Meigs’ syndrome (MS) is an uncommon disorder characterized by the clinical triad of presentations including, benign ovarian tumor, ascites, and pleural effusion (PE), which disappear after tumor resection [1]. MS occurs in approximately 1% of all ovarian tumors. It is most commonly associated with ovarian fibromas, identified in 2–5% of surgically resected ovarian tumors [2]. MS is most frequently diagnosed in postmenopausal women, especially those around 50 years of age [3]. Presenting symptoms include fatigue, dyspnea, dry cough, weight loss, and abdominal distension. Due to non-specific symptoms and signs, many patients with MS are initially referred to general practitioners. Thus, a correct diagnosis is often postponed, and appropriate patient treatment is delayed in cases of potential malignant ovarian tumors in terms of systemic tumor cell dissemination.

An 85-year-old menopausal woman was referred to our hospital for diagnostic evaluation of worsening dyspnea over 6 weeks. The patient had a history of chronic atrial fibrillation, hypertension, and chronic kidney disease (CKD) of uncertain etiology. She had a uterine fibroid diagnosed at 64 years of age. Pre-admission medication included amlodipine (10 mg/day), valsartan (40 mg/day), verapamil (120 mg/day), digoxin (0.125 mg/day), and rivaroxaban (10 mg/day).

Her vital signs were as follows: blood pressure 146/97 mmHg, heart rate 90 beats/min and irregular, and respiratory rate 21 breaths/min. Physical examination revealed a third heart sound, diminished breath sounds from the right lower lungs, and notable bilateral leg edema, but no remarkable jugular vein distention (JVD) was observed. A hard mass was palpable in the lower abdomen. The electrocardiogram revealed atrial fibrillation. Chest radiography revealed cardiomegaly and right-sided PE (Fig. 1a). Laboratory testing revealed elevated levels of serum creatinine (1.36 mg/dL, reference, 0.65–1.07 mg/dL) and brain natriuretic peptide (BNP) (183 pg/mL, reference: < 18.4 pg/mL). Hepatic and thyroid function, C-reactive protein levels, and urinalysis were within normal ranges.

Echocardiography demonstrated normal left ventricular (LV) cavity size and systolic function, with an ejection fraction of 54% and left atrial dilation (35 mL/m²) (Additional files 1 and 2). Doppler and tissue Doppler profiles for the assessment of LV diastolic function revealed a decreased septal e′ of 5.8 cm/sec and an elevated E/e′ of 17, indicating elevated LV filling pressure. In addition, continuous wave Doppler revealed a peak tricuspid regurgitation velocity of 2.6 m/s, consistent with a pressure gradient of 27 mmHg and an estimated right ventricular systolic pressure of approximately 35 mmHg. Echocardiographic evaluation of the right heart revealed almost normal systolic function; tissue Doppler of the free lateral wall (S′) = 9 cm/s (reference: ≥ 10 cm/s), tricuspid annular plane systolic excursion = 18 mm (reference: 16 ≥ mm), and fractional area change = 53% (reference: ≥ 35%), respectively.

Thus, a tentative diagnosis of heart failure with preserved ejection fraction (HFpEF) was made. The patient was administered oxygen at 3 L/min and treated with intravenous loop diuretics (furosemide 40 mg daily). On day 6, although diuretic treatment improved leg edema, PE remained unchanged (Fig. 1b).

A subsequent diagnostic workup of unexplained PE was performed. The patient underwent thoracentesis with drainage of 1240 mL of serosanguineous PE. PE analysis revealed lymphocyte-predominant exudates fulfilling Light’s criteria (Table 1). Additionally, the serum-to-effusion albumin gradient was 0.3 g/dL (reference: ≤ 1.2 g/dL), further confirming the true exudative effusion. The adenosine deaminase activity in PE was 9.3 U/L. PE cytology, as well as the bacterial and mycobacterial cultures, were unremarkable.

Chest computed tomography revealed an absence of lung tumors or inflammatory infiltration after the removal of PE. Abdominal/pelvic computed tomography scan revealed bilateral inhomogeneous ovarian masses (Fig. 2). Magnetic resonance imaging further characterized the right substantial mass and detected a trivial ascites (Fig. 3). Axial and sagittal T2-weighted images demonstrated the peripheral hypointense mass, which contained hyperintense and multilocular areas in the central portion, mimicking a malignant ovarian tumor with a central necrosis or a degenerated subserosal fibroid. Gadolinium-enhanced axial imaging showed inhomogeneous enhancement correspondently on the peripheral solid portion, suggesting malignancy. In addition, screening tests for tumor markers revealed elevated CA-125 levels (382 U/mL, reference: < 35 U/mL). Repeated serial thoracentesis was ineffective, and PE reaccumulated within a week (Fig. 1c-f). Thus, we highly suspected of ovarian cancer with pleural dissemination. Nevertheless, a repeated cytological examination of PE revealed no evidence of malignancy, which led us to consider the possibility of MS.

On day 26, the patient underwent bilateral salpingo-oophorectomy (Fig. 4). The resected masses exhibited yellow-to-tan fleshy cut surfaces, with hemorrhage and extensive hyaline degeneration. Histopathological examination revealed a mitotically active cellular fibroma (MACF) of the ovary. Spontaneous resolution of the right-sided PE was noted post-operatively after 7 days of follow-up, confirming a definitive diagnosis of MS. A follow-up echocardiography revealed no significant changes. The post-operative course was uneventful, and the patient made a full recovery and was discharged with no changes to her pre-admission medication regimen on day 33. She remained clinically stable upon subsequent follow-up.

Typically, MS presents with right-sided PE and ascites in the presence of a benign ovarian tumor (e.g., fibroma). MS is common in middle-aged to elderly postmenopausal women. On the contrary, there are some reported cases of atypical MS with either PE or ascites and bilateral PE without ascites [4].

PE is a common finding caused by a wide variety of diseases and conditions. The leading causes of PE include chronic heart failure (HF), chronic renal failure, malignancy, pneumonia, and pulmonary embolism; thus, PE caused by such conditions requires differentiation from MS-associated PE. Our case also exhibited atypical MS manifestations, characterized by right-sided PE, notable leg edema, and trivial ascites, which was initially mistaken as HFpEF.

HFpEF is characterized by signs and symptoms of HF with preserved LV ejection fraction (≥ 50%) and evidence of diastolic dysfunction. Epidemiologically, the ratio of patients with HFpEF increases strikingly with age, especially in postmenopausal women having multiple noncardiac comorbidities, such as obesity, hypertension, CKD, and diabetes [5]. HFpEF is gaining considerable attention because of rapid population aging around the world [6].

Although MS and HFpEF are similar in terms of gender and age of onset and are accompanied PE, they differ in terms of prerequisite treatment strategies. Thus, MS-associated PEs must be clinically differentiated from HF-associated PEs. In our case here, PEs were non-responsive to diuretics, and bilateral leg edema was notable despite the absence of JVD; the findings suggested venous stasis yield by ovarian tumors. These mismatched findings might be a crucial key to the diagnosis of the uncommon disease presentation observed in our patient. Presumably, despite the evidence for LV diastolic dysfunction, mildly elevated circulating BNP levels are considered to be attributable to physiological elevation caused by aging and CKD.

Second, the serum-to-effusion albumin gradient was more useful in identifying exudative effusion in patients receiving diuretic therapy than were Light’s criteria [7]. A systematic review of the literature demonstrated that the majority of MS-associated PEs are exudates [3]. The mode of MS-associated PE is significantly right-sided (70%), followed by being bilateral (19%) and left-sided (11%). On the contrary, HF-associated PEs are transudates, and the mode of HF-associated PE is predominantly bilateral (64%), followed by being right-sided (24%) and left-sided (12%) [8]. Detailed analyses, including those for biochemical characteristics of PE, can provide valuable information concerning properties, etiologies, and possible mechanisms involved in PE formation. PE analysis is the first diagnostic approach for PE of unknown etiology, and Light’s criteria can distinguish transudate effusion and exudative effusion [7]. However, there is a pitfall in the evaluation of Light’s criteria because of enrichment of the protein or lactate dehydrogenase component of the PE caused by diuretic use. In fact, 29% of HF-associated PEs are misclassified as exudative in HF patients receiving diuretic therapy [9]. The serum-to-effusion albumin gradient has superior diagnostic value in detecting true exudative effusions compared with Light’s criteria (sensitivity, 87%; specificity, 92% and sensitivity, 98%; specificity, 83%, respectively) [7]. Moreover, the serum-to-effusion albumin gradient allowed for a correct diagnosis in our patient.

Although the etiology of PE and ascites remains unknown, MS has been considered to be a subset of porous diaphragm syndrome, characterized by a congenital or acquired anatomical defect, typically in the right hemidiaphragm, through which ascites can passage into the right-sided pleural space [10]. Another possible mechanism is that proinflammatory cytokines cause increased vascular permeability and capillary leakage. In fact, considerably elevated levels of vascular endothelial growth factor and interleukin-6 have been observed in serum, ascitic effusions, and PEs of patients with MS [11]. Moreover, the evidence that the majority of MS-associated PEs are exudative, strongly support this hypothesis [3]. However, we could not measure levels of any proinflammatory cytokines in the present case.

Finally, repeated cytological examination was helpful in the diagnosis of MS.

MACF of the ovary is a rare histopathologic entity; it is defined as a benign ovarian cellular fibrous tumor with high mitotic activity without severe atypia, has a different behavior from the distinct malignant behavior of ovarian fibrosarcoma, and is associated with a favorable outcome [12]. Owing to the high count of mitotic figures, MACF often provides diagnostic challenges in cases of pelvic mass with ascites, PE, and elevated tumor marker CA-125 levels. Nevertheless, our patient, after repeated benign cytologic findings, did undergo successful surgical treatment. Thus, this case highlights the clinical importance of MACF in the diagnostic workup of a potential malignant ovarian tumor. While its prognosis is considered generally favorable, poor prognostic factors, including postoperative residual tumor tissue, peritoneal adhesion, and capsular rupture, have been reported [13]. Long-term monitoring is needed for patients with MACF, since the natural history remains poorly understood.

Overall, herein, we described a case of MACF with MS mimicking HFpEF.

MS is extremely rare, yet frequently causes PE and ascites. The correct diagnosis and appropriate treatment are often missed, since a variety of diseases are also associated with the development of these common signs. Therefore, all clinicians should be aware of the clinical significance of MS in the diagnostic assessment of PE in postmenopausal female patients, and PE analysis and abdominal screening are warranted. Given the favorable prognosis of MS, clinicians should consider the possibility of performing surgical resection, even if a potentially malignant pelvic mass with PE, ascites, or both, are present.