Chronic Pneumonia

Slide 1 · Chronic Pneumonia

Etiology • Host response • Morphology • Diagnosis

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Chronic pneumonia: Learning objectives

Define the clinicopathologic syndrome and distinguish it from acute pneumonia.

Relate persistent organisms and cell-mediated immunity to granulomatous injury.

Recognize characteristic lesions of tuberculosis, NTM, nocardiosis, and endemic mycoses.

Select tissue-based investigations without overinterpreting morphology alone.

Slide 3 · Chronic pneumonia is a clinicopathologic pattern

Most often a localized pulmonary lesion in an immunocompetent patient.

Regional lymph node involvement may be present or absent.

The typical tissue reaction is granulomatous inflammation.

The category includes bacterial and fungal causes—not a single organism.

Slide 4 · Persistent infection differs from acute pneumonia

Acute bacterial pneumonia

Rapid alveolar accumulation of neutrophil-rich exudate.

Often diffuse lobar or patchy bronchopneumonia.

Consolidation reflects exudate within air spaces.

Chronic pneumonia

Persistent local lesions develop over a longer course.

Granulomas frequently contain the offending organism.

Necrosis, scarring, nodules, or cavities may evolve.

Slide 5 · Clinical context narrows the etiologic differential

Persistent infiltrate

Subacute/chronic pulmonary lesion

Host context

Immunocompetent or immunosuppressed

Tissue pattern

Granuloma, suppuration, or mixed reaction

Organism detection

Stains, culture and molecular testing

Schematic

Slide 6 · Principal infectious causes

Group

Representative agents

Predominant clue

Mycobacteria

M. tuberculosis; nontuberculous mycobacteria

Granulomatous inflammation

Actinomycetes

Nocardia; Actinomyces

Chronic or suppurative lesions

Endemic fungi

Histoplasma; Blastomyces; Coccidioides

Granulomatous or mixed reaction

Slide 7 · What the host response tells the pathologist

An organized granuloma usually implies a functioning cellular immune response.

Necrosis may reflect immune-mediated injury, persistence, and local destruction.

Suppurative inflammation does not rule out a chronic infectious cause.

Severe immunodeficiency can prevent classic granuloma formation.

Slide 8 · Chronic lesion: Three morphologic questions

At low magnification

Is the process focal, multifocal, or diffuse?

Is there central necrosis, cavitation, or fibrosis?

Are bronchi, vessels, or pleura affected?

At higher magnification

Are epithelioid histiocytes and giant cells present?

Are neutrophils prominent at the center?

Can microorganisms be demonstrated?

Slide 9 · Granuloma: An organized chronic response

Granulomas are aggregates of activated epithelioid macrophages.

Lymphocytes are commonly present at their periphery.

Multinucleated giant cells may form by macrophage fusion.

A granuloma attempts to contain material that is difficult to eradicate.

Slide 10 · Anatomy of an immune granuloma

Schematic — not histologic evidence

Central persistent stimulus ± necrosis

Epithelioid histiocytes / giant cells

Outer lymphocytes and fibroblasts

Slide 11 · T-cell–mediated granuloma formation

Persistent antigen

Resists elimination

Antigen presentation

Drives T-cell activation

Th1 cytokines

Interferon-γ released

Macrophage activation

Epithelioid cells and granuloma

Schematic

Slide 12 · Caseating versus noncaseating granulomas

With caseous necrosis

Granular, acellular central debris may be present.

A characteristic finding in tuberculosis.

Also occurs in certain fungal infections.

Without caseous necrosis

Central necrosis is absent on the section examined.

Does not exclude tuberculosis or infection.

Sarcoidosis and other mimics remain possible.

Slide 13 · Caseation is a tissue pattern, not an etiology

Schematic — not histologic evidence

Necrotic core: Cellular architecture lost

Inflammatory and granulomatous rim

Requires microbiological correlation

Slide 14 · Granulomatous and suppurative responses

Granulomatous pattern

Macrophage-rich immune containment.

Caseation or fibrosis may develop.

Prominent in tuberculosis and histoplasmosis.

Suppurative pattern

Neutrophil-rich destructive inflammation.

Central liquefaction or abscesses may occur.

Important in nocardiosis and blastomycosis.

Slide 15 · Possible fates of a chronic pulmonary lesion

Persistent organism

Sustained inflammatory reaction

Tissue injury

Necrosis ± liquefaction

Structural change

Cavity, consolidation or scarring

Systemic extension

Lymphatic or hematogenous spread

Schematic

Slide 16 · Why organisms must be identified

Granuloma architecture overlaps across infectious and noninfectious disorders.

Caseation is suggestive, not proof, of tuberculosis.

Special stains may identify bacteria or fungi within affected tissue.

Culture and molecular studies distinguish morphologically similar infections.

Slide 17 · Tissue-based investigation: Complementary roles

Method

Main contribution

Interpretive caution

H&E morphology

Classifies inflammation, necrosis and injury

Usually not etiologically specific

Special stains

Visualizes acid-fast bacilli or fungal forms

Negative stain does not exclude infection

Culture

Can identify a viable pathogen

Depends on sample handling and growth

Molecular studies

Detects species-specific nucleic acid

Interpret with lesion and clinical context

Slide 18 · Specimen handling affects diagnostic yield

A biopsy for histology demonstrates tissue response and may reveal organisms.

A separate appropriately collected sample may be required for microbiology.

Sample a viable interface as well as necrotic areas when feasible.

Share the differential diagnosis with the microbiology laboratory.

Slide 19 · Tuberculosis: Prototype chronic pneumonia

M. Tuberculosis causes chronic pulmonary and potentially systemic disease.

Transmission is usually airborne from a patient with active pulmonary disease.

Clinical states include infection without disease and active disease.

Cell-mediated immunity both contains bacilli and injures lung tissue.

Slide 20 · Initial M. Tuberculosis infection

Inhaled bacilli

Reach distal air spaces

Alveolar macrophage

Phagocytosis of organisms

Blocked maturation

Limited phagolysosome formation

Early amplification

Intracellular replication and dissemination

Schematic

Slide 21 · Why tuberculosis survives in macrophages

The bacillus interferes with phagosome maturation and fusion with lysosomes.

Intracellular survival permits early multiplication before adaptive immunity.

Antigen-presenting cells recruit antigen-specific T-cell responses.

Successful host defense requires macrophage activation rather than antibodies alone.

Slide 22 · Th1 immunity is pivotal in tuberculosis

Dendritic cells

Present mycobacterial antigen

IL-12 / IL-18

Promote Th1 differentiation

Th1 cells

Release IFN-γ

Activated macrophages

Antimicrobial responses and granuloma

Schematic

Slide 23 · Protective and destructive effects of Th1 immunity

Containment

IFN-γ activates macrophage antimicrobial functions.

Nitric oxide, reactive oxygen species and autophagy contribute.

Granuloma formation restricts infection.

Collateral injury

Sustained cellular immune activation damages tissue.

Caseous necrosis may become extensive.

Necrotic foci can progress to cavitation.

Slide 24 · TNF helps maintain granulomatous containment

Activated macrophages secrete TNF and chemokines.

These mediators recruit additional monocytes to infected lesions.

Granuloma maintenance contributes to control of latent infection.

TNF-antagonist treatment increases risk of tuberculosis reactivation.

Slide 25 · Primary tuberculosis: Pulmonary focus and nodes

Lung focus

Regional node

Schematic — not histologic evidence

Subpleural pulmonary focus (Ghon focus)

Draining lymphatics to regional nodes

Ghon complex = focus plus nodal disease

Slide 26 · Primary tuberculosis: Early morphologic course

Initial implantation is often near the pleura in a lower upper lobe or upper lower lobe.

A small gray-white focus of consolidation develops.

The center often undergoes caseous necrosis.

Regional lymph nodes can show similar caseating inflammation.

Slide 27 · Primary infection: Possible outcomes

Primary complex

Parenchymal + nodal lesions

Immune control

Fibrosis ± calcification

Latent persistence

Viable bacilli may remain

Later reactivation

Occurs if host defenses weaken

Schematic

Slide 28 · The histologic tubercle

An epithelioid macrophage aggregate often surrounds caseous necrosis.

Multinucleated giant cells and peripheral lymphocytes may be seen.

Some tuberculous granulomas are noncaseating.

Bacillary yield varies across lesions and stages.

Slide 29 · Primary versus secondary pulmonary tuberculosis

Primary disease

Often a peripheral focus with regional nodal involvement.

May heal as a fibrocalcific complex.

Commonly recognized as the initial encounter.

Secondary (postprimary) disease

Classically favors apical lung parenchyma.

Fibrosis and central caseation are common.

Progressive lesions can erode into bronchi and cavitate.

Slide 30 · Secondary tuberculosis and cavitation

Schematic — not histologic evidence

Apical focus with central caseation

Bronchial erosion drains necrotic material

Cavity contributes to infectious sputum and bleeding

Slide 31 · Consequences of progressive cavitary tuberculosis

Cavitation follows drainage of caseous necrotic material into airways.

Involvement of blood vessels can cause hemoptysis.

Bronchogenic spread creates additional pulmonary foci.

Healing can leave fibrosis and distorted lung architecture.

Slide 32 · Routes of progression in tuberculosis

Route

Pulmonary consequence

Possible systemic consequence

Bronchogenic

New air-space foci; endobronchial disease

Laryngeal involvement

Lymphatic / venous

Numerous small pulmonary nodules

Miliary involvement

Arterial bloodstream

Variable pulmonary involvement

Disseminated organ lesions

Contiguous extension

Pleural inflammation or effusion

Local tissue extension

Slide 33 · Immune competence changes tuberculosis morphology

Adequate T-cell response

Organized granulomas and tissue caseation.

Fibrosis and local containment are possible.

Cavitation may accompany destructive disease.

Advanced immunodeficiency

Granuloma architecture may be poorly formed.

Macrophages may harbor numerous bacilli.

Disseminated infection becomes more likely.

Slide 34 · Tuberculous infection cannot be inferred from H&E alone

Granulomatous inflammation suggests a limited etiologic differential.

Acid-fast stains are indicated even when granulomas lack caseation.

Culture or molecular testing establishes organism identity.

A paucibacillary lesion may be stain-negative despite active infection.

Slide 35 · Nontuberculous mycobacteria (NTM)

NTM are mycobacteria outside the M. Tuberculosis complex and M. Leprae.

Human pathogens include M. Avium complex, M. Abscessus complex, and M. Kansasii.

The environment—water and soil—is an important reservoir.

Unlike tuberculosis, person-to-person transmission is generally uncommon.

Slide 36 · Who is vulnerable to pulmonary NTM disease?

Structural lung disease

Bronchiectasis or cystic fibrosis.

Chronic obstructive pulmonary disease.

Primary ciliary dyskinesia or pneumoconiosis.

Host defense impairment

HIV infection and transplantation.

TNF antagonists.

Rare IL-12 / IFN-γ pathway disorders.

Slide 37 · Two patterns of pulmonary NTM disease

Schematic — not histologic evidence

Fibrocavitary lesions often affect upper lobes

Nodular bronchiectasis produces small clustered nodules

Imaging pattern alone is not a species diagnosis

Slide 38 · NTM requires organism-level interpretation

Species identification is important because organism-specific treatment differs.

Culture isolation must be related to clinical and radiologic disease.

Chronic productive cough, fever, and weight loss may occur.

Advanced immunodeficiency may produce disseminated MAC infection.

Slide 39 · Tuberculosis versus pulmonary NTM

Feature

Tuberculosis

NTM

Typical source

Person with active disease

Environmental water / soil

Transmission

Airborne human-to-human

Usually environmental acquisition

Host context

Any immune status

Structural lung disease or impaired defenses common

Pathologic reaction

Granulomatous ± caseation

Granulomatous/chronic lesions; pattern overlaps

Slide 40 · Nocardia: Chronic infection by filamentous bacteria

Nocardia species are aerobic gram-positive, soil-associated bacteria.

They form branching, filamentous structures resembling fungal hyphae.

Pulmonary disease often follows an indolent course.

Glucocorticoid use, HIV infection, and diabetes increase vulnerability.

Slide 41 · Nocardia: Branching filamentous morphology

Schematic — not histologic evidence

Slender branching Gram-positive organisms

Irregular, beaded staining

Modified acid-fast stain can be positive

Slide 42 · Nocardial lung pathology is often suppurative

Nocardia causes a neutrophil-rich inflammatory reaction.

Central liquefaction can create abscess-like lesions.

Granulation tissue and fibrosis may surround destructive foci.

The lesion can imitate tuberculosis or pulmonary malignancy.

Slide 43 · Nocardial dissemination: A clinical warning

Pulmonary entry

Indolent respiratory infection

Persistent infection

Necrotizing / suppurative lesions

Hematogenous spread

Potential extrapulmonary dissemination

CNS infection

Focal deficits depend on lesion site

Schematic

Slide 44 · Nocardia versus Actinomyces: Key laboratory clue

Feature

Nocardia

Actinomyces

Filamentous Gram-positive bacteria

Yes

Yes

Modified acid-fast stain

Often positive

Negative

Interpretation

Possible pulmonary nocardiosis

Separate consideration in chronic suppuration

Slide 45 · Do not confuse bacterial filaments with fungal hyphae

Branching architecture is not proof that an organism is a mold.

Nocardia is a bacterium despite superficial resemblance to mycelia.

Gram stain and modified acid-fast staining can resolve key distinctions.

Culture and species identification remain important.

Slide 46 · Endemic dimorphic fungi: Pulmonary entry

Major organisms are Histoplasma, Blastomyces, and Coccidioides.

Geographic and environmental exposures alter pretest probability.

Pulmonary infection follows inhalation of environmental forms.

Tissue morphology differs markedly among these organisms.

Slide 47 · Dimorphism must be interpreted by organism

Histoplasma and Blastomyces

In tissue: Yeast forms.

Environmental phase: Mold with hyphae.

Host immunity influences persistence or dissemination.

Coccidioides

In tissue: Large endospore-filled spherules.

Not classified by a typical budding yeast in tissue.

Spherule rupture can induce suppuration.

Slide 48 · Histoplasma: Environmental acquisition

Infection follows inhalation of microconidia from contaminated soil dust.

Bird or bat droppings are an important exposure clue.

The Ohio and Mississippi River Valleys among endemic areas.

Organisms are found predominantly within phagocytic cells.

Slide 49 · Histoplasma: T-cell–macrophage defense

Inhaled spores

Enter the lung

Phagocytosed yeast

May survive and multiply initially

Th1 activation

IFN-γ and TNF response

Immune containment

Granuloma formation; Possible fibrosis

Schematic

Slide 50 · Histoplasmosis has several pulmonary courses

Self-limited primary infection may leave a small pulmonary nodule.

Chronic progressive lesions can involve the lung apices.

Clinical symptoms may resemble tuberculosis.

Severe cell-mediated immune impairment favors widespread dissemination.

Slide 51 · Histoplasma granuloma: Necrosis to calcification

Schematic — not histologic evidence

Pulmonary granulomas often develop necrosis

Resolution may produce fibrosis and concentric calcification

Small yeasts may persist in tissue

Slide 52 · Histoplasma: Critical microscopic clue

Numerous small thin-walled yeasts may be found within macrophages.

Yeast forms in the approximately 3–5 µm range.

Disseminated disease may show yeast-filled phagocytes without granulomas.

Special fungal stains assist in demonstrating organisms.

Slide 53 · Localized versus disseminated histoplasmosis

Effective cellular immunity

Granulomatous lesions may necrose.

Fibrosis and calcification can follow.

Persistent small pulmonary lesions may remain.

Deficient cellular immunity

Granulomas may fail to organize.

Yeast-laden macrophages accumulate widely.

Extrapulmonary disease becomes important.

Slide 54 · Blastomyces: Clinical-pathologic spectrum

Blastomyces dermatitidis is a soil-associated dimorphic fungus.

Pulmonary infection may resolve or progress to a chronic lesion.

Disseminated disease can involve extrapulmonary sites.

A rare primary cutaneous infection follows direct inoculation.

Slide 55 · Blastomyces: Suppurative granulomas

Schematic — not histologic evidence

Granulomatous macrophage response

Prominent neutrophilic suppuration

Thick-walled yeast with broad-based budding

Slide 56 · Blastomyces morphology: Distinguish the yeast

Rounded yeast typically measures approximately 5–15 µm in tissue.

A thick, double-contoured wall is characteristic.

Broad-based budding is a defining morphologic clue.

Skin or laryngeal epithelial hyperplasia can mimic squamous carcinoma.

Slide 57 · Coccidioides: Pulmonary infection after inhalation

Coccidioides immitis and C. Posadasii are relevant species.

Exposure is linked to endemic arid regions of the Americas.

Many infections remain asymptomatic.

A small subset causes progressive pulmonary or disseminated disease.

Slide 58 · Coccidioides in tissue: Spherules, not budding yeast

Schematic — not histologic evidence

Large thick-walled tissue spherule

Internal endospores; No broad-based bud

Rupture releases endospores and recruits neutrophils

Slide 59 · Coccidioidal inflammation is morphologically variable

Unruptured spherules

Granulomatous inflammation may predominate.

Tissue reaction can resemble other fungal granulomas.

Identification of spherules is highly informative.

Ruptured spherules

Endospore release triggers a pyogenic response.

Granulomatous and suppurative components may coexist.

Mixed histology is not contradictory.

Slide 60 · Coccidioides: Sites of progressive disease

Progressive infection may involve lung parenchyma and regional nodes.

Disseminated foci can develop in meninges, skin and bone.

Reduced T-cell immunity increases the risk of dissemination.

Pregnancy is identified by Robbins as another risk context.

Slide 61 · Distinguish the three endemic fungi in tissue

Organism

Typical tissue form

Characteristic reaction

Histoplasma

Small yeast, often inside macrophages

Necrotizing granulomas; absent in severe dissemination

Blastomyces

Thick-walled, broad-based budding yeast

Suppurative granulomas

Coccidioides

Endospore-filled spherule

Granulomatous, pyogenic, or mixed

Slide 62 · Tissue differential for chronic granulomatous pneumonia

Finding

Leading consideration

Necessary next step

Caseating granuloma

Tuberculosis; endemic fungal disease

AFB and fungal stains; culture / molecular study

Suppurative granuloma

Blastomyces; Nocardia; other infection

Evaluate yeast/filament morphology and stains

Noncaseating granuloma

Infections; sarcoidosis among mimics

Do not exclude infection on necrosis alone

Few granulomas in immune suppression

Disseminated infection possible

Search carefully for abundant organisms

Slide 63 · The noninfectious differential is essential

Sarcoidosis may cause pulmonary granulomas without an infectious agent.

Foreign material can induce granulomatous reactions.

Necrotizing or suppurative injury may overlap with noninfectious processes.

Positive organism identification is decisive when morphology overlaps.

Slide 64 · A pathology-centered diagnostic algorithm

Recognize pattern

Granuloma ± necrosis / suppuration

Search for organisms

AFB and appropriate fungal stains

Correlate

Exposure, host state, radiology

Confirm identity

Microbiology and molecular tests

Schematic

Slide 65 · How not to overread a negative stain

A negative tissue stain means

Organisms were not demonstrated in those sections.

Low numbers or sampling may impair visualization.

A targeted microbiologic evaluation may still be required.

A positive specific morphology means

Fungal tissue forms may be strongly suggestive.

Acid-fast bacilli identify a group, not necessarily species.

Clinical and microbiologic interpretation remain necessary.

Slide 66 · Case discussion: An apical cavitary lesion

An adult with cough, weight loss and an apical cavitary pulmonary lesion undergoes tissue sampling. The biopsy contains necrotizing granulomas.

Diagnostic questions

What is the priority infectious consideration?

Can the H&E appearance alone prove the diagnosis?

Tuberculosis is a leading consideration; Request acid-fast testing and appropriate microbiologic confirmation. Fungal causes remain in the differential.

Slide 67 · Case discussion: A suppurative lung mass

An immunosuppressed adult presents with a slowly progressive pulmonary mass. Sections show central liquefaction, neutrophils and surrounding fibrosis.

Diagnostic questions

Which filamentous bacterium merits examination?

What second organ system warrants clinical attention?

Nocardia is a relevant possibility; Seek branching organisms with Gram/modified acid-fast stains, and consider the potential for CNS dissemination.

Slide 68 · Case discussion: Small yeasts in macrophages

A patient with prolonged fever and a pulmonary infiltrate has biopsy specimens with phagocytes containing numerous small yeast forms. Organized granulomas are sparse.

Diagnostic questions

Which endemic mycosis best matches the tissue clue?

What feature of host defense might explain weak granuloma formation?

Histoplasma is a leading consideration. Severe impairment of cell-mediated immunity can blunt granuloma organization.

Slide 69 · Case discussion: Broad-based budding

A lung biopsy shows neutrophils mixed with granulomas. Round, thick-walled yeast cells with broad-based buds are identified.

Diagnostic questions

Which fungal cause does the morphology suggest?

Why might a purely granulomatous description be misleading?

Blastomyces is strongly suggested; Its characteristic inflammatory pattern is suppurative granulomatous rather than exclusively epithelioid.

Slide 70 · Case discussion: An endospore-filled body

A pulmonary biopsy demonstrates large thick-walled spherules containing internal small structures. Neutrophils cluster around a ruptured form.

Diagnostic questions

Name the likely pathogen group.

Explain the coexistence of suppuration and granulomas.

Coccidioides is favored; Rupture releases endospores and may superimpose a pyogenic reaction.

Slide 71 · Integrated pathologic reporting principles

Describe the inflammatory pattern and the extent of necrosis.

Record whether organisms are visible and which stains were used.

Separate a suggestive morphology from proven microbiologic identity.

Flag diagnostic alternatives when the reaction is nonspecific.

Slide 72 · Five morphology-to-organism clues

Clue

Most useful association

Caseating, epithelioid granuloma

Tuberculosis; other granulomatous infection

Branching, beaded Gram-positive filaments

Nocardia

Small yeasts inside macrophages

Histoplasma

Broad-based budding thick-walled yeast

Blastomyces

Endospore-containing spherule

Coccidioides

Slide 73 · Core synthesis: Mechanisms to diagnosis

Chronic pneumonia often involves persistent intracellular or difficult-to-clear microbes.

Th1–macrophage immunity promotes containment and contributes to tissue damage.

Necrosis, suppuration, fibrosis and cavitation reflect different lesion pathways.

Morphology directs testing; Organism identification establishes the etiology.

Slide 74 · References and source boundaries

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026.

Pulmonary infections: chronic pneumonia and its etiologic groups.

Mycobacterial infections, nocardiosis, and endemic mycoses.

Granulomatous inflammation and inflammatory tissue injury.