A radiologist-focused review of HLHS, Fontan anatomy, absent IVC with azygos continuation, and Fontan-associated liver disease.

A 25-Year-Old Man With Persistent Chest Pain

Edited by ScholarGen MediAI Team

Executive Answer

A 25-year-old man presented with persistent chest pain, and contrast-enhanced cardiac CT demonstrated the characteristic anatomy of hypoplastic left heart syndrome (HLHS) after Fontan palliation. The key findings include a severely underdeveloped left-sided cardiac system, mitral stenosis, a lateral-tunnel Fontan pathway, a widely patent atrial septal communication, and marked right ventricular enlargement. The CT also shows a prominent systemic venous anomaly consistent with an absent inferior vena cava (IVC) with azygos continuation. An additional upper-abdominal image shows an irregular hepatic contour consistent with cirrhosis, illustrating an important long-term complication of Fontan physiology.

Why This Case Matters

Hypoplastic left heart syndrome is one of the most important forms of complex congenital heart disease encountered in cardiovascular imaging.

Although HLHS is primarily recognized as a neonatal and pediatric condition, patients who undergo staged surgical palliation can survive into adulthood. Consequently, radiologists increasingly encounter adults with surgically altered congenital cardiac anatomy rather than the native anatomy of untreated HLHS.

This case illustrates why interpretation of adult congenital heart disease requires more than recognizing a single abnormal chamber or valve. The radiologist must understand the surgical pathway, systemic venous anatomy, pulmonary blood flow, ventricular morphology, and extracardiac consequences of Fontan physiology.

The case is particularly valuable because the CT findings extend beyond the heart. The imaging demonstrates not only the reconstructed circulation but also an irregular liver contour compatible with cirrhosis, highlighting the systemic consequences that can develop after Fontan palliation.

Clinical Scenario

A 25-year-old man presented with persistent chest pain.

His prior medical history was not available in the clinical information provided.

Contrast-enhanced cardiac CT was performed.

The CT examination demonstrated features of previously treated hypoplastic left heart syndrome, including:

Mitral stenosis
A lateral-tunnel Fontan pathway
A widely patent atrial septal communication
Marked right ventricular enlargement
Abnormal systemic venous anatomy
An irregular hepatic contour compatible with cirrhosis

The final diagnosis in the case is hypoplastic left heart syndrome.

Imaging Findings

Cardiac CT

The cardiac CT demonstrates the characteristic postoperative anatomy of a patient with HLHS who has undergone Fontan palliation.

The most important findings are:

Hypoplastic left-sided cardiac structures
Mitral valve stenosis
Lateral-tunnel Fontan circulation
Widely patent atrial septal communication
Marked enlargement of the right ventricle
Abnormal systemic venous anatomy consistent with absent IVC and azygos continuation

The combination of these findings provides a coherent explanation for the patient's unusual adult congenital cardiac anatomy.

Figure 1. Sagittal Cardiac CT

Figure 1. Sagittal contrast-enhanced cardiac CT demonstrating surgically reconstructed cardiac anatomy in an adult with hypoplastic left heart syndrome and Fontan palliation.

ALT text: Sagittal cardiac CT showing hypoplastic left heart syndrome with lateral-tunnel Fontan anatomy in an adult patient.

Figure 2. Coronal Cardiac CT

Figure 2. Coronal contrast-enhanced cardiac CT demonstrating the Fontan circulation and abnormal systemic venous anatomy in a patient with hypoplastic left heart syndrome.

ALT text: Coronal cardiac CT demonstrating Fontan circulation and systemic venous anatomy in an adult with hypoplastic left heart syndrome.

The Key Vascular Clue: Absent IVC With Azygos Continuation

One of the most important vascular findings in this case is the absence of the inferior vena cava, with the azygos system continuing inferior systemic venous return.

This finding is particularly important in patients with complex congenital heart disease because systemic venous anatomy can be substantially different from normal anatomy.

The azygos system provides an alternative pathway for venous return when the hepatic segment of the IVC is absent or interrupted. In a patient with Fontan physiology, recognizing this anatomy is clinically important because the systemic venous pathway is an integral component of the surgically reconstructed circulation.

The case quiz specifically identifies absent IVC with azygos continuation as the prominent vascular abnormality.

For a radiologist, this is more than an incidental vascular variant. It changes the way the entire venous circulation should be interpreted.

Understanding the Fontan Circulation

The Fontan procedure is designed for patients with functionally univentricular congenital heart disease.

In conventional biventricular circulation, the right ventricle pumps blood toward the pulmonary arteries while the left ventricle pumps blood into the systemic circulation.

In HLHS, the left-sided structures are severely underdeveloped. The right ventricle therefore becomes the dominant systemic ventricle.

Fontan palliation creates a cavopulmonary connection, allowing systemic venous blood to reach the pulmonary arteries without requiring a dedicated ventricular pump for pulmonary blood flow.

The source case describes modified Fontan palliation as a complete cavopulmonary shunt that allows the dominant right ventricle to support systemic circulation.

This distinction is essential when interpreting postoperative CT.

A radiologist should not evaluate the heart as if it were a conventional two-ventricle circulation. Instead, the examination should be approached as a surgically reconstructed circulation.

Why the Right Ventricle Is Enlarged

The marked enlargement of the right ventricle is an important structural clue.

In HLHS, the left-sided cardiac structures are severely underdeveloped. After staged palliation, the right ventricle becomes the systemic ventricle and carries the major workload of systemic circulation.

Therefore, adult patients with Fontan physiology may demonstrate substantial right-sided remodeling.

The finding should be interpreted in the context of:

Ventricular morphology
Fontan pathway anatomy
Systemic venous return
Pulmonary arterial anatomy
Atrial-level communication
Surgical history

A large right ventricle in this setting should not automatically be interpreted using the same framework applied to isolated acquired right ventricular enlargement.

What Was the Original Congenital Heart Defect?

The underlying congenital heart defect in this case is hypoplastic left heart syndrome.

HLHS is characterized by severe underdevelopment of the left-sided cardiac structures. The source discussion describes involvement of the ascending aorta, aortic valve, mitral valve, and left ventricle, with compensatory enlargement of the right-sided cardiac structures.

The differential diagnosis listed in the case includes:

Hypoplastic left heart syndrome
Interrupted aortic arch
Endocardial fibroelastosis
Anomalous left coronary artery from the pulmonary artery

The final diagnosis is hypoplastic left heart syndrome.

Diagnostic Reasoning: How to Recognize HLHS on CT

A practical approach is to move from anatomy to physiology and then to surgical reconstruction.

Step 1: Identify ventricular morphology

Determine which ventricle is dominant and which ventricle is underdeveloped.

In this case, the right ventricle is markedly enlarged, while the left-sided system is hypoplastic.

Step 2: Evaluate the mitral and aortic valves

Look for severe abnormalities of the left-sided valves.

The case specifically identifies mitral stenosis.

Step 3: Assess the ascending aorta and aortic arch

The aorta should be evaluated carefully because left-sided obstructive abnormalities are fundamental to the HLHS spectrum.

Step 4: Identify the surgical pathway

Look for evidence of staged palliation and determine whether a Fontan pathway is present.

In this case, a lateral-tunnel Fontan is identified.

Step 5: Trace systemic venous return

Do not assume that the IVC follows normal anatomy.

The presence of an absent IVC with azygos continuation is a major vascular clue.

Step 6: Examine extracardiac organs

The field of view should be reviewed beyond the heart.

In this case, the upper abdomen demonstrates an irregular hepatic contour compatible with cirrhosis.

This final step is particularly important because Fontan-associated disease can extend beyond the cardiovascular system.

Fontan-Associated Liver Disease

The upper-abdominal CT image provides an important additional clue.

The liver demonstrates an irregular contour consistent with cirrhosis.

Figure 3. Axial Upper-Abdominal CT

Figure 3. Axial contrast-enhanced CT image of the upper abdomen demonstrating an irregular hepatic contour consistent with cirrhosis in a patient with Fontan physiology.

ALT text: Axial abdominal CT showing irregular hepatic contour consistent with cirrhosis after Fontan palliation.

This finding illustrates an important principle in adult congenital heart imaging: the examination should not stop at the heart.

The source discussion identifies congestive hepatopathy and cirrhosis among the important complications associated with Fontan physiology. Central venous congestion and thrombosis contribute to morbidity in patients after Fontan palliation.

Therefore, when reviewing CT examinations in Fontan patients, the liver deserves deliberate attention.

Why This Finding Can Be Missed

Adult congenital heart disease creates several potential diagnostic traps.

1. Treating the anatomy as if it were conventional

A radiologist unfamiliar with Fontan anatomy may misinterpret surgically redirected blood flow as abnormal vascular connections.

2. Focusing only on the presenting symptom

The patient presented with chest pain, but the major diagnostic information lies in the underlying congenital and postoperative anatomy.

3. Failure to trace systemic venous pathways

An absent IVC with azygos continuation can be missed if the venous system is not followed systematically.

4. Incomplete review of the upper abdomen

The irregular hepatic contour could be overlooked if attention remains focused exclusively on the cardiac findings.

5. Satisfaction of search

Once Fontan anatomy is recognized, there is a risk of prematurely concluding the interpretation without evaluating extracardiac complications.

The SGMP diagnostic-risk framework emphasizes missed findings, non-target abnormalities, incomplete field-of-view review, satisfaction of search, and cognitive bias when supported by the case.

Differential Diagnosis

The differential diagnosis for this imaging pattern should be driven by the anatomy rather than by the presenting symptom alone.

Hypoplastic Left Heart Syndrome

This is the final diagnosis in the case and is supported by the combination of hypoplastic left-sided structures, mitral abnormality, dominant right ventricle, and Fontan palliation.

Interrupted Aortic Arch

Interrupted aortic arch is included in the case differential diagnosis. It can produce severe congenital systemic outflow abnormalities but does not by itself explain the complete pattern of HLHS anatomy and Fontan reconstruction described here.

Endocardial Fibroelastosis

Endocardial fibroelastosis can produce significant ventricular dysfunction and remodeling but does not provide the same explanation for the characteristic surgically reconstructed circulation.

Anomalous Left Coronary Artery From the Pulmonary Artery

Anomalous left coronary artery from the pulmonary artery is another congenital cardiac abnormality in the listed differential, but it does not account for the overall Fontan anatomy and left-sided hypoplasia described in this case.

The Clinical Significance of the Fontan Operation

The Fontan procedure is not simply a surgical repair of one anatomic defect.

It fundamentally changes cardiovascular physiology.

The procedure establishes a pathway in which systemic venous blood flows toward the pulmonary circulation without passing through a subpulmonary ventricle.

This means that the Fontan circulation depends heavily on:

Low pulmonary vascular resistance
Efficient systemic venous return
Adequate pulmonary arterial anatomy
Appropriate ventricular function
Absence of significant venous obstruction
Effective cardiac output

The article emphasizes that Fontan patients can survive into adulthood, while also noting the important morbidity associated with venous congestion, thrombosis, congestive hepatopathy, and cirrhosis.

Imaging Physics and CT Interpretation

Contrast-enhanced CT is particularly useful for defining complex postoperative cardiovascular anatomy because it can simultaneously demonstrate:

Cardiac chambers
Great vessels
Pulmonary arteries
Systemic veins
Surgical pathways
Collateral vessels
Adjacent thoracic structures
Upper-abdominal organs

In complex congenital heart disease, multiplanar reconstruction is especially valuable.

Sagittal and coronal reformations can clarify the three-dimensional course of surgically created pathways and systemic venous structures that may be difficult to understand on axial images alone.

For the radiologist, the goal is not simply to identify a postoperative connection. The goal is to reconstruct the patient's circulation mentally and determine whether each component is anatomically coherent.

AI Perspective: Where Could Medical AI Help?

Medical imaging AI could potentially assist with selected components of complex congenital heart CT interpretation, particularly where the task involves structured detection, segmentation, or quantitative assessment.

Potential applications include:

Cardiac chamber segmentation
Great-vessel segmentation
Identification of vascular structures
Automated quantitative measurements
Detection of abnormal vascular pathways
Comparison with prior imaging
Structured reporting assistance
Longitudinal assessment of ventricular remodeling

However, this case also illustrates why congenital heart disease is a difficult environment for fully automated interpretation.

A postoperative Fontan circulation is highly dependent on patient-specific surgical anatomy. An AI system trained predominantly on conventional adult cardiac CT may encounter substantial domain shift when confronted with surgically reconstructed congenital anatomy.

AI Failure Modes in Fontan Imaging

If AI is used as a second reader, several failure modes should be anticipated.

False Negative

An AI model may fail to recognize an unusual venous pathway because the anatomy differs substantially from its training distribution.

False Positive

Normal postoperative structures may be flagged as abnormal because the system interprets surgically altered anatomy using a conventional anatomical model.

Anatomical Mislocalization

A model may identify a vessel correctly but assign it the wrong anatomical identity.

Dataset Bias

Training datasets may contain insufficient numbers of adult congenital heart disease examinations.

Domain Shift

A model developed using routine adult cardiac CT may not generalize reliably to complex postoperative congenital anatomy.

Automation Bias

Radiologists may place excessive confidence in an apparently normal AI output.

The appropriate role of AI is therefore decision support rather than replacement of expert interpretation. The SGMP framework specifically requires consideration of false positives, false negatives, domain shift, dataset bias, image quality, alert fatigue, generalization, and human oversight.

AI Workflow Opportunity

A potential enterprise imaging workflow could conceptually follow:

DICOM → PACS → AI Orchestration → AI Model → Inference → PACS Visualization → Radiologist → RIS → EHR/EMR

For this case, AI should function as a supporting layer rather than as an autonomous diagnostic authority.

For example, an AI system could potentially flag unusual systemic venous anatomy or identify morphological features that warrant closer review.

The radiologist would still need to verify:

The actual vascular anatomy
The surgical pathway
Ventricular morphology
Pulmonary arterial anatomy
Extracardiac findings
The clinical significance of abnormalities

This is particularly important in rare congenital disease, where unusual anatomy may fall outside the model's training distribution.

Diagnostic Risk and Workflow Impact

This case demonstrates a broader diagnostic principle:

Complex anatomy increases the importance of structured image review.

The risk is not necessarily that a radiologist will fail to recognize HLHS. The more subtle risk is that the radiologist may correctly recognize the major diagnosis but overlook an additional clinically relevant finding.

For a Fontan patient, the review should therefore extend systematically from:

Cardiac anatomy → Surgical pathway → Systemic veins → Pulmonary circulation → Great vessels → Liver → Remaining field of view

This approach reduces dependence on a single pattern-recognition moment and encourages deliberate review of anatomy that may otherwise be considered secondary.

Practical Radiology Pearls

Pearl 1: In an adult with unusual cardiac anatomy, always determine whether the circulation has been surgically reconstructed.

Pearl 2: A dominant right ventricle in the appropriate congenital and postoperative context can be a major clue to HLHS physiology.

Pearl 3: Do not assume a normal IVC in patients with complex congenital heart disease.

Pearl 4: Azygos continuation of systemic venous return is an important vascular clue and should be traced carefully.

Pearl 5: A Fontan pathway should be evaluated as a complete circulation rather than as an isolated surgical connection.

Pearl 6: Review the entire CT field of view, including the upper abdomen.

Pearl 7: An irregular hepatic contour in a Fontan patient should raise concern for chronic Fontan-associated liver disease.

Pearl 8: Postoperative congenital anatomy can be difficult for AI systems because of domain shift and anatomical variability.

Pearl 9: AI should be treated as a second-reader or workflow-support technology, not as a substitute for expert interpretation.

Pearl 10: In adult congenital heart disease, understanding the surgical history is part of understanding the imaging.

Common Pitfalls

Assuming the patient has conventional biventricular anatomy.
Failing to identify the dominant systemic ventricle.
Misinterpreting the Fontan pathway as an abnormal vascular connection.
Overlooking absent IVC with azygos continuation.
Reviewing only the cardiac structures and ignoring the upper abdomen.
Assuming that the presenting symptom explains all relevant imaging findings.
Failing to distinguish congenital anatomy from postoperative anatomy.
Overrelying on AI-generated findings in unusual anatomy.
Ignoring the possibility of clinically important extracardiac complications.
Stopping the interpretation after recognizing the primary congenital diagnosis.

Educational Quiz

Question 1

What is the prominent vascular finding on the cardiac CT?

A. Total cavopulmonary shunt
B. Absent inferior vena cava with azygos continuation of inferior venous return
C. Aberrant right subclavian artery
D. Duplicated inferior vena cava
E. Obstructive pulmonary embolus in the right pulmonary artery

Answer: B. Absent inferior vena cava with azygos continuation of inferior venous return.

This is the key systemic venous abnormality highlighted by the case.

Question 2

What congenital heart defect most likely underlies this patient's anatomy?

A. Tetralogy of Fallot
B. Hypoplastic left heart syndrome
C. Pulmonary atresia
D. Transposition of the great arteries

Answer: B. Hypoplastic left heart syndrome.

The case's final diagnosis is hypoplastic left heart syndrome.

Question 3

Which cardiac operation is demonstrated by the postoperative anatomy?

A. Modified Fontan procedure
B. Glenn procedure
C. Waterston-Cooley procedure
D. Rastelli procedure

Answer: A. Modified Fontan procedure.

The CT demonstrates a lateral-tunnel Fontan pathway, and the discussion identifies modified Fontan palliation as one of the treatment strategies for HLHS.

Question 4

What circulation is fundamentally addressed by the Fontan procedure?

A. Pulmonary circulation
B. Systemic circulation

Answer: A. Pulmonary circulation.

The Fontan pathway establishes a cavopulmonary connection, directing systemic venous blood toward the pulmonary arteries while the dominant ventricle supports systemic circulation.

Question 5

What long-term complication is demonstrated in the upper-abdominal CT image?

A. Liver cirrhosis
B. Splenic infarction
C. Gastric carcinoma
D. Abdominal aortic dissection

Answer: A. Liver cirrhosis.

The case describes an irregular hepatic contour consistent with cirrhosis and discusses congestive hepatopathy and cirrhosis as important complications after Fontan palliation.

Frequently Asked Questions

What is hypoplastic left heart syndrome?

Hypoplastic left heart syndrome is a severe congenital heart defect characterized by underdevelopment of the left-sided cardiac structures. In affected patients, the right ventricle becomes the dominant ventricle supporting systemic circulation.

What is the key CT finding in this case?

The key CT pattern is hypoplastic left-sided cardiac anatomy with mitral stenosis, a lateral-tunnel Fontan pathway, a widely patent atrial septal communication, marked right ventricular enlargement, and abnormal systemic venous anatomy.

Why is the inferior vena cava important in Fontan patients?

The systemic venous pathways are fundamental components of Fontan physiology. An absent IVC with azygos continuation therefore has important implications for understanding the patient's reconstructed circulation.

What is a lateral-tunnel Fontan?

A lateral-tunnel Fontan is a type of Fontan reconstruction in which an intra-atrial pathway directs systemic venous blood toward the pulmonary circulation.

Why is the right ventricle enlarged?

In HLHS, the right ventricle becomes the dominant systemic ventricle. After Fontan palliation, it remains responsible for systemic ventricular output.

What liver complication can occur after Fontan surgery?

Fontan physiology can be associated with chronic venous congestion and congestive hepatopathy, with cirrhosis among the recognized long-term complications described in the case. casestudy_12(1)

Can AI detect Fontan anatomy?

AI may potentially assist with segmentation, vascular analysis, quantitative measurements, and workflow support, but complex postoperative congenital anatomy presents challenges including dataset bias, domain shift, false positives, and false negatives.

Why should the entire CT field of view be reviewed?

Because important complications may occur outside the heart. In this case, the upper-abdominal CT demonstrates an irregular hepatic contour compatible with cirrhosis.

Key Takeaways

Hypoplastic left heart syndrome can be encountered in adults after successful staged palliation.
The right ventricle becomes the dominant systemic ventricle in HLHS.
A lateral-tunnel Fontan pathway is a critical postoperative imaging finding.
Absent IVC with azygos continuation is an important systemic venous clue.
Fontan physiology should be interpreted as a complete circulation rather than an isolated surgical connection.
The upper abdomen should be carefully reviewed in Fontan patients.
Cirrhosis and congestive hepatopathy are important long-term complications of Fontan physiology.
AI may assist with complex congenital cardiac imaging, but unusual postoperative anatomy creates significant opportunities for false-positive, false-negative, and domain-shift errors.
Expert radiologist oversight remains essential.

Continue Learning

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Hypoplastic Left Heart Syndrome in an Adult: CT Findings After Fontan Palliation