Echinococcus Infection and Hydatid Pericarditis
Cardiac
Echinococcus Infection
Even in endemic regions, the heart is rarely affected by Echinococcus disease; the incidence of primary myocardial involvement is less than 2% in human echinococciasis (echinococcosis). The parasitic six-hooked embryo reaches the myocardium through the coronary circulation, having passed through the gastric or intestinal mucosa into the portal circulation, and through both the hepatic and the pulmonary capillary bed. It can establish itself and develop into an echinococcus cyst in almost any part of the myocardium, but cysts are mostly located in the walls of the ventricles (see Plate 6-149). There is a higher incidence of cysts in the myocardium of the left ventricle because its vascular bed is more abundant. The developing parasitic membranous cyst is surrounded by a fibrous sac or capsule, the adventitia. When it grows larger, the cyst may protrude into a cardiac cavity, the pericardial sac, or both, its greater and more prominent part usually projecting toward the pericardium.
Primary echinococcus cyst of the heart
is mostly single and slow growing. Less often, more than one cyst and rarely multiple
cysts may develop. A single cyst infrequently remains univesicular and intact. In addition to free hydatid
fluid, the adventitial capsule usually contains degenerated fragments of the ruptured
original membranous cyst the mother cyst and multiple, even hundreds of, daughter cysts,
both unruptured and ruptured and varying in size. Rupture of the membranous cyst
is likely because of the repeated trauma of continuous heart movement. On
rupture, the membranous cysts may die, the content of the adventitia becomes caseous
and inspissated, and the adventitial capsule may calcify.
During the progressive enlargement of
the echinococcus cyst, disastrous complications can occur. The cyst may rupture
into a cardiac cavity or into the pericardial sac. Such ruptures may cause sudden
death from anaphylactic shock and hydatid embolism, which is usually cerebral (less
often, pulmonary). If the person survives, hematogenous dissemination occurs
(more often in the CNS), with the eventual development of multiple metastatic or
secondary cysts in the brain, usually with a fatal outcome. Rupture into the pericardial
sac produces acute hydatid pericarditis (hydatid disease). Implantation of brood
capsules and scolices in the pericardium leads to chronic hydatid pericarditis (hydatidopericardium)
with fibrous tissue reaction and secondary cyst formation.
Clinically, the uncomplicated single
cyst, when small and particularly if dead, may be asymptomatic. As it grows larger,
atypical or even undetermined symptoms may appear, although these do not lead to
the diagnosis. Radiographs show an eccentric deformity protruding from the contour
of the cardiac shadow, generally as a circular or ovoid, homogeneous, welldefined
opacity continuous with the outline of the heart silhouette. Calcification may also
appear and is more distinct on
CT. Transmitted cardiac pulsation in
the opacity is demonstrated on fluoroscopy. The ECG may be useful in diagnosis and
more accurate localization of the cyst, showing myocardial ischemia and conduction
changes more often than with other imaging. Angiocardiography is a valuable adjunct
to the radiologic investigation, whereas heart catheterization is of no diagnostic
value. Casoni intradermal and Weinberg tests add greatly to the establishment of
the diagnosis. The correlation of radiographic and angiocardiographic findings with
ECG changes, supplemented by positive
biologic tests and eosinophilia, in a person living in an endemic region, should
lead to the diagnosis of cardiac echinococcus disease.
Treatment of cardiac Echinococcus infection (echinococciasis, echinococcosis, hydatid disease, hydatid pericarditis) should remove the cyst. In select patients, surgery should be performed under extracorporeal circulation. If the cyst has not ruptured into a heart chamber, surgery probably will result in cure.