This document summarizes the neuroradiology findings of central nervous system fungal infections. It describes the imaging appearance of common fungal infections like cryptococcosis, aspergillosis, mucormycosis, and candidiasis. Key findings include ring-enhancing lesions on MRI for abscesses, meningeal enhancement for meningitis, and restricted diffusion on DWI for early detection of fungal infections. Imaging plays an important role in the diagnosis and management of CNS fungal diseases.

1. Neuroradiology of CNS
Fungal Infections
Dr. Rahi Kiran.B
Senior Resident
Department of Neurology
GMC, Kota.

2. Introduction
• CNS fungal infections are also called cerebral mycosis.
• A focal “fungus ball” is also called a mycetoma or fungal
granuloma.
• CLINICAL SPECTRUM:
• Meningoencephalitis.
• ICSOL-Parenchymal brain abscesses or granulomas.
• Skull base syndrome
• Vasculitis.
• Vascular thrombosis leading to infarction or ICH or SAH
• Spinal syndrome

3. Introduction
• most common - Cryptococcal, aspergillosis and candidiasis.
• opportunistic - Candidiasis, mucormycosis, and cryptococcal.
• most commonly - parenchymal granuloma formation are
Aspergillus species, Mucorales fungi, and C neoformans

5. • Findings vary with the patient's immune status.
• Well-formed fungal abscesses are seen in immunocompetent
patients.
• Imaging early in the course of a rapidly progressive infection
in an immunocompromised patient may show diffuse cerebral
edema more characteristic of encephalitis than fungal
abscess.
• any lesion of the frontal lobes in an immunocompromised
patient, especially in an inferior location- suspect
mucormycosis & aspergillosis

6. CT FINDINGS
• NECT - hypodense parenchymal lesions
caused by focal granulomas or ischemia.
• Hydrocephalus is common in meningitis.
• Multifocal parenchymal hemorrhages -
angioinvasive fungal species.

7. MR FINDINGS
• Parenchymal lesions- (mycetomas) - T1 –
hypo, hyper if bleed associated
• typical - Irregular walls with
nonenhancing projections into the cavity
• T2/FLAIR - show bilateral but asymmetric
cortical/subcortical and basal ganglia
hyperintensity, peripheral hypointense
rim, surrounded by vasogenic edema.
• may show “blooming” - hemorrhages or
calcification.

8. • DWI-The high viscosity and cellularity of fungal pus leads to
reduced diffusion - the earliest diagnostic imaging clue to
fungal infection, even preceding enhancement
• 3 Patterns -heterogeneous, ring-like, or punctate.
• Focal paranasal sinus and parenchymal mycetomas usually
restrict on DWI.

9. • T1 C+ FS - diffuse, thick, enhancing basilar
leptomeninges.
• enhancement depends on the acuity and
typically develops 24–48 hours after the
infarction, with resolution within 3–4 days
• Abscess - only a thin rim of peripheral “weak
ring” enhancement due to less inflammatory
response
• Parenchymal lesions - punctate, ring-like, or
irregular enhancement.

10. • MRS - mildly elevated Cho and decreased
NAA.
• A lactate peak is seen in 90% of cases, while
lipid and amino acids are identified in
approximately 50%.
• aneurysms due to fungal infections typically
are fusiform , Aspergillus and Candida
• most commonly involve the proximal
vasculature such as the ICA and the vessels
that form the circle of Willis

11. Angioinvasive fungi
• erode the skull base, cause plaque-like dural thickening, and
occlude one or both carotid arteries.
T1 - isointense Hypointense/ mixed
Peripheral
enhancement
around the
margins
diffusion restriction

12. Abscesses
• Nonenhanced CT-low attenuating, with or
without surrounding vasogenic edema
• peripheral rim enhancement on contrast-
enhanced CT images
• T1 - Hypointense center, hyperintense rim,
• T2-Hyperintense center, hypointense rim
• T1 C+- peripheral rim enhancement, “weak
ring”
• T2 & FLAIR-hyperintense with surrounding
hyperintense perilesional edema
• DW & ADC- hyper and hypo

14. Differential Diagnosis

15. Aspergillosis
• Aspergillus fumigatus is the most common human pathogen.
• patterns of cerebral aspergillosis -
– edematous lesions,
– hemorrhagic lesions,
– solid enhancing lesions referred to as aspergilloma or
tumoral form,
– abscess like ring-like enhancing lesions
– Infarction
– Mycotic aneurysms

16. Aspergillosis
• NECT scan shows multifocal
hemorrhages. Angioinvasive aspergillosis
was documented at surgery.
• CECT scan shows an irregular, crenulated
enhancing lesion- solitary aspergilloma.

17. • characteristic intermediate to low
peripheral T2 signal intensity with central
hypointensity in a target-like pattern
• infarction of the corpus callosum is not
typically seen in thromboembolic
infarction or pyogenic infection, when
present, it suggests aspergillosis

18. • Axial T1 post-gadolinium
image shows typical lesions
of multifocal angioinvasive
aspergillosis at the gray–
white junction
(arrowheads).

19. Cryptococcosis
• most common mycotic agent to affect the CNS.
• up to 30% of the patients have been reported with no
predisposing condition.
• Men > women
• can be either meningeal or parenchymal
• Meningitis - primary manifestation , most pronounced at the
base of the brain.
• Parenchymal - cryptococcomas, dilated VR spaces or
enhancing cortical nodules.
• Mc parenchymal sites - midbrain and the basal ganglia.

20. Cryptococcosis
Meningeal disease
• T1 C+ (Gd): can show
leptomeningeal enhancement
Cryptococcomas
• variable density masses on CT
• T1: low signal
• T2 / FLAIR: high signal
• T1 C+ (Gd): variable, ranging from
no enhancement to peripheral
nodular enhancement(depends on
immunity as capsule is non-
immunogenic)
• No DWI

21. • Immunocompetent - more likely to present with
cryptococcomas.
• Enhancement of these lesions might occur as a result of an
immunologic reaction by the host.
• Immediate and delayed imaging with a double dose of
contrast has been reported to reduce the false negative
studies by showing meningeal enhancement in
immunocompromised patients.

22. • Axial T1 post-gadolinium
image shows typical
cryptococcal meningitis
with ventricular wall
enhancement and subtle
frontal and occipital
leptomeningeal
enhancement.

23. Gelatinous pseudocysts
• Tend to give a "soap bubble"
appearance.
• low-density lesions on CT
• T1: low to intermediate (from mucin)
signal , no T1C+ (avascular)
• T2: hypointense ring surrounding a
hyperintense center
• FLAIR: low signal
• DWI - may or may not
• Hydrocephalus is the most common,
although nonspecific finding.

24. Mucormycosis
• Diabetics comprise at least 70% of the reported cases and less
than 5% occur in normal hosts.
• The rhinocerebral form is the most common infection.
• Isolated CNS mucormycosis, a focal intracerebral infection, is
rare and is mostly seen in drug abusers.
• Infarcts and abscesses are found on imaging studies, most
commonly in the basal ganglia.
• almost always involves the frontal lobes
• Restricted diffusion may be the earliest detectable
abnormality in rhinocerebral mucormycosis.

25. Mucormycosis
• Axial T1 post-gadolinium
image shows mucormycosis
with intracranial extension
and enhancement at the
inferior frontal lobe
following a sinus infection.

26. Candidiasis
• can cause vasculitis, intraparenchymal hemorrhage,
aneurysms and thrombosis of small vessels with secondary
infarction.
• Microabcesses - NCCT iso to hypo - multiple punctate
enhancing nodules on contrast study less than 3 mm at the
CMJ, BG or cerebellum are most common,
T1 hypo, variable T2,
• Granuloma - hyperdense nodule on CT with nodular or ring
enhancement.
• On MRI - granuloma formation and brain abscess may have
hypointense signals on T2WI due to the magnetic
susceptibility effect of hemorrhage, ring-enhancement.

27. Candidiasis
• Cerebral candidiasis usually
appears as microabscesses
measuring less than 3 mm.
• Axial T1 post-gadolinium
sequences show punctate
subcortical foci of
enhancement.
• Axial DWI shows reduced
diffusion of multiple lesions,
including several not seen
on contrast-enhanced
sequence.

28. Spinal Infections
• Fungal infections of the spine are relatively uncommon.
• They have been reported with Candida, aspergillosis,
cryptococcus, coccidioidomycosis and histoplasmosis.
• rarely present as myelopathy and myeloradiculopathy.
Infectious processes –
– Intramedullary granuloma or abscess,
– Epidural abscess
– Focal spinal meningitis
– Fungal myelitis.
• Upper thoracic level –MC site -contiguous spread from lung.

29. Spinal Infections
• CT and MR are useful in determining soft tissue involvement
and spinal abnormalities.
• low intensity on T1WI and high on T2WI with intervening disc
involvement.
• The typical imaging features include disc involvement,
heterogeneous marrow signal alteration and extensive extra-
osseous involvement with lack of bony deformity.
• As the disease is multifocal, MR screening of the entire
vertebral column often reveals occult areas of involvement.

32. Leukemia– Post HSCT with altered
sensorium
• T1C+ DWI ADC
Mucormycosis, aspergillosis

33. patient
with poorly
controlled
diabetes
Bone invasion, destruction at
orbital apex and sphenoid sinus
left cavernous sinus mass and
occluded ICA
T1 C+ FS- invaded enhancing left side with absent flow void
Mucormycosis

34. Multiple abscesses
thick ring enhancement
T1- hypo with hyper periphery and vice versa for T2,

36. FLAIR – hyper, Enhancing, DWI restricted
ring-enhancing lesions.
A 46-year-old male with a history of chronic
hepatitis C and injection drug abuse
Candida albicans micro abscesses