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KEY FACTS

Terminology
- Cerebrovascular autoregulatory disorder
- Many etiologies with HTN as common component - Preeclampsia, eclampsia - Drug toxicity (e.g., chemotherapy) - Uremic encephalopathies
Imaging
- General - Patchy parietooccipital cortical/subcortical edema in patient with severe acute/subacute HTN
- CT: May be normal or subtly abnormal - If PRES suspected, perform MR to confirm
- MR: Parietooccipital T2/FLAIR hyperintensities in 90% of cases - ± basal ganglia, pontine, cerebellar involvement - 3 patterns of hemorrhage: Focal parenchymal hemorrhage, microhemorrhages, convexity SAH - Generally no restriction on DWI - Variable patchy enhancement; atypical imaging patterns common
Top Differential Diagnoses
- Acute cerebral ischemia-infarction
- Hypoglycemia
- Reversible cerebral vasoconstriction syndrome
- Status epilepticus
- Thrombotic microangiopathies
- Cerebral hyperperfusion syndrome
Pathology
- Failure of autoregulation
- Endothelial dysfunction
- Result = vasogenic (not cytotoxic) edema
Clinical Issues
- Headache, seizure, ↓ mental status, visual symptoms
- Caution: Some patients may be normotensive or have only minimally elevated BP

TERMINOLOGY

Abbreviations
- Posterior reversible encephalopathy syndrome (PRES)
Synonyms
- Acute hypertensive encephalopathy
- Reversible posterior leukoencephalopathy syndrome (RPLS)
Definitions
- Variant of acute hypertensive encephalopathy characterized by headache, visual disturbances, altered mental function
- Cerebrovascular autoregulatory disorder - Multiple etiologies; most caused by acute HTN

IMAGING

General Features

Best diagnostic clue

- Patchy parietooccipital cortical/subcortical edema in patient with severe acute/subacute HTN

Location

- Most common: Cortex, subcortical white matter
        - Parietooccipital lobes (≥ 90%)
        - Superior frontal (≥ 70%), temporal lobes (≥ 60%), cerebellum (≥ 50%)
        - Basal ganglia (≥ 30%), midbrain (< 20%), pons, medulla, splenium of corpus callosum (< 10%)
        - At junctions of vascular watershed zones
        - Usually bilateral, often asymmetric
- Rare: Predominant/exclusive brainstem involvement

Size

- Extent of abnormalities highly variable

Morphology

- Patchy > confluent; atypical patterns common

CT Findings

NECT

- May be normal or subtly abnormal
        - If PRES suspected, perform MR to confirm
- Common: Bilateral nonconfluent hypodense foci
        - Posterior parietooccipital lobes
        - Cortical watershed zones
- Less common: Petechial cortical/subcortical or basal ganglionic hemorrhages
- Uncommon: Thalamic, basal ganglia, brainstem, cerebellar hypodensities

CECT

- Usually no enhancement
- Occasionally mild patchy/punctate enhancement

CTA

- Major vessels usually normal
- Distal vessels may show diffuse vasoconstriction, focal irregularity, & beaded appearance

MR Findings

T1WI

- Hypointense cortical/subcortical lesions

T2WI

- **Typical**PRES **(p****arietooccipital pattern****)**
        - Parietooccipital lobes, cortical watershed zones
- **Atypical**PRES: Almost as common as **typical**PRES
        - **Superior frontal sulcus pattern**
                  - Hyperintensities in mid & posterior aspects of superior frontal sulcus
        - **Holohemispheric watershed pattern**
                  - Involvement of frontal, parietal, & occipital internal watershed zones
        - Hyperintensities in basal ganglia, brainstem, cerebellum

FLAIR

- Same as T2
- "Leaky" blood-brain barrier may cause gadolinium accumulation in CSF, FLAIR hyperintensity

T2* GRE

- 3 patterns of hemorrhage: Focal parenchymal hemorrhage, microhemorrhages, convexity subarachnoid hemorrhage (SAH)

DWI

- Usually negative
- 15-30% small foci of restricted diffusion within larger regions of vasogenic edema

PWI

- CT & MR perfusion may show both ↑ & ↓ relative cerebral blood volume (rCBV) in occipital regions, cortical watershed zones

T1WI C+

- Variable patchy cortical/subcortical enhancement

MRS

- May show widespread metabolic abnormalities
        - ↑ Cho, Cr, mildly ↓ NAA
        - Usually return to normal within 2 months

DTI - Shows foci of ↑ diffusivity & anisotropy loss

Nuclear Medicine Findings
- SPECT - Variable findings reported; more common hypoperfusion in affected areas

Imaging Recommendations

Best imaging tool
```
- Contrast-enhanced MR + DWI
```
Protocol advice
```
- Repeat scan after BP normalized
```

DIFFERENTIAL DIAGNOSIS

Acute Cerebral Ischemia-Infarction
- Middle cerebral artery distribution > > posterior cerebral artery
- Infarcts restrict on DWI; PRES usually does not
Hypoglycemia
- Severe parietooccipital edema
- Can resemble PRES, so history important
Reversible Cerebral Vasoconstriction Syndrome
- Shares some features with PRES
- Typically limited to solitary sulcus or few adjacent sulci
Status Epilepticus
- May cause transient gyral edema, enhancement
- Can mimic PRES, stroke, infiltrating neoplasm
- Unilateral (PRES often bilateral)
Thrombotic Microangiopathies
- Malignant HTN, DIC, hemolytic uremic syndrome (HUS), TTP
- Significant overlap as PRES common imaging manifestation
Cerebral Hyperperfusion Syndrome
- Postcarotid endarterectomy, angioplasty, or stenting - Hyperperfusion syndrome occurs in 5-9% of cases - Perfusion MR imaging or CT scans show elevated relative cerebral blood flow (rCBF) - Aggressive control of BP associated with clinical, radiologic improvement

PATHOLOGY

General Features

Etiology

- Not yet completely understood
- Diverse causes & clinical entities
- **2 leading theories** regarding pathophysiology of PRES
- **1st hypothesis**
        - Rapid ↑ of arterial BP above upper autoregulatory limit → cerebral hyperperfusion → vascular leakage & vasogenic edema
        - ↑ cerebral perfusion pressure → blood-brain barrier dysfunction → extravasation of plasma & macromolecules through tight-junction proteins
- **2nd hypothesis**
        - PRES triggered by endothelial dysfunction caused by circulating endogenous or exogenous toxins
        - Excessive release of proinflammatory cytokines → vascular leakage & edema formation
- Predilection for parietooccipital lobes
        - Posterior circulation sparsely innervated by sympathetic nerves
- Frank infarction with cytotoxic edema rare in PRES

Associated abnormalities

- Acute/subacute systemic HTN
- Preeclampsia, eclampsia
        - Typically occurs after 20-weeks gestation
        - Rare: Headache, seizures up to several weeks post partum
- Drug toxicity ± tumor lysis syndrome
        - Chemotherapeutic agents (e.g., cyclosporine, cisplatin)
- Thrombotic microangiopathies (DIC, TTP, malignant HTN)
- Uremic encephalopathies
        - Acute glomerulonephritis, lupus nephropathy, etc.
- Severe infection
        - 25% of septic patients in shock develop PRES
        - BP can be normal or elevated

Gross Pathologic & Surgical Features
- Common - Cortical/subcortical edema - ± petechial hemorrhage in parietooccipital lobes
- Less common - Anterior frontal lobes, basal ganglia, brainstem, cerebellum
- Uncommon - Lobar hemorrhage - Frank infarction
Microscopic Features
- Autopsy in severe cases shows microvascular fibrinoid necrosis, ischemic microinfarcts, variable hemorrhage
- Chronic: Demyelination, laminar necrosis, older hemorrhage

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Headache, seizure, ↓ mental status, visual disturbances
- Caution: Some patients, especially children, may be normotensive or have only minimally elevated BP

Clinical profile

- Pregnant female with acute systemic HTN, headache ± seizure
- Middle-aged, older adult on chemotherapy
- Child with kidney disease or transplant

Demographics

Age
```
- Any, but young > old
```
Sex
```
- F > > M
```

Epidemiology

- Preeclampsia in 5% of pregnancies
- Eclampsia has lower rate (< 1%)

Natural History & Prognosis
- Usually no residual abnormalities after HTN corrected - Reversibility related to BP normalization - Brainstem, deep white matter lesions less reversible than cortical/subcortical - Eclampsia more reversible than drug-related PRES
- Severe PRES may be life-threatening
- Permanent infarction rare
Treatment
- Control BP, remove precipitating factors
- Delayed diagnosis/therapy can result in chronic neurologic sequelae

DIAGNOSTIC CHECKLIST

Consider
- Patchy bilateral parietooccipital hypodensities may be earliest NECT manifestation of PRES
Image Interpretation Pearls
- Major DDx of PRES is cerebral ischemia; DWI is positive in latter, usually negative in former

700d7e3a-7e08-44be-8153-ef41cef115a6

References

Selected References

Differential diagnosis

Intracranial Hemorrhage

DDX:3a9cbed6-aa2c-45a0-88bf-b39f1523ee85

Cases

{'cases': [{'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'fde3bc1c-5b51-4c9f-b4a1-ac78603790e5', 'description': 'Axial FLAIR scan (#1) shows gyral edema in both occipital lobes and the posterior left frontal lobe. T1C+ scan (#2) shows multifocal punctate areas of enhancement indicating active blood-brain barrier disruption in this case of PRES.', 'history': 'Patient with bone marrow transplant on cyclosporin developed severe hypertension.', 'imagePoolId': '35fe9e0a-6629-447c-a764-160f8e332bbf', 'name': 'Enhances', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'aee88fd4-9fc2-4b54-8eda-c503d4959535', 'description': "Axial NECT scan was initially read as normal but shows subtle hypodensities in both occipital lobes (, Fig. 1). T2WI shows subtle hyperintensity in the right occipital lobe and definite hyperintensity on the left side (, Fig. 2). DWI (Fig. 3) was normal. ADC shows mild "T2 shine-through" in the left occipital lobe (, Fig. 4).", 'history': 'Pregnant patient developed eclampsia.', 'imagePoolId': '7095dae7-cac3-492b-9b35-3459f05bc035', 'name': 'Subtle', 'teachingPoint': None, 'demographics': '26 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'b33ecc59-2ab9-4d2c-abfa-19dd54d7265b', 'description': 'Axial NECT scans (#1-2) show relatively symmetric low density in the posterior parietal and occipital lobes (arrows). A suggestion of low density foci more anteriorly along the vascular watershed zone (#2, open arrows) can be identified. The basal ganglia appears normal. Axial T2 weighted (#3) and FLAIR scans (#5-7) show bioccipital foci of high signal intensity involving the cortex and subcortical white matter. Findings are classic for acute hypertensive encephalopathy, which has many possible etiologies.', 'history': 'Young patient with HUS/TTP and severe hypertension.', 'imagePoolId': '84d7acc7-1001-4c62-9fc5-fa881c44b9f9', 'name': 'Classic', 'teachingPoint': None, 'demographics': '20 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'b8ec88d1-96ba-46cf-beba-357ff73fefe7', 'description': 'Axial T2WI MR images (#1, 2) show bilateral cortical/subcortical occipital hyperintensities (arrows) with more subtle lesions in the anterior watershed zones (open arrows, #2). Axial T1 C+ MR images (#3, 4) show patchy enhancement in the posterior circulation lesions (arrows) as well as in the more anterior watershed zone (open arrows, #4). Images #5 and 6 are post-contrast T1WI obtained two days after delivery and normalization of blood pressure. The enhancement has disappeared.\n\nComment: Classic PRES represents transient opening of the blood-brain barrier and usually resolves without either clinical or imaging residua.', 'history': 'Patient presents with a history of eclampsia.', 'imagePoolId': '4137cb09-f09d-45bd-93ec-97888416d291', 'name': 'Classic', 'teachingPoint': None}, {'authors': [{'key': '815f3e98-b5da-43c7-8f99-d3db52947320', 'value': 'Hank Baskin, MD'}], 'caseVersionId': 'ad497cf6-cde6-4c6c-9f00-14a0b1018819', 'description': 'Axial FLAIR images (#1,2) show patchy areas of abnormal, increased signal in the bilateral occipital lobes (arrows), a typical location to see signal changes associated with acute hypertensive encephalopathy. As is typical, there is no diffusion restriction on diffusion-weighted imaging (#3) and no abnormal enhancement on post-contrast imaging (#4).', 'history': 'Young girl with renal artery stenosis and hypertension presented with metal status changes.', 'imagePoolId': 'd440e808-f5fc-4959-9f11-10fc37408c9a', 'name': 'No enhancement or diffusion abnormality', 'teachingPoint': None, 'demographics': '12 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '48dc907f-f3c2-450b-a232-8670a575b5d0', 'description': 'Axial T2 (#1-6) and FLAIR (#7-11) MR scans show symmetric increased signal intensity in the white matter of the cerebellum as well as the centrum semiovale of the cerebral hemispheres (arrows). Abnormal signal intensity is also present in the pons and basal ganglia (curved arrows) as well as the cortex and subcortical white matter in the territory supplied by the posterior cerebral arteries and along the vascular watershed zone (open arrows). DWI sequence (#12-15) shows no definite restriction, the usual pattern observed in patients with acute hypertensive encephalopathy (PRES).', 'history': 'Patient on Cyclosporin with acute onset of extreme systolic hypertension.', 'imagePoolId': 'f47d1fda-d2d2-4b02-b126-226330cfe495', 'name': 'Florid', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '62822f9f-426c-4331-b921-f9cedabf6bb0', 'description': 'Axial T1WI shows sulcal effacement, blurred gray-white interface in both parieto-occipital lobes (arrows, #1). T2WIs (#2,3) show loss of CSF hyperintensity in the adjacent sulci caused by gyral edema, well-seen compared to the normal frontal, temporal lobe sulci. Note subtle hyperintensity in the parieto-occipital cortex, underlying white matter, and watershed zone (arrows, #2-4). FLAIR hyperintensity in the same areas is easier to distinguish (arrows,#5-7). Coronal T1 C+ scan shows some blood-brain-barrier leakage with patchy contrast enhancement (arrows, #8). \n\nComment: Findings are those of PRES, posterior reversible encephalopathy syndrome. Findings resolved when cyclosporine was stopped and blood pressure normalized.', 'history': 'Patient with acute myelogenous leukemia, bone marrow transplant, on cyclosporine. Developed acute onset of hypertension, seizures.', 'imagePoolId': 'b45439b3-cbe9-430f-b2f1-760bb3713f26', 'name': 'Seizure', 'teachingPoint': None, 'demographics': '41 Years old female'}], 'caseType': 'typical', 'name': 'TYPICAL'}
{'cases': [{'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'a41ccec1-f7c0-488e-bed9-d65bdab740ab', 'description': 'Axial NECT scans (#1-3) show profound hypodensity in the basal ganglia and thalami (open arrows). The brain is generally edematous as seen by the lack of surface sulci on the most superior scan (#3). \n\nComment: Involvement of the basal ganglia without affecting the occipital lobes, white matter or watershed zones is a variant pattern of PRES.', 'history': 'Child with known hemolytic-uremic syndrome (HUS) and renal failure presented with severe hypertension, GI bleeding and acute neurologic decline. The patient died 2 days after this scan was obtained.\n', 'imagePoolId': '9632dde5-4612-4a30-b4b8-8caf4912ec43', 'name': 'Atypical involvement', 'teachingPoint': None, 'demographics': '4 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '015f2e1f-e7d5-482b-9f2f-11dd5a6fee68', 'description': 'Axial T1WIs (#1,2) show swollen cortex in both occipital lobes with blurring of gray-white junctions (arrows). T2WIs (#3-5) and FLAIR (#6,7) show hyperintensity in these same areas. Also note anterior extension along the vascular watershed zones (arrows, #5,7). T2GRE scans (#8-10) show several small hemorrhagic foci (open arrows). DWI and ADC (#11-14) show T2 "shine-through" but no definite restriction. T1C+ scans (#15-17) show no definite enhancement.\n\nComment: Except for the microhemorrhages, this is a typical case of PRES. The presence of microhemorrhages may indicate a component of thrombotic microangiopathy which can be caused by acute malignant hypertension. Most cases of typical PRES do not cause hemorrhage although "variant" PRES with unusual location, hemorrhage, and/or diffusion restriction has been reported to occur in up to 15% of cases.', 'history': 'Acute malignant hypertensive crisis with markedly elevated blood pressure.', 'imagePoolId': '39fe796f-beac-49cb-b603-f095f5e98fdf', 'name': 'PRES plus microhemorrhages', 'teachingPoint': None, 'demographics': '46 Years old female'}, {'authors': [{'key': '5d8b4b75-dddc-4514-9e16-4073e4b8b24a', 'value': 'Nivedita Agarwal, MD'}], 'caseVersionId': '03d6e392-e864-4d75-9211-bf11c80528fd', 'description': 'FLAIR and T2W images show a hyperintense lesion in the right cerebellar hemisphere (arrows, #1-2). Part of this lesion restricts in diffusion-weighted images (arrow, #3) and presents blooming artifact on GRE images, most likely representing blood products (arrows, #5). There is slight enhancement (open arrow, #4) with a prominent vessel seen after contrast administration, a sign of a leaky blood brain barrier (arrow, #4). \n\nThe differential diagnosis with this constellation of findings includes possible infarct with hemorrhagic transformation (either arterial or venous infarct) and/or variant posterior reversible encephalopathic syndrome (PRES). Repeat MR after 3 weeks shows complete resolution of MR findings (#6-8) except for persisting blooming artifact on GRE images (arrow, #9).\n\nComment: The patient has been symptom-free since her first MR. During the 3 weeks, she has been treated with antihypertensive drugs. Given the follow-up MR findings, the most likely diagnosis is PRES with hemorrhagic transformation likely due to a prolonged vasoconstriction and delayed hypertensive treatment.\n\nPRES is typically seen in the posterior part of the brain, though not exclusively. While its etiology remains largely unknown, it is important to consider this diagnosis in patients with hypertension and positive MR findings in the cerebellum, brain stem, and occipital regions.', 'history': 'Patient with sudden headache and seizure-like episode; history of breast cancer; on chemotherapeutic drugs; hypertension noted on admission.', 'imagePoolId': '3b507201-7070-43f5-a36d-26ffb3f1ee41', 'name': 'Complete resolution, GRE remains positive', 'teachingPoint': None, 'demographics': '52 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '2e6ea715-afb5-4306-af99-de03fb3fe716', 'description': 'Axial NECT scans (#1,2) show hypodensity in both occipital lobes and cortical/subcortical watershed zones (arrows). Axial T1WI MR obtained 5 days after emergency delivery (#3), shows large, asymmetric hemorrhagic occipital infarcts (arrows). Axial T2WI MR (#4) shows very large mixed signal lesions in both occipital lobes. \n\nComment: Frank ischemia/infarction are uncommon complications of PRES.', 'history': 'Pregnant female patient with headaches, severe HTN and cortical blindness. CT was obtained on admission. Emergency delivery was performed. Follow-up MR scan was obtained approximately 5 days after initial presentation.', 'imagePoolId': '1bb243df-cfd5-4224-afa5-8785c50b8bb6', 'name': 'Sequelae (gross hemorrhage)', 'teachingPoint': None, 'demographics': '15 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '64c52f30-61ab-4bfa-b3d4-a3badea8b047', 'description': "A series of CECT scans (Figs. 1-4) show hypodensity in the cerebellar white matter with severe cerebellar swelling (, Fig. 1). Upward herniation of the cerebellum into the tentorial incisura displaces the quadrigeminal plate cistern anteriorly (, Fig. 2). The aqueduct is occluded, and there is severe hydrocephalus with transependymal CSF flow. The cerebral white matter appears more hypodense than normal on image 4; this could be from the obstructive hydrocephalus or can also be seen with acute hypertensive encephalopathy, also known as PRES (posterior reversible encephalopathy syndrome). Comment: This case is deemed a variant because of the cerebellar (rather than occipital lobe) predominance.", 'history': 'Patient with acute renal failure presented with seizures. Patient arrested and died after the scan was obtained.', 'imagePoolId': '0e9d3349-ed98-46f1-93fc-ee1b6261cb6f', 'name': 'Cerebellar PRES', 'teachingPoint': None, 'demographics': '2 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '6ac9187c-383c-4516-83a9-6649068bc46c', 'description': 'Axial NECT scans (#1-3) show bilateral hypodensities in both occipital lobes (arrows) with a single focus of high density indicating hemorrhage (open arrow, #1). MR was obtained. Sagittal (#4) and axial (#5) T1WIs show hypodensity in the occipital cortex and subcortical white matter (arrows). T2WIs (#6-8) and FLAIR (#9-11) show hyperintensity in the same areas along with a very hyperintense focus (open arrows, #6, 10) of acute hemorrhage. No enhancement was seen on T1 C+ study (#12). DWI scans (#13-15) showed some hyperintensity in both occipital lobes that are also hyperintense on ADC (#16-18). The hemorrhage is hypointense.\n\nComment: Hemorrhage is uncommon (although not rare) in cases of PRES.', 'history': 'Renal transplant patient on cyclosporin developed severe headaches, vision problems. Markedly elevated blood pressure on admission.', 'imagePoolId': 'ba656ee6-6fba-454f-8d92-ff00565111f1', 'name': 'Hemorrhage', 'teachingPoint': None, 'demographics': '24 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '7ad1099c-4b7a-42c4-8c36-3f0a46cf3f6a', 'description': 'Axial FLAIR scans (#1-8) show multiple cortical/subcortical foci of increased signal intensity (arrows) mostly in the occipital lobes, cerebellum, thalami and watershed zones. Signal in the subarachnoid spaces indicates some subarachnoid hemorrhage as well (open arrows, #5,6). T2WIs (#9-16) show multifocal hyperintensities (arrows) in the same areas. Coronal T2 GRE scans (#17-22) show no evidence for petechial hemorrhage.\n\nComment: Findings of PRES-like changes in malignant hypertension with thrombocytopenia and hemolytic anemia are consistent with one of the causes of thrombotic microangiopathy, TTP.', 'history': 'History of COPD and poorly controlled hypertension presented with cutaneous hemorrhages, seizure, deteriorating mental status, markedly elevated blood pressure. Laboratory findings on admission indicated anemia with thrombocytopenia, acute renal failure.\n\n', 'imagePoolId': '0360329d-f9fa-4680-b158-b534991a139d', 'name': 'TTP', 'teachingPoint': None, 'demographics': '66 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '7cede56b-33c4-4c03-9d81-b750f79fab9d', 'description': 'Axial FLAIR scans (#1, 2) show patchy areas of increased signal intensity in the pons and both caudate nuclei. A small focus of hyperintensity is also present in the left putamen/external capsule. Axial DWI scans (#3, 4) show restriction in all areas that were abnormal on the FLAIR scans. The putamen lesion (#4, arrow) shows only mild restriction; the other lesions show striking hyperintensity on DWI. \n\nThe remainder of the brain, including the posterior cortex, was normal.\n\nThis case is unusual for two reasons: (1) The distribution of the lesions, with pontine and caudate involvement sparing the occipital lobes and (2) the presence of restricted diffusion on DWI. Most cases of so-called posterior reversible encephalopathy syndrome (PRES) involve areas supplied by the posterior cerebral artery and are diffusion-negative.', 'history': 'Pregnant patient with eclampsia.', 'imagePoolId': 'dc63ab19-6d53-4e80-8d21-9514cb642ac5', 'name': 'DWI positive', 'teachingPoint': None, 'demographics': '25 Years old female'}, {'authors': [{'key': '07a2c087-6202-49e7-870b-7aa162d18f06', 'value': 'Bronwyn E. Hamilton, MD'}], 'caseVersionId': 'bf1937b7-c97c-4f80-9c4e-88331be0dd8d', 'description': "Axial T2 (#1) and FLAIR (#2) on day 1 demonstrate bilateral confluent areas of hyperintensity (arrows) that were extensive but demonstrated a posterior hemispheric predilection. Cortex is spared, as is typical for uncomplicated PRES. T1-weighted images show mild mass effect with sulcal effacement, without significant signal abnormality (#3). No abnormal enhancement was seen on post contrast scan (#4). DWI (#5) shows no acute restriction but extensive vasogenic edema (curved arrows) on ADC (#6). \n\nPatient returned for limited perfusion imaging on the 2nd day, which showed low relative cerebral blood volume in the affected white matter (arrows, #7). DWI obtained concurrently (not shown) was stable, with no acute restriction. Day\n2 axial FLAIR (#8) shows extensive abnormal hyperintense signal diffusely throughout the subarachnoid fluid spaces (open arrows), compatible with gadolinium enhancement due to extravascular leakage of contrast. \n\nComment: Since the patient's renal function remained normal throughout her hospitalization, the contrast accumulation is consistent with altered blood-brain barrier permeability during the patient's acute hypertensive crisis. The patient also had no other known explanations for cerebrospinal fluid hyperintensity on FLAIR, such as scanner artifacts or administration of high fractional inspired oxygen concentration during the exam.", 'history': 'Patient admitted with acute hypertensive crisis and altered mental status. During hospital stay, renal function was normal. ', 'imagePoolId': '1232d9c8-7a70-4f6e-8ca7-cdfb887bd45a', 'name': 'Enhancing CSF', 'teachingPoint': None, 'demographics': '78 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'cf6e03ba-3b5c-482b-9b74-aad31df98e3d', 'description': 'Axial T2 (Figs. 1-5) and FLAIR (Figs. 6-9) scans show hyperintensity in the pons, midbrain, both medial thalami, and occipital lobes. No diffusion restriction is seen, although there is mild T2 shine-through on the DWI image (Fig. 10).', 'history': 'Eclamptic patient presents with seizures, severe hypertension.', 'imagePoolId': '91599018-c7e8-4190-9ab6-3550cab38f48', 'name': 'Bilateral thalami', 'teachingPoint': 'The brainstem and thalamic involvement in this patient with posterior reversible encephalopathy syndrome (PRES) is unusually striking. In a few cases, involvement of the brainstem and cerebellum may be the only manifestations of PRES. In this case, the occipital involvement and clinical history make the diagnosis all but certain.', 'demographics': '22 Years old female'}, {'authors': [{'key': '815f3e98-b5da-43c7-8f99-d3db52947320', 'value': 'Hank Baskin, MD'}, {'key': 'f7b0bbaf-fa5e-42e3-9d52-3d0c72fbf3ba', 'value': 'Jill Stein, MD'}], 'caseVersionId': 'e8767621-6380-4cb8-b716-f41f17656bed', 'description': "Axial T2 FLAIR MR images (Figs. 1-4) show multiple foci of abnormal hyperintense signal throughout the brainstem and deep nuclei, including the pons, left cerebral peduncle, left anterior thalamus, and left centrum semiovale .\n\nAxial T1 post-contrast (Fig. 5) and diffusion-weighted images (Fig. 6) demonstrate lack of enhancement and restricted diffusion, respectively. This pattern of brainstem and deep nuclei involvement can be seen in an atypical distribution of acute hypertensive encephalopathy [also known as Posterior reversible encephalopathy syndrome (PRES)].", 'history': 'Patient presents with altered mental status and hypoplastic left heart syndrome.', 'imagePoolId': '33566052-c477-4dd5-9a8b-fb544232d86b', 'name': 'Atypical distribution in the brainstem and deep nuclei', 'teachingPoint': None, 'demographics': '3 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'b0a7c4a5-53e1-48e5-ad08-9933940c239a', 'description': 'While acute hypertensive encephalopathy typically affects the posterior circulation, occasionally it can predominately or exclusively involve the brainstem, cerebellum, or thalami.\n\nAxial T2 weighted MR scans (#1-4) show increased signal intensity in the cerebellum, pons, midbrain and thalami. The posterior circulation is completely normal.', 'history': 'Pregnant patient with eclampsia, coma.', 'imagePoolId': '0efc4e48-53ab-4786-b98a-4032c5d56f49', 'name': 'Striking BS', 'teachingPoint': None, 'demographics': '40 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '82d712d4-cc39-4eb9-8778-4d821fc80bf1', 'description': 'The majority of cases with acute hypertensive encephalopathy resolve without residua. In exceptionally severe cases, gross hemorrhage with hydrocephalus, brain herniation and death may result.\n\nAxial NECT scans show massive intraventricular hemorrhage with severe obstructive hydrocephalus and blood-CSF levels (#1, open arrows). Presence of symmetric low density in both basal ganglia (#1, arrows) and at the posterior parieto-occipital cortex and subcortical white matter (#2, curved arrow) suggest this case represents a variant of posterior reversible encephalopathy syndrome (PRES).', 'history': 'Pregnant patient with seizure followed by coma and decerebrate posturing.', 'imagePoolId': '4e227daa-264d-4f24-a3ae-4354fcd6ed40', 'name': 'Atypical eclampsia', 'teachingPoint': None, 'demographics': '30 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '567e2296-a61c-47de-814f-865a137b7691', 'description': 'Axial NECT scans (#1-3) show profound hypodensity throughout the cerebral white matter and especially within both parietal lobes (open arrows, #2, 3). There is a focal hyperdense area, (arrow, #2) that probably represents frank parenchymal hemorrhage.\n\nThe findings are those of acute hypertensive encephalopathy or PRES (Posterior Reversible Encephalopathy Syndrome). The findings are identical to PRES caused by eclampsia, cyclosporine toxicity, etc. This case is deemed variant because cocaine is an unusual cause of PRES.', 'history': 'Patient presents with extreme, sudden hypertension after using cocaine.', 'imagePoolId': '636ad180-0c98-4293-8b68-f290a9678dbc', 'name': 'Florid', 'teachingPoint': None, 'demographics': '18 Years old female'}], 'caseType': 'variant', 'name': 'VARIANT'}

Images

Selected Images

Axial graphic shows the classic posterior circulation cortical/subcortical vasogenic edema characteristic of posterior reversible encephalopathy syndrome (PRES). Petechial hemorrhage occurs in some cases.

Gross pathology of a patient with complicated PRES demonstrates diffuse cerebral edema with swollen gyri. Multifocal petechial microhemorrhages are present in the occipital cortex with several areas of focal encephalomalacia secondary to infarction . (Courtesy R. Hewlett, MD.)

Axial NECT of a 54-year-old patient with liver transplant on Tacrolimus FK 506 who presented with seizures demonstrates asymmetric subcortical edema in the occipital lobes bilaterally . Findings are typical of PRES.

Axial FLAIR MR in a 20-year-old eclamptic woman who presented with severe HTN, seizures, & altered sensorium shows classic findings of PRES with occipital cortical/subcortical edema . Her BP at presentation was 210/140.

Axial FLAIR MR in a patient with renal failure presenting with headache, seizures, & visual disturbances demonstrates bilateral parietooccipital cortical/subcortical hyperintensities .

Axial DWI MR in the same patient shows patchy areas of cortical restricted diffusion . Diffusion is usually negative in PRES. PRES with restricted diffusion occurs in 15-30% of cases & is usually seen as smaller cortical foci of restricted diffusion within larger regions of vasogenic edema, as in this case.

Axial FLAIR MR in an 11-year-old patient with acute lymphoblastic leukemia (ALL) on chemotherapy shows cortical/subcortical edema in frontal (superior frontal sulcus pattern) & parietal lobes (typical parietooccipital pattern).

Axial T1 C+ MR in the same patient shows extensive patchy areas of juxtacortical enhancement . Although etiology of PRES is not completely understood, leading theories include loss of autoregulation & endothelial dysfunction. FLAIR changes & enhancement resolved on follow-up MR.

Axial SWI MR in a hypertensive patient who presented with visual disturbances & seizures demonstrates the 3 patterns of hemorrhages which can be seen in PRES. This case shows lobar hemorrhage , cortical SAH , and microhemorrhages .

Axial FLAIR MR in a patient with preeclampsia shows atypical findings of PRES with vasogenic edema involving the pons & cerebellum . It is important to remember that edema in PRES is not just posterior and not always reversible.

Additional Images

Axial NECT shows variant findings of PRES, notably bilateral but asymmetric occipital lobe hypodensities & focal hemorrhage . Most cases of PRES do not hemorrhage. If they do, multifocal small cortical petechial-type bleeds are typical. Gross hemorrhage is uncommon.

Axial NECT in an eclamptic patient shows some variant changes of PRES with bilateral basal ganglia lesions & intraventricular hemorrhage with fluid-fluid levels in the occipital horns .

Axial NECT in an eclamptic woman shows bilateral hypodensities in the occipital lobes , characteristic of PRES.

Axial NECT shows bioccipital as well as watershed hypodensities in this patient with severe HTN.

Axial FLAIR MR in the same patient shows hyperintensity in the white matter of both occipital lobes . Subtle cortical hypointensity may represent petechial hemorrhage.

Axial FLAIR MR shows cortical & subcortical edema in both occipital lobes, as well as the posterior left frontal lobe .

Axial T1 C+ MR in the same patient shows multifocal punctate areas of enhancement indicating active blood-brain barrier disruption in this case of PRES.

Axial FLAIR MR shows bilateral occipital hyperintensity in the cortex & subcortical white matter . There is striking hyperintensity in the pons .

Axial NECT in a 4-year-old hypertensive child with hemolytic uremic syndrome & renal failure shows hypodensity in the basal ganglia & thalami . The occipital lobes are normal.

Axial NECT of a 26-year-old pregnant patient with eclampsia was initially read as normal; however, it shows subtle but definite hypodensities in the cortex & subcortical white matter of both occipital lobes.

Axial T2 MR in the same patient shows hyperintensities in both occipital lobes corresponding to the hypodensities noted on NECT. DWI (not shown) was normal. If clinical suspicion of PRES is high & NECT is scan normal/subtly abnormal, MR with T2WI, FLAIR, & DWI is helpful.

Axial T2 MR in a patient on cyclosporine who developed acute onset of extreme HTN shows symmetric hyperintensities in both cerebellar hemispheres .

Axial T2 MR in the same patient shows florid changes in the cortical watershed zones . DWI showed no restriction, which is typical even in severe cases of PRES. All findings resolved when the patient was taken off chemotherapy & BP normalized.

Axial T2 MR in the same patient shows striking hyperintensity in both basal ganglia with relatively subtle findings in the occipital poles .

Axial T2 MR in a patient with PRES shows pontine-predominant pattern with only subtle change in the occipital lobe . Sometimes pontine or cerebellar abnormalities can be found without other imaging evidence of PRES.

Axial T1 C+ MR in a patient with eclampsia shows numerous patchy cortical & subcortical enhancing foci in both occipital lobes & along the watershed zones. T2WIs (not shown) demonstrated hyperintensities in the same areas.

Repeat scan was obtained 2 days after delivery & normalization of BP. MR is normal with the disappearance of the enhancing foci previously seen. Even florid MR changes of PRES usually resolve without clinical or imaging residua.

Axial FLAIR MR in a patient with systemic lupus erythematosus (SLE) & renal failure demonstrates cortical/subcortical edema in the frontal & parietal lobes .The frontal lobes are involved in > 70 % of PRES cases.

Axial DWI MR in the same patient shows some patchy areas of frontal cortical restricted diffusion . Because most cases of PRES are caused by vasogenic & not cytotoxic edema, DWI is usually negative. Diffusion restriction has been reported like in this case & may lead to residual abnormalities.

Axial T2 MR in a patient with sepsis & slightly elevated BP shows atypical findings of PRES. There is extensive edema involving the pons & both the middle cerebellar peduncles .

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