Other Ancillary Studies |
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Indications. The velocity and flow profile (laminar or turbulent) of the blood flowing within a particular vessel depend, among other things, on the vessel’s caliber and on the nature of its wall. Ultrasound studies aid in the detection of vascular stenosis and occlusion, vessel wall irregularities, abnormalities of the speed and direction of blood flow, and turbulent flow. Insonation of the extraand intracranial vessels (e. g., of the middle cerebral a. through the thin bone of the “temporal window,” or of the basilar a. through the foramen magnum) yields an informative picture of the current state of blood flow in the brain (Fig. 4.27). This diagnostic technique is inexpensive, non-invasive, and free of risk.
Fig. 4.27 c MR angiography reveals occlusion of the internal carotid artery.
Other Ancillary Studies
Cerebrospinal Fluid Studies
Technique. Cerebrospinal fluid is usually obtained by lumbar puncture (LP) below the level of the conus medullaris, i. e., at L4−5 (occasionally at L3−4 or L5−S1). Suboccipital puncture is fraught with a much higher rate of complications and is performed only when meningitis is suspected and no fluid can be obtained by lumbar puncture (“dry tap”), or when LP is contraindicated because of a known purulent process in the lumbar region. LP is performed with sterile technique on a patient in the lateral decubitus position (or, occasionally, sitting up). The recommended positioning is shown in Fig. 4.28. The physician performing the puncture measures the CSF pressure with a manometer and visually assesses the color of the fluid. The laboratory tests to be performed include cell count, glucose and protein content, and others (esp. cultures), depending on the clinical situation. The most important CSF tests are listed in Table 4.7.
Normal CSF values are listed in Table 4.8 together with the corresponding serum values.
Indications. Lumbar puncture is useful in the diagnosis of diseases affecting the meninges, the brain and spinal cord, and the nerve roots, which can manifest themselves with changes in the biochemical or cellular properties of the cerebrospinal fluid. The most important abnormal CSF findings are listed in Table 4.9.
Table 4.7 Clinically relevant CSF studies
Routinely performed tests pressure
color (turbidity? xanthochromia? bloody tinge?) cell count and differential
protein glucose
Tests to be performed under special circumstances immunoglobulins
IgG−albumin index oligoclonal bands
measurement of specific IgG, IgA, and IgM against Borrelia, parasites, and viruses
cultures: bacterial, fungal, viral, mycobacterial gram and Ziehl−Neelsen staining, touch prep VDRL and FTA tests for syphilis
cytological examination for malignant cells
DNA amplification (polymerase chain reaction) in suspected tuberculosis or viral diseases
cystatin C in amyloid angiopathy
antineuronal antibodies in suspected paraneoplastic syndromes
4
Ancillary Tests
Fig. 4.28 Patient position for lumbar puncture. |
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64 4 Ancillary Tests in Neurology
Contraindications. Intracranial hypertension is the most important contraindication to lumbar puncture. Before any LP is performed, the patient’s optic discs should be inspected with an ophthalmoscope to rule out papilledema. Nor should an LP ever be performed if the platelet count is below 5000/μl. It should only rarely be performed, for strict indications and with extreme caution, in anticoagulated patients or when the platelet count is below 20 000/μl.
Complications of lumbar puncture are rare overall. If the patient harbors an intracranial mass causing elevated intracranial pressure, CSF removal may be followed by herniation of parts of the brain into the ten-
Table 4.8 Normal CSF values and corresponding serum values in adults1
|
CSF |
Serum |
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Pressure |
5−18 cm H2O |
|
Volume |
100−160 ml |
|
Osmolarity |
292−297 mosm/l |
285−295 mosm/l |
Electrolytes |
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Na |
137−145 mmol/l |
136−145 mmol/l |
K |
2.7−3.9 mmol/l |
3.5−5.0 mmol/l |
Ca |
1.0−1.5 mmol/l |
2.2−2.6 mmol/l |
Cl |
116−122 mmol/l |
98−106 mmol/l |
pH |
7.31−7.34 |
7.38−7.44 |
Glucose |
2.2−3.9 mmol/l |
4.2−6.4 mmol/l |
CSF/serum glucose |
0.5−0.6 |
|
ratio1 |
|
|
Lactate |
1−2 mmol/l |
0.6−1.7 mmol/l |
Total protein |
0.2−0.5 g/l |
55−80 g/l |
Albumin |
56−75 % |
50−60 % |
IgG |
0.010−0.014 g/l |
8−15 g/l |
IgG index2 |
0.65 |
|
Leukocytes |
4/μl |
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Lymphocytes |
60−70 % |
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1Because there is normally an equilibrium between CSF and serum, it is advisable to measure CSF and serum values at the same time.
2IgG index = [CSF IgG (mg/l) serum albumin (g/l)]/[serum IgG (mg/l) CSF albumin (mg/l)]
Table 4.9 CSF analysis: main indications and findings
torial notch or the foramen magnum, potentially resulting in death. If an intraspinal mass is present, preexisting paraparesis may worsen after LP. After the procedure is performed, persistent leakage of CSF out of the subarachnoid space through the puncture hole(s) in the dura mater may result in symptomatic intracranial hypotension with orthostatic headache. Other possible complications include iatrogenic infection and epidural hematoma, potentially causing cauda equina syndrome.
Tissue Biopsies
Muscle biopsy is justified in patients with neuromuscular disease when the clinical history, physical examination, and electromyographic, chemical, and/or genetic studies fail to yield a sufficiently precise diagnosis. The biopsy should be performed under local anesthesia in a muscle that is known to be affected by the disease process, but is not so atrophic as to reduce the chance of a diagnosis. In many cases, a needle biopsy alone suffices. Depending on the clinical situation, histochemical and/or electron-microscopic study of the tissue specimen may be indicated in addition to conventional histological staining.
Nerve biopsy is performed under local anesthesia. A relatively unimportant sensory nerve is chosen for biopsy, usually the sural n. The ensuing sensory deficit on the lateral edge of the foot is generally an acceptable price to pay for a firm diagnosis, but the patient must be informed of it before granting his or her consent to the procedure. Part of the specimen is used to make a teased preparation in which nerve fibers and their myelin sheaths can be seen over a certain length of nerve. More importantly, very thin cross-sections of the nerve are prepared, which can be microscopically examined for various abnormalities, including disordered myelination or inflammatory changes of the vasa nervorum.
Brain biopsy is performed by a neurosurgeon, usually with stereotactic technique, for very strict indications.
Condition/suspected pathology |
Appearance |
Cell count and type |
Protein |
Pressure |
Special remarks |
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Purulent meningitis |
turbid |
mostly |
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possibly |
LP is urgent—the most |
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granulocytes |
|
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important diagnostic |
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|
|
|
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study |
Chronic meningitis |
clear |
mostly lympho- |
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possibly |
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|
cytes |
|
|
|
Encephalitis |
clear |
mostly lympho- |
possibly |
possibly |
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cytes |
|
|
|
Subarachnoid hemorrhage |
bloody— |
erythrocytes |
possibly |
possibly |
xanthochromia in 6 |
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xanthochromic |
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|
|
hours to 6 days |
Intracerebral hemorrhage |
xanthochromic |
possibly erythro- |
normal |
|
LP not indicated |
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cytes |
|
|
|
Subdural hematoma |
xanthochromic |
usually normal |
|
normal, , |
LP not indicated |
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Low CSF pressure syndrome |
clear |
normal |
to |
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aspirate if no spon- |
|
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taneous CSF flow |
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Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme All rights reserved. Usage subject to terms and conditions of license.
Other Ancillary Studies |
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Its purpose is the histological diagnosis of (potentially treatable) structural alterations of the brain whose presence has been revealed by imaging studies, but whose precise nature is nonetheless unclear. Examples are brain tumors and inflammatory processes.
Perimetry
Perimetry is used to detect visual field defects (p. 181).
Goldmann perimetry is a dynamic method in which moving spots of light of variable size and intensity are
presented in the patient’s visual field, starting in the periphery and moving toward the center. The findings associated with different types of visual field defect are illustrated in Fig. 3.6, p. 19.
Static computed perimetry is performed with the socalled Octopus apparatus. The brightness of a stationary light source is increased until the patient can see it. The measured brightness thresholds at all tested points in the visual field can be displayed visually as raw numbers, on a gray scale, or as a pseudo-three-dimensional visual field “landscape.” Illustrative findings in a case of homonymous quadrantanopsia are shown in Fig. 4.29.
Fig. 4.29 Automatic (Oc- |
a |
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topus) perimetry in right |
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Gray scale of measured values |
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Gray scale of measured values |
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homonymous hemianop- |
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30° |
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30° |
sia. a Gray-scale represen- |
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tation of the visual field |
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defect. b Differential value |
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chart representing the loss |
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of light sensitivity at each |
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point in the visual field, |
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measured in decibels (dB), |
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as compared to the aver- |
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age local sensitivity in a |
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normal control population. |
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There is no measurable |
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loss at the points marked |
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with solid black squares. |
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See also Fig. 3.6. |
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b |
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Differential values |
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Differential values |
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30° |
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30° |
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4
Ancillary Tests
adfsköb
Mumenthaler / Mattle, Fundamentals of Neurology © 2006 Thieme
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All rights reserved. Usage subject to terms and conditions of license.