Second edition

10.qxd 3/10/08 5:52 PM Page 444
444 Vascular disorders
Computed tomography scanning may reveal bilaterally
symmetric areas of hypodensity in the occipitoparietal
white matter. Magnetic resonance scanning is far more
sensitive and, on T2-weighted or FLAIR imaging,
increased signal intensity will be seen in the same areas
(Hauser et al. 1988); gradient echo imaging may reveal evidence
of petechial hemorrhages (Weingarten et al. 1994).
Diffusion-weighted imaging is generally normal unless
infarction has occurred. Rarely, these MRI findings may be
found in the brainstem and cerebellum (Cruz-Flores et al.
2004; Kanazawa et al. 2005).
Course
Untreated hypertensive encephalopathy may be fatal. In
cases in which blood pressure is corrected, symptoms gradually
resolve over a matter of days and white matter abnormalities
seen on CT or MR scanning typically clear within
a week or so. In those cases in which focal findings were
noted, these may persist, and MR scanning will show persistent
abnormalities consistent with infarction. With a
sufficient number of strategically placed infarctions,
patients may be left with a multi-infarct dementia.
Etiology
As blood pressure rises above a critical level, autoregulation of
small- and medium-sized cerebral arteries fails and there is
extravasation of proteinaceous fluid into the surrounding
white matter; some vessels may also rupture, causing petechial
hemorrhages, and others may undergo fibrinoid necrosis and
occlusion, causing infarction (Chester et al. 1978).
Differential diagnosis
Not all deliria occurring in the setting of grossly elevated diastolic
pressures occur due to hypertensive encephalopathy.
Indeed, in patients with chronic and gradually increasing
blood pressure, such very high pressures, being very gradually
reached, may be well tolerated without any immediate sequelae.
As noted earlier, renal failure is not uncommon, and uremic
encephalopathy must also be considered. Intracerebral
hemorrhage may also be considered in the differential, but
is generally of more acute onset and is easily recognized on
neuroimaging. Reversible posterior leukoencephalopathy
should be considered in cases that are clinically identical to
hypertensive encephalopathy in all respects except for the fact
that hypertension is either lacking or only mild.
Treatment
Hypertensive encephalopathy is a medical emergency and
the pressure must be lowered within an hour. Normotensive
levels, however, are not the goal because, with a loss of
autoregulatory capacity, a systemic pressure within normal
limits may be followed by cerebral hypoperfusion and watershed
infarctions. Consequently, during acute treatment the
diastolic pressure should be lowered to between 110 and
120 mmHg; once this has been accomplished, further treatment
may be aimed at bringing the pressure down further in
a more leisurely manner over the next few days. Acute treatment
may be accomplished with intravenous sodium nitroprusside,
labetalol or diazoxide. In cases in which
intravenous access is not immediately available or when the
clinical situation is not as urgent, intramuscular hydralazine
may be utilized. Seizures may be treated with intravenous
lorazepam and fosphenytoin, as described in Section 7.3. The
general treatment of delirium is discussed in Section 5.3.
10.13 REVERSIBLE POSTERIOR
LEUKOENCEPHALOPATHY SYNDROME
The reversible posterior leukoencephalopathy syndrome is
a recently described disorder marked by delirium, cortical
blindness, and seizures, occurring secondary to treatment
with various chemotherapeutic agents. As noted in the preceding
section, this disorder is clinically identical to hypertensive
encephalopathy and differs only in mechanism.
Clinical features
The syndrome (Hinchey et al. 1996) presents acutely, over
hours, and manifests with delirium or lethargy, accompanied
typically by headache, nausea or vomiting, and grand
mal seizures, which may have a focal onset. Cortical blindness
is common and other symptoms may also occur, such
as hemianopia, hemiparesis, abulia, or asterixis.
T2-weighted or FLAIR MR scanning (Lamy et al. 2004)
reveals areas of increased signal intensity bilaterally in the
white matter of the occipital and parietal lobes, with similar
findings, in many cases, noted in the posterior aspects
of the temporal lobes.
Course
With prompt and adequate treatment, clinical findings
resolve within days to weeks.
Pathology and etiology
Vasogenic edema is seen within the white matter, as indicated
by both brain biopsy (Lavigne et al. 2004) and MRI
findings. In cases with an unfavorable outcome, infarction
of the white matter occurs.
This syndrome has been noted secondary to treatment
with a variety of chemotherapeutic and immunomodulatory
agents, including tacrolimus, cyclosporine, vincristine,