Human Brain Bank, NIMHANS, Bangalore 13

II. Fungal InFectIons

Chronic Meningitis Meningoencephalitis Brain abscess or granulomaCryptococcus Cryptococcus AspergillusCoccidioides Coccidioides ZygomycetesHistoplasma Histoplasma CandidaCandida Dematiaceousfungi(Chromomycosis)Blastomyces Nocardia CoccidioidesParacoccidioides HistoplasmaPhaeohyphomycosis Pseudo AllescheriaAspergillosis Fusarium SporothrixNocardia Paracoccidioides Streptomyces etc.

Nocardia

The systematic approach that may facilitate diagnosis of CNS mycoses:

History Geographic location; History of Diabetes, cancer, chemotherapy, organ transplantation Risk factors /Systemic disease symptomsPhysical examination Signs of fungal infection in other organs like lung, skin, sinuses, joints, liver, paranasal sinuses, spleen & lymph nodes.Radiology Chest x-ray, CT & MR imagingLaboratory test CSF examination, tests for Immune functions of the hostCulture CSF /Meningeal biopsy/ brain biopsy/aspirate from brain abscesses/ Bronchial lavage, paranasal biopsy/urine/body fluids Serology Antibody /Antigen detectionMetabolite detection D-arabinitol, MannitolProduct of cell wall β-1, 3- glucan detectionNucleic acid (PCR) Blood/ CSF/Tissue

Common Infections of the Nervous System

14 National Institute of Mental Health and Neuro Sciences

rIsk Factors tHat PredIsPoses to Fungal InFectIons oF nervous system

Risk factor Type of fungal infectionInfancy Candida, HistoplasmaPregnancy Candida, Coccidioides

Immunocompromised patientsDiabetics/Ketoacidosis Candida, ZygomycosisLongtermsteroids/Antibiotictherapy/AnticancerTherapy

Candida, Aspergillus, Zygomycosis

Systemic malignancy Candida, ZygomycosisDebilitatingimmunemediateddiseases,Malnutrition

Candida

HIVinfection Cryptococcus, Candida

ImmunosuppressionfollowingtransplantationZygomycosis, Aspergillosis, Candida, Cryptococcus, Histoplasma, Coccidiodes

Neutrophilfunctionaldefects(Genetic)Aspergillosis, Zygomycosis, Candida, Cryptococcus, Histoplasma, Blastomycosis, Sporothrix

Macrophagephagocyticdefect Cryptococcus, Histoplasma, Blastomycosis

Infective Focus - Lung, paranasal sinuses, esophagus/nasopharynx – Zygomycosis, Aspergillosis - Wounds, Head Injury, prosthetic heart valve, Intra cranial shunt tubes, Intra arterial/venous catheters, Burns – Candida

Fungi in tissues - (a) Yeast form (20µm): Candida, Cryptococcus, Histoplasma, Coccidioides, Sporotrichum (b) Branching hyphae of variable sizes: Septate – Aspergillus, Cladosporium etc Non-septate – Zygomycosis (Mucor) (c) Non septate pseudohyphae – small size, candida, absidia etc

PatHology

(a) Yeast forms enter microcirculation, capillaries – cause leptomeningitis.(b) Pseudohyphae occlude small arterioles / microcirculation – produce tissue necrosis – microabscesses.(c) Large hyphae obstruct large/intermediate arteries – cause infarcts (ischemic / haemorrhagic)

granulomas / foreign body reaction.

useFul staIns:(a) Periodic acid Schiff (PAS) – fungal wall is magenta colored (Glycoprotein)(b) Methenamine silver – stains the wall black(c) Mucicarmine – stains the mucoid fungal capsule

• Patients with fungal infection – have some degree of immunosuppression, though not clinically evident.• Can cause disease in the absence of known predisposing factors.

to dIagnose Fungal InFectIons oF nervous system:High index of clinical suspicionSubmit fresh tissue for mycological cultureAvoid empirical mycobacterial treatment for granulomatous lesions diagnosed on neuro imaging

Human Brain Bank, NIMHANS, Bangalore 15

Fungal Infections

CASE 7: CRYPTOCOCCAL MENINGITIS: (Slide 7A: H&E, B: Periodic Acid Schiff stain, C: Gomori Methenamine Silver stain)

HIstology:Section through the cerebral cortex shows expansion of the subarachnoid space by clumps of

encapsulated, round yeast forms of Cryptococcus neoformans with a sparse inflammatory component of lymphohistiocytes and plasma cells. Numerous giant cells and macrophages engulfing Cryptococci are seen. The meningeal vessels are engorged and congested. Cryptococci are seen invading the parenchyma along the Virchow Robin spaces and distending the perivascular spaces.

CASE 7- CRYPTOCOCCAL MENINGITIS

Fig A: Numerous, budding yeast forms of Cryptococcus neoformans admixed with sparse inflammatory exudates. The underlying brain parenchyma is spared with intact pia-glial membrane and reactive subpial astrocytosis (H&E Obj X 20)Fig B & C: Spreading of the Cryptococcal pathology along the perivascular Virchow Robin space forming pseudocysts. (H&E; B: Obj X 5, C: Obj X 40)Fig D: The Cryptococci have PAS positive, magenta colored capsule. (PAS Obj X 20)Fig E: Methenamine silver highlights budding yeast forms in the brain parenchymal pseudocysts. (GMS Obj X 20)Fig F: Electron micrograph of Cryptococcus neoformans- the yeast form of the fungus with strands of mucin, phagocytosed by a macrophage. The yeast form has a thick double layered capsule and inside dense mitochondria. (X 6000)