Tuberculosis (Lecture 2)

Slide 1 · Tuberculosis

of the central nervous system

Tuberculous meningoencephalitis, tuberculomas, and their complications

Neuropathology · morphology linked to mechanisms

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Distinguish diffuse tuberculous meningoencephalitis from parenchymal tuberculomas.

Explain the origin and pattern of basal meningeal inflammation.

Link vascular and arachnoid pathology to infarction and hydrocephalus.

Interpret the characteristic but variable CSF profile and host response.

Slide 3 · CNS tuberculosis: Two dominant morphologic patterns

Meningeal / diffuse

Parenchymal / focal

Diffuse meningoencephalitis

One or more circumscribed tuberculomas

Basal gelatinous or fibrinous exudate

Caseating granulomatous mass

Endarteritis and adhesive arachnoiditis

Local mass effect; potential calcification

Hydrocephalus, infarction, cranial nerve injury

Symptoms of an intracranial space-occupying lesion

Slide 4 · CNS disease may accompany or outlast pulmonary illness

Concurrent active tuberculosis

CNS involvement can occur with known active disease.

Pulmonary or systemic lesions provide a plausible source for dissemination.

The neurologic syndrome is not necessarily the first manifestation.

Apparently isolated CNS tuberculosis

A patient may have no clinically obvious pulmonary disease.

Seeding may originate from silent lesions elsewhere, usually lung.

Absence of known active lung disease does not exclude CNS involvement.

Slide 5 · Anatomical route from lung to nervous system

Pulmonary infection

Bloodborne spread

CNS seeding

Meningeal or parenchymal disease

Slide 6 · Why hematogenous dissemination matters

Pulmonary and nervous-system disease must be considered together.

Primary pulmonary infection can disseminate before full cell-mediated control develops.

Organisms deposited at distant sites may remain clinically silent.

Later CNS disease can therefore arise without conspicuous concurrent pulmonary symptoms.

Slide 7 · Temporal framework of CNS seeding

Early mycobacterial replication

Bloodborne dissemination

Host immune containment or failure

Clinically evident CNS lesion

Simplified explanatory sequence; Not every patient follows the same course.

Slide 8 · Host immunity is both protective and injurious

Protection

Th1 cells activate macrophages to kill or contain mycobacteria.

Effective immunity limits dissemination and bacterial growth.

Granulomas help localize infection.

Tissue injury

The same inflammatory response organizes caseating granulomas.

Inflammation damages vessels and meninges.

Fibrosis and necrosis produce neurologic consequences.

Slide 9 · Initial cellular events in mycobacterial infection

Macrophage uptake

Intracellular survival

Recruitment of immune cells

Th1-mediated control

Mechanism is established for tuberculosis generally; Applied here as pathogenesis context.

Slide 10 · How mycobacteria persist in macrophages

This helps explain the need for a strong cell-mediated response.

M. Tuberculosis is phagocytosed through macrophage surface receptors.

The pathogen interferes with phagosome maturation and phagolysosomal fusion.

Intracellular persistence permits replication before effective T-cell immunity.

Slide 11 · Th1 differentiation and macrophage activation

Antigen-presenting cell

IL-12 / IL-18 signaling

Th1 response

IFN-γ → macrophage activation

Native vector summary of the textbook pathway.

Slide 12 · IFN-γ-dependent antibacterial mechanisms

Failure of these processes increases vulnerability to disseminated disease.

Activated macrophages generate microbicidal reactive oxygen and nitrogen species.

Autophagy helps target intracellular organisms.

Antimicrobial peptides contribute to bacterial containment.

Slide 13 · Granuloma assembly

Persistent intracellular antigen

IFN-γ-activated macrophages

Epithelioid histiocytes ± giant cells

Organized granulomatous focus

The diagram represents cellular organization, not a photomicrograph.

Slide 14 · Why a granuloma is not simply a sign of control

Tuberculosis links cellular immunity to tissue damage.

Granulomas are a manifestation of effective T-cell recognition of persistent antigen.

The cellular reaction may wall off organisms without eradicating them.

Caseating necrosis reflects tissue-destructive consequences of host inflammation.

Slide 15 · Immune status changes lesion morphology

More effective cellular response

Marked cellular immune deficiency

Well-developed epithelioid granulomas

Poorly formed or absent granulomas

Organisms may be difficult to find

Macrophages may contain numerous organisms

Necrosis and inflammation can be prominent

Host inflammatory reaction may be blunted

Morphology reflects containment efforts

Morphology may obscure the classic diagnostic pattern

Slide 16 · Clinical settings that weaken antimycobacterial control

These are systemic tuberculosis risk contexts, not CNS-specific risk estimates.

HIV-associated loss of effective Th1 function is a major risk factor.

Glucocorticoids, TNF antagonism, and transplant immunosuppression increase susceptibility.

Malnutrition and renal failure can impair host resistance.

Slide 17 · CNS compartments relevant to tuberculosis

Tuberculosis affects connected but anatomically distinct CNS compartments.

Leptomeningeal

Subarachnoid space

Meningeal

Arteries

Ventricular /

Ependymal surfaces

Cerebral

Parenchyma

Exudate and fibrosis

Obliterative endarteritis

CSF-associated spread

Tuberculoma mass

Schematic compartment map; Anatomical topology simplified.

Slide 18 · Two paths of nervous-system injury

Diffuse meningeal route

Subarachnoid exudate and chronic inflammation.

Vessel encasement and endarteritis.

Arachnoid scarring and CSF-flow disturbance.

Focal parenchymal route

Localized caseating granulomatous mass.

Compression/displacement of neighboring structures.

Signs consistent with an intracranial mass lesion.

Slide 19 · Most common pattern: Diffuse meningoencephalitis

Meningeal distribution provides key clinicopathologic clues.

CNS tuberculosis most commonly produces widespread involvement of the meninges and adjacent brain.

The dominant macroscopic feature is inflammatory material within the subarachnoid space.

The distribution shows a characteristic predilection for the base of the brain.

Slide 20 · Basal leptomeningeal exudate: Key distribution

Basal subarachnoid inflammatory exudate

Gelatinous or fibrinous material occupies basal subarachnoid spaces.

Normal cisternal anatomy may be obscured.

Cranial nerves may be surrounded by inflammatory exudate.

This gross pattern is more informative than a nonspecific statement of “meningitis.”

Schematic basal distribution; Not a specimen or scale diagram.

Slide 21 · Macroscopic appearance of tuberculous exudate

The visual relationship between exudate and vital structures is central to clinical effects.

Exudate may be gelatinous or fibrinous.

The basal cisterns can become effaced.

Inflammatory material may encase cranial nerves and other structures in the subarachnoid compartment.

Slide 22 · From basal inflammation to nerve dysfunction

Basal subarachnoid inflammation

Cranial nerve encasement

Local neural irritation / dysfunction

Neurologic deficits

Causal interpretation based on anatomical distribution; Deficits vary by affected nerve.

Slide 23 · Disseminated surface lesions may be visible

These nodules do not imply a tumor without histologic context.

Some brains show scattered, discrete white inflammatory foci on the leptomeninges.

These foci accompany the more diffuse meningeal reaction.

Macroscopic foci should be correlated with the tissue reaction microscopically.

Slide 24 · Microscopic cells in affected meninges

Population

Pathologic implication

Lymphocytes

Cell-mediated chronic inflammatory response

Plasma cells

Component of chronic inflammatory infiltrate

Macrophages

Granulomatous / phagocytic response

Epithelioid histiocytes and giant cells

Organized granulomatous inflammation in florid cases

Slide 25 · Recognizing a necrotizing tuberculous granuloma

Caseation

Central caseous necrosis

Epithelioid histiocytes / giant cells

Surrounding chronic inflammatory cells

Original editable schematic of lesion architecture; Not H&E microscopy.

Slide 26 · Epithelioid histiocytes are activated macrophages

In tissue, interpret architecture together with organism testing and clinical context.

The epithelioid appearance follows cell-mediated macrophage activation.

These cells aggregate within granulomatous foci.

The organization is informative but is not microbiologically specific by itself.

Slide 27 · Giant cells: Cellular response, not a species label

Giant cells support a granulomatous pattern rather than proving TB.

Some activated macrophages fuse to form multinucleated giant cells.

Giant cells may accompany caseating granulomas in florid CNS tuberculosis.

Their presence alone cannot establish the causative microorganism.

Slide 28 · Caseous necrosis and the viable lesion edge

Necrotic center

Granular, acellular tissue destruction may occupy the granuloma center.

Necrosis is a response to persistent infection and immune injury.

The central zone need not contain an easily identifiable bacillus.

Cellular margin

Activated macrophages and other inflammatory cells surround the necrosis.

The margin may form a recognizable epithelioid aggregate.

The extent of organization depends on the host response.

Slide 29 · Why acid-fast organisms can be difficult to identify

Avoid equating bacillary visibility with disease severity.

The pathologist may find very few demonstrable bacilli in inflammatory lesions.

A negative or sparsely positive acid-fast stain does not negate granulomatous morphology.

Extensive searching may be required in some tissue sections.

Slide 30 · Histology and microbiology answer different questions

Histologic assessment

Organism demonstration

Defines inflammation, necrosis and tissue injury

Seeks the causative bacillus directly

Suggests a granulomatous infectious process

May support a specific mycobacterial etiology

Shows vascular damage and fibrosis

May have low yield in paucibacillary tissue

Does not prove species identity by morphology

Must be interpreted alongside tissue architecture

Slide 31 · Tuberculous obliterative endarteritis

Inflammation around a meningeal artery

Marked intimal thickening

Progressive luminal narrowing

Occlusion and ischemic injury

Cross-sections are schematic and not to anatomic scale.

Slide 32 · The key vascular lesion is obliterative endarteritis

CNS tuberculosis can cause destructive neurologic deficits without a large tuberculoma.

Arteries traversing the inflamed subarachnoid space may develop marked intimal thickening.

Severe narrowing can progress to vascular occlusion.

The downstream consequence is ischemic injury or cerebral infarction.

Slide 33 · Vascular complication sequence

Basal meningeal inflammation

Arterial intimal proliferation

Reduced perfusion / occlusion

Cerebral infarction

Causal relationship follows the vascular pathology.

Slide 34 · Why an infarct may accompany chronic meningitis

Look beyond the meningeal exudate when evaluating a neurologically deteriorating patient.

The same basal inflammatory process involves nearby vessels.

Intimal thickening compromises the vessel lumen.

Tissue loss depends on the territory supplied by the occluded artery.

Slide 35 · Adhesive arachnoiditis: A late tissue response

Persistent subarachnoid inflammation

Fibroproliferative arachnoid reaction

Dense adhesions around basal brain

Hydrocephalus

Sequence illustrates the source-described complication without specifying a single universal CSF obstruction site.

Slide 36 · Arachnoid fibrosis links inflammation to hydrocephalus

Hydrocephalus is a consequence of chronic tissue organization, not granuloma size alone.

Longstanding inflammation may evolve into dense, fibrous adhesive arachnoiditis.

The changes are especially conspicuous near the base of the brain.

Altered CSF circulation/resorption may then produce hydrocephalus.

Slide 37 · CSF pathways can also carry the inflammatory process

Meningeal infection

Spread through CSF

Choroid plexus / ependymal involvement

Additional ventricular interface disease

Spread to these surfaces; Schematic does not assert its frequency.

Slide 38 · Choroid plexus and ependymal spread

The route emphasizes the connected nature of ventricular and subarachnoid spaces.

Mycobacterial inflammation can involve the choroid plexus.

The ependymal surface may also be affected through CSF-associated spread.

Such involvement extends the disease beyond the meningeal surface alone.

Slide 39 · Spinal subarachnoid extension and nerve roots

The expected deficits depend on which roots are involved.

The infectious process can extend to the spinal cord subarachnoid compartment.

Adjacent spinal nerve roots may be affected.

This extension broadens the neurologic manifestations beyond intracranial disease.

Slide 40 · Major chronic meningeal complications

Pathologic lesion

Mechanistic consequence

Potential clinical effect

Obliterative endarteritis

Arterial narrowing / occlusion

Brain infarction

Adhesive arachnoiditis

Impaired CSF dynamics

Hydrocephalus

Basal cranial nerve encasement

Nerve-associated inflammation

Cranial neuropathy

Spinal subarachnoid involvement

Affected nerve roots

Root-related neurologic symptoms

Slide 41 · Typical clinical presentation of tuberculous meningitis

Clinical features need to be integrated with CSF and pathology.

Headache and generalized malaise are common presenting symptoms.

Mental confusion points to neurologic involvement.

Vomiting may occur in the clinical syndrome.

Slide 42 · Clinical deterioration: Anatomical reasoning

Chronic meningeal illness

Basal inflammatory complications

Vessel / CSF pathway injury

Focal deficits or increased pressure

An explanatory framework; Individual cases vary.

Slide 43 · CSF pleocytosis can have a mixed differential count

Cell differential alone is insufficient to exclude tuberculosis.

CSF usually contains increased inflammatory cells.

Mononuclear cells may predominate.

A mixture of neutrophils and mononuclear cells is also described.

Slide 44 · Marked CSF protein elevation is a useful clue

Interpret alongside cell profile, glucose, and clinical course.

CSF protein concentration rises in tuberculous meningitis.

The elevation may be striking.

This finding is compatible with substantial meningeal inflammation, but is not disease-specific.

Slide 45 · CSF glucose may be low—or not

Avoid replacing variable findings with rigid diagnostic cutoffs.

Glucose as moderately reduced or even normal.

Normal CSF glucose therefore does not rule out tuberculous meningitis.

A single chemical variable should not override the total clinical picture.

Slide 46 · Tuberculous meningitis: The source-described CSF pattern

CSF feature

Typical finding

Interpretive caution

White blood cells

Mononuclear or mixed pleocytosis

Neutrophils can coexist with mononuclear cells

Protein

Elevated, sometimes markedly

Not specific to tuberculosis

Glucose

Moderately reduced or normal

Normal level does not exclude disease

Slide 47 · Tuberculomas are intraparenchymal mass lesions

The focal pattern contrasts with diffuse meningoencephalitis.

One or several well-circumscribed granulomatous masses may occur.

They may appear with or without concurrent meningeal disease.

Lesions can become several centimeters across and produce substantial mass effect.

Slide 48 · Tuberculoma: Cellular pathology of a focal mass

Caseating granuloma

Surrounding inflammatory tissue

Well-circumscribed intraparenchymal lesion

Mass effect on nearby parenchyma

Editable, not-to-scale schematic; Not diagnostic radiology or gross specimen.

Slide 49 · Inactive tuberculomas may calcify

The source does not establish a universal time course for calcification.

Tuberculomas typically have central caseous necrosis.

Inactive lesions may develop calcification.

Calcification should be interpreted within the full clinical and morphologic setting.

Slide 50 · Why tuberculomas mimic tumors clinically

Focal granulomatous mass

Displacement of neighboring tissue

Space-occupying brain lesion

Tumor-like neurologic syndrome

The source requires distinction from CNS neoplasms; This diagram does not imply identical imaging.

Slide 51 · Meningoencephalitis versus tuberculoma

Diffuse meningoencephalitis

Tuberculoma

Basal leptomeningeal exudate

Focal intraparenchymal mass

Diffuse meningeal inflammatory changes

Circumscribed caseating granuloma

Endarteritis / arachnoid fibrosis

Mass effect / possible calcification

Hydrocephalus or infarction

Space-occupying lesion symptoms

Often meningeal CSF abnormalities

May coexist with meningitis

Slide 52 · HIV-associated CNS tuberculosis: Pathology changes

Preserved cellular immune response

More conspicuous immune-mediated tissue reaction.

Well-organized granulomatous inflammation may be evident.

Organisms may be sparse on acid-fast staining.

Advanced immune deficiency / AIDS

The overall pathology may be similar in distribution.

The host inflammatory reaction is usually less developed.

Classical granulomatous morphology may be attenuated.

Slide 53 · Do not equate scant granulomas with absence of infection

A weaker inflammatory response can occur despite significant infection.

The ability to form a granuloma depends on cellular immunity.

Advanced immunosuppression can blunt the expected histologic pattern.

Atypical tissue responses should prompt careful integration of microbiologic and clinical evidence.

Slide 54 · Chronic infectious meningoencephalitis: Key etiologic context

Organism group

Illustrative agent

Scope in this lecture

Mycobacteria

M. tuberculosis

Primary focus: basal meningitis and tuberculoma

Spirochetes

Treponema pallidum

Separate neurosyphilis morphology and presentation

Spirochetes

Borrelia species

Separate neuroborreliosis manifestations

Slide 55 · Acute pyogenic versus tuberculous meningitis

Acute pyogenic meningitis

Tuberculous meningitis

Usually acute symptomatic illness

Frequently subacute or chronic course

Cloudy/purulent CSF with numerous neutrophils

Mononuclear or mixed pleocytosis

CSF glucose markedly reduced

CSF glucose moderately reduced or normal

Predominantly suppurative reaction

Granulomatous / chronic meningeal reaction

Slide 56 · Case study 1 · meningitis pattern

A patient has a progressive headache, malaise, vomiting, and confusion. CSF shows elevated protein with mixed inflammatory cells; Glucose is not markedly depressed.

Discussion prompts

Which CNS infection pattern from this lecture is compatible?

Which macroscopic distribution should be sought?

Why does the glucose value not settle the diagnosis?

Slide 57 · Case study 1 · morphologic interpretation

Interpret the case from anatomical pathology and source-consistent clinical findings.

The syndrome is compatible with tuberculous meningitis, but the findings are not independently diagnostic.

The expected gross pattern is gelatinous / fibrinous exudate concentrated at the brain base.

CSF glucose can be normal or moderately reduced.

Slide 58 · Case study 2 · focal intracranial lesion

A patient has a well-defined intracerebral lesion with mass effect. Tissue examination reveals a circumscribed granulomatous focus with central caseation.

Discussion prompts

Which CNS tuberculosis manifestation best fits the lesion?

What alternative disease class must be considered clinically?

What late change may appear in an inactive lesion?

Slide 59 · Case study 2 · pathology and differential

Interpret the case from anatomical pathology and source-consistent clinical findings.

The lesion is consistent with a tuberculoma.

Because it acts as a space-occupying lesion, a CNS neoplasm must be considered in the differential.

Inactive tuberculomas may undergo calcification; Organism evidence is still required for etiologic certainty.

Slide 60 · Case study 3 · two complications

A patient with chronic basal meningitis develops hydrocephalus and a new focal neurologic deficit.

Discussion prompts

Which chronic meningeal lesion explains hydrocephalus?

Which vascular lesion can account for focal ischemic injury?

Why can both complications coexist?

Slide 61 · Case study 3 · linking anatomy to injury

Interpret the case from anatomical pathology and source-consistent clinical findings.

Adhesive arachnoid fibrosis can impair CSF dynamics and lead to hydrocephalus.

Obliterative endarteritis with intimal thickening can occlude arteries and produce infarction.

Both lesions may result from a common persistent basal meningeal inflammatory process.

Slide 62 · Specimen-oriented interpretation of suspected CNS TB

Identify distribution

Describe tissue reaction

Assess vessels and arachnoid

Seek organisms / correlate

This is a pathology reading strategy, not an independent clinical diagnostic guideline.

Slide 63 · Morphology-to-syndrome integration

Anatomic pathology

Dominant mechanism

Clinical expression

Basal inflammatory exudate

Meningeal inflammatory disease

Headache, malaise, confusion, vomiting

Endarteritis

Luminal narrowing / infarction

Focal neurologic deficits

Adhesive arachnoiditis

Impaired CSF circulation

Hydrocephalus

Caseating tuberculoma

Local mass effect

Tumor-like space-occupying symptoms

Slide 64 · Common interpretive pitfalls

Tuberculosis of the CNS can occur without recognized active pulmonary disease.

A normal CSF glucose or a mixed neutrophilic response does not exclude tuberculous meningitis.

Few visible acid-fast organisms do not invalidate convincing granulomatous pathology.

Reduced granuloma formation in advanced immune deficiency should not be mistaken for low infection burden.

Slide 65 · Summary · a unified pathobiologic model

Systemic mycobacterial infection

CNS seeding and chronic inflammation

Meningeal or parenchymal lesions

Vascular, CSF, and mass effects

Mechanistic synthesis of Robbins Chapters 8 and 28.

Slide 66 · Source and image provenance

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026). Chapter 28, pp. 1149–1150: CNS tuberculosis, morphology and clinical features.

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026). Chapter 8, pp. 334–338: tuberculosis pathogenesis, host immune response and dissemination.

Adjacent CNS sections: acute pyogenic meningitis and chronic bacterial meningoencephalitis, Chapter 28, pp. 1147–1150.

Figures in this presentation are original native PowerPoint schematics; no external specimen images have been embedded.