RADIOLOGY MCQ -----CNS FUNGAL INFECTION

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.