Inflammatory diseases of the central nervous system

Causes of inflammation:

123 Bacterial: e.g.:

 Meningitis

 Parenchymal, circumscribed (abscess, disseminated septic)

 Tuberculosis

Clinical symptoms: the bacterial infection can be due hematogenous dissemination, due to the continuous spread of an infection or secondary to trauma.

An aseptic form is also differentiated (lymphocytic, viral).

In tuberculosis meningitis can turn to a chronic infection (tuberculous basal meningitis) Localization: can occur at the vicinity of an external infection, entry point, it can also spread in the basal cisterns, it can spread along the subarachnoid space and penetrate inside the sulci.

Meningitis has to be based on the clinical data: liquor pressure, cytology, meningeal signs.

Diagnostic imaging is mostly restricted to detect its complications.

Radiology: Negative scans are not uncommon, the ventricles can appear expanded at an early stage.

Contrast agent enhancement can be noted in the meninges / along the dura mater not just at the dural base (TB) but also in the sulci (bacterial - frontoparietal) on both CT and MRI.

Abscess:

Clinical symptoms: It can be secondary to the invasion of an inflammatory disease (otitis, mastoiditis, sinusitis), thus abscess localization is determined by the site of the original infection. Traumatic origin is rare, postoperative complications are a lot more common.

Abscesses that develop from a hematogenous dissemination (endocarditis, pneumonia) are usually multiplex.

In case of uncontrolled states mulilocular states can develop and produce complications such as meningitis, ependymitis or in cases of ventricular breach, ventriculitis.

Localization: according to its infectious source (see above) Radiology:

CT:

In the early stages (cerebritis) the imaging results can be normal,

perifocal edema might be apparent or mass effect might be visible. In some cases, gas production can occur (its localization is influenced by the supine position of the patient).

In more advanced stages of abscess development (―mature‖ abscess, early capsule phase) the central hypodensity deepens further, the rim of enhancement becomes better defined and thin.

The multilocular appearance is also possible. A slight vasogenic edema is seen outside the

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enhancing rim of the abscess.

In the late capsule phase – during the healing process – the central necrotic lesion starts shrinking while the capsule (granulation tissue) begins to thicken. The mass effect and the edema begins to moderate.

Tuberculosis:

Clinical sings: it is usually a complication of the secondary stage of TB infection. There are three forms of TB differentiated in the CNS, each of them having a different predilection sites:

 Leptomeningeal TB (tuberculous basal meningitis) + extracerebral tuberculosis

 Pachymeningeal TB

 Intraparenchymal TB

Radiologically the density, or the signal intensity of meningeal TB is not different from any abscess. It also shows a pronounced contrast enhancement.

Tuberculoma (intraparenchymal form) needs to be differentiated from other space occupying lesions of the brain.

One of the goals of radiologic examination is to monitor their most common complication, hydrocephalus that is present in 3/4ths of the cases. Other tasks are to identify possible

cerebral infarcts (in more than 1/3rds of the cases) as well as radiology needs to inform/follow up meningeal – ependymal sclerosis.

Viral inflammations (encephalitis):

The cause of encephalitis is usually a viral infection of the central nervous system. The most common form is herpes encephalitis, that is neither epidemic nor sporadic and cannot be connected to any seasonal occurrence. Acute and chronic encephalitis are differentiated.

MRI is the method of choice for examination.

Localization might be typical of certain types of encephalitis.

Demyelinating diseases:

The method of choice is MRI

It is a very important field of MR diagnostics, since none of the other imaging methods can compete with the sensitivity of MRI in relation with demyelinating diseases. Today, the suspicion of multiple sclerosis is the primary indication for a cerebral MRI examination. In about 90% of the cases a certain diagnosis can be reached with its help. However, it is not just multiple sclerosis, but other demyelinating diseases (leukoencephalopathies,

leukodystrophies) that can also be identified only with MRI.

125 Multiple Sclerosis:

Multiple sclerosis typically appears with lesions presenting in the hemispheric white matter with a periventricular predilection. Other less usual locations for MS lesions include the cerebellum and the pons.

In the later stages the periventricular lesions can become confluent.

The method of choice for the imaging of multiple sclerosis is MRI. MS lesions secondary to their increased water content appear as increased signal intensity lesions on (T2 weighted), PD images and on FLAIR sequence.

Figure 20.: Left fronto-parietal abscess, ring-like enhancing wall. a) Contrast enhanced CT és b) MRI T1W (air bubble)

Figure 21.: MS (Multiple Sclerosis), MRI sagittal T2W hyperintensive nodules 10.1.3.4. Developmental disorders of the central nervous system:

Developmental disorders are characterized by the complete lack or the partial development of the normal anatomic structures. MDCT with coronal and sagittal reconstructions is able to provide a detailed anatomic image that is capable to show developmental anomalies (except for migration disorders).

MRI examination with its multiplanar imaging ability is capable to produce an excellent anatomic image with T1 weighed sequences.

Arnold – Chiari malformation

Type I. the cerebellar tonsil appears pointy and extends below the level of the foramen magnum, but it does not exceed 5 mm. In Type II. the caudal part of the cerebellum also extends below the foramen magnum while the medulla oblongata and IV. ventricle sink to the widened segment of the spinal canal. It is accompanied by neural tube closing disorders.

Type III is the combination of type II. with occipital cephalocele.

Radiologically they are the best depicted in sagittal (+ coronal) imaging planes.

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Corpus callosum

Developmental disorders: Grades of developmental anomalies can be found from partial development (dorso-rostal appearance according to its developmental process) to the complete agenesis of corpus callosum.

Radiology: due to its lack, the sulci can extend down to the level of the 3rd ventricle.

CT: coronal plane (tall 3rd ventricle) and sagittal reconstructions are needed.

MRI: In adults the lack of the hyperintense white matter components of the corpus callosum is easily distinguishable from grey matter on T1 weighed images. No cingulate gyrus is apparent either.

Dandy-Walker spectra

The imaging spectra can constitute of cases of simple hypoplasia of the cerebellar vermis; at other times, the 4th ventricle can show various grades of expansion together with the

elevation of the tentorium (the confluence of sinuses is elevated). The gravest form of these states is the consequential development of hydrocephalus.

The common characteristics of Dandy-Walker syndrome include expanded posterior fossa with a large liquor cyst, the lack of the 4th ventricle, elevated tentorium, bulked occipital bone with thin internal lamina (scalloping).

Its mildest form is mega cisterna magna that does not cause any compression nor does it create any hypoplasia of the vermis and even the 4th ventricle is preserved.

Developmental abnormalities of the cortex, migration disorders

Microlissencephaly: is represented by a small skull and decreased gyrification.

Hemimegalencephaly: is the enlargement of a cerebral hemisphere or the enlargement of one isolated part of the brain.

Disorders of the neuronal migration: the neurons in their migration – in a nodular or fusiform manner – are hindered or they lose their track. Heterotopy, lissencephaly (agyria, pachygyria) Cortical organization disorders include polymicrogyria and schizencephaly (opened –

communicates with the CSF, closed – does not communicate with CSF)

MRI is the imaging method of the cortical migration and organization disorders (strong T1 weighted imaging).

22. Arnold Chiari 23. Dandy Walker

127 10.2. Spine

10.2.1. Imaging methods 10.2.1.1. X-ray

Radiographs are especially useful to detect degenerative bone diseases (spondylo/phytes);

structural abnormalities of the bones (e.g.: primary – hemangioma, secondary – metastatic bone destruction or osteoplastic lesions);

developmental disorders and instability (dynamic /functional), and is also capable to depict traumatic bone lesions (fractures).

Myelography:

Conventional myelography due to its invasive nature is not used for diagnostic purposes any more. MRI myelography provides an equal diagnostic gain and can readily replace its conventional predecessor.

CT myelography is still applied in exceptional cases during which intrathecal contrast material is necessary to be injected. It is still recommended if the communication of the cerebrovascular fluid spaces (e.g.: CSF leakage) is needed to be determined, for which MRI is not completely informative.

10.2.1.2. CT

It can depict bone abnormalities. Reconstructions in the transversal plane are able to represent complex fractures or depict the spinal architecture. 3D HRCT reconstructions provide detailed spatial representations. In cases when MRI examination is contraindicated CT is able to provide some information on herniated intervertebral discs. However, CT is not able to depict the intraspinal status. The use of X-ray exposition on young and fertile female patients for lumbar spine imaging has to be avoided; the method of choice is MRI.

10.2.1.3. MRI

As opposed to CT examination MRI, thanks to its superior soft-tissue contrast, is excellent for the representation of intraspinal structures. Depending on the magnetic field strength /

resolution ability it is a unique imaging method of the spinal chord.

In document Development of an electronic educational material for the analysing of the structures and the bio-chemical processes of living organisms by imaging technology (Pldal 123-129)