Chest X-ray: lung anatomy

Okay, let’s get into some basic anatomy of the lungs. First off it is critical for you to know that there is an “anatomic” position, meaning there is a standard convention for locating body parts. A person could be pictured laying on their back with hands down at their sides and palms up. Viewing is done from head/cranial/cephalad to feet/caudad with the patient’s right side of their body appearing on the left side of the image. For chest X-ray this usually not a problem. The heart is on the left, virtually always (situs inversus!).

The chest/thorax contains two lungs, conveniently named right and left. The right lung has 3 lobes. The left lung has 2 lobes. The lobes are separated by fissures/clefts and membranes surrounding each lobe. These fissures may or may not be visible on chest X-ray, but are always seen on CT scan.

Right Lung: The right lung has upper, middle, and lower lobes.

The minor/horizontal fissure separates the right upper lobe from the right middle lobe and is seen best on the frontal view.

Frontal Chest X-ray showing the RUL = Right Upper Lobe
Frontal Chest X-ray showing the RML = Right middle lobe

The major/oblique fissure separates the right upper lobe, and right middle lobe from the right lower lobe and is seen best on the lateral view.

CXR - right lat 2
Lateral Chest X-ray showing the RLL = Right lower lobe

As you can see from this lateral image, the right lower lobe actually overlaps with the right upper and right middle lobes on the frontal view as depicted below.

Frontal Chest X-ray showing the overlapping RLL = Right lower lobe


Left Lung: The left lung has only two lobes separated by an oblique/major fissure. However, the left upper lobe includes the lingula, which anatomically corresponds to the middle lobe on the right lung. But it is not demarcated by a left minor/horizontal fissure, hence only two lobes.

Frontal Chest X-ray illustrating the LUL = Left upper lobe

The oblique fissure best seen on the lateral view shows the upper and lower lobes.

CXR - left lat
Lateral Chest X-ray showing the LLL = Left lower lobe

On this lateral image, there is shown tremendous overlap between the left upper and left lower lobes on the frontal view.

Frontal Chest X-ray illustrating the LLL = Left lower lobe

Okay that was a quick tour of some very basic chest X-ray anatomy where we only talked about the lungs, and just the lobes! There is much deeper anatomy than that and maybe we will touch on segmental airway anatomy when we tackle CT of the chest, but for now this is definitely enough. I think we will continue next time with more anatomy covering the heart and mediastinum (all the stuff in the middle of the chest). I was given some advice today to shorten my articles and make them more accessible to the lay public. Believe me I am trying. Medicine has a language to itself, seriously!

So if you can think of anyway I can make this more simplified, please help me by sounding off in the comments below.



Featured Image Credit

Images within post from prior powerpoint. Appreciate the help!

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I am an American Board of Radiology certified Diagnostic Radiologist with a certificate of additional qualification in Neuroradiology. I absolutely love my job. I have learned a tremendous amount about the human body, including its’ expected complications given our extraordinary complexity, and get to use that knowledge to help people. I personally have experienced emotional devastation and loss, which has made me compassionate and empathetic. I really care about people, and I hope I can use this site to help you. I graduated medical school in 2004 from New York Medical College. My wife and I had our first son in NY where we bought our 900 sf two bedroom one bath starter home. I stayed at Westchester Medical Center for radiology residency, where we had our second son. I obtained a neuroradiology fellowship position at Yale New Haven Medical Center commuting about an hour and a half each way for a year while we had our third boy. Upon graduation I was fortunate to return to Westchester Medical Center to work in Neuroradiology, Body Imaging, and Women’s Imaging departments, a rarity in academic medicine. Almost a decade later and I am living in a larger home in Reno working in a private practice community based outpatient radiology group which contracts with a rural hospital in Elko, Nevada. My wife and I now have four boys and gave up on the girl. We also have a male Bernese mountain Dog named Helmut and female Newfoundland named Lucy. Despite all its hardships and tremendous struggles, I have an absolutely amazing life, which is a gift I cherish. It’s down to my philosophy. I am a firm believer in teamwork. So much comes down to communication. When healthcare providers talk to each other one-on-one, the patient care is always improved, every time! We might not find an answer to your problem, but our collective knowledge sure can help improve your chances. At Yale the best conference I ever regularly attended was a head and neck tumor board. The head and neck surgeon (otolaryngologist = ENT) presented the patient’s clinical history, the radiologist showed the images, the oncologist discussed the tumor and chemotherapy options, and the patient came to the conference and we all did a physical exam looking into their mouth to directly visualize a tumor. It was incredible! Patients came from far and wide to see this highly trained, world-renowned, humble, Japanese, gentleman surgeon. It was also an epiphany. I found that when I see the patient, talk to them, listen to their story, examine them and discuss the patient with my colleagues, the patient felt better and I had a lot of fun. It’s weird but reminds me of seeing a comedy where it is always funnier in a packed theater with everyone laughing. Knowledge and compassion are both infectious and contagious. My greatest days are helping patients deal with some of their most difficult days, and I am good at it.

4 thoughts on “Chest X-ray: lung anatomy

  1. I knew about all of the lobes but have never seen them individually selected on an XR image. I also did not know about the lobe overlaps! Thanks for the great explanation!


  2. When you see an irregularity that is located on the overlap of the lobes, how do you decide how to dictate where it is precisely? Or is that the time for additional imaging beyond XR?


    1. Hi Leah, I’m sorry I thought I had replied to this comment earlier. Technical error or human malfunction, or both. So the frontal view will give you the lung “field/zone” being upper, middle, or lower. Combining the information from the frontal view with a lateral view can give you very good localization, pretty much to the lobar segmental level. The exact anatomical location can best be depicted with CT scans though, getting down to a subsegmental level. Eventually we will get to CT of the chest and I can further detail. Thanks for the excellent question!


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