What are the key features of a normal chest x-ray. How to identify common anatomical landmarks on a chest radiograph. Why is it important to recognize normal chest x-ray patterns. What structures form the cardiac silhouette on a chest x-ray. Where is the aortic knob typically located on a chest radiograph.

The Importance of Recognizing Normal Chest X-Ray Patterns

Chest x-rays are one of the most commonly performed diagnostic imaging studies in medicine. For healthcare professionals, particularly those in training, developing the ability to interpret these radiographs accurately is crucial. One of the fundamental skills in chest x-ray interpretation is recognizing normal anatomical structures and patterns. This knowledge forms the foundation for identifying abnormalities and potential pathologies.

Why is this skill so important? Consider the following reasons:

• It allows for quick differentiation between normal variations and true abnormalities
• It helps prevent unnecessary follow-up tests or interventions
• It improves confidence in identifying subtle pathological changes
• It enhances overall diagnostic accuracy in clinical practice

Key Anatomical Landmarks on a Normal Chest X-Ray

To effectively interpret a chest x-ray, one must be familiar with the normal anatomical structures visible on the radiograph. These include:

Bony Structures

• Ribs and intercostal spaces
• Clavicles
• Scapulae
• Vertebral bodies
• Sternum (on lateral view)

Soft Tissue Structures

• Heart and great vessels
• Lungs and airways
• Diaphragm
• Breast shadows (in females)

How can one systematically evaluate these structures on a chest x-ray? A common approach is to use the “ABCDE” method:

1. Airway: Assess the trachea and main bronchi
2. Breathing: Evaluate lung fields for symmetry and aeration
3. Circulation: Examine the heart size, shape, and great vessels
4. Diaphragm: Check diaphragm position and contour
5. Everything else: Look for any additional findings or abnormalities

Understanding the Cardiac Silhouette on Chest Radiographs

The cardiac silhouette is a crucial component of chest x-ray interpretation. It represents the outline of the heart and great vessels as they appear on the radiograph. What structures form the cardiac silhouette on a chest x-ray?

• Right border: Formed by the right atrium
• Left border: Comprised of the left ventricle and a portion of the left auricle
• Inferior border: A combination of the right and left ventricles

It’s important to note that the anterior surface or sternocostal surface, mainly formed by the right ventricle, is not typically visible on an anteroposterior (AP) view.

Locating and Assessing the Aortic Knob

The aortic knob is another significant landmark on chest radiographs. Where is the aortic knob typically located on a chest x-ray?

In a normal chest radiograph, the aortic knob should be visible around the level of the T3 to T4 vertebrae, or just lateral to the carina (the point where the trachea divides into the right and left main bronchi). The appearance and position of the aortic knob can provide valuable information about potential cardiovascular abnormalities, such as aortic aneurysms.

Distinguishing Between Normal Variations and Pathological Findings

One of the most challenging aspects of chest x-ray interpretation is differentiating between normal anatomical variations and true pathological findings. This skill is particularly important when assessing lung markings and vascular patterns. How can one develop this ability?

• Study a large number of normal chest x-rays to understand the range of normal appearances
• Learn to recognize common artifacts and technical factors that can mimic pathology
• Understand how patient factors like age, sex, and body habitus can influence x-ray appearance
• Practice comparing bilateral structures for symmetry
• Develop a systematic approach to evaluating each radiograph

The Impact of Patient Factors on Chest X-Ray Interpretation

Patient-specific factors can significantly influence the appearance of a chest x-ray, even in the absence of pathology. What are some key factors to consider?

• Age: Older patients may have more prominent lung markings due to normal aging changes
• Sex: Breast tissue in females can create additional shadows on the radiograph
• Body habitus: Obesity can reduce overall image quality and alter the appearance of structures
• Patient positioning: Rotation or tilting can create asymmetry and potentially misleading findings
• Inspiration depth: The degree of lung inflation affects the visibility of structures and can mimic pathology if suboptimal

Common Pitfalls in Normal Chest X-Ray Interpretation

Even experienced radiologists can sometimes be tripped up by normal variants or technical factors on chest x-rays. What are some common pitfalls to be aware of?

• Misinterpreting normal vascular markings as infiltrates or nodules
• Confusing overlapping structures (e.g., rib crossings) for lung nodules
• Mistaking nipple shadows for pulmonary nodules
• Overinterpreting prominence of the pulmonary vasculature in the upper lobes on supine films
• Misdiagnosing cardiomegaly due to magnification on AP portable films

How can one avoid these pitfalls? The key lies in developing a systematic approach to chest x-ray interpretation, maintaining a high index of suspicion for normal variants, and correlating radiographic findings with clinical information.

Leveraging Technology in Chest X-Ray Education

Advancements in technology have revolutionized medical education, including the teaching of radiology. How can technology enhance the learning process for chest x-ray interpretation?

• Digital teaching files with annotated images
• Interactive online modules with self-assessment quizzes
• Virtual reality simulations for 3D visualization of anatomical structures
• Artificial intelligence-assisted learning tools that highlight key features
• Mobile apps for on-the-go learning and reference

These technological tools can complement traditional teaching methods, providing learners with more opportunities for practice and self-directed study.

The Role of Chest X-Rays in Modern Medical Practice

Despite the advent of more advanced imaging modalities like CT and MRI, chest x-rays remain a cornerstone of diagnostic imaging. Why do chest x-rays continue to play such an important role in modern medicine?

• They are widely available and relatively inexpensive
• They deliver a lower radiation dose compared to CT scans
• They can be performed quickly, making them ideal for emergency situations
• They provide valuable information for a wide range of conditions, from pneumonia to heart failure
• They serve as an excellent screening tool and can guide further diagnostic workup

Understanding normal chest x-ray findings is therefore not just an academic exercise, but a crucial skill for healthcare providers across various specialties.

Continuing Education and Skill Development in Chest Radiograph Interpretation

Mastering chest x-ray interpretation is an ongoing process that extends well beyond formal medical education. How can healthcare professionals continue to refine their skills in this area?

• Regularly review teaching files and case studies
• Participate in multidisciplinary radiology conferences
• Seek feedback from experienced radiologists on challenging cases
• Stay updated on the latest literature and guidelines in chest imaging
• Engage in quality improvement initiatives focused on imaging interpretation

By maintaining a commitment to continuous learning and improvement, healthcare providers can ensure they stay proficient in this essential diagnostic skill.

Understanding normal chest x-ray findings is a fundamental skill for healthcare professionals, particularly those in training. By developing a systematic approach to chest radiograph interpretation and familiarizing oneself with common anatomical landmarks, one can more confidently identify abnormalities and provide accurate diagnoses. As medical imaging continues to evolve, the ability to interpret chest x-rays remains a crucial component of clinical practice across various medical specialties.

UPENN SCHOOL OF MEDICINE || CXR LEARNING WEB SITE

– developed by David G. Chu, MD –

Welcome! This website was created to help introduce medical students to chest radiology. One of the most difficult things to learn when first reading Chest X-Ray (CXR) films is what is “normal” and what is really “active disease.” This website aims to help students become comfortable with accepting artifacts of blood vessels as “normal,” with the hopes that students will then more easily identify “abnormal” signs of active disease.

We have assembled 100 “normal” Chest X-Rays that were given the Diagnosis of “No Active Disease” (NAD) at the Hospital of the University of Pennsylvania (HUP). By reading this series of Normal CXR, students will learn to appreciate the range of “normal” markings, the basics of CXR reading, and how patient age and sex influence differentials. Use the Navigation Bar to the right to either begin the Learning Module from the begining or jump to any case within the module.

Chest X-Ray Teaching Lessons:

• Introduction
• Anatomy
• Soft Tissues and Bone
• Black vs. White
• Infiltrates vs. Consolidation
• Differentials

Other Radiology Resources:

• Intro Chest Radiology Tutorial
• CXR Dx of Disease
• ICU Chest X-Ray Atlas
• Chest X-Ray Atlas
• Chest X-Ray Education (by finding)
• Chest X-Ray Education (by topic)
• CT Imaging
• CT Dx of Diffuse Lung Disease
• CT Lung Atlas
• Cardiothoracic Imaging
• Congenital Heart Disease
• Chest Radiology Journal Articles
• Chest Radiology/Pathology Practical (cases)
• STR Thoracic Imaging Syllabus (no images)
• Thoracic Imaging Disease Reference (no images)

About the Authors:

This website was created in 2005 by Dr. David G. Chu and Dr. Wallace Miller, Jr. at the University of Pennsylvania School of Medicine. We are especially grateful to Anthony Robertson and Alethea Pena of the University of Penn SOM Web Design Team for their expertise.

David G. Chu, MD

David G. Chu graduated from the University of California at San Diego in 1999 and graduated from the University of Pennsylvania School of Medicine in 2005. He is currently completing his internship at the Presbyterian Medical Center of UPHS and his residency in ophthalmology at the UC Davis Medical Center.

Wallace Miller, Jr, MD

Dr. Wally Miller, Jr. has been the recipient of numerous teaching awards at the University of Pennsylvania School of Medicine, and is dedicated to clinical, academic, and teaching excellence. He graduated from University of Pennsylvania School of Medicine and completed his residency in radiology at the Hospital of the Univ of Penn of UPHS.

Navigation

Launch the 100 Normal CXR Leaning Module

Click on the link above to launch the 100 Normal CXR learning module, and begin with Case 1.

Use the dropdown menu below to jump to a specific case within the module.

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Radiology Chest Xray Normal

It is important to know the normal chest radiograph and common landmarks so that you can recognize what is abnormal.  

Cardiac Silhouette

On an antero-posterior (AP) or postero-anterior (PA) view of the chest, the borders of the heart have common landmarks:

• Right Border:  Formed by the right atrium which is in between the SVC and IVC
• Left Border: Formed by the left ventricle & portion of the left auricle
• Anterior Surface or Sternocostal Surface:  Mainly the right ventricle (not seen on AP view)
• Inferior Border:  Combination of the right & left ventricles

Aortic Knob

The aortic knob should be visualized in the normal chest radiograph around the level of T3 to T4 or just lateral to the carina.  In patients with aortic aneurysm, this can be the area contributing to the “widened mediastinum”. 

Costocardiac & Costophrenic Angles

The costocardiac angles (as well as the costophrenic angles) should fairly sharp and well defined if the patient does not have significant effusions or pulmonary edema.  

• If they are blunted or lost, you should be concerned for the presence of fluid in the lung or a mass obstructing the view. Additional imaging with a chest CT may sometimes be warranted if the etiology is not clear from the patient’s presentation. 

Carina

The carina is the point or level at which the trachea divides into the right and left main bronchi.  This is usually midline with the spinous process being behind it.  The carina is also the location that is used by healthcare providers when assessing the proper position of an endotracheal tube (ET) after intubation.  Typically, the tip of the ET tube should be 3-4 centimeters above the carina so that both lungs are properly oxygenated.  

Clavicle

The head of the clavicle is attached to the lateral surface of the sternum. The location of the clavicular heads in relation to the trachea can help determine proper positioning of the patient at the time the chest radiograph was taken.  The two clavicular heads should be on either side of the trachea and with the spinous processes being in the middle.

Hemidiaphragms

The right hemidiaphragm normally sits slightly higher than the left due to the presence of the liver under the diaphragm which prevents the right hemidiaphragm from going down further with inspiration.  Important clinical pearls include:

• Each dome of the diaphragm is innervated by its own nerve supply from the phrenic nerve.  Therefore, damage to the nerves for one side will not affect the other. On chest radiograph you would see the the paralyzed hemidiaphragm as being higher than the other hemidiaphragm during inspiration (creating a paradoxical pattern of movement with respiration).
• You should also not see free air under the hemidiaphragm.  If free air is found you will see a black line under the hemidiaphragm which would be concerning for a bowel perforation. This requires emergent evaluation with a CT scan and surgical consult. Do not confuse the normal gastric bubble seem on many chest radiographs with free air.

Trachea

The trachea should sit midline and be in between the right and left clavicular heads.  Any deviation from the midline could suggest that the patient was either rotated at the time of the chest radiograph, the presence of a mediastinal mass, or presence of a tension pneumothorax.  

Other Related Anatomy

Click on the images below to see related anatomy:

             

Editors & Reviewers

Editors:

• Anthony J. Busti, MD, PharmD, FNLA, FAHA
• Dylan Kellogg, MD

Last Reviewed:  July 2015

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References

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• Terminologia anatomica: international anatomical terminology By the Federative Committee on Anatomical Terminology (FCAT). Stuttgart: George Thieme Verlag. ISBN-10: 3-13-114361-4. ISBN-13:978-3-13-114361-7
• Pocket Atlas of Human Anatomy: 5th edition – W. Dauber, Founded by Heinz Feneis
• Pocket Atlas of Radiographic Anatomy – Torsten B. Moeller, E. Reif – Thieme
• Cardiac silhouette findings and mediastinal lines and stripes: X-ray and computed tomography correlation- R. Marano et Al. – ECR 2009 – DOI : 10.1594/ecr2009/C-222
• Mediastinal lines, stripes and interfaces on PA chest radiograph with CT correlations – N. Bystrická, H. Poláková, J. Sykora; Bratislava/SK – poster C-0442 – ECR 2013 – DOI: 10.1594/ecr2013/C-0442
• La radiographie pulmonaire – TP de radioanat – IFMEM – Montpellier
• L’abdomen sans préparation – TP de radioanat – IFMEM – Montpellier

anatomical structures

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Chest X-Ray – Systematic Approach

Introduction

A systematic approach in the analysis of chest X-rays is used to ensure that important structures are not missed, and a flexible approach is needed for different clinical situations.

Although there is no single agreed upon order of image analysis, you can find many examples of chest x-ray descriptions.

Below is a short example.

Checklist of anatomical structures

1. Trachea and major bronchi

2. Lung roots

3. Lung fields

4. Pleura

5. Lung lobes/interlobar fissures

6. Costophrenic sinuses

7. Diaphragm

8. Heart

9. Mediastinum

10. Soft tissue

11. Skeletal framework

This guide will help you develop your own analysis system, starting with the analysis of patient data, image data and image quality. Next, you will study where and what pathological changes can be described. The manual also discusses an overview of blind spots where it is easy to miss a pathological process. Your results will be better if you are able to analyze and relate clinical data to radiological findings.

Patient and image data

Patient identifiers and date

Patient identification must be performed before X-ray image interpretation. The date of the examination, as well as, necessarily, the time, must be noted, as the patient may have more than one radiograph on the same day.

Image Projection

Note which view, AP or AP, the image was taken; standing, lying or sitting; stationary or mobile device.

Image annotations

Useful information is often displayed on an image. If the projection is not marked, it is likely that the image was taken in a standard anterior-posterior (PA) projection. If there are side markers, pay attention to the correct position of their position.

Image quality

Image quality should always be assessed as clinical questions cannot be answered if the image quality is inadequate.

Pay attention to the rotation of the chest, the depth of inspiration and the adequacy of the penetrating power of the x-ray radiation.

Image annotations

Artifacts

When you describe a chest x-ray, it is good practice to comment on the presence of any artifact.
Below is an example.

Central catheter position ?

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A large number of radiographs are taken to assess the position of medical equipment such as a nasogastric tube or central catheter. If you are evaluating a chest x-ray for this purpose, remember to evaluate the entire image systemically.

Obvious pathology

It is advisable to start the analysis with the most pronounced pathology. However, once done, it is important to continue analyzing the rest of the image according to the checklist. Remember that a more prominent pathology may not be of clinical significance.

For example, don’t make the mistake of devoting most of your time to rigorously following a systems approach while ignoring obvious pathology.

The rule can be summarized as – don’t ignore the “elephant” in the picture – describe its long trunk, its large ears, tusks and rough, gray skin and you will be more likely to diagnose the “animal” you are dealing with, but then you must continue analysis using a systematic approach to watch the rest of the image.

Description of pathology

The art of radiology, not simply in stating and describing pathological signs, but knowing how to relate the meaning of these pathological signs and knowing which of them can be omitted. First, describing radiographic features can be difficult and many medical students want clear terminological rules. However, in reality there are no clear rules. The main difficulties begin when describing the pathology of the lung parenchyma. What one radiologist describes as “darkening” may be referred to by others as “decrease in pneumatization” or “infiltration.” In fact, all of these terms are acceptable.

The description of the pathology on a chest x-ray can be compared with the description of a skin rash in a dermatological patient. Attention should be directed to such features as quantity, localization, size, shape, density and structure.

Special Findings

There are many specific X-ray findings that can guide you to the correct diagnosis. For example, occlusion of the costophrenic sinus, forming obtuse angles with the chest wall, should make you think of a pleural effusion. Obvious consolidations (infiltrations) with a sign of an air bronchogram should first of all suggest an infectious process. These signs must be indicated in the descriptive picture.

If you see one of these clear signs, try not to jump to conclusions. Continue the systematic description of the changes and perhaps you will see that the blunting of the angle of the costophrenic sinus is caused by emphysematous enlargement of the lung fields, and the consolidation of the lung tissue is combined with the destruction of the rib, making cancer a more likely diagnosis? than pneumonia.

Location of changes

In addition to determining the side of the identified changes, it is necessary to evaluate the localization in the anterior-posterior projection. A lateral view helps to localize changes in 3D space, but it is also possible from a direct view, with knowledge of x-ray anatomy and understanding of shadow contours.

Contour sign

Contour sign is an erroneous name, it is more correct to call it a “lost contour” sign. Normal adjacent anatomical structures of varying density form clear “silhouettes” or contours. Violation of normal boundaries can help determine the position of the pathological process.

For example, the heart (soft tissue density, white) borders on the lung tissue (air density, dark color). A clear contour, or “silhouette” is formed at the junction of two fabrics of different density. The loss of a clear contour of the right heart (formed by the right atrium) suggests localization of the disease in the right middle lobe, which is adjacent to the right atrium. The loss of the density difference of the left heart contour indicates the pathology of the lingular regions (the part of the upper lobe of the left lung that surrounds the left ventricle).

Changes simulating a contour sign

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Changes simulating a contour sign

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47

After a systematic complete inspection chest, it is worth re-checking areas that may hide an important pathology.

It is always worth double-checking that there is no pneumothorax or pneumoperitoneum. And indicating their absence in the descriptive part is a good practice.

Pneumothorax is easily seen at the apex on an anterior-posterior radiograph. Pneumoperitoneum (free gas under the diaphragm), only visible on standing x-rays

Other areas to look at include soft tissue, bone, posterior mediastinum, and image margins.

Inspection areas – Tops

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Inspection areas – Bones

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Area Inspection – Heart Shadow

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Area Inspection – Aperture

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Area Inspection – Edges of Image

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Clinical Tasks 900 47

At first, most students think that radiography gives accurate answers without comparison with clinical data. Sometimes this may be the case, but ideally radiography should always be interpreted in full correlation with the clinical findings. Most radiological conclusions can only be given in the light of clinical data. Thus, you should always be provided with specific clinical data when requesting an x-ray.

Often the results will confirm the preliminary diagnosis, and the absence of changes will improve the prognosis, since an experienced clinician often knows the diagnosis before the x-ray examination, and uses it to clarify the extent and localization of the pathological process.

Therefore, results should only be interpreted in relation to clinical data. Remember, the radiologist does not treat the patient. Occasionally there will be incidental findings that require careful consideration, especially if they can be interpreted in two ways or if they do not correspond to clinical data.

No clinical data provided

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Clinical data provided

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missing important changes.