Uterine fibroids are non-cancerous growths that develop in the uterus, also known as leiomyomas or myomas. They can vary significantly in size. While many people with fibroids experience no symptoms, others may have heavy bleeding or pelvic discomfort. This article explores the internal characteristics of uterine fibroids, offering insight into their appearance from a macroscopic to a microscopic level.
General Characteristics of Fibroids
Uterine fibroids are benign growths composed of smooth muscle cells and fibrous connective tissue, originating from the muscular wall of the uterus. They are the most common non-cancerous tumor in females. Their external appearance typically presents as firm, round, well-defined nodules that are often pale or whitish.
Fibroids can develop in various locations within the uterus. Intramural fibroids grow within the muscular wall, making them the most common type. Submucosal fibroids form under the inner lining, sometimes protruding into the uterine cavity. Subserosal fibroids grow on the outer surface and can become quite large. Some fibroids, called pedunculated fibroids, are attached by a stalk.
Macroscopic Internal Appearance
When a uterine fibroid is cut open, its internal appearance reveals distinct characteristics. The cut surface often displays a characteristic whorled or swirling pattern, which can resemble the grain of wood. This pattern is due to the interwoven bundles of smooth muscle and fibrous tissue that make up the fibroid.
The color of the cut surface is typically pale white or grey, though this can vary based on vascularity or degenerative changes. For instance, increased blood supply might appear reddish, while certain types of degeneration could lead to yellowish areas. The texture is generally firm, rubbery, or tough to the touch. Fibroids often possess a distinct boundary, sometimes referred to as a pseudo-capsule, which helps separate them from the surrounding normal uterine tissue.
Microscopic Internal Features
Under a microscope, the internal composition of a uterine fibroid provides a more detailed view. Fibroids are primarily made up of bundles of smooth muscle cells. These muscle cells are arranged in an interwoven or fascicular pattern, sometimes described as a “herringbone” arrangement.
Interspersed among the smooth muscle cells are varying amounts of fibrous connective tissue. Blood vessels are also present within the fibroid, though their density can differ. The cells within a fibroid typically appear uniform, lacking the atypical features or high cell division rates characteristic of cancerous growths. This cellular uniformity and low mitotic activity underscore their benign nature.
Factors Influencing Internal Appearance
The internal appearance of fibroids can be altered by various degenerative changes, which occur when the fibroid outgrows its blood supply. These changes lead to different visual characteristics.
Hyaline degeneration is the most common type, affecting about 60% of fibroids, and results in the fibroid tissue taking on a glassy, homogeneous appearance. Myxoid degeneration occurs when the fibroid becomes filled with a gelatinous substance, as smooth tissue is replaced by a transparent, mucus-like connective tissue.
Cystic degeneration, which occurs in about 4% of fibroids, involves the formation of fluid-filled spaces within the fibroid, often after hyaline degeneration, and can appear as a liquid, honeycomb pattern. Red degeneration, also known as carneous degeneration, typically occurs during pregnancy. It results from a hemorrhagic infarction, where blood supply is restricted, causing the fibroid to appear reddish and hemorrhagic. Calcification is another type of degeneration where calcium deposits accumulate, making the fibroid hard and chalky. This often gives it a “popcorn-like” appearance on imaging.