Thoracic Imaging 2003 - Society of Thoracic Radiology

will usually display the limbs of the baffle well. In addition, it is
important to assess right ventricular function, as the right ventricle
is not designed for the job of pumping blood against systemic
pressures. Right ventricular size, function, and mass can
be measured using double oblique short axis cine images. A
failing right ventricle is an indication for cardiac transplantation.
More recently, the Mustard and Senning repairs have mostly
been replaced with the Jatene or arterial switch procedure. In
the Jatene procedure, the great vessels are divided above the
semilunar valves, with reattachment of the aorta to the left ventricle
and the main PA to the right ventricle. Coronary arteries
are reimplanted onto the ascending aorta. Complications include
obstruction of the proximal pulmonary arteries, narrowing of the
RV outflow, enlargement of the aortic root, and supravalvar AS.
L-Transposition of the great arteries (synonyms L-TGA,
corrected transposition, or congenitally corrected transposition)
results from an abnormal L-loop of the heart embryologically,
leading to a ventricular switch, with the systemic veins connecting
to the right atrium, the anatomic left ventricle, and the main
PA, with the pulmonic venous blood draining to the left atrium,
the anatomic right ventricle, and the aorta. Associated septal
defects and valvular stenoses are common. Physiologically, the
connections are the same as those seen in D-TGA after Mustard
repair, and as such patients may present in adulthood as the
right ventricle begins to fail. Multiplanar spin echo and cine
images are of use in evaluation of ventricular size, ventricular
mass, valvular function, and presence of septal defects.
Tetralogy of Fallot (TOF) and TOF-pulmonary atresia
account for about 10% of congenital heart disease. The classic
“Tetralogy” consists of pulmonary stenosis, VSD, overriding
aorta, and RV hypertrophy. Repair depends on the severity of
the pulmonary stenosis and involves closure of the VSD with
enlargement of the pulmonary outflow, usually with an extracardiac
patch. Sagital spin echo and cine MR images can demonstrate
complications in the RV outflow and PA patch, including
stenoses, aneurysms, and regurgitation. Right ventricular mass
and function can be assessed on short axis cine images.
Peripheral pulmonic stenoses and systemic collateral vessels are
well demonstrated on Gd-MRA.
In cases of severe stenosis or atresia, a conduit must be
placed from the right ventricle to the pulmonary artery, which
until repair receives blood from the requisite PDA. If the pulmonary
arteries are too small to allow definitive repair in one
stage, the patient must first undergo a palliative PA shunt to supply
increased pulmonary flow and allow for pulmonary arterial
growth. These shunts are listed in the appendix. The most common
shunt performed currently a modified Blalock-Taussig
(BT) shunt involving a graft from the subclavian artery opposite
from the side of the aortic arch to the pulmonary artery.
Complications include stenosis or thrombosis of the shunt,
which can be demonstrated on axial and coronal cine MR
images, as well as through lack of visualization on Gd-MRA.
Single ventricle repairs. The classification of single ventricles
is a topic that by itself could easily cover this entire ses-
sion. Lesions necessitating a single ventricle repair include tricuspid
atresia and hypoplastic left heart syndrome. No child
with a single ventricle will survive past infancy without palliative
surgery, thus all adults presenting for MR evaluation with
single ventricle will be post-op, often after multiple staged surgeries
and revisions. Regardless of the origin of the ventricle
(left, right, or monoventricle), the ventricle must be connected
to the systemic circulation to act as the systemic pumping
chamber. Pulmonic flow returns to the lungs either without a
pumping chamber or with the right atrium as the pumping
chamber.
In the Glenn shunt, the SVC is connected to the right PA,
with the IVC remaining admixed with the pulmonary venous
return. Later, the IVC can be anastamosed with either the right
or the left pulmonary artery, separating the pulmonic and systemic
circulations. In the classic Fontan operation, the right
atrial appendage is anastamosed with the pulmonary artery.
There are several variations. Two of the more common are the
lateral tunnel Fontan, in which the IVC is baffled through the
atrium, and a fenestrated Fontan, in which a hole is left in the
baffle to allow for decompression of the systemic venous circuit.
The Fontan pathway is often well demonstrated on axial and
coronal spin echo and cine MR images. Complications include
systemic venous hypertension, with right atrial enlargement,
which can then secondarily compress the right inferior pulmonary
vein. This is most common in the classic Fontan, as the
right atrium is not designed to pump against pulmonary arterial
pressure. Obstruction or stenosis of the conduit may also develop,
and residual atrial septal defects may be present. MR is
superior to echocardiography for demonstrating pulmonary
artery anastamoses. Several different obliquities angled to the
plane of the anastamosis may be necessary for a complete evaluation.
In addition, cine MR images through the ventricle can
determine size, mass, and function. Precise delineation of cardiac
anatomy and associated anomalies can be of use in preoperative
planning for cardiac transplantation.
Conclusions
The CT and MR evaluation of adult patients with congenital
heart disease is a complex topic that defies easy summary. A
few of the entities I have not even touched opon include truncus
arteriosis, double outlet ventricles, patent ductus arteriosis, and
Ebstein’s anomaly. Patients vary in their anatomy, mental status,
and stamina, yielding wide variation in ability to cooperate with
the breath hold images required for ideal evaluation.
Examinations must be tailored to the individual patient based on
the clinical questions to be answered and the patient’s ability to
cooperate. The radiologist must usually personally monitor each
case. I urge all thoracic radiologists to develop a familiarity with
cardiac MR imaging. If radiologists are not willing to undertake
this challenging but rewarding task, there are many cardiologists
who are willing to fill the void.
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