DISCUSSION
The first description of an intracardial BC was reported by Elsässer as late as 184466, while Houser and colleagues are credited with the first use of echocardiography to identify such peculiar lesions4. In 1968 the first surgical removal of a MV BC was reported by Leatherman et al.3; as described by the authors ‘The cyst was attached to the septal leaflet at the point where the leaflet was joined by chordae tendineae. During excision the cyst was opened and blood drained out. Extracorporeal circulation lasted 18 minutes, and recovery was uneventful’3.
Intracardiac BCs are usually incidental necropsy findings or are diagnosed clinically predominantly in children, being extremely rare after the first year of life and particularly in adults1,2. They are considered benign tumors, nevertheless, while benign from the histologic point of view, they have been associated to relevant complications such as LVOT obstruction and coronary or systemic embolization with consequent severe sequelae such as stroke or myocardial infarction4,5,9,11,15,18,20,48. Transthoracic or transesophageal 2D echo are usually considered adequate to detect intracardiac masses even of small dimensions and the presence of an echo-free space within the mass may usually rise the suspicion of the presence of a blood cyst; others have considered formation of microbubbles inside the cyst, when using contrast real-time echocardiography, as pathognomonic of the presence of a BC12,17. However, sometimes solid cardiac tumors, such as myxomas, may present with similar echocardiographic features therefore being difficult to be differentiated from a benign BC7,8. Furthermore, it must be underlined that other intracardiac masses must be ruled out such as fibroelastomas or infectious vegetations which also frequently involve the cardiac valves and, therefore, the diagnosis of a BC is not always straightforward and needs histology to be confirmed. The potential role of magnetic resonance imaging has also been stressed in the diagnostic assessment of such patients particularly because of its specificity in ruling out signs of myocardial infiltration and therefore to exclude the presence of a malignant lesion26.
From this review it appears that management of patients with a blood cyst is still controversial21. Many advocate surgical excision while according to others serial clinical and echocardiographic surveillance can be adequate especially in the presence of masses of small size to monitor the rate and degree of growth15. Indeed, in 30% of the patients analysed surgery was not considered either for BC small size, clinical stability, patient refusal or advanced age. However, due to the potential for embolization of even small cardiac masses, including BCs, we believe that surgical removal should always be indicated not only to prevent the risk of complications but also to determine or confirm the exact diagnosis.
The origin of BCs of the cardiac valves is still unknown. The first hypotheses were formulated in the early 1900’ by Bayne-Jones, studying the blood vessels of the heart valves67. Large studies on hearts of dogs and mainly cows and calves obtained from slaughter houses, have demonstrated the presence of valvular BCs in almost 20% of hearts; the results of histological and ultrastructural evaluations support the hypothesis that BCs most likely derive from dilatation of the thin-walled valvular arteries due to the mechanical stresses induced by the pressure gradient when the atrio-ventricular valves are closed with consequent cyst formation68,69. This theory, however, does not explain the occurrence of BCs in low pressure structures such as the pulmonary valve55. Furthermore, it is not clear whether what observed in animal studies can be also be completely applied to human beings. According to Tsutsui et al., BCs could derive by blood trapped in valvular crevices or microscopic invaginations during development13; this might explain the finding of BCs in children but not BCs in adults with previously normal echocardiograms. Other consider BCs to derive from valvular hematomas24, or being secondary to endocardial inflammation; accordingly, the few cases observed following previous open heart surgery might indicate an additional risk factor of cardiac surgery in the development of BCs, although this most likely is just an occasional association22.
This review has some limitations. Since we have excluded from our analysis cases possibly contained in specific textbooks or pathological reviews and those with an uncertain diagnosis, the number of MV BCs may be underestimated. Even if the American Academy of Pediatrics has identified the upper age limit as 21 years for pediatric patients70, we arbitrarily considered 18 years as the lowest age for this review; elevating this limit would have further reduced the number of recognizable cases. Although some of the data which could be obtained from single cases were not complete, this review provides enough evidences to assess the clinical presentation, diagnostic modalities and management of patients with a cardiac valve BC found in adult patients.
In conclusion, BCs are rarely found in patients ≥18 years of age and predominantly affect the MV. Although in most cases they represent an incidental finding, sometimes they are heralded by serious acute complications such as syncope and stroke. For such reason surgical removal, which is a low-risk procedure and can be performed with minimally invasive techniques, should be advisable for BCs of the MV, even if of small size; on the other hand, BCs in the right heart may be treated conservatively unless they cause TV regurgitation or obstruction to blood flow. The origin of valvular BCs is still quite uncertain but since their histological benign nature is well known further studies on pathogenesis would have only a speculative interest. It is likely that the current widespread use of multimodality imaging will increase the number of intracardiac BC detected and hopefully the present review will help to improve management of such patients.