Giant Ovarian Leiomyoma Mimicking a Malignant Intra-Abdominal Tumor

Introduction

Leiomyoma is a benign mesenchymal tumor characterized by smooth-muscle differentiation, most commonly arising in the uterus. Its occurrence in the ovary is exceedingly rare, with fewer than 100 reported cases since it was first described in 1862 [1]. Ovarian leiomyoma presents across a wide range of ages, ranging from 17 to 79 years, with diverse and nonspecific symptoms, making preoperative diagnosis challenging [2]. Additionally, large ovarian masses, especially when associated with degenerative changes or infarction, can resemble malignant neoplasms due to their size and imaging characteristics. In this report, we present the case of a 68-year-old woman with a large intra-abdominal mass initially suspected to be malignant, which was ultimately diagnosed as an ovarian leiomyoma. We describe her clinical presentation, surgical management, and histological findings.

Case Report

A 68-year-old para 4 woman with diabetes mellitus, hypertension, and seropositive rheumatoid arthritis presented with progressive abdominal distension over 4 years, with rapid enlargement in the past 2 years.

On physical examination, the abdomen was distended with a palpable mass reaching midway between the umbilicus and xiphoid process. Transabdominal ultrasound revealed a normal uterus with a large pelvic mass (16–30 cm), with no normal ovaries visualized. Tumor markers showed normal CEA and CA19.9 levels, while CA-125 was slightly elevated at 51 U/mL. The Risk of Malignancy Index (RMI) score for ovarian cancer was 153.

CT thorax, abdomen, and pelvis (CT-TAP) demonstrated a well-defined, lobulated, heterogeneously enhancing, solid-cystic mass predominantly occupying the left lower quadrant, measuring 16.9×25×16.9 cm, with an apparent right ovarian origin. The uterus and left ovary were normal (Figure 1).

Total abdominal hysterectomy and bilateral salpingo-oophorectomy (TAHBSO) was performed. Intraoperatively, a right ovarian mass measuring 20×20 cm was identified along with 50 ml of intraperitoneal fluid.

Gross examination revealed a right ovarian tumor measuring 12.0×18.5×21.0 cm, continuous with residual ovarian tissue. Serial sectioning showed a firm, whitish, solid surface with cystic changes and focal hemorrhage and necrosis. The uterus measured 12.0×6.0×3.2 cm, with a 0.7×0.6×0.5 cm intramural tan-whitish lesion in the myometrium. The cervix, fallopian tubes, and left ovary appeared normal.

Microscopic examination revealed a well-circumscribed mass composed of interlacing bundles of spindle cells. The cells were uniform with elongated cigar-shaped nuclei and eosinophilic cytoplasm (Figure 2). Areas of cystic degeneration were present. No atypical cells, increased mitotic activity, or malignant features were noted. The tumor in the myometrium exhibited similar morphology. Lymph nodes and omentum were unremarkable with no evidence of malignancy. Immunohistochemistry showed strong, diffuse positive staining for smooth-muscle actin (SMA) (Figure 3) and desmin (Figure 4), with a Ki-67 proliferation index of <1%.

A final diagnosis of ovarian leiomyoma was made. Postoperatively, the patient was well with no complications. During the 10-month follow-up visit, CT thorax, abdomen, and pelvis (CT-TAP) showed no evidence of local recurrence and CA-125 was in normal range (18 U/mL).

Discussion

Primary ovarian leiomyomas are rare benign tumors, with only a limited number of cases reported in the literature. The largest documented ovarian leiomyoma measured 29.5 cm and was identified in a young nulliparous woman [3]. In general, giant leiomyomas are defined as tumors weighing more than 11.4 kg or having a diameter greater than 17 cm [4].

The histogenesis of ovarian leiomyoma is still unclear. Some authors have stated they arise from smooth muscle of ovarian hilar blood vessels, while others suggest they arise from smooth muscle of the ovarian ligaments, smooth muscle metaplasia of cortical stroma, ovarian ligament, multipotent ovarian stromal cells, and other smooth muscle components in ovarian tumors [5,6].

The clinical presentation of ovarian leiomyomas depends on the size; in most reported cases they are small (<3 cm), and the patient is usually asymptomatic, and some are detected incidentally during physical examination or surgery. An enlarged tumor mass can result in pelvic pain and can be further complicated by acute abdomen due to torsion or necrosis of the tumor [7].

Preoperative assessment of patients with suspected ovarian tumors includes a thorough clinical history and physical examination, radiological imaging, and evaluation of tumor markers, particularly when malignancy is a concern. Among the available tumor markers, cancer antigen 125 (CA-125) is one of the most widely utilized for ovarian cancer. In the present case, the CA-125 was mildly elevated at 51 U/mL. While CA-125 is valuable for monitoring treatment response and disease recurrence, its limited specificity can lead to false-positive results in benign conditions such as benign ovarian tumors, uterine leiomyoma, endometriosis, and pelvic inflammatory disease [8,9]. Elevated CA-125 levels can occur due to irritation or inflammation of the peritoneal lining, during the premenopausal phase, or in early pregnancy [9,10]. Furthermore, elevated CA-125 levels are not exclusive to ovarian cancer and are also observed in malignancies of the endometrium, lung, breast, and colorectal tissue [10]. CA-125 also varies with age – Funston et al analyzed data from over 50 000 women in UK primary care settings and found PPV varied significantly with age, from 3.4% in women <50 years to 15.2% in women ≥50 years [11]. Therefore, interpretation of CA-125 levels should always be integrated with demographic details, clinical findings, imaging results, and histopathological evaluation to ensure diagnostic accuracy.

Imaging plays a crucial role in the characterization of ovarian tumors and facilitating preoperative planning. Ultrasound and magnetic resonance imaging (MRI) are the primary modalities used for evaluating ovarian lesions. Ovarian leiomyomas on ultrasound typically resemble their uterine counterparts, often demonstrating echogenicity similar to myometrium, with a heterogeneous, predominantly hypoechoic echotexture, comparable to the myometrium. In the present case, a transabdominal ultrasound revealed a normal uterus with a large pelvic mass (16–30 cm), with no normal ovaries visualized. Although MRI offers soft-tissue contrast and is more effective in detecting degenerative changes, only computed tomography (CT) was performed. The CT scan imaging revealed a giant ovarian mass with a heterogeneously enhancing solid-cystic appearance, raising the suspicion of malignancy. CT scans are known to have limitations in assessing degenerative changes within soft tissues or differentiating benign from malignant ovarian tumors [12]. In general, on MRI, leiomyomas appear as solid masses with low signal intensity on both T1- and T2-weighted sequences and exhibit early contrast enhancement [6,13]. A systematic review by Wang et al supports the use of MRI as a superior imaging modality for evaluating ovarian tumors due to its enhanced diagnostic capability, especially in characterizing tissue composition and identifying benign features [14]. Therefore, when available, MRI may be the best method for preoperative assessment of ovarian masses.

Intraoperative frozen section can play a crucial role in the diagnosis of ovarian tumors and helps determine the necessary extent of surgical intervention. Palakkan et al found, the overall diagnostic accuracy of frozen sections for ovarian masses was 93.3%. For benign ovarian tumors, frozen section demonstrated a sensitivity of 95.5%, specificity of 100%, positive predictive value (PPV) of 100%, and negative predictive value (NPV) of 88.24%. While for malignant ovarian tumors, the sensitivity was 90.91%, specificity 97.96%, PPV 90.91%, and NPV 97.96% [15]. A similar result was seen in another study, which showed high sensitivity (90%) and specificity (97%) [16]. A study by Zhang et al found that only 40% of cases were correctly diagnosed as leiomyoma on frozen section, while the remaining cases were misdiagnosed as fibroma (30%) or ovarian spindle cell tumors (30%) [1]. In the present case, frozen section was not requested by the attending surgeon, as there was suspected ovarian malignancy. Subsequently, an extensive surgical removal (staging laparotomy, total abdominal hysterectomy, bilateral salpingo-oophorectomy, infracolic omentectomy, and bilateral pelvic lymph node dissection) was performed. This underscores the importance of frozen section in surgical management of ovarian masses.

Although the histological features of ovarian leiomyomas share distinct characteristics with their uterine counterparts, their rarity often necessitates consideration of other tumors in the differential diagnosis. The primary differential diagnoses include sex cord-stromal tumors such as fibromas and thecomas, and, most importantly, leiomyosarcoma [17].

Immunohistochemical analysis is essential for distinguishing between leiomyomas and sex cord-stromal tumors. Desmin is typically positive in leiomyomas but is generally negative in sex cord-stromal tumors. In contrast, smooth-muscle actin is frequently expressed in both leiomyomas and sex cord-stromal tumors, making it less useful for differential diagnosis [17]. Additionally, ovarian leiomyomas must be differentiated from leiomyosarcomas. Leiomyosarcomas are often hypercellular and exhibit a fascicular and/or storiform growth pattern with marked cytological atypia and high mitotic activity. However, some tumors contain leiomyoma-like areas. Furthermore, leiomyosarcomas can present with tumor cell necrosis and/or infarct-type necrosis [18].

The management of leiomyoma involves multiple approaches, including medical treatment, surgical intervention, and uterine artery embolization. The choice of approach varies depending on several factors, such as patient age, symptom severity, risk of malignancy, and reproductive plans [19]. Surgical intervention remains the primary treatment modality for leiomyoma. In the present case, the patient underwent staging laparotomy, total abdominal hysterectomy, bilateral salpingo-oophorectomy, infracolic omentectomy, and bilateral pelvic lymph node dissection due to clinical suspicion of ovarian malignancy.

Conclusions

Ovarian leiomyoma is a rare entity, and cystic degenerative changes can mimic a malignant ovarian tumor, potentially leading to unnecessary radical surgery. This case highlights the importance of considering ovarian leiomyoma in the differential diagnosis of ovarian masses to ensure a timely and effective treatment plan.