C20090551288 b9780323067942000493 main, medycyna, radiologia haslo radiologia, radiology secrets plus anoxic seizure

C20090551288 B9780323067942000493 main, medycyna, radiologia haslo radiologia, radiology secrets plus

Brain: inflammatory, infectious,

And vascular diseases

49

Gul moonis, MD, and

Laurie A. Loevner, MD

1. How is multiple sclerosis (MS) diagnosed?

MS is the most common of the acquired demyelinating disorders. The disease has a characteristic relapsing-remitting

Course and usually manifests between the third and fifth decades of life with a female predominance. On magnetic

Resonance imaging (MRI), the demyelinating lesions of MS are ovoid and hyperintense (bright) on T2-weighted images

And occur predominantly in the white matter, especially in the periventricular location (usually perpendicular to the


Ventricular surface) (

anoxic seizure

Fig. 49-1

). The corpus callosum, white matter around the temporal horns of the lateral ventricles,

And middle cerebellar peduncles are other favored locations of MS plaques. There may be enhancement of the plaques

(ringlike or solid) that denotes active disease. Occasionally, MS plaques can be large and masslike (tumefactive MS),

In which case differentiation from a tumor may be difficult.

2. What is the differential diagnosis of MS based on imaging findings?

The diagnosis of MS is a clinical one (neurologic symptoms spaced over time and in multiple distributions), with

Supporting radiologic findings. The diagnosis cannot be made on imaging findings alone because other inflammatory

And vascular processes can manifest with similar imaging findings.Anoxic seizure white matter lesions similar to MS can be seen with

A spectrum of inflammatory conditions, including lyme disease, sarcoidosis, and vasculitis.

3. What are the causes of intracranial

Abscesses?

Infectious agents gain access to the central nervous

System (CNS) by direct spread from a contiguous

Focus of infection, such as sinusitis, otitis media,

Mastoiditis, orbital cellulitis, or dental infection.

Infection from these locations may also spread to

The intracranial compartment by retrograde venous

Reflux. Hematogenous spread of infection can also

Occur from a distant nidus of infection, such as the

Lung. Polymicrobial infection is common with brain

Abscesses. Four stages have been described in

Abscess evolution: early cerebritis, late cerebritis,

anoxic seizure

Early capsule formation, and late capsule formation.

A mature abscess is characterized by a “ring-

Enhancing” lesion on cross-sectional imaging.

4. What is the imaging differential

Diagnosis of a ring-enhancing lesion

In the brain?

The following disease processes can have an

Imaging presentation identical to brain abscess:

Metastatic disease, primary CNS glioma, resolving

Hematoma, and demyelinating disease. Interpreting

The radiologic findings in conjunction with the

Clinical history is usually helpful in differentiating

Among these possible etiologies.

5. What advanced MRI techniques may

Be useful in distinguishing brain

Abscess from neoplasm?

Differentiating a subclinical brain abscess from

Cystic or necrotic tumor with conventional

anoxic seizure

Figure 49-1.

MS in a young patient. Axial fluid-attenuated inversion

Recovery (FLAIR) MR image shows numerous ovoid, periventricular

Lesions characteristic of MS plaques. These are oriented along the

Perivascular spaces, and the appearance has been referred to as

“dawson’s fingers.”

336

337

Neuroradiology

A

B

Figure 49-2.

A,

Frontal lobe abscess secondary to frontal sinusitis. Axial contrast-enhanced T1-weighted MR image shows two ring-

Enhancing lesions in the left frontal lobe (

Arrow

) and enhancing soft tissue within and anterior to the frontal sinus.

B,

On the corresponding

Diffusion-weighted image, there is restricted diffusion (high signal intensity) within these lesions that is compatible with abscesses.Anoxic seizure

Computed tomography (CT) or MRI can be difficult.

1

H magnetic resonance spectroscopy and diffusion-weighted MRI

Can be useful in this regard (

Fig. 49-2

). Typically, on diffusion-weighted MRI, an abscess is hyperintense (bright).

6. What anatomic location in the brain is preferentially involved by herpes simplex

Encephalitis?

In adults, type 1 herpes simplex virus is responsible for fulminant, necrotizing encephalitis. The virus preferentially

Involves the temporal lobes, but involvement of the frontal lobes (especially the cingulate gyrus) is common. Often, there

Is bilateral temporal lobe involvement, although this is usually asymmetric. On MRI, there is T2-weighted hyperintensity

In the temporal and frontal lobes with enhancement (

anoxic seizure

Fig. 49-3

). Clinically, the patient presents with acute confusion,

Disorientation, or seizures progressing to stupor and coma. Most cases are a result of reactivation of dormant virus in

The trigeminal ganglion. There is commonly asymmetric temporal lobe involvement. Hemorrhage in the affected area is

Common.

7. What is the differential diagnosis of an intracranial mass in a patient with human

Immunodeficiency virus (HIV) infection?

It is crucial to determine whether the cause of HIV-related brain mass is neoplastic or infectious because these entities

Are managed differently. Among infectious etiologies, toxoplasmosis and brain abscesses secondary to fungal or

Bacterial etiologies have to be considered.Anoxic seizure the major neoplastic consideration is primary CNS lymphoma. Toxoplasmosis

Is the leading cause of focal CNS disease in acquired immunodeficiency syndrome (AIDS) and results from infection by

The intracellular parasite

Toxoplasma gondii

. It is usually caused by reactivation of old CNS lesions or by hematogenous

Spread of a previously acquired infection. On imaging, single or multiple ring-enhancing lesions in the white matter

Or basal ganglia or both with mass effect may be observed. A single lesion favors the diagnosis of lymphoma over

Toxoplasmosis (

Fig. 49-4

). Occasionally, progressive multifocal leukoencephalopathy, a demyelinating disease caused by

A viral infection, may result in ring-enhancing lesions.Anoxic seizure progressive multifocal leukoencephalopathy is caused by a virus

That infects the oligodendrocytes in immunocompromised patients.

8. What is a stroke?

A stroke occurs when the blood supply to a vascular territory of the brain is suddenly interrupted (ischemic stroke),

Or when a blood vessel in the brain ruptures, spilling blood into the spaces surrounding the brain cells (hemorrhagic

Stroke). Ischemic stroke is the more common form, responsible for approximately 80% of vascular accidents. In adults,

These blockages are usually associated with two conditions: atherosclerosis-related occlusion of vessels (60%) and

Cardiac embolism (20%).

338

BraiN: inflammatory, infectious, and vascular diseases

A

B

Figure 49-3.Anoxic seizure

A,

Herpes simplex encephalitis. Axial FLAIR MR image shows abnormal T2 hyperintensity in the left medial temporal lobe

Involving gray and white matter.

B,

Axial enhanced T1-weighted MR image shows mild patchy enhancement (

Arrow

) that is consistent with

Cerebritis.

A

B

Figure 49-4.

A,

Toxoplasmosis in an HIV-positive patient. Axial FLAIR MR image shows extensive signal abnormality involving the left basal

Ganglia and adjacent frontal and temporal lobes with mass effect.

B,

Axial enhanced T1-weighted MR image at the same axial level as

A

Shows a rim-enhancing lesion in the center of the left basal ganglia (

Arrow

) with extensive surrounding edema and midline shift from left to

Right.

339

Neuroradiology

9. What are the common causes of stroke that one must consider in children and young

anoxic seizure

Adults?

Only 3% of cerebral infarctions occur in patients younger than 40 years old. The most common causes of stroke in

Young patients are cardiac disease, hematologic diseases (hypercoagulable states), and vascular dissection (from

Trauma or disease of the vessel wall). Other causes include CNS vasculitis, fibromuscular dysplasia, and venous sinus

Thrombosis.

10. What are the imaging manifestations of ischemic stroke in the acute stage?

Commonly, in the acute setting, a CT scan of the head may be normal. The earliest signs

(

6 hours) of an acute infarct

On CT are loss of the gray-white differentiation with obscuration of the lateral lentiform nucleus. There may be a high

Density noted in the proximal middle cerebral artery, representing acute thrombus or calcified embolus; this is referred

anoxic seizure

To as the “hyperdense artery” sign (

Fig. 49-5A

). Within 12 to 24 hours, there is low density in the appropriate vascular

Distribution, with increasing mass effect. Mass effect peaks between 3 and 5 days. Findings of acute ischemia are

Detected earlier on MRI. With the use of diffusion-weighted imaging, acute ischemic changes can be seen within

Minutes of onset of the ictus. High signal intensity is noted within the involved vascular territory on T2-weighted images,

With characteristic restricted diffusion (also hyperintense) on diffusion-weighted images (

Fig. 49-5B and C

). Swelling of

The involved cortex and arterial enhancement are noted early in the time course.

11. How can one differentiate acute from chronic stroke on imaging?Anoxic seizure

Chronic stroke is manifested by encephalomalacic change in the involved vascular territory with accompanying

Dilation of the sulci and cisterns. There is also ex vacuo dilation of the ipsilateral ventricle. There is absence of mass

Effect. If it is difficult to distinguish the age of a stroke on CT, MRI that includes a diffusion-weighted sequence can

Be invaluable.

12. What are watershed infarctions?

Also known as “border zone infarcts,” watershed infarctions occur in the vascular watersheds (the distalmost arterial

Territory with connection between the major arterial branches). In severe hypotension or shock, the systemic blood

Pressure is insufficient to pump arterial blood to the end arteries. In the cerebrum, not enough blood gets to the

anoxic seizure

“watershed zones” between the anterior and middle cerebral arteries or the middle and posterior cerebral artery

Territories, and in those areas infarcts are likely to develop. Some other causes of cerebral watershed infarcts include

Heart failure, decreased systemic perfusion pressure, and low blood pressure in the setting of a high-grade stenosis of a

Major artery (internal carotid) supplying the brain.

13. What are lacunar infarctions?

Lacunar infarctions are small infarcts caused by occlusion or disease of the perforating arteries (arteriolar

Lipohyalinosis). Initially, these are slightly hypodense on CT. By 4 weeks, sharply circumscribed, cystic lesions develop.

These lesions are most commonly seen in the deep gray matter (basal ganglia, thalami), brainstem, internal capsule,

anoxic seizure

And corona radiata. These small infarctions are usually 1 cm or smaller.

A

B

C

Figure 49-5.

Hyperdense middle cerebral artery consistent with acute thrombus or calcified embolus.

A,

Axial unenhanced CT scan of

The head shows hyperdensity in the left middle cerebral artery (

Arrow

) that is compatible with acute thrombus.

B

And

C,

Corresponding

Axial FLAIR and diffusion-weighted MR images shows diffuse hyperintensity involving gray and white matter in the left middle cerebral

Artery territory, which is characteristic of stroke. The hyperintensity on the diffusion-weighted image represents restricted diffusion, which is

Compatible with acute ischemia.

340

BraiN: inflammatory, infectious, and vascular diseases

14. What are the risk factors for venous sinus thrombosis and venous infarction?Anoxic seizure

Venous sinus thrombosis is associated with many systemic conditions, including acute dehydration, hypercoagulable

States, chemotherapeutic agents (

L

-asparaginase), sinusitis and mastoiditis, hematologic malignancies, pregnancy, and

Trauma. Unenhanced CT reveals the presence of high density and enlargement of the dural venous sinuses. The “empty

Delta” sign, which refers to enhancement around the clot in a dural venous sinus, may also be present (

Fig. 49-6A

).

The diagnosis of venous thrombosis is improved significantly with MRI. On unenhanced T1-weighted images, high

Signal intensity clot is noted within the venous sinuses (

Fig. 49-6B

). There may be associated venous infarction. Venous

Infarctions have a high rate of hemorrhagic transformation compared with arterial infarctions.Anoxic seizure

15. What is the most common cause of nontraumatic subarachnoid hemorrhage (SAH)?

An aneurysm rupture is the most common cause of nontraumatic SAH. An aneurysm is a focal dilation of an artery, most

Commonly encountered at branching points in the intracranial vasculature. Aneurysms are usually due to a congenital

Weakness in the media and elastica of the arterial wall, but can be acquired in the setting of trauma or mycotic

Infections. The approximate relative frequency of aneurysm formation in the intracranial vasculature is as follows:

Anterior communicating artery (30%), distal internal carotid artery and posterior communicating artery (30%), middle

Cerebral artery (25% to 30%), and the posterior vertebral-basilar circulation (10% to 15%).Anoxic seizure multiple aneurysms are seen

In approximately 15% of cases. There is increased incidence of intracranial aneurysms in patients with polycystic kidney

Disease, marfan syndrome, and fibromuscular dysplasia (and other rarer entities, including moyamoya disease, ehlers-

Danlos syndrome, and takayasu arteritis).

16. What is the work-up of a patient presenting with SAH?

If the patient presents with the classic history of “the worst headache of my life,” a CT scan should be obtained to look

For SAH. If the results of the CT scan are negative, but there is high clinical suspicion for SAH, a lumbar puncture should

Be performed to look for red blood cells or xanthochromia or both in the cerebrospinal fluid (CSF).Anoxic seizure if CSF analysis is

Positive for subarachnoid blood, a diagnostic conventional catheter angiogram is the next step to find the aneurysm,

Providing an anatomic road map for the neurosurgeon. Increasingly, CT angiography is being used rather than

Conventional catheter angiography for aneurysm detection.

17. If multiple aneurysms are seen on catheter angiography in a patient with SAH, which

One most likely bled?

If multiple aneurysms are identified, greater suspicion falls on the aneurysm that is the largest in size, on the aneurysm

With a lobulated contour (nipple sign), or on the aneurysm closest to the largest clot on CT. Extravasation of contrast

Agent from the aneurysm is rarely seen, but is diagnostic.Anoxic seizure

A

B

Figure 49-6.

A,

Venous sinus thrombosis. Axial contrast-enhanced T1-weighted MR image shows acute clot in the superior sagittal sinus.

Note the characteristic “empty delta” sign (

Arrow

) that represents nonenhancing clot within the superior sagittal sinus.

B,

Sagittal unenhanced

T1-weighted MR image taken in the midline shows relative high signal intensity in the superior sagittal sinus (

Arrows

), which is consistent

With acute thrombosis.