An ovarian mass often prompts immediate concern about cancer. One such growth is an ovarian fibroma, a non-functional tumor arising from the ovary’s structural tissues. Understanding the specific nature of these solid masses is important. This article clarifies the composition of ovarian fibromas and addresses their risk of malignancy.
The Nature of Ovarian Fibromas
Ovarian fibromas are solid, non-functional tumors originating from the stromal component (connective tissue framework) of the ovary. Classified as sex cord-stromal tumors, they are the most common type of benign solid ovarian tumor, accounting for approximately 4% of all ovarian neoplasms. Histologically, these growths are composed primarily of spindle-shaped stromal cells interspersed with abundant collagen fibers.
The vast majority of fibromas are benign and non-cancerous, meaning they do not metastasize. They are most frequently found in middle-aged women, with the average age at diagnosis being around 48 years. Their size is highly variable, ranging from a few millimeters to over 20 centimeters, but the tumors are typically slow-growing and unilateral, affecting only one ovary.
Separating Fibromas from Malignancy
A pure ovarian fibroma is overwhelmingly benign. The risk of a standard fibroma transforming into a malignant growth is extremely low, with some reports suggesting less than 1% undergo sarcomatous change. The primary concern is not transformation, but that a different, aggressive tumor may be mistakenly identified as a fibroma before surgery. Malignant counterparts, such as ovarian fibrosarcomas, are exceedingly rare but can appear similar to fibromas on initial imaging.
Pathologists must carefully distinguish standard fibromas from higher-risk tumors, such as cellular fibromas or Stromal Tumors of Uncertain Malignant Potential (STUMPs). This differentiation relies on microscopic features, including the number of dividing cells (mitotic figures) and the presence of severe nuclear atypia. A correct diagnosis ensures the patient receives appropriate treatment and avoids unnecessary interventions.
Ovarian fibromas are uniquely associated with Meigs syndrome, a triad of symptoms that can alarm both the patient and the clinician. This syndrome involves the ovarian fibroma, a build-up of fluid in the abdominal cavity (ascites), and fluid around the lungs (pleural effusion). This presentation mimics advanced ovarian cancer, which frequently causes ascites and pleural effusions.
The fact that Meigs syndrome is caused by a benign fibroma highlights the diagnostic challenge, as symptoms strongly suggest widespread malignancy. However, the defining feature of true Meigs syndrome is that both the ascites and pleural effusion resolve completely once the ovarian fibroma is surgically removed. This resolution confirms the benign nature of the cause.
Identifying and Managing Fibromas
Many ovarian fibromas are discovered incidentally during routine pelvic examinations or imaging, as they often cause no symptoms. When symptoms occur, they may include pelvic heaviness, chronic pelvic pain, or abdominal swelling due to the mass or the development of ascites. In a small percentage of cases, fibromas can cause the ovary to twist (torsion), leading to sudden, acute abdominal pain that requires emergency intervention.
The diagnostic workup typically begins with imaging, such as a transvaginal or transabdominal ultrasound, to characterize the mass as solid and determine its size. Magnetic Resonance Imaging (MRI) may be used to differentiate a fibroma from a pedunculated uterine fibroid or a potentially malignant solid tumor. A blood test for the tumor marker CA-125 is often performed, which can be confusing because its level is frequently elevated in ovarian cancer.
The CA-125 level can also be raised with an ovarian fibroma, particularly when the mass is large or associated with ascites. This non-specific elevation contributes to the diagnostic dilemma, heightening suspicion of malignancy even in a benign case. The standard treatment is surgical removal, either through a conservative ovarian cystectomy (which preserves the ovary) or an oophorectomy. Surgery is often necessary for a definitive diagnosis, as only a full pathological examination of the removed tissue can conclusively confirm the mass is a benign fibroma and not a malignant mimic.