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.