Choose an answer, then open any option to work its reasoning.
Respiratory
Centrilobular versus panacinar emphysema
Two patterns of alveolar destruction, two different causes, and one question on the stem that tells them apart every time.
What this page makes you able to do
- Distinguish centrilobular from panacinar emphysema by which part of the acinus is destroyed
- Connect smoking and alpha-1 antitrypsin deficiency to their lobar distributions
- Predict which lung region is worst affected from the cause alone
- Recognise the stem features that separate the two patterns
- Dr. Fatima Ali, DOPsychiatry residentPrimary reviewer
Last reviewed
From the Attending:
Smoking damages the acinus from the middle outward and prefers the upper zones. That single sentence separates it from every other pattern.
Prove it
Opening question
A 62-year-old with a 40 pack-year smoking history has three years of worsening exertional breathlessness. Imaging shows destruction that is worst in the upper zones, with the lung bases relatively preserved.Which pattern of emphysema does this describe, and which part of the acinus is lost?
- Why this is rightSmoke reaches the respiratory bronchioles first and the inflammatory response concentrates there, so the central acinus goes while the distal alveoli are initially spared. Upper zones take the larger dose.
- Why this failsPanacinar disease destroys the whole acinus uniformly and favours the bases. Nothing here suggests loss of antiprotease protection, which is what produces that pattern.
- Why this failsParaseptal disease sits against the pleura and interlobular septa and classically presents with a spontaneous pneumothorax in a young adult, not with three years of progressive exertional breathlessness.
- Why this failsScar-related emphysema is focal and follows previous injury. It does not produce a zonal gradient across both lungs.
Work the reasoning
The respiratory bronchiole, which sits at the centre of the acinus.
The inflammatory infiltrate and the protease burden concentrate where the particles land, so destruction begins centrally and spreads outward.
Prove it
Four patients, one acinus
Four people in a clinic morning, and the same question hiding inside every one of them.
Where each pattern strikes
One takes the middle of the acinus. The other takes all of it.
Centrilobular emphysema destroys the respiratory bronchioles and the central portion of the acinus while the distal alveolar ducts and sacs are initially preserved.
Panacinar emphysema destroys the acinus uniformly from the respiratory bronchiole through to the terminal alveoli.
The zone the disease picks is the first thing worth reading off a chest film. Smoking driven destruction concentrates in the upper lobes, while destruction that spares the apices and hollows out the bases points away from smoke and toward an inherited cause.
Which part of the acinus does each pattern destroy?
Pearl. If the stem tells you which part of the acinus is gone, it has already told you the cause.
How smoke destroys the centre first
The damage follows the particles, and the particles stop at the bronchiole.
Inhaled smoke reaches the respiratory bronchiole and recruits macrophages and neutrophils to that point in the acinus.
Those cells release proteases that exceed local antiprotease capacity, and elastin in the surrounding alveolar walls is degraded.
Inhaled smoke deposits heaviest where the airway first opens into gas exchanging tissue, so the respiratory bronchiole takes the worst of the protease load. That is why the centre of the acinus goes while the distal sacs still look intact early on.
Upper zones also clear less well, so the insult accumulates there. Zone and mechanism are the same story told twice.
Put the steps of smoke-driven destruction in order.
Particles travel as far as the first airway that opens into gas exchanging tissue and stop there. Nothing downstream is touched yet.
The inflammatory infiltrate gathers at the point of deposition rather than spreading evenly through the acinus.
Local antiprotease defence is finite. Once the recruited cells outproduce it, the balance tips and digestion begins.
Elastin is the target, so the wall loses its recoil and the airspace it bounded enlarges permanently.
The finished lesion is a hole in the middle of the acinus with intact tissue around it, worst where the dose was largest.
Why alpha-1 deficiency takes the whole acinus
Lose the brake and the damage stops being local.
Alpha-1 antitrypsin inhibits neutrophil elastase throughout the lung, so its deficiency removes protection from the entire acinus rather than from one region of it.
When the antiprotease is missing rather than merely overwhelmed, nothing restrains elastase anywhere in the acinus. The destruction is uniform, which is what panacinar means, and it falls hardest on the lower lobes where perfusion and therefore neutrophil delivery is greatest.
Age at presentation is a usable clue. A smoker with the deficiency tends to present roughly a decade earlier than a non smoker with the same genotype, because smoke adds protease burden on top of absent defence.
Four situations should make you check a level: obstructive disease at a young age, obstructive disease with little or no smoking history, disease that is worse at the bases than the apices, and unexplained liver disease. Inheritance is codominant, so a family history counts.
Which pattern follows loss of antiprotease protection?
Panacinar, lower zones. The inhibitor is absent everywhere, so no part of the acinus keeps its protection and the whole unit is destroyed uniformly. Centrilobular, upper zones. That pattern needs a locally concentrated insult. Antiprotease loss is systemic, so the damage cannot stay central. Paraseptal, subpleural. Paraseptal disease sits at the periphery of the lobule and is not the pattern that antiprotease loss produces. Irregular, scar-related. Scar-related disease follows a previous injury and is focal, so it cannot follow from a diffuse loss of inhibition.
Reading the zonal gradient
Upper or lower is the fastest discriminator on imaging.
Centrilobular disease is worst in the upper zones, where inhaled particle deposition is greatest relative to perfusion.
Panacinar disease is worst in the lower zones, where blood flow and therefore neutrophil delivery are greatest.
Apical predominant destruction with a heavy smoking history is the common path. Basilar predominant destruction is the one that should stop you, because it reverses the expected gradient and that reversal is the finding, not an incidental detail.
Mark the zone worst affected in each pattern.
Tap a region.
What the numbers do
Obstruction, hyperinflation, and a diffusion capacity that falls.
Emphysema produces a reduced FEV1 to FVC ratio with an increased total lung capacity and residual volume from air trapping.
Diffusing capacity falls because alveolar surface area is lost, which separates emphysema from chronic bronchitis.
Both patterns obstruct, so the ratio of forced expiratory volume to forced vital capacity falls in each. The pattern does not separate them; the zone and the history do. Confirmation of the inherited form is a serum level, and lung function testing is done alongside it rather than instead of it.
Which direction does each value move in emphysema?
Checked 0
The liver clue nobody expects
The same protein explains a second organ.
The misfolded alpha-1 antitrypsin variant accumulates in hepatocytes, so the same deficiency that causes basal emphysema can also cause liver disease.
The same misfolded protein that fails to reach the lung accumulates in the hepatocyte, so the liver is injured by retention while the lung is injured by absence. One defect, two organs, two entirely different mechanisms.
That is why a stem can open with neonatal jaundice, or with cirrhosis in an adult who barely smoked, and still be asking a lung question. Skin involvement as panniculitis is rarer but points the same way.
Why does one enzyme deficiency affect two organs differently?
Too little circulating inhibitor, so elastase runs unopposed.
Too much retained protein, so hepatocytes accumulate it.
Clinical walkthrough
