*Totals do not add to 100, because some
patients had more than one lobe involved
The
disappearance of the white matter changes needed 7- 23 days in this study group.
Since
the first case was diagnosed in July 2009,(31) recurrence was
not noted at King
Hussein Medical
Center till now.
None
of the patients included in this study had brain hemorrhage, and biopsy was not
performed for any of them.
All
the 13 patients complained of headache (100%), 4 had seizures (30.77%) and 3
had visual disturbances (23%)
Discussion
Recent
studies have suggested that lesions of hypertensive encephalopathy and PRES
represent vasogenic rather than cytotoxic edema in the majority of cases.(1,7,16,17,22,25,32,33)
The basic PRES pattern resembles the brain watershed zones, with the
cortex, subcortical and deep white matter involved to varying
degrees.(34)
Although
the PRES pattern could be identified by CT, the initial findings on CT were
usually normal or nonspecific, despite severe clinical symptoms. However, when
seen on CT scan, it is bilateral symmetrical white matter low attenuation
lesions(35) (Fig. 3). On MRI, T1-weighted images
show a hypointense area, and hyperintense onT2-weighted images (Fig.
1).(35)
Fluid attenuated inversion recovery (FLAIR) is a
routine sequence in most practices with current MR protocols. FLAIR images are
T2-weighted but have nulling of signal from cerebrospinal fluid (CSF) due to
the inversion recovery technique. This allows for better detection of T2
hyperintense lesions of the cortex that often are obscured on conventional T2 sequences
owing to adjacent hyperintense CSF. So FLAIR should be used in MR protocols for
suspected PRES, and may thus lead to prompter diagnosis and more appropriate therapy.
The usual imaging findings of PRES are hyperintensity on FLAIR images (Fig. 2).
DWI has been shown to be reliable in distinguishing
vasogenic edema in PRES from cytotoxic edema in the setting of cerebral
ischemia. It stands to reason that DWI could be used to monitor for ischemia as
a complication of PRES.(19,36)
We have used DWI in our series population with similar
results but have encountered occasional complicated cases with demonstrable
ischemia on ADC maps. Diffusion weighted MRI with ADC mapping shows increased
ADC values representing vasogenic edema in these areas, thus differentiating
atypical PRES from other brain disorders.(19,36)
Imaging
is thus an essential component of the diagnosis of PRES in the presence of the
proper clinical context. When typical clinical risk factors are not present,
or when the blood pressure is not severely elevated, improvement on follow-up
MR images may also be key in the diagnosis.
The
regions of predilection are the parieto-occipital and posterior frontal
cortical and subcortical white matter, less commonly brain stem, basal ganglia
and cerebellum are involved.(7,28,29,37) Follow-up MRI after
proper treatment shows resolution of the lesions, unless the condition
complicated by hemorrhage 15% or infarction (11%–26%).
In
this series, the occipital lobe involvement was noted in 100%, followed by the
parietal lobe in 76.9%. According to McKinney(38)
larger series of 76 patients having
PRES; the incidence of regional involvement was; parietooccipital, 98.7%;
posterior frontal, 78.9%; temporal, 68.4%; thalamus, 30.3%; cerebellum, 34.2%;
brainstem, 18.4%; and basal ganglia, 11.8%. The incidence of less common findings
was enhancement, 37.7%; restricted diffusion, 17.3%; hemorrhage, 17.1%; and a
newly described unilateral variant, 2.6%. It also shows that atypical
distributions and imaging appearances of PRES have a higher incidence than
commonly described and atypical manifestations do not correlate well with the
edema severity.
Lesion
confluence may develop as the extent of edema increases. The calcarine and
paramedian occipital-lobe structures are usually not involved, a fact that
distinguishes PRES from infarction of the posterior-cerebral-artery territory
bilaterally.
In
all, except one of the patients who had follow-up CT or MRI scans, there was
significant improvement or disappearance of white-matter abnormalities,
suggesting edema rather than infarction.(39) This patient
condition was complicated by cerebellar infarction.
The findings in our patients
tended to be symmetrical, however the degree of involvement and the clinical
manifestations were often asymmetric. Which could have implications related
to the mechanism responsible for the development of vasogenic edema
in PRES. Variable expression of PRES patterns could be related to
differences in vascular anatomy, preexisting diseases, or regional
hemispheric involvement in the underlying clinical toxic condition.
PRES is well known to develop after transplantation; Bartynski(40) demonstrate
several important features related to PRES in solid organ transplantation
(SOT) including:
1.
A low incidence of PRES in SOT in particular when compared
with allo-BMT.
2.
A similar incidence of PRES among the different SOT
subtypes.
3.
Marked difference in several features of PRES between liver
and kidney transplants including time point of onset, extent of
brain edema, and blood pressure at presentation.
4.
High frequency of bacterial infection, Cytomegalovirus (CMV) expression,
and organ rejection in the peripresentation period.
Although none of this study population was complicated
by brain hemorrhage, it is a well known complication which is reported in 5-17
% of PRES patients.(41)
Doss-Esper
et al(41) have proposed 2 theories for brain
haemorrhage: 1) nonaneurysmal subarachnoid (sulcal) hemorrhage due to rupture
of pial vessels in the face of severe hypertension and impaired cerebral
autoregulation, and 2) postischemic reperfusion injury leading to multifocal
brain hemorrhages.(42,43)
The
results in our patients demonstrated several important observations related to
the imaging appearances of PRES: 1- common involvement of "atypical"
brain locations other than the parietal or occipital regions 2- partial or
asymmetrical expression of the vasogenic edema. These observations are of importance
for proper diagnosis of PRES.
Conclusion
The
frequency of regional involvement of brain lobes in PRES was consistent with published
literature. Reversible vasogenic edema, which is usually symmetrical and
bilateral, mainly in the parieto-occipital and posterior frontal lobes are the
usual imaging findings in this syndrome. Neuroradiological findings along with
clinical signs are consistent enough that this entity should be readily
recognizable which ensures early treatment, also prevention of potential
complications as brain hemorrhage and infarction.
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