Ординатура / Офтальмология / Английские материалы / Imaging of Orbital and Visual Pathway Pathology_Muller-Forell_2005

damage to the affected brain depends on vulnerability, collateral supply, degree and duration of the cerebral ischemia (Osborn 1994d). This may result in some form of disproportion as even large ischemic areas or hemorrhagic infarction may only cause a little deficit and vice versa (Figs. 7.68, 7.71, 7.72–7.74). The complex tissue changes include loss of ion homeostasis,accumulation of Ca2+,Na+,and Cl- along with osmotically required water, and anaerobic glycolysis with production of intracellular and extracellular metabolic acidosis (Siesjö 1992).

These alterations of cell membrane function and loss of cytoskeletal integrity with subsequent cell death are reflected in standard imaging studies (Hankey and Warlow 1991). In particular, MRI studies, including T2-weighted, DWI, PWI, and MRA

sequences, identify the localization of the occlusion and also the area of brain damage earlier and more sensitively than with CT (Jansen and Brückmann 2001), but indirect signs, also known on CT, with subtle swelling of the affected gyri and compression of the sulci (Fig. 7.71) should not be disregarded. Additional FLAIR sequences enable the exclusion of intracerebral hemorrhage as sensitively as CT (Kueker et al. 2000; Lansberg et al. 2001). The acute accumulation of intraand extracellular edema induces a prolongation of both T1 and T2, resulting in a high signal intensity on T2-weighted images. The early cytotoxic edema restricts the water diffusion, resulting in a high signal intensity of infarcted tissue compared with unaffected normal brain tissue, where Brown’s molecular movement of protons is

Fig. 7.74. CT of a 41-year-old woman with acute incomplete hemianopia to the left. Diagnosis: spontaneous intracranial hemorrhage of the right thalamus, extending to the proximal part of the right optic radiation. (From Müller-Forell and Lieb 1995)

unrestricted, apparent as normal low to intermediate signal intensity on DW images (Fig. 7.71, 7.75). In the course of the infarction,hemorrhagic transformation at the gray-white matter border may become evident within the first few days, while BBB disruption is identified best after the 10th day (Figs. 7.68–7.70, 7.76, 7.77) (Osborn 1994d).

7.3.2.1.2

Others (Vasculitis, Sturge-Weber)

7.3.2.1.2.1 Vasculitis

As only 5% of cerebral infarctions is caused by nonatheromatous occlusions (Hankey and Warlow 1991), vasculitis should be taken into consideration in the differential diagnosis especially in younger patients (Ferro 1998). Vasculitis is defined by its pathological findings of inflammation and necrosis of the blood vessel walls, with involvement of virtually any size or type of organ system (Fauci et al. 1978). CNS involvement is rather uncommon, classifications vary of primary (e.g., periarteritis nodosa, giant cell arteritis, Wegener’s granulomatosis) or secondary in collagen vascular disease (e.g., systemic lupus erythematosus, rheumatoid arteritis), and infectious (e.g., bacterial, fungal) or noninfectious (e.g., immune/cellmediated, chemical/drug-induced disorders, Behçet disease (Fig. 7.78), (see chapter 6.1.3.2.1) (Banna and El-Ramahi 1991; Huss et al. 1992; Osborn 1994d;

Proebstle et al 1996; Ferro 1998; Wechsler et al. 1999), while isolated CNS vasculitis is a rather rare disorder (Block and Reith 2001). Multiple laboratory parameters [e.g., erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (CF), complement, cryoglobulin, and different antibodies] should rule out or prove a specific, systemic vasculitis, while CSF findings may be unspecific.

Clinical symptoms of patients suffering from cerebral vasculitis are variable and range from headache, meningeal irritation, and cranial nerve palsies to seizures or psychiatric syndromes and stroke, which may arise singly or in combination with the above.In case of additional neuropathy,myopathy and/or other organ involvement (liver, kidney), the clinical symptoms lead to the diagnosis of a systemic vasculitis (Block and Reith 2000).

As the pathologic process of perivascular inflammation may affect not only capillaries but also arterioles and arteries, MRI findings of patients with CNS vasculitis show various lesions (although not specific) with a simultaneous occurrence of microinfarctions, territorial and hemodynamic infarctions (Figs. 7.75, 7.76), and hemorrhages, but normal findings will not rule out a cerebral involvement (Block and Reith 2000). Cerebral angiography showing multiple arterial vessel irregularities with stenosis or vessel occlusion confirms the diagnosis (Fig. 7.75) (Osborn 1994d;

Block and Reith 2000).

7.3.2.1.2.2 Sturge-Weber Syndrome

Sturge-Weber syndrome (synonym: encephalotrigeminal angiomatosis) is a sporadically occurring phacomatosis, one of the congenital disorders, that affects both the skin and the CNS. It is characterized by a “port wine” stain of the face (nevus flammeus) in the trigeminal nerve distribution, leptomeningeal venous angiomatosis, seizures, dementia, hemiplegia, hemianopia, buphthalmos, and glaucoma. Although the etiology is still unknown, it may be an isolated and sporadic vascular malformation with faulty development of cortical venous drainage (Elster and

Chen 1990; Smirniotopoulos and Murphy 1996). The reddish-brown cutaneous stain, present at birth, is composed of abnormal, immature, small vessels with the histologic feature of both dilated capillaries as well as small veins (Enjolras et al. 1985). The intracranial involvement is always ipsilateral to the nevus flammeus of the face, affecting the occipital lobe preferentially, followed by the posterior temporal and the parietal lobe. With increasing demand of cerebral blood flow, the abnormalities of the venous drainage become

significant, leading to secondary venous hypertension and thus reduced oxygen tension, leading to electrical instability of the cortex and ultimately to seizures. In the course of the disease, cellular death enables deposition of dystrophic calcification into the atrophic cortex (Fig. 7.79), which can be seen on plain skull films (Schmauser and Bittner 1990; Osborn 1994e).

MRI is more sensitive than CT in identifying the secondary changes of the affected areas, with

cerebral cortical atrophy, (compensatory) ventricular and choroid plexus enlargement, and calvarial hemihypertrophy. The explanation for the superficial “gyriform” enhancement after application of gadolinium (Fig. 7.80) may be slowly flowing blood within the persistent plexus of the subarachnoid space and/or BBB loss within the cerebral cortex from chronic ischemia (Smirniotopoulos and Murphy

1996).

7.3.2.1.2.3 Wyburn-Mason Syndrome

Another disease in the group of neurocutaneous disorders is Wyburn-Mason syndrome. This rare genetic disease without any sex predominance represents an arteriovenous malformation (AVM) that may involve parts of or even the entire visual pathway (Wyburn-Mason 1943; Lasjaunias 1997; Moussa et al. 2001). It is characterized by a diffuse nidus extending from the retina to the (mainly) ipsilateral visual pathway on its way to the calcarine fissure with involvement of the thalamus. The defect occurs early during embryogenesis, when the medial portion of the rostral and middle primitive vascular mesoderm develops, which should supply the prosencephalon and diencephalon with nasofrontal and maxillary arteries (Kupersmith 1993c; Patel and Gupta 1990; Couly et al. 1995; Lasjaunias 1997). Associated

cutaneous, mainly facial abnormalities are infrequent, clinical symptomatology with progressive deficits and even retinal or intracranial hemorrhage develops over time. Visual or neurologic deficits depend on the site and extent of the malformation. CT and MRI show serpiginous vessels and alterations of the tissue in the vicinity of the lesion, cerebral angiography visualizes a typical network of small and/or large arterial feeders and draining veins supplying the AVM in the orbit, face, or brain (Kupersmith 1993c; Lasjaunias 1997).

7.3.2.2

White Matter Diseases and Inflammatory Lesions

White matter diseases include a broad spectrum of different disorders, associated with a wide range of diseases. The classification includes demyelinating disorders, characterized by a secondary loss of

myelin (e.g., multiple sclerosis) and dysmyelination, and conditions in which the process of myelination is disturbed,leading to abnormal,irregular myelination (e.g., damaged white matter after perinatal hypoxia or inherited metabolic disorders as leukodystrophy). Neurodegenerativediseasesincludecorticaldementia among others and also primary degeneration of the deep gray matter (e.g., Wernicke’s encephalopathy) (van der Knaap and Valk 1995d).

7.3.2.2.1

Multiple Sclerosis

The wide range of CNS diseases affecting the myelin sheath and largely sparing the axon (Okazaki 1989) include acute demyelinated encephalomyelitis (ADEM), demyelinating disorders associated with systemic diseases, and multiple sclerosis (MS) as the most common demyelinating disorder of the CNS.

However, the etiology of MS is still poorly understood. Two main theories can be distinguished: one favors genetic factors, while the other advocates environmental factors. One might be influenced by the other, so that the expression of a susceptibility gene (or genes) depends on environmental factors. The chromosomal localization of the genetic material determining susceptibility for MS is probably in or near the HLA (human leukocyte antigen) region, or its expression depends on the action of certain HLA alleles (van der Knaap and Valk 1995a). The other most likely suggested pathomechanism is an autoimmune process in a genetically primed immune system assumed to produce an abnormal response, resulting in focal episodes of immune-mediated destruction of myelin sheaths (Prineas and McDonald 1997).In a vicious circle,exogenic factors may activate T-lymphocytes, which pass the BBB, express interferon-gamma and cytokines, and act as toxic agents for oligodendrocytes. Other toxic cytokines are liberated by activated macrophages, whichagaindestroyoligodendrocytes.Inthepresence of additional BBB disruption, other immune cells, antibodies, and complements are involved in the inflammatory disease (Hickey 1991; Olson 1992;

Arnason and Reder 1994).

Theonsetof MSusuallyoccursinpatientsagedfrom 20 to 40 years (15% before 20 years of age, 10% after 50 years) with a female predominance (Osborn 1994f;

Fig. 7.79. A 7-year-old girl with occipital EEG flattening and nevus flammeus of the left face. Diagnosis: Sturge-Weber syndrome. Axial CT: gyral calcification and occipital lobe atrophy. Note the additional hemiatrophy of the left hemisphere

Edwards-Brown and Bonin 1996). Most often, the first and only clinical symptom consists of impaired vision, presenting as retro-bulbar neuritis (RBN) (see chapter 6.4.2.1), followed or combined with fluctuating periods of sensomotoric or gait disturbances. The clinical course of disease progression can be divided

into a relapsing-remitting and a chronic progressive form (Heaton et al. 1985). For the diagnosis of MS recently published new guidelines on diagnostic criteria of MS enable the physician to define the diagnosis for MS, possible MS or nor MS, replacing the diagnostic criteria of Poser et al from 1983 (McDonald et al. 2001). These guidelines include the evidence of dissemination in time and space of lesions typical for MS, objectively determined with clinical and imaging signs. The obtained imaging criteria for MS should require evidence of at least three of the four following findings:

1.one gadolinium enhancing lesion or nine T2hyperintense lesions if there is no gadolinium enhancing lesion,

2.at least one infratentorial lesion,

3.at least one juxtacortical lesion,

4.at least three periventricular lesions.

Additional findings of CSF abnormalities with the

presence of autochtone IgG production (oligoclonal bands) (McLean et al.1990),lymphocytic pleocytosis, and abnormal VEP, typical for MS (delayed but with well preserved wave form) provide supplement information (Halliday 1993) to clinical finding of neurological disturbances typical for MS.

Imaging Characteristics. MRI is the imaging tool of choice in suspected demyelinating disorders (Sartor

1992; Osborn 1994f; van der Knaap and Valk 1995a; Edwards-Brown and Bonin 1996; McDonald et al. 2001).Although the sensitivity in detecting MS lesions

is about 85% (Lee et al. 1991), the correlation of neurological symptoms and localization of imaging findings is generally poor as most foci are clinically silent (Barkhof et al. 1992), but in some cases a correlation of clinical and imaging findings is probable (Fig. 7.81). The imaging protocol should include axial and sagittal PD/T2-weighted and FLAIR sequences, where the demyelinated areas demonstrate a high signal (Filippi et al.1999a; Reiche et al.2000).The sagittal view is best in order to show the characteristic periventricular/ pericallosal, ovoid lesions (so-called Dawson’s finger), caused by the centripetal course of the medullary veins, representing the perivascular inflammation (Horowitz et al. 1989). T1-weighted native and con- trast-enhanced sequences demonstrate acute or recurrent inflammatory lesions, which normally enhance contrast media, caused by BBB disruption (Paty 1997; Fazekas et al. 1999; Reiche et al. 2000).

7.3.2.2.2

Wernicke’s Encephalopathy

Wernicke’s encephalopathy (WE) is one of multiple exogenous toxic encephalopathies, the result of the interaction of a chemical compound with the brain, preferentially affecting the so-called topistic areas of selective vulnerability, such as e.g., basal ganglia, tectum, and tegmentum and/or the periaqueductal gray matter.AsWE is caused by a nutritional deficiency of vitamin B (thiamine), it is as such not confined, but is mainly found in chronic alcoholics. The acute

onset of clinical symptoms consists of ophthalmoplegia, ataxia, and confusion, sometimes with additional peripheral neuropathy (Okazaki 1989; Galluci et al. 1990). The thiamine deficit results in a reduced function of excitable membranes, glucose metabolism, and neurotransmitter production, altogether resulting in a characteristically spongy degeneration of the neuropil, but relative preservation of nerve cell bodies, and a hypertrophy and hyperplasia of capillary and small vessels may show fresh petechial hemorrhage. The lesions are distributed symmetrically in the diencephalon along the brainstem, involving the mammillary bodies, the periaqueductal gray matter, and the thalami around the third ventricle (Witt 1985; Okazaki 1989; van der Knaap and Valk 1995c). The chronic stage of WE corresponds to Korsakoff disease, with consistent atrophy of the mammillary bodies and variable involvement of the dorsomedial nuclei of the thalamus (van der Knaap and Valk 1995c).

MRI reflects the pathological findings with hyperintensities on T2-weighted images at the periventric-

ular nuclei of the thalami and mammillary bodies (Fig. 7.82); in acute stages, a contrast enhancement may be seen (Fig. 7.83) (Schroth et al. 1991).

7.3.2.2.3 Sarcoidosis

Sarcoidosis is a systemic granulomatous disease of unknown origin.With a slight predilection for women, most patients are younger than 40 years old and present with hilar adenopathy, anergy, hypercalcemia, uveitis, and a positive Kveim test. In up to 10% of the patients, neurologic involvement is evident, in rare cases as the only clinical manifestation (neurosarcoidosis) (Clark et al. 1985; Hayes et al. 1987; Zajicek et al. 1999). Histopathologic findings typically consist of noncaseating granulomas closely related to blood vessels in the leptomeninges, mostly around the base of the brain and in the posterior fossa. In some cases, an intraparenchymal extension via the Virchow-Robin spaces is seen, whereas cranial nerve