Pathologically,
the macroscopic appearance in GAE is one of focal edema of the cerebral hemispheres.
Multifocal parenchymal lesions with involvement of posterior cranial fossa structures,
the diencephalon,
and the thalamus are seen.
The presence of trophozoites and cysts,
along with a chronic granulomatous reaction containing multinucleated giant cells,
is characteristic.
Microscopically,
there is evidence of leptomeningitis,
most prominent adjacent to the parenchymal lesions.
There may be severe necrotizing angitis.
GAE is diagnosed by identifying Acanthamoeba trophozoites or cysts in CSF/brain biopsy.
Cultures of brain tissues or CSF can also reveal Acanthamoeba organisms.
Imaging findings are nonspecific and are rarely described in the literature,
but can include the following brain lesions: multiple parenchymal lesions; pseudotumoural lesions; meningeal exudates; haemorrhagic infarcts (more common in Balamuthia mandrillaris); necrosis (more common in Balamuthia mandrillaris)
On MR imaging,
multifocal lesions showing T2 hyperintensity and a heterogeneous or ringlike pattern of enhancement,
with a predilection for the diencephalon,
thalamus,
brain stem,
and posterior fossa structures,
are seen. Multiple punctate focal areas of enhancement bilaterally throughout the cerebellar hemispheres as well as a few scattered supratentorial lesions are also described. Intralesional hemorrhage was considered an important diagnostic feature. The differential diagnosis includes infarcts from septic emboli,
abscesses,
toxoplasmosis fungal granuloma,
or neoplastic lesions.
Solitary space-occupying lesions have also been described in cases of GAE, mimicking a low-grade glioma or lymphoma.
Imaging features of PAM are nonspecific and have rarely been described previously.
Findings of CT and MR imaging may be normal early in the disease,
with evidence of brain edema and associated hydrocephalus,
basilar meningeal enhancement subsequently and multiple cerebral infarcts.
The images shown are a MRI of a 19-year-old male,
previously healthy,
immunocompetent,
with moderate headache and evolution with aphasia and motor deficit in the right upper limb,
who only had his diagnosis of granulomatous amoebic encephalitis signed with an autopsy.
They show multifocal lesions with T2 hyperintensity with intralesional hemorrhage and a heterogeneous pattern of enhancement.