50	4 Ancillary Tests in Neurology
		Tabelle 4.2 MRI signal intensities of normal and abnormal structures (after Edelmann)1
		Tissue	T1-weighted image	T2-weighted image
		Contrast enhancement with gadolinium−
		DTPA
		Low concentration	Very bright	Bright
		High concentration	Intermediate to dark	Very dark
		Hematoma
		Hyperacute	Intermediate	Intermediate to bright
		Acute	Intermediate to dark	Dark to very dark
		Subacute	Bright rim, intermediate	Bright rim, dark center, later all bright
		Chronic	Dark rim, bright center, later all dark	Dark rim, bright center, later all dark

1 Bright = hyperintense, dark = hypointense, intermediate = isointense in comparison to brain tissue

only if it is excited by two radio wave pulses arriving one after the other at the same location. If the blood rapidly passes through the imaging plane, the bit of blood that received the first excitatory pulse has already flowed away by the time the second pulse arrives and no signal is generated—the vessel appears dark (there is a “flow void”). However, if the blood flows slowly enough to receive both pulses in the imaging plane, the vessel appears bright. When gradient-echo sequences are used, flowing blood always appears bright, while stationary tissue appears dark. Computer algorithms can combine the individual sectional images, processing them to generate a projectional image resembling a conventional angiogram; this is a magnetic resonance angiogram (Fig. 4.7). With MR angiography, an occluded carotid artery, for example, can be diagnosed noninvasively. Contrast-en-

a

b

Fig. 4.7 MR angiography of the intracranial vessels. a Coronal and b axial projections. The arteries in this study are normal except for hypoplasia of the main stem of the right anterior cerebral a. (arrow).

hanced MR angiography is currently being performed increasingly often. In this technique, the signal is produced not by the flowing of the blood per se, but by the contrast medium in the bloodstream.

The indications for MRI and CT scanning of the brain and spinal cord are listed and compared with each other in Table 4.1.

Angiography with Radiological Contrast Media

Diagnostic imaging of the cerebral blood vessels is indicated when a vascular stenosis, occlusion, or malformation is suspected as the cause of a neurological illness.

Methods. Conventional arteriography, also known as angiography with radiological contrast media, is indicated for certain special purposes, e. g., the preoperative visualization of intracranial aneurysms or arteriovenous malformations. This type of study involves the introduction of an intra-arterial catheter by way of the femoral a. along a guide wire all the way up to the great vessels supplying the brain. Contrast medium is injected into these vessels while fluoroscopic images are simultaneously obtained. The image changes from one second to the next, as the contrast medium distributes itself in the vascular system of the brain. All of the images are digitized and an image obtained before any contrast medium was injected is subtracted from each to generate a digital subtraction angiogram, which shows nothing but the blood vessels supplying the head and brain (both extraand intracranial). Contrast medium can be injected into the carotid a. to display the anterior circulation (Fig. 4.8), or into the vertebral a. to display the posterior circulation (Fig. 4.9).

The blood vessels of the spinal cord can also be studied angiographically, e. g., for the diagnosis and treatment of spinal arteriovenous malformations or fistulae.

Intravenous angiography has largely been abandoned.

The potential complications of angiography include hemorrhage or dissection at the femoral puncture site, the detachment of atherosclerotic plaques from arterial walls by the tip of the catheter, and the induction of vasospasm with consequent cerebral ischemia, possibly leading to stroke. The contrast media that are used can also have side effects.

Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme All rights reserved. Usage subject to terms and conditions of license.

Imaging Studies

a

b

c

Fig. 4.8 Normal digital subtraction angiogram of the intracranial anterior circulation (carotid distribution). a Anteroposterior projection. b Lateral projection. c Venous phase, lateral projection. a and b: 1 MCA = middle cerebral a., 2 ICA = internal carotid a., 3 ACA = anterior cerebral a., 4 pericallosal a. c: 1 Superior

Fig. 4.9 Selective angiography of the left vertebral a. a Arterial phase, anteroposterior projection. b Arterial phase, lateral projection.

1 posterior cerebral a.

2 superior cerebellar a.

3 anterior inferior cerebellar a. (AICA)

4 left vertebral a.

5 basilar a.

6 posterior inferior cerebellar a. (PICA)

The general rule, when a diagnostic study of the blood vessels is desired, is to choose the type of study that is expected to yield sufficient information for effective diagnosis and treatment while putting the patient at the lowest risk. MR angiography (Fig. 4.10) and Doppler ultrasonography (Fig. 5.61) now suffice for most purposes.

The indications of cerebral angiography are listed in Table 4.3.

cerebral vv. (rolandic and Trolard), 2 superior sagittal sinus, 3 inferior sagittal sinus, 4 septal v., 5 thalamostriate v., 6 internal cerebral v., 7 straight sinus, 8 v. of Labbé = inferior anastomotic v., 9 basal v. of Rosenthal, 10 cavernous sinus, 11 inferior petrosal sinus, 12 lateral sinus, 13 jugular v.

Table 4.3 Indications for angiography of the intracranial vessels

Visualization of saccular aneurysms

Visualization of arteriovenous malformations and fistulae

Detailed representation of saccular aneurysms (after diagnosis by MRI, as an aid to treatment by neurosurgical or interventional neuroradiological methods)

Detailed representation of arteriovenous malformations (after diagnosis by MRI, as an aid to treatment by neurosurgical or interventional neuroradiological methods)

Visualization of other vascular anomalies:

moya−moya

agenesis of vessels and other developmental anomalies

vascular stenosis or occlusion

arterial dissection

Fig. 4.10 Arteriovenous malformation on the surface of the cervical spinal cord. The malformation is visible in this T2-weighted MR image as a void in the midst of the bright CSF signal of the subarachnoid space.

51

4

Ancillary Tests

adfsköb

Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme

adköb

All rights reserved. Usage subject to terms and conditions of license.

52 4 Ancillary Tests in Neurology

	Myelography and Radiculography	Diagnostic Techniques of
	Technique. Radiculomyelography (the visualization of	Nuclear Medicine
	intraspinal structures with contrast medium) is gener-	CSF Scintigraphy/Isotope Cisternography
	ally performed after the injection of 10−15 ml of water-
	soluble contrast medium into the subarachnoid space	Technique. The subarachnoid space is entered with a
	via lumbar puncture—or, rarely, via suboccipital punc-
	ture. The passage of contrast medium through the sub-	fine needle in the suboccipital or lumbar region and a
	arachnoid space, including the nerve root sleeves, can	radiolabeled substance, e. g., human albumin labeled
	then be followed on the radiologic image and any ob-	with 131I, is injected into the cerebrospinal fluid. The
	structions to the flow of contrast medium can be iden-	radioactive contrast medium should be detectable one
	tified (e. g., spinal tumors). The nerve roots appear as	to two hours later in the basal cisterns, four to six hours
	filling voids within the nerve root sleeves. The bony	later over the cerebral convexity, and 24 hours later in
	spine is seen on the myelographic images as well and	the superior sagittal sinus. In normal individuals, it is
	can be evaluated at the same time.	never detected in the lateral ventricles.
	The indications for myelography and radiculography	The indications for this type of study are, for example,
	are listed in Table 4.4 together with those of other, com-	the localization of a fistula through which CSF is leaking
	peting types of study. CT and MRI have now replaced	from the subarachnoid space into the nasal cavity
	radiculomyelography for many of its earlier indications.	(where it can be detected on a nasal tampon), or the de-
		monstration of malresorptive hydrocephalus, in which
	Findings. Some of the more common myelographic	contrast medium can be seen to enter the lateral ven-
	findings are depicted schematically in Fig. 4.11. Further	tricles (Fig. 4.12).
	myelographic images can be found elsewhere in this
	book: lumbar intervertebral disk herniation, Fig. 12.7,
	p. 212; cervical myelopathy, Fig. 7.8, p. 148; spinal cord

tumors, Figs. 7.4−7.7, p. 147.

Table 4.4 Indications for contrast myelography as compared with other imaging techniques

Condition/suspected pathology	Plain	CT	MRI	Contrast myRemarks
	radio-			elography,
	graphs			radiculogra-
				phy, myelo-CT
Pain without neurologic deficit	++
Clinically localizable radiculopathy		+++	++	Plain films may be
				useful, e. g., in
				vertebral body
				tumors
Clinically evident lumbar radiculopathy with unclear CT findings				++
Suspected radiculopathy, but no clear segmental localization		+	+++
Suspected spinal cord compression		++	+++
Suspected spinal stenosis	++	++	+++
Clinically evident spinal stenosis			++	+++
Suspected myelopathy due to cervical spondylosis		+	+++	+
Suspected myelitis or demyelination			+++
+++ = most suitable study, usually adequate for diagnosis;
++ = study generally useful;

+= study occasionally necessary or indicated in addition to other tests

Fig. 4.11 Typical findings in contrast myelography (schematic diagram).

Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme All rights reserved. Usage subject to terms and conditions of license.

Imaging Studies 53

Fig. 4.12 CSF scintigram in a patient with malresorptive hydrocephalus. After injection of iodine-131-labeled human albumin into the cisterna magna, the radioactive contrast medium refluxes into the lateral ventricles, because of slow CSF flow.

a

b

Fig. 4.13 SPECT studies. a Normal study. b SPECT in a patient with Alzheimer disease. Hypoperfusion is seen bilaterally in the parietal and temporal lobes, particularly on the right. Cf. normal finding in a. c This SPECT study in a patient with medically intractable com-

4

Ancillary Tests

c

plex partial seizures, performed after the intravenous administration of 180 MBq of 133I-iomazenil, reveals diminished binding to benzodiazepine receptors in the left temporal region.

SPECT

Technique. Single photon emission computed tomography uses either a 99m-technetium compound or 133I-am- phetamine as a tracer. The purpose of this type of study is to measure regional cerebral blood flow.

Indications. SPECT can be performed to demonstrate reduced perfusion of the brain, e. g., in stroke or in Alzheimer disease, which is associated with reduced activity in the temporoparietal region (Fig. 4.13a, b). It can also be used to detect focal pathological processes of other kinds, e. g., epileptogenic foci (Fig. 4.13c).

PET

Technique. Positron emission tomography uses the short-lived positron-emitting radionuclides 11C, 14O, or 18F. This type of study can therefore only be performed near a cyclotron in which these isotopes are produced. PET can be used to produce quantitative tomographic images of regional cerebral blood flow (rCBF), cerebral blood volume (CBV), oxygen consumption (the cerebral metabolic rate for oxygen = CMRO2), and glucose consumption (CMR−Glu).

Indications. With PET, physicians can perform biochemical studies in vivo. The radioactive labeling of substances metabolized in the human brain makes it possible to measure their concentration and kinetics in specific brain areas. Thus, for example, the localization and concentration of injected DOPA can be studied in patients with suspected Parkinson disease.

adfsköb

Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme

adköb

All rights reserved. Usage subject to terms and conditions of license.