Infectious Vasculitis

Slide 1 · Infectious Vasculitis

Direct vessel-wall infection, vascular injury and clinical consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Distinguish direct infectious vasculitis from immune-mediated vasculitis

Trace infection to the arterial wall through local and blood-borne routes

Link wall injury to aneurysm, thrombosis and infarction

Interpret angioinvasive fungal and infective endocarditis examples

Slide 3 · Vasculitis means inflammation of the vessel wall

The defining process is inflammation centered on a vascular wall.

Manifestations depend on the affected vascular bed.

Disease can be organ-limited or affect multiple vascular beds.

Vessel wall

Vascular lumen

Wall inflammation

Schematic vessel cross-section — not a histologic specimen

Slide 4 · Infectious vasculitis requires direct vascular invasion

Infectious agents directly invade and inflame vascular walls.

The mechanism differs from an infection that only triggers a remote immune reaction.

Arteritis is the arterial-wall form emphasized in this Robbins subsection.

Infectious agent

Direct vessel-wall invasion

Arteritis

Schematic

Slide 5 · Two major routes to vasculitic injury

Direct microbial wall invasion produces infectious arteritis.

Immune-mediated inflammation produces noninfectious vasculitis.

The distinction changes the implications of immunosuppression.

Direct microbial invasion

Infectious vasculitis

Immune-mediated inflammation

Noninfectious vasculitis

Schematic

Slide 6 · Infection may also drive indirect immune vasculitis

An infectious trigger can generate immune complexes.

An infection can also initiate vascular cross-reactivity.

These mechanisms do not establish direct organisms within a vascular wall.

Infection

Immune complexes / cross-reactivity

Noninfectious vasculitis

Schematic

Slide 7 · Why the infectious–immune distinction matters

Question

Direct infectious

Immune-mediated

Immediate driver

Organisms invade wall

Inflammatory immune response

Robbins warning

Immunosuppression may harm

May require immunosuppression

Slide 8 · Distribution: Local disease versus systemic involvement

Vasculitis may initially be restricted to a single organ.

Systemic disease may involve several vascular beds.

Organ-specific injury and constitutional inflammation may coexist.

Single affected territory

Organ-limited disease

Several vascular beds

Systemic disease

Schematic

Slide 9 · Symptoms derive from two simultaneous processes

Vascular-bed injury produces local functional effects.

Systemic inflammation may cause fever, myalgias, arthralgias and malaise.

The clinical phenotype depends on where vessel damage occurs.

Affected vascular bed

Organ findings

Systemic inflammatory response

Constitutional findings

Schematic

Slide 10 · The principal infectious agents named

Category

Named example

Teaching relevance

Bacteria

Pseudomonas

Direct infectious arteritis

Fungi

Aspergillus

Angioinvasion; infarction

Fungi

Mucor

Arterial invasion; thrombi

Slide 11 · Pseudomonas: Bacterial arteritis as a mechanism

Pseudomonas as a bacterial example of direct arterial-wall infection.

Vessel injury can accompany an existing tissue infection or occur through hematogenous seeding.

The organisms and source of infection require patient-specific evaluation.

Bacterial infection

Direct vascular invasion

Arterial-wall injury

Schematic

Slide 12 · Aspergillus: Fungal infection with vascular tropism

Invasive aspergillosis occurs in immunosuppressed hosts.

Aspergillus has a propensity for vascular invasion.

Hemorrhage and infarction often accompany necrotizing infection.

Invasive fungal growth

Vascular invasion

Hemorrhage + infarction

Schematic

Slide 13 · Mucor species: Vascular injury in invasive infection

Invasion of arterial walls by mucormycetes.

Thrombosis can produce cerebral or pulmonary infarction.

Anatomic spread from the nasal sinuses may affect orbit and brain.

Tissue invasion

Arterial-wall penetration

Thrombus + infarction

Schematic

Slide 14 · A microbial label is not a complete mechanism

“Infectious vasculitis” specifies direct wall invasion, not merely a positive blood culture.

Different pathogens may converge on thrombosis or aneurysmal wall damage.

Always describe organism, entry route, involved vessel and downstream lesion separately.

Organism

Entry route

Vessel injury

Consequence

Schematic

Slide 15 · Two anatomic routes deliver microbes to vessels

Contiguous spread begins in an infected neighboring tissue.

Hematogenous spread brings organisms through the bloodstream.

Local spread as a familiar setting and hematogenous seeding as less common.

Local pneumonia / abscess

Contiguous invasion

Septicemia / septic embolus

Blood-borne seeding

Schematic

Slide 16 · Local spread: Infection abutting a vascular wall

Bacterial pneumonia can extend into nearby vascular structures.

An abscess is another source of adjacent microbial invasion.

The spatial relationship between infected tissue and vessel matters.

Local infected tissue

Adjacent vascular wall

Localized arteritis

Schematic

Slide 17 · Pneumonia-associated vascular invasion

Pneumonic inflammation is an example of a local infectious source.

Microbes can invade vessels within the infected tissue field.

Vascular injury may then compound parenchymal tissue damage.

Pneumonia

Vascular infection

Local vascular complication

Schematic

Slide 18 · Abscess-associated vascular invasion

An abscess contains an infectious inflammatory focus.

A nearby artery may be reached by extension of the suppurative process.

The same extension pathway can contribute to an infected aneurysm.

Abscess

Adjacent arterial wall

Infectious arteritis / weakening

Schematic

Slide 19 · Contiguous spread is an anatomical sequence

The original infection need not begin in the vessel.

Direct invasion occurs when the infected focus reaches its wall.

This is distinct from circulating microorganisms seeding a remote vessel.

Primary tissue infection

Local extension

Vascular wall involvement

Schematic

Slide 20 · Hematogenous route: Organisms reach vessels in blood

Septicemia can distribute organisms through the circulation.

Circulating organisms may directly infect an arterial wall.

Blood-borne infection is a separate pathway from contiguous spread.

Septicemia

Circulating microorganisms

Arterial-wall seeding

Schematic

Slide 21 · Infective endocarditis supplies infected emboli

Infective endocarditis forms organism-containing valvular vegetations.

Friable vegetations can embolize.

The embolic fragments may infect arterial sites where they lodge.

Infected valve vegetation

Septic embolus

Remote vascular infection

Schematic

Slide 22 · An infected embolus can injure two compartments

The embolus may occlude an arterial lumen.

Its organisms can also establish infection at the lodging site.

Distinguish mechanical obstruction from subsequent destructive infection.

Luminal obstruction

Ischemic consequence

Microbial seeding

Infected vessel wall

Schematic

Slide 23 · Three origins of a mycotic aneurysm

Septic embolus, commonly from infective endocarditis.

Direct extension of an adjacent suppurative focus.

Circulating microorganisms infecting the arterial wall.

Septic embolus

Adjacent suppuration

Circulating microbes

Infected arterial wall

Schematic — three alternative routes converge on the same lesion

Slide 24 · The word “mycotic” does not identify a fungus

Term

What it identifies

What it does not prove

Infectious arteritis

Infected arterial wall

A single causative organism

Mycotic aneurysm

Infection-associated aneurysm

Fungal infection specifically

Slide 25 · Fungal angioinvasion adds organ-specific mechanisms

Fungus

Important portal / territory

Vascular consequence

Aspergillus

Lung; later dissemination

Hemorrhage or infarction

Mucormycetes

Sinus–orbit–brain; lung

Thrombi and infarction

Slide 26 · Aspergillus enters the host as inhaled conidia

The pulmonary tract is the major portal of entry.

Inhaled conidia can reach distal airspaces.

Invasive disease follows germination and tissue invasion in susceptible hosts.

Inhaled conidia

Pulmonary deposition

Hyphal invasion

Schematic

Slide 27 · Neutrophil defense normally restricts Aspergillus

Alveolar macrophages recognize and remove conidia.

Neutrophils help kill fungal hyphae.

Neutropenia and impaired neutrophil function favor invasive infection.

Conidia / hyphae

Macrophage + neutrophil response

Control of invasion

Schematic

Slide 28 · Invasive aspergillosis centers on tissue penetration

Invasive aspergillosis is an opportunistic infection in immunosuppressed hosts.

Lung lesions commonly show necrotizing pneumonia.

Its vascular tropism permits infarction and hematogenous dissemination.

Impaired host defenses

Invasive pulmonary lesion

Vascular invasion / spread

Schematic

Slide 29 · Pulmonary aspergillosis: The necrotizing target lesion

Sharply demarcated rounded gray foci.

The lesions have hemorrhagic borders.

Vascular invasion explains associated hemorrhage and infarction.

Necrotizing focus

Rounded gray pulmonary lesion

Hemorrhagic peripheral border

Associated vascular injury

Schematic

Slide 30 · Aspergillus vascular invasion enables dissemination

Fungal hyphae invade vascular structures in the primary lesion.

Hematogenous spread can extend infection beyond the lung.

Skin, brain, eyes, liver and kidneys among affected sites.

Pulmonary infection

Bloodstream dissemination

Extrapulmonary lesions

Schematic

Slide 31 · Aspergillus histomorphology: Septate hyphae

Septate filaments with acute-angle branching.

The pattern is useful for recognizing an angioinvasive mold in tissue.

Observe whether fungi are within vessel walls or lumina, not only nearby parenchyma.

Aspergillus hyphae

Septate / acute-angle

Simplified original schematic; Not a tissue photomicrograph

Slide 32 · Fungal morphology alone has diagnostic limits

Observation

Supports

Does not establish

Septate acute-angle hyphae

Compatible Aspergillus pattern

Definitive organism species

Hyphae inside a vessel

True angioinvasion

Every underlying predisposing factor

Slide 33 · Mucormycosis particularly affects susceptible hosts

Mucormycetes cause opportunistic invasive disease.

Immunosuppression and diabetes with ketoacidosis in relevant presentations.

Their ability to invade arteries drives major tissue injury.

Susceptible host

Invasive mucormycosis

Angioinvasion

Schematic

Slide 34 · Mucormycete entry sites determine the disease field

Primary invasion may involve nasal sinuses, lungs or gastrointestinal tract.

The route depends on inhaled or ingested spores.

The involved site determines the adjacent vascular territories at risk.

Nasal sinuses

Rhinocerebral spread

Lungs

Pulmonary lesions

Gastrointestinal tract

Local infection

Schematic

Slide 35 · Rhinocerebral mucormycosis follows local extension

Invasion may advance from the nasal sinuses toward the orbit and brain.

The organism can cross into periorbital tissues and cranial structures.

Infected cerebral arteries may become thrombosed.

Nasal sinus infection

Orbit / cranial extension

Arterial invasion

Schematic

Slide 36 · Cerebral infarction in mucormycosis

Mucormycetes penetrate arterial walls.

Intravascular thrombosis may obstruct cerebral blood supply.

Brain infarction can accompany meningoencephalitis.

Arterial invasion

Thrombotic occlusion

Cerebral infarction

Schematic

Slide 37 · Pulmonary mucormycosis: Vascular thrombi

Lung disease may be primary in severe immunodeficiency.

Hemorrhagic pneumonia can coexist with vascular thrombosis.

Distal infarction follows compromised arterial perfusion.

Pulmonary fungal invasion

Vascular thrombi

Hemorrhage + infarction

Schematic

Slide 38 · Mucormycete morphology: Broad irregular hyphae

Nonseptate hyphae with irregular width.

Near right-angle branching contrasts with the Aspergillus pattern.

Angioinvasive fungi in meningeal vessels.

Mucor hyphae

Nonseptate / near right-angle

Simplified original schematic; Not a tissue photomicrograph

Slide 39 · Aspergillus versus Mucor: Tissue comparison

Feature

Aspergillus

Mucormycetes

Hyphal septation

Septate

Nonseptate

Branching

Acute angles

Often near 90°

Vascular effect

Hemorrhage, infarction

Thrombosis, infarction

Slide 40 · Vascular injury produces two major outcomes

Wall destruction and weakening predispose to aneurysm formation.

Inflammation-associated thrombosis compromises downstream blood flow.

These are distinct, potentially coexisting complications.

Wall weakening

Infected aneurysm

Luminal thrombosis

Downstream infarction

Schematic

Slide 41 · Infected aneurysm: Failure of arterial wall integrity

Direct infection weakens the normal vessel-wall structure.

Loss of mechanical integrity can permit abnormal dilation.

An infection-associated aneurysm is termed mycotic.

Infected vessel wall

Structural weakening

Aneurysmal dilation

Schematic

Slide 42 · An infected thrombus can erode the artery

Thrombi becoming infected during bacteremia.

An infected thrombus can form an inflammatory mass.

Erosion and weakening of the wall may produce a mycotic aneurysm.

Thrombus + bacteremia

Infected inflammatory mass

Wall erosion / aneurysm

Schematic

Slide 43 · Aneurysm and pseudoaneurysm are not synonymous

Lesion

Defining structural relationship

True aneurysm

Dilated vessel wall remains part of sac

Pseudoaneurysm

Wall breach; blood outside wall communicates with lumen

Slide 44 · Why an infected aneurysm is dangerous

Arterial wall damage reduces resistance to hemodynamic stress.

Progressive disruption may predispose to rupture.

Location and the involved vessel determine clinical severity.

Wall destruction

Loss of mechanical resistance

Rupture risk

Schematic

Slide 45 · Thrombosis: The alternative vascular pathway

Infectious inflammation can promote formation of a luminal thrombus.

The thrombus may restrict or obstruct perfusion.

Vulnerable downstream tissue can become infarcted.

Vasculitic injury

Arterial thrombosis

Reduced perfusion

Infarction

Schematic

Slide 46 · A thrombus is a local lesion; Infarction is downstream

The obstructing event is in the vessel lumen.

The tissue injury develops in the supplied vascular territory.

Identifying both sites clarifies the causal interpretation.

Upstream arterial thrombus

Reduced tissue perfusion

Downstream infarction

Schematic

Slide 47 · Bacterial meningitis can cause meningeal vasculitis

Inflammation can involve meningeal vessels during bacterial meningitis.

Associated thrombosis may reduce perfusion of the underlying brain.

Cerebral infarction is a recognized complication.

Bacterial meningitis

Meningeal vessel thrombosis

Brain infarction

Schematic

Slide 48 · The meningitis example links adjacent compartments

The infection is centered in meningeal structures.

Vessel-wall inflammation extends the injury to the vascular compartment.

Infarction involves underlying brain supplied by affected vessels.

Infected meninges

Meningeal arteritis / thrombus

Underlying brain injury

Schematic

Slide 49 · Hemorrhage and infarction can occur together

Angioinvasive fungal lesions can produce hemorrhagic tissue damage.

Vascular occlusion simultaneously favors ischemic necrosis.

This combination in invasive pulmonary mold disease.

Vessel-wall damage

Hemorrhage

Vascular occlusion

Ischemic infarction

Schematic

Slide 50 · Compare four source-supported clinical settings

Setting

Route of vessel injury

Consequence

Abscess / pneumonia

Local extension

Infected arteritis

Endocarditis

Septic embolization

Infected aneurysm

Bacterial meningitis

Meningeal inflammation

Brain infarction

Angioinvasive molds

Tissue / wall penetration

Thrombi, hemorrhage, infarction

Slide 51 · Interpretation requires locating the infected wall

Infected tissue adjacent to a vessel is not automatically proof of vessel-wall invasion.

A finding of intravascular or wall-associated organisms is stronger evidence of angioinvasion.

Never label a synthetic diagram as a histological finding.

Adjacent infection

Does not alone prove angioinvasion

Organisms invading vessel wall

Supports direct infectious vasculitis

Schematic

Slide 52 · Distinguishing mechanisms at the microscope

Key question

Direct infectious mechanism

Indirect immune mechanism

What drives injury?

Microbial invasion

Immune effector response

Required causal link

Organisms reach wall

Infection triggers immunity

Pitfall

Mistaking adjacency for invasion

Assuming every postinfection vasculitis is microbial

Slide 53 · Clinical exercise: Infarction after bacterial meningitis

HYPOTHETICAL TEACHING CASE

Bacterial meningitis → new focal neurological deficit

PATHOLOGY QUESTION

Which vascular event could connect these findings?

Apply the source-based pathogenesis to this illustrative scenario.

Slide 54 · Case interpretation: Meningeal thrombosis

Meningeal infection can cause inflammation involving meningeal vessels.

Thrombotic occlusion may interrupt supply to the underlying brain.

This mechanism can produce infarction rather than only diffuse inflammation.

Meningeal infection

Vascular thrombosis

Cerebral infarction

Schematic

Slide 55 · Clinical exercise: An embolizing valve vegetation

HYPOTHETICAL TEACHING CASE

Infected valve vegetation → septic arterial embolus

PATHOLOGY QUESTION

How could this cause aneurysmal enlargement?

Apply the source-based pathogenesis to this illustrative scenario.

Slide 56 · Case interpretation: Infected aneurysm

An embolus containing organisms lodges in an artery.

Local infection and inflammation can damage the vessel wall.

Loss of structural integrity favors a mycotic aneurysm.

Septic embolus

Wall infection

Weakening / aneurysm

Schematic

Slide 57 · Clinical exercise: Necrotizing pulmonary aspergillosis

HYPOTHETICAL TEACHING CASE

Immunosuppressed host → pulmonary necrotizing focus

PATHOLOGY QUESTION

What mechanism can explain hemorrhage plus necrosis?

Apply the source-based pathogenesis to this illustrative scenario.

Slide 58 · Case interpretation: Fungal vascular invasion

Hyphal tissue invasion reaches vessel walls.

Vascular compromise produces hemorrhagic and ischemic injury.

The pathology links the necrotizing lung lesion to angioinvasion.

Invasive Aspergillus

Vascular invasion

Hemorrhage / infarction

Schematic

Slide 59 · Clinical exercise: Sinus-to-brain fungal infection

HYPOTHETICAL TEACHING CASE

Sinus infection → orbit / brain extension

PATHOLOGY QUESTION

Why might cerebral infarction develop?

Apply the source-based pathogenesis to this illustrative scenario.

Slide 60 · Case interpretation: Thrombosed cerebral arteries

Mucormycetes can invade cranial and meningeal vessels.

Arterial-wall invasion promotes thrombotic obstruction.

Downstream cerebral infarction may complicate meningoencephalitis.

Rhinocerebral spread

Arterial thrombosis

Cerebral infarction

Schematic

Slide 61 · Diagnostic reasoning: Separate four questions

Is vessel-wall inflammation actually present?

Is direct microbial invasion documented or suspected?

Did infection spread locally or through blood?

Is the dominant complication aneurysm, thrombosis, or infarction?

Wall lesion?

Microbial mechanism?

Entry route?

Complication?

Schematic

Slide 62 · The most consequential diagnostic pitfall

Systemic inflammatory symptoms alone cannot assign an infectious or immune cause.

An infection may directly invade vessels or indirectly trigger immune vasculitis.

The two mechanisms have substantially different therapeutic implications.

Direct infection

Treat infection as the driver

Immune process

Different management logic

Schematic

Slide 63 · Mechanism summary: Trace the complete causal chain

Identify the tissue source or circulating route.

Establish direct involvement of the vessel wall.

Recognize either loss of wall integrity or luminal occlusion.

Predict the relevant organ consequence.

Infectious source

Vessel-wall invasion

Wall weakness or thrombus

Organ consequence

Schematic

Slide 64 · Five facts to retain

Direct microbial invasion distinguishes infectious arteritis from indirect immune vasculitis.

Local extension and hematogenous seeding are principal access routes.

Pseudomonas, Aspergillus and Mucor are Robbins examples.

Mycotic aneurysm denotes an infection-associated lesion, not necessarily a fungus.

Vascular thrombosis can produce downstream infarction.

Slide 65 · Source references

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th ed. (2026), Ch 11 — Vasculitis and Aneurysms.

Related Robbins source sections: Ch 8 — Aspergillosis and Mucormycosis; Ch 12 — Infective Endocarditis.

Related Robbins source sections: Ch 4 — Thrombosis; Ch 15 — Lung Abscess.

Exact markdown source locators and visual provenance appear in speaker notes and accompanying manifest.