Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" EpidemiologyFrequency: 1–2:100 000 · Peak age: 3–5 years · The disorder can manifest itselfat any age.

" Etiology, pathophysiology, pathogenesisHistopathology resembles multiple sclerosis, with acute demyelinating inflam-mation of the brain and spinal cord · In contrast to MS, the course is monopha-sic · Acute disseminated encephalomyelitis is often difficult to differentiatefrom the initial episode of MS · The cause is unknown but may represent a hy-persensitivity reaction such as can occur 1–2 weeks after infection, inoculation,or chemotherapy.

Imaging Signs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" Modality of choiceMRI.

" CT findingsMultiple, subcortical, often round hypodensities that enhance with contrast.

" MRI findingsMultiple, subcortical, often round focal lesions with high signal intensity on T2-weighted images · All lesions are in the same stage, meaning that they enhanceuniformly · Often there is a ring-shaped pattern of enhancement in the acutestage of inflammation · Enhancement decreases as the inflammation subsides ·Occasionally bull’s eye signs will be visible on T2-weighted images, lesionsshowing significant central hyperintensity (cystic necrosis secondary to demye-lination) surrounded by moderate perifocal hyperintensity (edema).

Clinical Aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" Typical presentationSimilar to multiple sclerosis, although the onset of symptoms is typically abruptand monophasic · Often accompanied by fever, meningism, mental statuschanges, and convulsions, which are nearly invariably absent in MS.

" Treatment optionsGlucocorticoids · Plasmapheresis and cyclophosphamide may be indicated.

" Course and prognosisMortality of the postinfectious form is about 10–40% · Neurologic deficits oftenpersist.

" What does the clinician want to know?Differentiate from tumor or infarction.

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Postinfectious Encephalomyelitis (ADEM)2

Inflamm

ation

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Fig. 2.5 a–d Postinfectious encephalomyelitis or acute disseminated encephalomyelitis(ADEM). Axial T2-weighted MR images (a, c) and axial T1-weighted MR images after con-trast administration (b, d). Multiple subcortical hyperintensities on T2-weighted MR im-ages that are ring-enhancing on T1-weighted MR images. Identical enhancement in all le-sions (b, d). The patient had undergone surgery to remove an oligodendroglioma and re-ceived chemotherapy several weeks previously. Right frontal postoperative tissue defect.

Postinfectious Encephalomyelitis (ADEM) 2Inflam

mation

Differential Diagnosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cerebral abscess – ADC usually reduced in cystic portion

Cerebral ischemia – Pattern of distribution corresponds to area suppliedby one or more vessels

– In acute stage is ADC invariably reduced

Parasitic disorders(such as toxoplasmosis)

– Often immunocompromised persons– CSF findings

Multiple sclerosis – Predilection for periventricular white matter

Metastases and highergrade multifocal glialtumors

– Solid portion: relative regional cerebral blood volume(rrCBV) on perfusion MR images at least twice as highas in normal white matter

Tips and Pitfalls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Misinterpreting the disorder as brain tumor or metastasis.

Selected References

Hartmann M et al. Funktionelle MR-Verfahren in der Diagnostik intraaxialer Hirntumo-ren: Perfusions- und Diffusionsbildgebung. Rofo Fortschr Geb Rontgenstr Neuen Bild-geb Verfahr 2002; 174 (8): 955–964

Niedermayer I et al. Neuropathologische und neuroradiologische Aspekte akuter dissemi-nierter Enzephalomyelitiden (ADEM). Radiologe 2000; 40 (11): 1030–1035

Schwarz S et al. Akute disseminierte Enzephalomyelitis (ADEM). Nervenarzt 2001; 72 (4):241–254

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Postinfectious Encephalomyelitis (ADEM)2

Inflamm

ation

Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" EpidemiologyPrevalence: 1–8%.

" Etiology, pathophysiology, pathogenesisAn aneurysm is dilatation of a blood vessel · Saccular aneurysms are the mostcommon form.Risk factors: Family history of intracranial aneurysms · Autosomal dominantcystic kidney disease · Fibrous dysplasia · Coarctation of the aorta · Smoking.Pathogenesis: Degeneration and weakening of the internal elastic lamina and thecollagen fibers of the arterial wall · Hemodynamic aspects.Localization: Bifurcations or origins of the following vessels in order of frequen-cy: anterior cerebral, middle cerebral, internal carotid, basilar, and vertebral ar-teries.

Imaging Signs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" Modality of choiceDSA.

" CT findingsRound to oval extra-axial hyperdensity at one of the typical locations · An aneu-rysm visible on plain CT is usually larger than 5 mm · Arterial wall calcifica-tions · Significant enhancement on CT after contrast administration and on CTangiography · A partially thrombosed vessel is recognizable as a filling defector gap in the contrast medium · Sensitivity of CT angiography for aneurysmslarger than 5 mm is about 94%; for aneurysms smaller than 5 mm it is only about60%.

" MRI findingsThe MR signal is complex because it depends on the MRI sequence and the rateand direction of blood flow · There may be partial or complete thrombosis · Sig-nal loss due to blood flow (flow void) is most apparent on proton density-weighted and T2-weighted images · The signal intensity of a suspected throm-bus depends on its age · Sensitivity of MR angiography for aneurysms largerthan 5 mm is about 86%; for aneurysms smaller than 5 mm it is only about 35%.

" DSA findingsAneurysm is visualized as a dilatation of the underlying vessel · The preciseanatomy is demonstrated (proportional relation of aneurysmal neck to sac, rela-tionship to vessels arising from the aneurysm) · DSA is also required to demon-strate smaller aneurysms (measuring less than 5 mm) in the presence of sub-arachnoid hemorrhage · DSA aids in planning treatment and in determiningwhether the aneurysm can be treated by occlusion of the underlying vessel (col-lateral circulation).

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Saccular Aneurysm3

Aneurysm

s

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Fig. 3.3 a–c Saccular aneurysm of thetrifurcation of the right middle cerebral ar-tery. Axial T2-weighted MR image (a), co-ronal DSA after injection of the right inter-nal carotid artery (b) and 3D rotational an-giogram (c). Oval signal void originating atthe main trunk of right middle cerebral ar-tery (a, arrows). Vascular dilatation mea-suring approximately 15 mm (b, c).

Saccular Aneurysm 3A

neurysms

Clinical Aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" Typical presentationUsually asymptomatic · Oculomotor and trochlear nerve palsy with impairedvision · Headache · Thromboembolic disease with ischemic stroke from parti-ally or completely thrombosed aneurysms · The most severe complication isrupture with subarachnoid hemorrhage.Estimated cumulative rupture risk over 5 years:– Aneurysm less than 7 mm: 0% (internal carotid, anterior cerebral, middle ce-

rebral arteries) or 2.5%, respectively (vertebral and basilar arteries).– Aneurysm measuring 7–12 mm: 2.6% (internal carotid, anterior cerebral, mid-

dle cerebral arteries) or 14.5%, respectively (vertebral and basilar arteries).– Aneurysm measuring 13–24 mm: 14.5% (internal carotid, anterior cerebral,

middle cerebral arteries) or 18.4%, respectively (vertebral and basilar arteries).– Aneurysm larger than 24 mm: 40% (internal carotid, anterior cerebral, middle

cerebral arteries) or 50%, respectively (vertebral and basilar arteries)." Treatment options

Coiling · Where coiling is not feasible, clipping." Course and prognosis

Subarachnoid hemorrhage is fatal in 30% of cases, in 30% it leads to disability,and in 30% there are no neurologic deficits.

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Fig. 3.4 a, b Aneurysm of the tip of the basilar artery. Coronal DSA after injection of theleft vertebral artery. Aneurysm measuring approximately 10 mm before (a) and after (b)endovascular embolization (coiling) with platinum coils.

Saccular Aneurysm3

Aneurysm

s

Ruptured aneurysm: Risk of severe disability or death after coiling is about 24% ·Risk of severe disability or death after clipping is about 31%.Unruptured aneurysm: Morbidity after coiling is about 5% · Morbidity after clip-ping is about 10%.

" What does the clinician want to know?Size · Localization · Number and anatomy of aneurysms.

Differential Diagnosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Vascular sling – Several different views with demonstration of thesling

Infundibular vascularorigin

– Symmetrical origin of arising vessel

Extra-axial brain tumor(can be confused withthrombosed aneurysm)

– Thrombus usually does not enhance

Venous aneurysm inarteriovenous mal-formation (AVM)

– AVM demonstrated on DSA

Tips and Pitfalls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Thrombosed aneurysms on TOF MRA (without contrast enhancement) appear hy-perintense like flowing blood.

Selected References

Jayaraman MV et al. Detection of intracranial aneurysms: multi-detector row CT angiog-raphy compared with DSA. Radiology 2004; 230 (2): 510–518

Molyneux A et al. International Subarachnoid Aneurysm Trial (ISAT) of neurosurgical clip-ping versus endovascular coiling in 2143 patients with ruptured intracranial aneu-rysms: a randomised trial. Lancet 2002; 360 (9342): 1267–1274

Wanke I et al. Intrakranielle Aneurysmen: Entstehung, Rupturrisiko, Behandlungsoptio-nen. Röfo Fortschr Geb Röntgenstr Neuen Bildgeb Verfahr 2003; 175 (8): 1064–1070

Weir B. Unruptured intracranial aneurysms: a review. J Neurosurg 2002; 96 (1): 3–42Wiebers DO et al. Unruptured intracranial aneurysms: natural history, clinical outcome,

and risks of surgical and endovascular treatment. Lancet 2003; 362 (9378): 103–110

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Saccular Aneurysm 3A

neurysms

Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" Etiology, pathophysiology, pathogenesisPrimary neurulation disturbance (defective closure of the neural tube) in thefourth to fifth weeks of pregnancy.Chiari I malformation: Slight incongruity between the posterior cranial fossa(slightly too small) and the cerebellum (normal size), resulting in low-lying cer-ebellar tonsils · Associated malformations: hydrocephalus, syringomyelia, skel-etal anomalies (basilar invagination, Klippel–Feil syndrome, atlantoaxial fusion).Arnold–Chiari malformation (Chiari II malformation): Complex anomaly withskull, dural, brain, spinal, and spinal cord manifestations · Associated malfor-mations: almost invariably lumbar myelomeningocele, syringomyelia (50–90%), diastematomyelia, anomalies of the corpus callosum, heterotopia.Chiari III malformation: Arnold–Chiari malformation with deep occipital or highcervical encephalocele with cerebellar herniation.

Imaging Signs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" Modality of choiceMRI.

Chiari I Malformation" CT findings

Abnormally high quantity of brain tissue in the foramen magnum · There maybe ventricular enlargement · Narrowed peripheral CSF spaces above the surfaceof the cerebellum.

" MRI findingsTriangular tonsils · Narrowed peripheral CSF spaces above the surface of the cer-ebellum · Low-lying cerebellar tonsils, more than 5 mm below the level of theforamen magnum (opisthion–basion line) · Syringomyelia in 20–40% of all pa-tients · Reduced CSF flow in the foramen magnum.

Arnold–Chiari Malformation (Chiari II Malformation)" CT findings

Calvarial defects · Concave clivus." MRI findings

Extreme elongation of the cerebellar tonsils, which can extend to the level of theC4 vertebra · Elongated fourth ventricle · Beak-shaped tectum · Z-shaped kinkat the junction of the medulla oblongata and cervical spinal cord · Interdigita-tion of the gyri of the cerebral hemispheres · Cerebellum is pressed against thebrainstem and bulges superiorly past the tentorial notch · Hydrocephalus ·Large interthalamic adhesion · Fenestrated flax cerebri · Low-lying transversesinus and confluence of sinuses · Narrowed posterior cranial fossa, concave cli-vus.

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Chiari Malformations11

CongenitalMalform

ations

Clinical Aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

" Typical presentation/Course and prognosisChiari I malformation: Fifty percent of all cases are asymptomatic · Brainstemcompression produces cranial nerve dysfunction · Somnolence · Neck pain ·Symptomatic syringomyelia can imitate the clinical picture of multiple sclerosis.Arnold–Chiari malformation (Chiari II malformation): Myelomeningocele · Mac-rocephaly · Sphincter weakness · Bulbar signs · Elevated a-fetoprotein.

" Treatment optionsTreatment of myelomeningocele or hydrocephalus where present · Decompres-sive osteotomy of the foramen magnum.

" What does the clinician want to know?Follow-up with hydrocephalus · Demonstrate associated malformations such asmyelomeningocele.

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52

3

6

10

9

1

4

8

7

Fig. 11.1 Schematic diagram of the pathology in Arnold–Chiari malformation (1 =elongated fourth ventricle; 2 = pronounced elongation of the cerebellar tonsils displacedinto the spinal canal; 3 = spinal cord “spurs” 4 = spinal cord kink; 5 = cerebellum pressedagainst the brainstem; 6 = low-lying confluence of the sinuses; 7 = concave clivus;8 = beak-shaped tectum; 9 = large interthalamic adhesion; 10 = partial agenesis of thecorpus callosum).

Chiari Malformations 11CongenitalM

alformations

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Fig. 11.2 Chiari I malformation. SagittalT1-weighted MR image. Low-lying cere-bellar tonsils, approximately 10 mm low-er than the foramen magnum, are theonly abnormal findings.

Fig. 11.3 a, b Arnold–Chiari (Chiari II) malformation. Sagittal T2-weighted MR image (a)and axial T1-weighted MR image (b). Beak-shaped tectum, hydrocephalus, and a nar-rowed posterior cranial fossa (a). Meshing of the gyri (b; arrows).

Chiari Malformations11

CongenitalMalform

ations

Differential Diagnosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Acquired low-lying cerebellar tonsils in thepresence of basilar impression or elevatedintracranial pressure

– Basilar impression– Elevated intracranial pressure

Hydrocephalus from other causes – Demonstrate the cause, best donewith MRI

Selected References

McLone DG et al. The Chiari II malformation: cause and impact. Childs Nerv Syst 2003; 19(7–8): 540–550

Naidich TP et al. Computed tomographic signs of the Chiari II malformation. Part I: Skulland dural partitions. Radiology 1980; 134 (1): 65–71

Shuman RM. The Chiari malformations: a constellation of anomalies. Semin Pediatr Neu-rol 1995; 2 (3): 220–226

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Chiari Malformations 11CongenitalM

alformations