Myxofibrosarcoma was first described in 1977 by Angervall et al. [6]. It is a rare soft tissue malignancy with a high recurrence rate that usually occurs in elderly men, mostly in the limbs, and rarely in the heart. It may affect any of the four heart chambers but is more common in the left atrium [7]. The clinical manifestation of cardiac myxofibrosarcoma depends on the size and anatomic location of the tumor. The main manifestations are hemodynamic abnormalities, including heart murmurs, cardiac insufficiency, syncope or sudden death, and embolism caused by the shedding of the tumor itself and its fragments [8]. The clinical presentation of left atrial myxofibrosarcoma may resemble left atrial myxoma. Myxofibrosarcoma of the left atrium can cause mitral valve obstruction and cause symptoms of mitral stenoses, such as dyspnea, cough, hemoptysis, and so on [9]. In this case, chest pain and tightness were the main symptoms.
Cardiac myxofibrosarcoma is a rare cardiac malignancy with rapid progression, so early detection and treatment are of crucial importance. Cardiac ultrasound examination can identify the tumor's location, scope, size, shape, and the relationship with the surrounding tissue and dynamically assess the activity pattern of tumors and the degree of dysfunction caused by it. It is an indispensable diagnostic technology for identifying the types of cardiac tumor. Cardiac ultrasound is divided into transthoracic ultrasound and transesophageal ultrasound. Transesophageal ultrasound is not affected by external factors, such as obesity and thoracic deformity. It also has a higher resolution of the tissue structure and can obtain more anatomical information about the heart. Unfortunately, our patient could not tolerate transesophageal ultrasound due to age and physical reasons.
The main ultrasonic manifestations of myxofibrosarcoma in the left atrium are low or moderate echogenicity mass attached to the valve or atrium wall in the left atrium, with unclear boundary with attachment, irregular shape, and uneven echogenicity. In addition, the tumor is generally large, with no pedicle and a wide base, which can invade pulmonary veins, etc. [10, 11]. Some patients are complicated with pericardial effusion. Differential diagnosis is required with the following diseases: (1) left atrial myxoma: most myxomas are attached to the edge of the oval fossa, and very few are attached to the atrial wall, valves, etc. The tumor body is mostly oval or round; the echo is relatively uniform, and the pedicle is relatively narrow and clear. Myxoma has a high degree of activity and can move with diastolic contractions [12, 13]. (2) Left atrial thrombus: thrombus is often accompanied by the primary disease. Most thrombi occur in the left atrial posterior wall, lateral wall, and left atrial appendage; a few can extend to the atrial septum. A thrombus is generally oval or irregular in shape. Its echo behaves differently over time. The thrombus is sessile, and its base is usually broad. Old thrombus does not move with diastolic cardiac contraction. However, fresh thrombus can slightly change, and can also fall off and free in the left atrium. In addition, the phenomenon of spontaneous development can be observed in the heart cavity. It can be greatly changed after anticoagulant application [14]. (3) Atrioventricular valve vegetation often occurs in patients with a history of primary diseases, such as rheumatic heart disease and infective endocarditis. Vegetation mostly occurs in the part of blood flow impact or local vortex, such as the atrial surface with incomplete mitral valve closure, the ventricular surface with incomplete aortic valve closure, etc. Vegetation varies in size but is usually small and varied in shape, and its echo varies with time. Discontinuous areas of echo can be found in newly formed vegetations, suggesting abscess formation. Complications, such as valve perforation, pseudovalvular tumor, fistula, valve regurgitation, and similar, can also occur [15, 16].
Magnetic resonance imaging (MRI) has been reported to be useful for classifying myxofibrosarcoma. Mucous components are predominant in low-grade myxofibrosarcoma while less in middle and high-grade myxofibrosarcoma. T1-weighted images of mucus components showed a slightly lower signal number, while their T2-weighted images showed a high signal and mild enhancement after enhancement. In some cases, serrated, meshlike, and mild patchy enhancement was observed [17]. Unlike myxoid degeneration, cystic degeneration and necrotic areas are more common in highly malignant myxofibrosarcoma without enhancement in enhanced scanning [18]. Lefkowitz et al. [19] suggested that the "tail sign" of myxofibrosarcoma was related to the malignancy of the tumor. The growth pattern of myxofibrosarcoma along fascia, neurovascular, or muscle tissue resulted in abnormal signals in MR T2-weighted images, enhanced MRI, and short-time inversion recovery (STIR) sequence images. It manifested as a curvilinear signal with a clear boundary and gradually tapering, namely, "tail sign", which was the most common imaging manifestation of myxofibrosarcoma, with a reported occurrence rate of 64–77% [19, 20]. To sum up, MRI figures have prominent importance in the grading of myxofibrosarcoma, which cannot be matched by ultrasound. Unfortunately, in this case, the patient was claustrophobic and unsubtible to undergo an MRI examination.
Fludeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) is another useful non-invasive imaged approach that can be used to accurately detect the number, location, and distant metastasis of primary cardiac tumors. FDG PET/CT imaging evaluates the glucose metabolism status of tumor tissues at the molecular level, reflects cell activity, and provides functional metabolism information beyond anatomical imaging [21]. FDG PET/CT imaging can provide information regarding tumor staging, guide tumor treatment, and evaluate its efficacy. However, due to its high expenditure, FDG PET/CT imaging is not considered as a routine test. In this case, the patient refused to undergo this test. Although MRI and PET/CT have unique advantages in diagnosing myxofibrosarcoma, these two tests cannot be used as routine examinations, mainly due to their high cost, and long time. On this basis, ultrasound should be considered as the first choice for myxofibrosarcoma imaging examination.
Although ultrasound, MRI, and PET/CT can provide an important basis for diagnosing myxofibrosarcoma, the final diagnosis depends on pathology. According to relevant literature reports, vimentin, CD34, and Ki-67 are mostly positive or strongly positive in myxofibrosarcoma, among which vimentin is the most characteristic for diagnosing high-grade myxofibrosarcoma [22]. In this case, vimentin and Ki-67 were positive and CD34 was negative. Cardiac myxofibrosarcoma progresses rapidly and has serious consequences due to its pathological characteristics. Therefore, surgery is still the main treatment for primary left atrial malignant tumor [23]. The effectiveness of adjuvant chemotherapy and radiotherapy is still controversial [24]. Therefore, early and complete surgical resection offers the best chance of survival.
Cardiac myxofibrosarcoma is a rare cardiac malignancy whose diagnosis is challenging. Cardiac ultrasound has a good diagnostic and differential diagnosis; it is simple and safe to perform; the diagnosis rate of cardiac myxofibrosarcoma can be greatly improved by summarizing the ultrasonographic manifestations of cardiac myxofibrosarcoma and differentiating it from other lesions. The combination of ultrasound, clinical manifestations, and pathological findings can provide a valuable reference for diagnosing and treating myxofibrosarcoma.
