Mucormycosis Zygomycosis

Slide 1 · Mucormycosis (Zygomycosis)

Opportunistic fungal disease • Innate immunity • Angioinvasion

An integrated morphologic and clinicopathologic lecture

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Pathology learning objectives

Classify mucormycosis as an opportunistic mycosis caused by environmental molds.

Explain how phagocyte defenses and iron availability influence invasive infection.

Recognize the characteristic fungal morphology and destructive vascular pathology.

Connect the entry site with rhinocerebral, pulmonary, gastrointestinal, and wound disease.

Identify the fungus

Explain host defenses

Recognize angioinvasion

Interpret organ injury

Slide 3 · Mucormycosis is an invasive opportunistic mycosis

Mucormycotina are widespread environmental fungi.

Exposure alone does not imply tissue-invasive disease.

A vulnerable host allows fungal growth and destructive invasion.

Environmental exposure

Susceptible host

Established infection

Tissue invasion

Slide 4 · Mucorales agents encountered

The disease name encompasses infections due to multiple environmental genera.

Mucor, Rhizopus, Rhizomucor, and Cunninghamella.

Morphologic recognition in tissue generally precedes species-level identification.

Mucor spp.

Rhizopus spp.

Rhizomucor spp.

Cunninghamella spp.

Slide 5 · Historical terminology: Zygomycosis

Robbins titles the section “Mucormycosis (Zygomycosis).”

It explicitly identifies zygomycosis as a former name.

The lecture uses mucormycosis for the invasive disease described in the source.

Former term

Zygomycosis

Current term

Mucormycosis

Slide 6 · Mold growth provides the morphologic context

Fungal molds form multicellular filaments called hyphae.

Molds extend by growth and division at hyphal tips.

Tissue hyphae are the key structures in mucormycosis morphology.

Yeasts: Round/oval cells

Molds: Filamentous hyphae

Mucormycetes: Invasive hyphae

Slide 7 · Opportunistic infection depends on the host

The textbook places mucormycosis among opportunistic mycoses.

Immunocompetent hosts usually resist these environmental fungi.

Impaired host defenses permit spores to establish infection.

Spores encountered

Host defenses sufficient?

Spores controlled / invasion prevented

Host defense failure → invasion

Slide 8 · Aerosolized spores make exposure common

Mucormycotina produce asexual spores dispersed in air.

Dust and air can carry infective propagules.

The severity of infection depends strongly on host context, not simply exposure.

Environmental mold

Asexual spores

Airborne exposure

Host interface

Slide 9 · Three principal entry routes

Inhalation of spores is the most common portal of entry.

Percutaneous contamination can follow injury or an operative procedure.

Ingestion provides an additional route to infection.

Routes of entry

Airborne → inhalation

Wound / surgical site → skin

Ingestion → gut

Slide 10 · Entry route influences anatomic distribution

Sinuses, lungs, and gastrointestinal tract are the principal organ sites.

Entry by air, wound contamination, or ingestion suggests different starting locations.

Subsequent vascular invasion can extend injury beyond the original focus.

Portal

Potential focus

Inhalation

Sinuses or lungs

Ingestion

Gastrointestinal tract

Percutaneous

Wound / skin

Slide 11 · Major susceptibility factors

Deficits in phagocyte number or function.

Metabolic changes affecting available iron also promote infection.

Damage to the cutaneous barrier enables direct inoculation.

Neutropenia

Corticosteroids

Diabetes / iron overload

Wounds / trauma

Slide 12 · Neutropenia removes an essential hyphal defense

Neutrophils directly injure fungal hyphal walls after germination.

Reduced neutrophil number compromises this defense.

Invasive growth becomes more likely when viable hyphae persist.

Hyphal germination

Neutrophil wall injury

If neutrophils are scarce

Hyphae persist and invade

Slide 13 · Corticosteroid exposure increases susceptibility

Corticosteroid use is named as a major predisposing condition.

It belongs to the immune-suppression component of the risk profile.

Interpret risk in conjunction with other host factors and exposure routes.

Corticosteroid use

Vulnerable host

Spore exposure

Invasive infection

Slide 14 · Diabetes mellitus is a major host context

Diabetes mellitus is one of the major predisposing factors.

The textbook links diabetes to altered free-iron availability.

Diabetic ketoacidosis is particularly associated with rhinocerebral disease.

Diabetes

Altered iron availability

Fungal growth advantage

Invasive disease

Slide 15 · Ketoacidosis increases accessible iron

Diabetic ketoacidosis with increased free iron.

The proposed mechanism involves diminished normal iron binding.

Free iron promotes Mucormycotina growth.

Diabetic ketoacidosis

More available free iron

Fungal growth favored

Higher infection probability

Slide 16 · Iron overload is a separate risk factor

Iron overload appears among the major predisposing conditions.

Mucormycotina benefit from available free iron.

The risk relates to usable iron, not merely the presence of iron in tissue.

Iron overload

Increased usable iron

Greater growth opportunity

Susceptible host

Slide 17 · Deferoxamine can facilitate fungal iron access

Chronic deferoxamine chelation as a special risk.

Deferoxamine can serve as a siderophore for these fungi.

This explains why chelation does not necessarily deprive them of iron.

Deferoxamine

Fungal siderophore function

Iron delivery to fungus

Fungal growth promoted

Slide 18 · Barrier breakdown creates a cutaneous portal

Burns, surgical wounds, and trauma disrupt the skin barrier.

Spores can enter directly at these vulnerable sites.

This pathway is distinct from the usual airborne route.

Intact epidermis

Barrier disruption

Spore introduction

Local invasive focus

Slide 19 · The risk factors act through different pathways

Neutropenia primarily compromises direct hyphal killing.

Metabolic and chelation states alter fungal access to iron.

Wounds create a direct route through a disrupted surface barrier.

Host problem

Principal vulnerability

Neutropenia

Reduced hyphal killing

Diabetes / iron

Enhanced fungal growth

Barrier injury

Direct inoculation

Slide 20 · Inhaled spores meet innate defenses

Inhalation is the most common entry route.

Germinating spores normally encounter tissue macrophages.

Neutrophils become critical when fungi develop hyphae.

Inhaled sporangiospore

Macrophage interaction

Germination

Neutrophil response

Slide 21 · Percutaneous exposure bypasses surface protection

Trauma or a surgical wound provides a break in the cutaneous barrier.

The wound can be exposed to environmental spores.

The resulting focus can undergo local tissue invasion and necrosis.

Wound / burn / surgery

Spore entry

Local fungal growth

Tissue injury

Slide 22 · Ingestion can seed gastrointestinal disease

Ingestion is a recognized alternative mode of entry.

The gastrointestinal tract is a primary site of fungal invasion.

Interpret organ involvement in light of the route of exposure.

Ingested spores

Gastrointestinal entry

Fungal establishment

Invasive lesion

Slide 23 · Macrophages are the first defensive barrier

Macrophages phagocytose germinating sporangiospores.

Early killing to nonoxidative mechanisms.

Effective macrophage function helps prevent establishment.

Sporangiospore

Phagocytosis by macrophage

Nonoxidative killing

Infection prevented

Slide 24 · Germination changes the host–pathogen interface

The source distinguishes sporangiospores from mature hyphae.

Macrophages act early during spore germination.

Neutrophils are particularly important after hyphae develop.

Early: Germinating spores

Later: Invasive hyphae

Slide 25 · TLR2 detects fungal hyphal components

Fungal hyphal components are recognized through TLR2.

This recognition triggers a pro-inflammatory response.

The innate reaction recruits and activates antifungal host defenses.

Mucormycotina hyphal component

TLR2 recognition

Pro-inflammatory signaling

Host response

Slide 26 · Inflammatory mediators include IL-6 and TNF

Robbins explicitly names IL-6 and tumor necrosis factor (TNF).

Both belong to the response induced by recognition of hyphal components.

Inflammation alone is not evidence that fungal growth is controlled.

TLR2 recognition

IL-6 / TNF cascade

Local inflammation

Control depends on phagocytes

Slide 27 · Neutrophils directly damage hyphal walls

Neutrophils have a key role once sporangiospores germinate.

Their antifungal effect includes direct hyphal-wall damage.

This action limits ongoing filamentous tissue invasion.

Germinating fungus

Hyphae form

Neutrophils attack walls

Hyphal growth inhibited

Slide 28 · Two coordinated phases of innate resistance

Macrophages act at the germinating-spore stage.

Neutrophils are emphasized at the hyphal stage.

Compromise of either population facilitates establishment and invasion.

Defense

Principal target

Macrophages

Germinating sporangiospores

Neutrophils

Germinated hyphae

Both impaired

Greater invasive risk

Slide 29 · Compromised phagocytes permit fungal persistence

Reduced cell number or impaired cell function raises the probability of infection.

Persistent fungal growth increases the likelihood of tissue invasion.

Host failure is the central switch from exposure to disease.

Phagocyte deficit

Insufficient fungal killing

Fungal persistence

Invasive disease

Slide 30 · Aggressiveness varies between Mucor species

The source reports species-related variation in resistance to phagocytosis.

Susceptibility to neutrophil-mediated damage also varies.

The reasons for these interspecies differences remain unknown.

Spore phagocytosis resistance

Hyphal resistance

Different clinical aggressiveness

Slide 31 · Free iron and defective defenses reinforce risk

Greater available iron can favor fungal growth.

Reduced phagocyte protection can fail to restrict germination and hyphae.

Either mechanism makes tissue invasion more likely in a susceptible host.

Greater free iron

Impaired phagocyte killing

Fungal persistence and growth

Angioinvasion

Slide 32 · Pathogenesis is a sequence, not a single event

Environmental spores encounter a permissive portal and host.

Germination overcomes early innate defenses.

Developing hyphae can invade tissue and blood vessels.

Exposure

Entry

Germination

Hyphal invasion

Vascular damage

Slide 33 · Tissue morphology identifies the invasive mold

The hallmark is broad, variably sized hyphae that lack regular septation.

Branches are often nearly perpendicular to the parent filament.

Recognition should include the tissue response and vessels, not hyphae alone.

Original schematic — not a tissue micrograph

Slide 34 · The hyphal caliber is variable

Hyphal widths of approximately 6–50 μm.

Width may vary appreciably along the same filament.

A uniform, narrow filament is less typical of the described pattern.

Original schematic — not a tissue micrograph

Slide 35 · Nonseptate architecture is a diagnostic clue

Nonseptate fungal hyphae.

Aseptate or sparsely septate appearance contrasts with regularly septate Aspergillus.

Interpret septation together with branching and vessel invasion.

Original schematic — not a tissue micrograph

Slide 36 · Near-right-angle branching distinguishes the pattern

Mucormycetes frequently exhibit approximately 90° branches.

Aspergillus in the adjacent Robbins section forms acute-angle branches.

Branching geometry is supportive, not a substitute for full morphologic assessment.

~90°

~40°

Mucormycetes

Aspergillus

Slide 37 · Mucormycetes versus Aspergillus: Tissue hyphae

The genera using hyphal width, septation, and branching.

Mucormycetes are broad and variably sized; Aspergillus filaments are narrower.

The distinction matters in tissue sections with angioinvasive fungi.

Feature

Mucormycetes

Aspergillus

Hyphae

6–50 μm; Variable

5–10 μm

Septa

Nonseptate

Septate

Branching

Near 90°

Acute (~40°)

Slide 38 · H&E and fungal stains reveal the hyphae

Invasive hyphae are visible with H&E.

Special fungal stains may also demonstrate the filaments.

Assess architecture, adjacent necrosis, and vascular involvement.

Hematoxylin & eosin

Special fungal stains

Slide 39 · Three morphologic observations belong together

Hyphal caliber: Broad and uneven.

Hyphal structure: No regular septa.

Branch pattern: Commonly near 90°.

Variable width

Nonseptate

Near-right-angle

Slide 40 · Tissue morphology has identification limits

Microscopic tissue patterns can support a fungal diagnosis.

The general fungal-infection section notes that culture may be required for some species.

Report observed structures separately from unverified species-level assignment.

Tissue pattern

Provisional fungal category

Species identity when established

Slide 41 · Angioinvasion defines the destructive lesion

The fungi invade arterial walls rather than staying on mucosal surfaces.

Invasion damages vascular integrity and can promote thrombosis.

The consequent ischemia contributes to tissue necrosis.

Thrombus

Arterial wall

Invasive hypha

Schematic cross-section

Slide 42 · Fungal vascular invasion promotes thrombosis

Hyphae penetrate or grow within vessel walls.

The involved artery can thrombose.

Reduced downstream perfusion creates infarction risk.

Invasive hyphae

Arterial injury

Thrombosis

Distal ischemia

Slide 43 · Thrombosis links microscopic invasion to infarction

Vascular obstruction compromises blood supply to tissue.

Distal tissue undergoes infarction when perfusion fails.

This vascular mechanism explains tissue destruction extending beyond visible fungal growth.

Thrombus

Reduced perfusion

Infarction

Necrosis

Slide 44 · Necrosis is a consequence of vascular and tissue invasion

The fungus directly invades local tissues.

Arterial thrombosis adds ischemic injury.

The combination underlies the destructive character of mucormycosis.

Local tissue invasion

Vascular obstruction

Necrosis

Slide 45 · Primary organ sites reflect the portal of entry

The nasal sinuses are a characteristic site after airborne exposure.

The lungs may be involved primarily or secondarily.

The gastrointestinal tract can be involved following ingestion.

Nasal sinuses

Lungs

Gastrointestinal tract

Slide 46 · Sinus disease may extend into adjacent tissues

Rhino-sinus infection may begin in the nasal sinuses.

Locally invasive growth can penetrate contiguous structures.

Robbins particularly links rhinocerebral disease with diabetic ketoacidosis.

Nasal sinuses

Local invasion

Orbit

Brain

Slide 47 · Orbital involvement follows spread from the sinuses

The sinus focus can penetrate periorbital tissues.

Spread is by contiguous invasion rather than merely airborne deposition.

Orbital extension signals anatomically advanced local disease.

Sinus focus

Periorbital tissues

Invasive extension

Slide 48 · Intracranial invasion extends the disease spectrum

The organism may breach the cranial vault.

Intracranial extension can lead to meningoencephalitis.

The route follows destructive invasion from the original sinus focus.

Sinus

Orbit / cranial boundary

Meninges / brain

Slide 49 · Rhinocerebral mucormycosis can cause meningoencephalitis

Fungal entry into the cranial compartment involves neural tissues.

The textbook specifically identifies meningoencephalitis.

This is a consequence of local extension and severe invasive disease.

Cranial extension

Meningeal involvement

Brain inflammation

Meningoencephalitis

Slide 50 · Cerebral infarcts can complicate rhinocerebral disease

Fungi may invade cerebral arteries.

Arterial thrombosis impairs cerebral blood flow.

Cerebral infarction may accompany the infectious meningoencephalitis.

Thrombus

Arterial wall

Invasive hypha

Schematic cross-section

Slide 51 · Rhinocerebral injury follows a coherent cascade

The likely chain begins with sinus infection.

Contiguous invasion can reach orbital and intracranial structures.

Arterial infection and thrombosis create infarctive complications.

Sinus infection

Periorbital extension

Cranial involvement

Arterial thrombosis

Infarction

Slide 52 · Pulmonary disease has two described pathways

Pulmonary mucormycosis may be primary in severe immunodeficiency.

Lung involvement may also arise secondary to rhinocerebral disease.

In both settings, vascular injury shapes the morphologic lesions.

Primary pulmonary disease

Secondary lung involvement

Slide 53 · Pulmonary lesions include hemorrhagic pneumonia

Hemorrhagic pneumonia in lung infection.

Tissue destruction coexists with bleeding.

Vascular invasion accounts for much of the accompanying ischemic damage.

Lung invasion

Vascular damage

Hemorrhage

Pneumonia

Slide 54 · Pulmonary thrombi reflect vascular invasion

Infected pulmonary tissue contains vascular thrombi.

Vessel obstruction disrupts normal perfusion.

Pulmonary morphology must be read as parenchymal and vascular injury.

Thrombus

Arterial wall

Invasive hypha

Schematic cross-section

Slide 55 · Distal lung infarcts complete the pulmonary triad

Pulmonary thrombi block blood flow to downstream tissue.

Distal infarctions with hemorrhagic pneumonia.

Recognize pneumonia, thrombi, and infarction as linked findings.

Hemorrhagic pneumonia

Vascular thrombi

Distal infarctions

Slide 56 · Gastrointestinal infection relates to ingestion

The gastrointestinal tract is one of three main invasion sites.

Ingestion is a possible route of entry.

Invasive disease can be understood through the same hyphal and vascular mechanisms.

Ingestion

Gastrointestinal entry

Invasive hyphae

Tissue necrosis

Slide 57 · Cutaneous infection begins at a disrupted barrier

Burns, surgery, or trauma allow direct fungal introduction.

The presenting tissue context differs from sinus or pulmonary inhalation.

Histologic investigation still focuses on invasive hyphae and injured tissue.

Burn / surgical wound / trauma

Environmental spore deposition

Tissue invasion

Slide 58 · Anatomic form and underlying host state correlate

Diabetic ketoacidosis is highlighted with rhinocerebral spread.

Severe immunodeficiency is highlighted in primary pulmonary involvement.

Barrier disruption is the distinctive context for wound inoculation.

Pattern

Textbook-linked setting

Rhinocerebral

Diabetic ketoacidosis

Primary pulmonary

Severe immunodeficiency

Cutaneous entry

Barrier breach

Slide 59 · A tissue-based diagnostic reasoning sequence

Establish whether there are invasive fungal hyphae in involved tissue.

Characterize width, septation, and branching in the section.

Look for vascular invasion, thrombosis, and necrosis.

Identify hyphae

Describe morphology

Assess vessel invasion

Correlate with organ/host

Slide 60 · Describe the finding before inferring the organism

Observation: Broad, nonseptate, variable-width, branching hyphae.

Interpretation: Morphologic pattern consistent with mucormycetes.

Do not claim a species from morphology alone when not established.

Observed tissue findings

Interpretive diagnosis

Species-level identification

Slide 61 · Case: Ketoacidosis with destructive sinus disease

A patient with diabetic ketoacidosis has invasive sinus disease.

Biopsy shows broad, nonseptate hyphae in necrotic tissue.

The tissue contains vessels infiltrated by fungal elements.

Clinicopathologic question

What mechanism explains the necrosis?

Slide 62 · Case reasoning: Rhinocerebral pathogenesis

The described hyphal pattern supports mucormycosis.

Diabetic ketoacidosis favors accessible free iron.

Angioinvasion and arterial thrombosis cause ischemic tissue necrosis.

Diabetic ketoacidosis

Fungal proliferation

Arterial thrombosis

Necrosis

Slide 63 · Case: Severe immunodeficiency with pulmonary lesions

A severely immunodeficient patient develops fungal lung disease.

The lung contains hemorrhagic pneumonia and vascular thrombi.

Broad irregular nonseptate hyphae are present in tissue.

Clinicopathologic question

How do the lung lesions fit together?

Slide 64 · Case reasoning: Pulmonary vascular injury

The hyphal morphology is compatible with mucormycetes.

Vascular invasion explains thrombus formation.

Hemorrhagic pneumonia with distal infarction is the textbook pattern.

Hyphal invasion

Vascular thrombi

Hemorrhagic pneumonia

Distal infarcts

Slide 65 · Case: Trauma followed by a fungal tissue lesion

A wound follows an episode of local tissue trauma.

A tissue section reveals broad, nonseptate invasive hyphae.

The clinical question is why this patient acquired the infection.

Clinicopathologic question

What route of entry is most relevant?

Slide 66 · Case reasoning: Disruption of the skin barrier

Trauma creates a portal for direct environmental inoculation.

Wound exposure can bypass normal cutaneous protection.

Once established, the same invasive fungal pathology may follow.

Barrier breach

Direct inoculation

Local fungal establishment

Invasive necrosis

Slide 67 · Aspergillus is the principal hyphal differential

Both infections may invade vessels and produce infarction.

Mucormycetes: Nonseptate, broad, variably sized, often near-right-angle branches.

Aspergillus: Narrower, septate filaments with predominantly acute-angle branches.

Mucormycetes: Broad / 90°

Aspergillus: Septate / acute

Slide 68 · Integrated pathology: one causal model

Exposure plus a susceptible host permits spores to germinate.

Invasive hyphae are associated with vascular thrombosis.

Ischemia and necrosis explain severe organ damage.

Spores + entry

Defense failure / iron

Hyphal invasion

Thrombosis

Organ necrosis