Can a leiomyoma completely replace ovarian architecture on histopathology?

Can Leiomyoma Completely Replace Ovarian Architecture on Histopathology?

Yes, ovarian leiomyomas can completely replace normal ovarian architecture on histopathology, though this is an uncommon occurrence. This represents a rare benign smooth muscle tumor arising within the ovary itself, distinct from the far more common uterine leiomyomas.

Understanding Ovarian Leiomyomas

Ovarian leiomyomas are rare benign tumors that can present as solid ovarian masses and may entirely replace the normal ovarian tissue 1, 2. These tumors:

• Occur predominantly in reproductive-age women, with a mean age of approximately 45.8 years 1
• Are strongly associated with concurrent uterine leiomyomas in approximately 78% of cases, suggesting a common hormonal or genetic predisposition 1
• Can reach substantial size, with some cases reporting masses as large as an adult head 2

Histopathologic Features

The histologic appearance of ovarian leiomyomas mirrors their uterine counterparts 3:

• Composed of interlacing fascicles of spindle-shaped smooth muscle cells that are histologically virtually indistinguishable from normal myometrium 4
• May exhibit degenerative changes including hyalinization (particularly in tumors ≥4 cm), central degeneration, and cystic changes 1, 5
• Typically have low mitotic indices (<1/10 high-power fields in most cases), confirming their benign nature 1
• Can be confirmed by immunohistochemistry showing desmin positivity and Masson trichrome staining, establishing smooth muscle origin 3

Critical Diagnostic Considerations

Preoperative Imaging Challenges

Ovarian leiomyomas are frequently misdiagnosed as other pathology preoperatively 2, 6:

• Pedunculated uterine fibroids are the most common solid adnexal masses and can be mistaken for ovarian masses 7
• Transvaginal ultrasound with color Doppler is the first-line examination with 90-99% sensitivity for detecting fibroids, but cannot reliably distinguish ovarian from uterine origin 7
• Carefully identify both ovaries during ultrasound to avoid misdiagnosing pedunculated uterine fibroids as ovarian masses 7

When Degenerative Changes Complicate Diagnosis

Large ovarian leiomyomas with extensive degenerative changes can mimic ovarian malignancy 6, 5:

• Rapid growth, cystic degeneration, and elevated CA-125 (up to 389.5 IU/ml reported) can create diagnostic confusion with ovarian carcinoma 6
• MRI with diffusion-weighted imaging is the most effective preoperative modality for distinguishing benign from malignant solid ovarian masses when ultrasound is inconclusive 7, 8
• Age and menopausal status are critical risk factors: postmenopausal women with growing masses warrant heightened suspicion for malignancy 7, 8

Differential Diagnosis of Solid Ovarian Masses

When encountering a solid ovarian mass that could represent complete replacement of ovarian architecture, consider:

• Fibrothecoma tumors, which present as solid adnexal masses diagnosable on ultrasound 7
• Ovarian leiomyosarcoma, though extremely rare (leiomyosarcomas comprise only 0.1% of all uterine tumors but 1.7% in women undergoing hysterectomy in their seventh decade) 9, 8
• Other spindle cell tumors that display gross anatomical and histological similarities 5

Histopathologic Criteria to Exclude Malignancy

Permanent sections are required for definitive diagnosis, as frozen section cannot reliably distinguish benign from malignant due to difficulty identifying mitoses 9, 8:

• Benign criteria: Low mitotic index (<10 mitotic figures per 10 high-power fields), absence of cellular pleomorphism, no coagulative tumor necrosis 9, 8
• Malignancy criteria: >10 mitotic figures per 10 high-power fields, cellular pleomorphism, and coagulative tumor necrosis 9, 8
• Degenerative changes alone (hyaline degeneration, calcification, cystic changes) are benign variants and do not indicate malignancy 9

Clinical Management Implications

The prognosis for ovarian leiomyomas is excellent, with no evidence of recurrence in available follow-up studies 1:

• Surgical excision (typically oophorectomy or salpingo-oophorectomy) is both diagnostic and curative 2, 3
• Avoid morcellation when malignancy cannot be excluded preoperatively, as tumor spillage dramatically worsens prognosis if leiomyosarcoma is present 7, 8
• En bloc resection is the standard approach when the diagnosis is uncertain 8

Key Clinical Pitfall

The most important pitfall is failing to recognize that a solid ovarian mass could be a benign ovarian leiomyoma rather than an ovarian malignancy 2, 5. This is particularly challenging when:

• The mass demonstrates rapid growth 6
• Degenerative changes create a complex solid-cystic appearance on imaging 6, 5
• CA-125 is elevated 6
• The patient is postmenopausal 7, 8

In these scenarios, maintain a high index of suspicion but proceed with appropriate surgical staging if malignancy cannot be excluded, while recognizing that benign ovarian leiomyoma remains in the differential diagnosis 7, 2.