Clinical overview
The fibroma is the commonest benign solid ovarian tumour and the prototype of the pure stromal (sex cord–stromal) group in the WHO Classification of Tumours of the Female Genital Tract, 5th ed (2020). It is a low-complexity ("LOTS") lesion in pathological terms, yet the clinical traps around it are out of all proportion to how bland the tumour itself is. A fibroma is a firm, white, fibroblastic neoplasm of the ovarian stroma that is almost always benign, yet it generates two important eponymous syndromes in gynaecology — Meigs syndrome (ovarian fibroma + ascites + pleural effusion, all of which resolve after removal of the tumour) and Gorlin (naevoid basal cell carcinoma) syndrome, in which bilateral, often calcified fibromas appear in young patients. The clinical problem the fibroma poses is therefore not malignancy but mistaken identity: a solid adnexal mass with ascites and a pleural effusion looks, to the untrained eye, exactly like advanced ovarian carcinoma, and the elevated CA-125 that frequently accompanies the effusions reinforces that false alarm.
In a South African public-sector setting this matters because access to definitive imaging (good-quality transvaginal ultrasound, MRI, CT) and to specialist gynaecological-oncology review is uneven, and a woman presenting at a district hospital with a solid pelvic mass, abdominal distension and breathlessness may be triaged straight onto a presumed-malignancy pathway. Recognising the fibroma–thecoma family on its pathological merits — and understanding that Meigs syndrome is a complete mimic that is cured by simple oophorectomy — prevents both over-treatment (radical surgery, neoadjuvant chemotherapy) and under-treatment. The objective centres on the gross, microscopic and molecular pathology, but the assessment and management that follow anchor that pathology to real decisions. Cross-link the broader differential of solid and cystic adnexal lesions at Adnexal mass in pregnancy, Genital tract cysts and the malignant end of the ovarian spectrum at Endometrial carcinoma and Gynaecological sarcomas.
Core knowledge
Classification and cell of origin
In the WHO-2020 scheme, the ovarian sex cord–stromal tumours are divided into pure stromal tumours, pure sex cord tumours, and mixed sex cord–stromal tumours. The fibroma sits in the pure stromal group, alongside the thecoma, fibrothecoma, sclerosing stromal tumour, signet-ring stromal tumour, microcystic stromal tumour and the malignant fibrosarcoma. Its cell of origin is the ovarian stromal fibroblast — the spindle cell of the ovarian cortex that, in the thecoma, acquires lipid and becomes hormonally active. Because fibroma and thecoma lie on a single morphological continuum, the hybrid fibrothecoma is a common and legitimate diagnosis, and the distinction matters clinically only insofar as it predicts oestrogen production.
Fibromas are not derived from germ cells or surface (Müllerian) epithelium, which is why they neither contain the teratomatous tissues of a dermoid nor the glandular/serous architecture of an epithelial tumour, and why their tumour markers behave differently from epithelial cancers. They account for roughly 4% of all ovarian neoplasms and the great majority of solid, hormonally silent ovarian masses. Most are unilateral and solitary; bilaterality and multiplicity should immediately raise the question of Gorlin syndrome.
Gross / macroscopic features
Figure D18.1 — The ovarian fibroma: a benign sex cord-stromal tumour of bland spindle fibroblasts in collagen — solid, firm, white, hormonally silent.
The classic fibroma is a firm, solid, well-circumscribed, encapsulated, often lobulated mass that replaces or expands the ovary. The key gross descriptors are:
- Cut surface: hard, chalky-white to greyish-white, with a whorled or trabeculated ("watered-silk") fibrous pattern, reflecting interlacing fascicles of collagen-producing spindle cells. This whorled white cut surface is the single most recognisable macroscopic feature.
- Consistency: firm to rubbery, frequently described as "rock-hard"; the firmness comes from dense collagen.
- Size: highly variable — incidental small nodules of a few centimetres up to massive tumours exceeding 20 cm. Larger tumours are far more likely to be symptomatic and to be associated with ascites.
- Secondary changes: focal oedema, cystic degeneration, hyaline change, and calcification are common, especially in larger lesions. Calcification is a particular hallmark of the fibromas of Gorlin syndrome, which are also typically bilateral, multinodular, and arise in younger patients.
- No haemorrhage or necrosis as a rule: extensive haemorrhage or necrosis is atypical and should prompt consideration of a cellular fibroma or fibrosarcoma.