Q.All are true regarding fungal infection of CNS except
a. Cryptococcus, Histoplasma result in leptomeningitis
more frequently than parenchymal lesions due to large size
b. the candidiasis abscess appears as “target appearance” on T2W image
c. “gelatinous pseudocysts” in CNS cryptococcosisis is noted primarily in the basal ganglia
and midbrain
d. an acute hemorrhagic infarction is seen in aspergillosis
e. the trehalose
resonance at 5.19 ppm is noted in cryptococcoma
ANS.---a
Fungi that grow in infected tissues
as yeast cells (Cryptococcus, Histoplasma)
are spread hematogenously and, due to their small size, reach the meningeal
microcirculation, penetrate the vessel walls, and result in acute or chronic
leptomeningitis. Less frequently, parenchymal lesions such as granulomas and/or
abscesses are encountered.
Fungi that grow in infected tissues
as hyphae (Aspergillus, Mucor)
or pseudohyphae (Candida) tend to involve the
parenchyma rather than the meninges because their larger size limits access to
meningeal microcirculation
C. neoformans is the most common fungus to involve the CNS, and
cryptococcosis is the most common fungus infection in AIDS patients
Cryptococcosis primarily manifests
as meningitis, most pronounced in the cranial base.
Four patterns of cryptococcal CNS
infection may be encountered: parenchymal mass lesions, also known as
cryptococcomas; dilated Virchow-Robin spaces (“gelatinous pseudocysts”);
parenchymal/leptomeningeal nodules; and a mixed pattern.Virchow-Robin spaces of
perforating arteries become distended with fungus and mucoid material,
primarily in the basal ganglia and midbrainGelatinous pseudocysts do not
display significant enhancement. The lesions may have mild mass effect, but
there is no surrounding edema.The gelatinous pseudocysts are isointense to CSF on
MR imaging, although they can often be slightly hyperintense on T1-weighted
images. Primarily located in the midbrain and basal ganglia, they can be
bilateral and are often symmetric . These pseudocysts do not enhance with
gadolinium because the blood–brain barrier is not disrupted, and they are
rarely associated with edema.
When there is hematogenous spread,
usually from a pulmonary focus, Aspergillus hyphae
lodge in cerebral vessels, cause occlusion, and grow through the vessel walls,
producing infectious vasculopathy. Thus, an acute hemorrhagic infarction occurs
at the beginning of the processes. Later, this converts to a septic infarction
with associated cerebritis and abscess formation, usually in the distribution
of the anterior and middle cerebral arteries . The basal ganglia and the
thalami are characteristically involved in aspergillosis, as well as the corpus
callosum and the brain stem. Involvement of the perforating arteries
illustrates the invasive character of Aspergillus
within the walls of the main cerebral arteries.
MR spectroscopy reveals decreased
NAA and markedly elevated lactate levels and the presence of succinate and
acetate in CNS mucormycosis.
