Radiology

Prepared by Paul B. DiDomenico, MD, Resident, Radiology Department, and Peter S. Palka, DO, Neuroradiologist, Department of Diagnostic Imaging, David Grant US Air Force Medical Center, Travis AFB, Calif

A 21-year-old woman was brought to the emergency department after having 2 episodes of generalized tonic-clonic seizures. The patient had a complex medical history that included systemic lupus erythematosus (SLE), hemodialysis-dependent status after bilateral nephrectomy, thrombotic thrombocytopenic purpura (TTP), and poorly controlled hypertension. A computed tomography (CT) scan of the brain (performed at an outside hospital) was reportedly normal. Magnetic resonance imaging (MRI) of the brain suggested the diagnosis (Figure 1).

Figure 1

What's Your Diagnosis?

• Lupus cerebritis
• Acute infarction
• Posterior reversible encephalopathy syndrome
• Acute disseminated encephalomyelitis

Quiz Answer

Posterior reversible encephalopathy syndrome—MRI findings included regions of high signal on T2 and fluid attenuation inversion recovery (FLAIR) sequences within the posterior parietal and occipital lobes. These sequences indicated edema in the posterior subcortical white matter, as well as cortical involvement. The patient was admitted to the hospital for blood pressure (BP) control. Repeat MRI 10 days later demonstrated a normal brain, with complete resolution of the previous T2/FLAIR signal abnormalities (Figure 2). This reversibility of the lesion confirmed the diagnosis. The patient improved clinically and did not experienceanother seizure.

Figure 2

Posterior reversible encephalopathy syndrome was first described in 1996 as a syndrome of neurologic findings including headache, altered mental status, visual changes, and seizures in 15 patients who demonstrated evidence of posterior leukoencephalopathy on imaging studies.¹ The findings included vasogenic edema predominantly in the posterior cerebral hemispheres, but also in the brain stem and cerebellum. Risk factors included abrupt increases in BP, impaired renal function (secondary to lupus nephritis or acute glomerulonephritis), immunosuppressive therapy, and eclampsia. The neurologic symptoms and imaging abnormalities resolved in all patients after adequate BP control or reduction in immunosuppressive therapy. Although posterior reversible encephalopathy syndrome has been often referred to as hypertensive encephalopathy, several of the patients described in the 1996 study were normotensive.¹ Other associations reported in the literature include TTP, SLE, and several immunosuppressive and cytotoxic drugs.² The precise pathogenesis is still unknown; however, imaging studies have consistently demonstrated vasogenic edema. This is likely related to a breakdown in cerebral vascular autoregulation, with fluid leakage into the cerebral interstitium.^2-4 These findings may be detected by CT,¹ but the imaging study of choice is MRI, which has greater sensitivity and can exclude infarction of the occipital lobes from the differential diagnosis (by using diffusion-weighted imaging).⁴

The patient described in this case had at least 4 of the known risk factors for posterior reversible encephalopathy syndrome hypertension, SLE, TTP, andimmunosuppressive therapy. SLE usually involves the central nervous system, resulting in vasculopathy in the cerebral arterioles and capillaries and producing perivascular inflammation.

Lupus cerebritis would be expected to demonstrate a more diffuse pattern of atrophy and T2/FLAIR signal abnormalities that would not be expected to reverse in a short interval, if at all.

Acute infarction would demonstrate high signal on diffusion-weighted imaging, which was not present in this case.

Acute disseminated encephalomyelitis is a monophasic demyelinating disease that is usually preceded by viral infection. In cases of posterior reversible encephalopathy syndrome, documentation and reversibility of imaging findings is an important part of the diagnosis and management. Early recognition allows for corrective action with BP control and withdrawal of cytotoxic medications, thus avoiding potentially permanent brain damage.

References

1. Hinchey J, Chaves C, Appignani B, et al. A reversible posterior leukoencephalopathy syndrome. N Engl J Med. 1996;334:494-500.
2. Bartynski WS, Boardman JF, Zeigler ZR, et al. Posterior reversible encephalopathy syndrome in infection, sepsis, and shock. AJNR Am J Neuroradiol. 2006;27:2179-2190.
3. Bartynski WS, Boardman JF. Distinct imaging patterns and lesion distribution in posterior reversible encephalopathy syndrome. AJNR Am J Neuroradiol. 2007;28:1320-1327.
4. Brubaker LM, Smith JK, Lee YZ, et al. Hemodynamic and permeability changes in posterior reversible encephalopathy syndrome measured by dynamic susceptibility perfusion-weighted MR imaging. AJNR Am J Neuroradiol. 2005;26:825-830.

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