their reproductive years. While many fibroids remain small and cause no symptoms, others can lead to a variety of issues, with abnormal uterine bleeding being one of the most frequently reported concerns. Whether a fibroid causes bleeding depends entirely on its specific location within the uterine structure. This article focuses on clarifying the role of subserosal fibroids in the context of abnormal bleeding.
Understanding Uterine Fibroids and Their Location
Fibroids originate from the myometrium, the thick muscular wall of the uterus. They are classified into distinct types based on the exact layer of the uterine wall where they grow. This classification is important because the location dictates the symptoms a person may experience.
The three primary categories are named relative to the uterine layers: the inner lining (endometrium), the muscle wall (myometrium), and the outer surface (serosa). Submucosal fibroids are situated just beneath the endometrium, bulging into the uterine cavity. Intramural fibroids are embedded entirely within the myometrial muscle wall. Subserosal fibroids grow on the outside wall of the uterus, just under the serosal layer.
Subserosal Fibroids: Characteristics and Impact on Bleeding
Subserosal fibroids grow outward from the uterus, projecting toward the abdominal cavity. This outward growth pattern is the primary reason they do not typically cause heavy or abnormal uterine bleeding. They are physically separated from the endometrium, the tissue that sheds monthly during menstruation.
Because the fibroid is situated on the outer surface, it does not distort the lining of the uterine cavity. This means the menstrual cycle’s normal shedding process is generally undisturbed. The mechanism responsible for menstrual bleeding—the breakdown and sloughing of the endometrial tissue—remains intact and functional.
Subserosal fibroids are generally unrelated to complaints of excessive menstrual flow or bleeding between periods. The symptoms they do cause are related to their size and the pressure they exert on neighboring pelvic and abdominal organs.
The Fibroid Types That Cause Abnormal Uterine Bleeding
When fibroids cause abnormal uterine bleeding, the culprit is most often a growth that impacts the endometrial lining or the muscle wall’s function. Submucosal fibroids are the type most strongly associated with heavy, prolonged, or irregular menstrual bleeding. Their position directly under the endometrium and bulging into the cavity causes significant disruption to the lining.
Even small submucosal fibroids can lead to substantial blood loss by increasing the total surface area of the endometrium available for shedding. They can also interfere with the localized vascular architecture and the proper formation of blood vessels needed for normal hemostasis. This interference can lead to an inability of the endometrium to heal correctly after a menstrual cycle.
Intramural fibroids, growing within the muscle wall, also contribute to heavy menstrual bleeding, particularly when they are large or numerous. They can distort the shape of the entire uterine cavity, which increases the area of the shedding endometrial surface. A large intramural fibroid can impede the uterus’s ability to contract effectively, which is the mechanical action necessary to compress blood vessels and stop bleeding after the endometrial lining has shed.
Non-Bleeding Symptoms of Subserosal Fibroids
Although subserosal fibroids rarely cause bleeding, they produce symptoms related to their outward growth and bulk. As they expand into the pelvic or abdominal space, they place mechanical pressure on surrounding organs. This pressure can lead to a feeling of heaviness or fullness in the lower abdomen.
Large subserosal fibroids commonly compress the bladder, resulting in symptoms such as a frequent or urgent need to urinate. If the fibroid is positioned posteriorly, it may press on the bowel, leading to constipation or discomfort.
Pedunculated Fibroids and Torsion
In some cases, a subserosal fibroid may be attached to the uterus by a slender stalk, classifying it as a pedunculated fibroid. If a pedunculated subserosal fibroid twists on its stalk, a condition known as torsion, it can cut off its own blood supply. This event causes sudden, severe pelvic pain, which requires immediate medical attention. Other pressure-related symptoms include lower back or leg pain if the growth impinges on nerves in the pelvic region.