What Are Lung Fissures and Why Are They Important?

Lung fissures are the thin, lining-covered grooves that split each lung into separate lobes: three on the right, two on the left. In many people the lobes are only partly separated, which is so common that it counts as normal anatomy.1PubMed. Anatomical Variations of the Lung Lobes and Fissures: A Systematic Review and Meta-Analysis A fissure note on a scan report is usually just a description of your anatomy, and it mainly matters for specific treatments and scan readings.

How Fissures Shape and Move Your Lungs

The right lung has two fissures: a long slanting one called the oblique (or major) fissure, and a shorter horizontal (or minor) one. Together they split the right lung into upper, middle and lower lobes. The left lung has only the oblique fissure, so it has an upper and a lower lobe, which leaves room for the heart.

The left lung does have a small tongue-shaped piece of upper lobe, called the lingula, sitting where the right middle lobe would be. No fissure separates it from the left upper lobe, so the left lung is described as having two lobes rather than three.

Each lung is wrapped in a thin, two-layer membrane called the pleura, and a fissure is where that membrane dips deep into the lung between two lobes. Because the dip is lined on both sides, neighboring lobes touch through slippery lining rather than raw tissue. That is why they can glide without rubbing.

A deep breath stretches the lower lobes more than the upper ones, so the lobes slide past each other along the fissures.

The sliding helps the lung adapt as the chest changes shape during breathing.2PubMed Central. Lobar Sliding Reduces Parenchymal Distortion More in the Right Lung Than the Left Lung In computer models of real lungs, it cut strain on lung tissue by about 13% in the right lung.3PubMed Central. Lobar Sliding Reduces Parenchymal Distortion More in the Right Lung Than the Left Lung In the left lung the benefit was smaller, about 5%.4PubMed Central. Role of lung lobar sliding on parenchymal distortion during breathing The right lung has more sliding surfaces, so it can adjust better.5PubMed Central. Lobar Sliding Reduces Parenchymal Distortion More in the Right Lung Than the Left Lung The benefit was clearest in the lower lobe, which moves most with the diaphragm.6PubMed Central. Role of lung lobar sliding on parenchymal distortion during breathing

Incomplete, Missing and Extra Fissures Are Common

An incomplete fissure only partly separates two lobes, so the lobes are fused in places.11Translational Research in Anatomy. Anatomical variations in lung fissures leading to supernumerary lobes in the lungs An accessory fissure, an extra one, can create an additional small lobe.12Translational Research in Anatomy. Anatomical variations in lung fissures leading to supernumerary lobes in the lungs An incomplete fissure is not a disease, and it usually causes no symptoms and needs no treatment. It becomes relevant mainly for valve treatment, surgery, or how a disease spreads, so it is worth asking your doctor whether it affects any planned procedure.

The horizontal fissure varies most because it is the shorter, thinner one on the right. The middle lobe is often partly fused with the upper lobe, and when the fissure is absent that simply means a larger combined upper lobe.

Numbers differ between sources. Individual studies report different rates, with some finding the right horizontal fissure absent in up to 20% to 25% of lungs.13PubMed Central. A Cadaveric Study of Variations in Lung Fissures and Drainage Patterns of Pulmonary Veins at the Hilum With Its Clinical Implications Studies define incomplete fissures differently and use different methods, such as examining lungs after death, reading CT scans, or looking during surgery. The figures above are pooled averages. These variations are present from birth, since they are seen in children too.14Journal of Pediatric Surgery Open. Prevalence of anatomical variations in children with congenital lung malformations investigated by video recordings of thoracoscopic lobectomy

An extra fissure is an additional groove, usually shallow, that partly marks off a small segment of a lobe. It is most often noticed by chance, when someone is scanned for another reason. It usually does nothing on its own, but a radiologist names it so it is not mistaken for scarring or fluid. Occasionally it matters in surgery planning, because it changes where the lobe boundaries lie.

How Fissures Affect Infections and Disease Spread

A complete fissure acts as a wall between lobes, which is why pneumonia often stays limited to one lobe on a scan. An incomplete fissure can allow disease to spread to the neighboring lobe.15RadioGraphics. Radiographic and CT appearances of the major fissures It also lets air pass from one lobe into another.16RadioGraphics. Radiographic and CT appearances of the major fissures Infections, inflammation, tumors and heart-related fluid can all change how a fissure looks on a scan.17PubMed. Radiographic and CT appearances of the major fissures

The wall is good but not perfect. Fluid and disease can sometimes track along the lining or spread through the airways and blood vessels, so lobe-limited pneumonia is typical but its pattern is one clue among others. Swelling in one lobe can push or bow the fissure on a scan, which helps radiologists tell which lobe is affected.

For a tumor near a fissure, doctors note whether the growth crosses into another lobe, which affects how much lung surgery might remove. It is reasonable to ask whether the finding changes the plan.

Air drifting between lobes through an incomplete fissure is normal in lungs with fused areas and does not cause symptoms by itself. It matters when a lobe is blocked or diseased, because neighboring lobes can then supply it with air and keep it inflated.

Why Fissures Decide Who Can Get Emphysema Valves

An endobronchial valve is a tiny one-way valve placed in an airway to shrink a badly damaged lobe in selected people with emphysema.18PubMed Central. The fissure: interlobar collateral ventilation and implications for endoscopic therapy in emphysema The goal is for that lobe to collapse so healthier lung can work better.19PubMed Central. The fissure: interlobar collateral ventilation and implications for endoscopic therapy in emphysema But air leaking in from a neighboring lobe keeps the lobe from collapsing.20PubMed Central. The fissure: interlobar collateral ventilation and implications for endoscopic therapy in emphysema That leakage travels through incomplete fissures.21PubMed Central. The fissure: interlobar collateral ventilation and implications for endoscopic therapy in emphysema So the best candidates for a lung valve are people with complete fissures and no leakage.22PubMed Central. The fissure: interlobar collateral ventilation and implications for endoscopic therapy in emphysema Even a small gap in a fissure can let enough air through to keep the target lobe inflated, so doctors look for a very high completeness score.

A CT scan estimates what percentage of the fissure is complete.23PubMed Central. An Integrative Approach of the Fissure Completeness Score and Chartis Assessment in Endobronchial Valve Treatment for Emphysema A test during bronchoscopy, often called Chartis on reports, measures leakage directly.24PubMed Central. The fissure: interlobar collateral ventilation and implications for endoscopic therapy in emphysema For the left major fissure, more than 95% completeness meant about 10 in 11 had no leakage.25PubMed Central. An Integrative Approach of the Fissure Completeness Score and Chartis Assessment in Endobronchial Valve Treatment for Emphysema At 80% or less, leakage was always present in that group.26PubMed Central. An Integrative Approach of the Fissure Completeness Score and Chartis Assessment in Endobronchial Valve Treatment for Emphysema Because a CT percentage is only an estimate, the direct test is used when the result is borderline. Using both CT and the airway test gives the most reliable answer.27PubMed Central. The fissure: interlobar collateral ventilation and implications for endoscopic therapy in emphysema Automated computer analysis of CT fissures is also being developed to predict who will respond.28PubMed Central. Using a fully automated, quantitative fissure integrity score extracted from chest CT scans of emphysema patients to predict endobronchial valve response

In Chartis, a thin tube is guided into the airway of the lobe being considered, and a small balloon temporarily blocks it. The system then measures whether air keeps flowing out of the blocked lobe, which would mean air is arriving from a neighbor. Steady flow suggests leakage and makes valves unlikely to work. Flow that drops to nothing suggests the lobe is sealed off enough for treatment.

Being ruled out reflects your anatomy, not your effort or your illness, and other options such as surgery or rehab may still apply. Useful questions for your lung specialist: What is my fissure completeness score for the target lobe? Was a direct leakage test done? If I’m not a candidate, which other treatments fit?

Fissures and Lung Surgery

Removing one lobe means dividing it from its neighbor, and the main artery to the lobe often runs right inside the fissure. Surgeons often separate lobes along the fissure to reach the blood vessels. If the fissure is complete, they can follow it to the artery. If it is fused, tissue has to be divided first.

Cutting through an incomplete fissure can tear lung tissue and cause air leaks.29PubMed. Decreasing the incidence of prolonged air leak after right upper lobectomy with the anterior fissureless technique Prolonged air leaks were much more common in people with incomplete or fused fissures.30PubMed. The approach of fused fissures with fissureless technique decreases the incidence of persistent air leak after lobectomy A prolonged leak means air escapes into the chest from the cut lung surface, so the chest tube stays in longer.

A “fissureless” approach works around the fused area. Instead of cutting through the fused lung first, the surgeon reaches the vessels and airway from other directions and leaves the fused tissue for last, often separating the lobes with staplers. Less raw lung surface is exposed during the operation. After right upper lobe removal, this cut prolonged leaks from about 22% to under 8%.31PubMed. Decreasing the incidence of prolonged air leak after right upper lobectomy with the anterior fissureless technique It also shortened hospital stays from about 15 days to 8.32PubMed. Decreasing the incidence of prolonged air leak after right upper lobectomy with the anterior fissureless technique If you are facing lobe removal, you can ask whether your CT shows fused fissures, which technique the surgeon plans, and how long a chest tube might stay.

Fissure Findings on X-Rays and CT Reports

On a chest X-ray, fissures show as fine hairline lines.33PubMed. Radiographic and CT appearances of the major fissures On CT they appear as thin bands or sharp lines.34PubMed. Radiographic and CT appearances of the major fissures Thin-slice CT detects fissures about as reliably as examining the lung directly.35IMAIOS e-Anatomy. Pulmonary fissures – e-Anatomy A small triangle at the bottom of a fissure is often just fat.36PubMed. Radiographic and CT appearances of the major fissures

An X-ray shows a fissure only when the beam happens to run along it, so some fissures cannot be seen at all. CT builds cross-sections, so fissures show far more reliably and in more detail. A fissure missing from an X-ray says nothing about whether it exists.

An azygos fissure is an extra fissure near the top of the right lung, made by a vein taking an unusual path.37PubMed. The azygos lobe: an unusual anatomical observation with pathological and surgical implications The lung folds around the vein, and that fold produces the fissure line. On X-ray it shows as an extra curved line with a teardrop shape at its base,38PubMed Central. The Empty Azygos Fissure and the vein itself forms the teardrop. It creates a small extra lobe and is rare.39PubMed. The azygos lobe: an unusual anatomical observation with pathological and surgical implications The vein still carries blood back toward the heart as usual, and the finding is usually incidental and needs nothing.

A phantom tumor is fluid collecting inside a fissure that looks like a mass.40UAPM Journal of Respiratory Diseases and Allied Sciences. Phantom Tumor of the Lung: A Radiological Masquerader of Pulmonary Mass Lesion It most often happens with heart failure.41PubMed Central. Multiple Phantom Tumor of the Lung: A Complex Appearance Resolving with Appropriate Intervention It is more common on the right side.42PubMed Central. A phantom tumour of the lung in a patient with heart failure was misdiagnosed as a lung mass It usually vanishes once heart failure is treated, which gives it the name vanishing tumor.43UAPM Journal of Respiratory Diseases and Allied Sciences. Phantom Tumor of the Lung: A Radiological Masquerader of Pulmonary Mass Lesion A suspected phantom tumor is confirmed with follow-up scans.

Report phrases decode simply. “Fissures are intact” means normal. “Thickened fissure” can reflect fluid or inflammation. “Incidental azygos lobe” is a harmless variant.

Some findings do call for follow-up. Fluid in a fissure with breathlessness or swelling can point to heart problems. A mass near a fissure needs comparison with older scans.