Thoracic Imaging 2003 - Society of Thoracic Radiology

Adult Manifestations of Congenital Heart Disease
Gregory Pearson, M.D., Ph.D.
Objectives:
1) To review the MR and CT manifestations of congenital
heart disease commonly seen in adult patients, including
those that present in adulthood and those seen in adulthood
after pediatric repair.
2) To familiarize radiologists with the relevant clinical questions
for which adult congenital heart disease patients are
referred.
3) To describe typical MR and CT protocols for the rapid and
efficient evaluation of adult congenital patients.
Introduction
With recent advances in pediatric cardiac surgery, patients
with severe congenital heart disease that would previously not
have survived past infancy are now surviving into adulthood,
necessitating that adult thoracic radiologists familiarize themselves
with common postoperative appearances. In addition, less
severe congenital cardiac defects may remain occult during
infancy and present de novo in adulthood. It is thus important
for the thoracic radiologist to have a familiarity with the common
presentations of congenital heart disease in the adult
patient.
CT and MR imaging of the adult congenital patient has several
advantages over the imaging of pediatric patients.
Structures are larger and thus easier to see. Adult patients are
more able to perform breath hold images, which greatly
improves the resolution of small structures. In an infant or small
child breath hold images require general anesthesia with intubation
and timed pauses of the respirator. In addition, a postoperative
adult patient will usually come with a history. A detailed
history and review of previous imaging studies (MRI, echo, and
catheterization) can allow the radiologist to specifically focus on
the relevant clinical questions, thus greatly facilitating the performance
of an exam. As many patients with complex congenital
heart disease have undergone multiple surgical procedures, it
is best to learn as much as possible about the expected anatomy
before the patient goes on the table. This can save considerable
“head-scratching” while the patient is in the scanner. Thus coordination
with our colleagues in Cardiology is essential.
I have divided congenital heart disease in the adult patient into
three broad categories: the (usually) nonpathologic entities,
pathologic entities with de novo adult presentation, and pathologic
entities seen in the adult after pediatric palliation or correction.
As my presentation is limited to 20 minutes, these will
not all be covered in detail.
(Usually) non-pathologic entities
These lesions mostly fall into the category of vascular anomalies.
Right sided aortic arch is usually discovered incidentally
on review of chest films performed for unrelated reasons, seen
as a right-sided indentation on the trachea and the lack of a visible
left sided aortic arch. Most patients found incidentally will
have an aberrant left subclavian artery, as most patients with
mirror image branching will have associated congenital heart
disease. Left arch with an aberrant right subclavian artery is
also a common anomaly found in asymptomatic individuals.
Occasionally, patients with aberrant subclavian arteries may
present with dysphagia due to esophageal compression from the
anomalous vessel or from an aortic diverticulum, but this is the
exception rather than the rule. Other anomalies such as bovine
arch (common origin of the bracheocephalic artery and the left
common carotid) are perhaps better thought of as normal variants.
These often show up as the last line in a CT report prefaced
by the phrase “incidental note is made of…” Vascular
anomalies may require no further evaluation, or can usually be
well demonstrated in adults on CT, spin echo, and gradient echo
MRI images.
Venous anomalies are also occasionally seen within the
chest. These include persistent left SVC, with or without a
right SVC or a vein bridging the two bracheocephalic veins, an
entity perhaps most commonly diagnosed after noting the anomalous
course of a central venous catheter or pacemaker. This is
also a common associated anomaly in complex congenital heart
disease. Azygous continuation of the IVC also deserves mention,
for although it most commonly occurs as an isolated incidental
finding it is also highly associated with polysplenia syndrome,
one of the heterotaxy syndromes, which in its mild
forms can present in adulthood. As with arterial anomalies,
venous anomalies are usually well demonstrated on CT and MR
images.
Abnormalities with de novo adult presentation
Although most patients with VSD will present in infancy,
small VSDs will sometimes present in adulthood, as do many
patients with an ASD. The role of MR imaging is to attempt to
define the size and location of the defect and the size and direction
of the associated shunt. The high-pressure jet from a VSD
can usually be easily visualized of double oblique short axis or
4 chamber ECG gated bright blood cine cardiac images. The
size of the jet is highly dependent on the repetition times, with
shorter TE leaving less time for spins to dephase and thus lower
sensitivity for turbulent flow and a smaller jet. Thus standard
(non-breath hold) cine images will demonstrate a larger jet than
breath hold segmented k-space cine images, which are more
sensitive than the newer steady state cine sequences (true FISP,
balanced FFE, or FIESTA, depending on the MR manufacturer.)
Since atrial pressure is much lower than ventricular pressure,
and the interatrial septum is much thinner than the ventricular
septum, the visualization of an ASD can be more problematic.
Turbulent jets are not typically seen, and the interatrial septum
may not be visualized in its entirety in normal individuals. An
ASD can sometimes be revealed by eddy currents within the
atria on cine sequences that traverse the expected location of the
interatrial septum. In addition, shunts can be quantified by the
use of velocity-encoded MR imaging. In velocity-encoded
imaging, two cine images are generated at the same level, one
of which shows the magnitude of blood flow (magnitude image)
and the other the direction (phase image). By quantifying the
flow in the aorta and the main PA, the shunt fraction can be calculated
using commercially available software packages.
139
TUESDAY