Diagnostic and Interventional Imaging (2013) 94, 957—971
CONTINUING EDUCATION PROGRAM: FOCUS. . .
Imaging of the optic chiasm andretrochiasmal visual pathways
N. Menjot de Champfleura,∗,S. Menjot de Champfleura, D. Galanaudb,N. Leboucqa, A. Bonaféa
a Service de Neuroradiologie, Hôpital Gui-de-Chauliac, CHRU de Montpellier, 80, avenueAugustin-Fliche, 34295 Montpellier cedex 5, Franceb Service de Neuroradiologie, Groupe Hospitalier Pitié-Salpétrière, Paris, France
KEYWORDSBrain;Cranial nerves;Orbits;MRI
Abstract The exploration of the chiasmal and retrochiasmal visual pathways is based on mag-netic resonance imaging. A bitemporal hemianopsis suggests a lesion of the optic chiasm whilehomonymous lateral hemianopsis should lead to a search for a lesion of the retrochiasmal visualpathways. The causes of chiasmal impairment are mainly tumoral. The exploration protocol isbased on MRI with T1-weighted sagittal sections, then T2- and T1-weighted coronal sections
The visual field is studied separately for each eye. The examination may involve a simpleclinical examination where the examiner presents either one of his fingers or a white ball,starting from the periphery and moving towards the centre in different sectors of the visualfield. Campimetry is a dynamic monocular exploration of the visual field on a flat screen
while perimetry is a dynamic monocular exploration of the visual field.
To analyse the results, it is necessary to take into account the fact that, for eacheye, the nasal hemiretina receives light rays from the temporal visual hemifield and thatthe temporal hemiretina receives light rays from the nasal visual hemifield. Both left
∗ Corresponding author.E-mail address: [email protected] (N. Menjot de Champfleur).
isual hemifields, corresponding to the right temporal andeft nasal hemiretinas, project themselves on the right fis-ure, while the right visual hemifields corresponding to theeft temporal and right nasal hemiretinas project themselvesn the left calcarine fissure.
ampimetryhe campimetre screen: a test light is moved along a flatcreen and its position is noted as soon as it is perceived. Thisimple method analyses the central visual field in a dynamicanner.Friedmann’s analyzer (static perimetry) is a fast method
o explore the central visual field: static white test lights ofhe same diameter are presented and their light intensity isodified.Amsler grids: the subject looks at the small dot in the
entre of a 10 cm grid and specifies whether he sees wavyines, a deformation or if lines are missing from the grid.his method detects small central scotomas.
erimetryerimetry uses a bowl-shaped screen, adapted to the curvef the eye. The projected tests are thereby at equal distancerom the eye.
inetic perimetryinetic perimetry is carried out with Goldman’s perimeterGoldman bowl). The visual field registers on a diagramhere the centre is the point of fixation corresponding to
he macula. The Mariotte blind spot corresponds to a holen the visual field, due to the optic papilla (zone of abso-ute scotoma or negative temporal paracentral physiologicalcotoma).
utomated perimetryore specific, automated perimetry helps visualize the
ntensity of impairment. Humphrey perimetry is most oftensed to study the central visual field. This perimetry is static,arried out by a computer.
hat imaging protocol?
he exploration of the chiasm and retrochiasmal visual path-ays relies on magnetic resonance imaging. If a lesion of
he optic chiasm is suspected, the millimetric acquisitionsn T2 and T1 weighting with and without contrast infusionre carried out in the three planes. If the level of suspectedmpairment is that of the optic tracts or optic radiations,he exploration will cover the entire brain, in T2 and T1eighting, without and then after contrast infusion, and
nclude diffusion imaging. The examination will be com-leted, if necessary, by perfusion imaging, spectroscopicmaging, and in case of vascular lesion, by angiographicmaging.
natomical-physiological review
he optic chiasm
t receives the optic nerves by its anterior angles and emitshe optic tracts by its posterior angles. The nerve fibres
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rom the two nasal hemiretina cross over there. In fact,he nerve fibres arising in each of the temporal hemiretinaeach the homolateral optic tract, while those coming fromach of the two nasal hemiretina reach the contralateralptic tract, the macular bundle comprising both direct androssed fibres. It is located in the chiasmal cistern, behindhe tubercle of sella turcica, behind the chiasmal groovelocated at the posterior part of the sphenoid planum),bove the sella turcica. The normal dimensions of the chi-sm are 8 mm (4—13 mm) in anterior-posterior diameter and—5 mm thick.
he tractus optici or optic tract
ach optic tract is formed by the temporal bundle comingrom the homolateral retina, and by the nasal bundle comingrom the contralateral retina as well as the macular fibresriginating in both retinas.
The tractus optici or optic tract starts at the posterior-ateral angle of the chiasm. It runs laterally and behind thenterior perforated substance and the tuber cinereum, andhereby forms the anterior-lateral limit of the interpedun-ular cistern. It runs around the upper part of the braineduncle, to which it adheres (Fig. 1). In this portion ofts path, it is indivisible from the uncus and parahippocam-al gyrus. The optic tract is positioned directly above theosterior cerebral arteries and ends in the lateral genicu-ate nucleus, at the posterior-lateral side of the thalamus.ach optic tract sends two contingents of fibres, the first andost abundant to the lateral geniculate nucleus and anotherinority contingent of fibres to the superior colliculus. The
ptic tracts divide at the lateral geniculate nucleus into twoathways: a lateral pathway that enters the lateral genic-late nucleus and a medial pathway that enters the medialeniculate nucleus. The optic tracts thereby end in the lat-ral geniculate nucleus, where nerve fibres provide a relay,ut before, the bundle of papillary fibres separates from itnd reaches the pretectal region, thereby entering in theormation of the pathway of the papillary light reflex.
he lateral geniculate nucleus
he lateral geniculate nucleus is an ovoid formation associ-ting grey matter and white matter, located at the posteriornd lateral side of the pulvinar thalamus. The anterior poleingles with the optic tracts. Optic radiations emerge from
he lateral geniculate nucleus, which run towards the visualortex.
ptic radiations or geniculocalcarine tract
ratiolet radiations arise in the lateral geniculate nucleus.hey leave the lateral geniculate nucleus by forming theptic peduncle. The optic radiations then divide into threeontingents of fibres that occupy the outer part of theagittal stratum, directly outside the atrium of the lateralentricle. The optic radiations then run towards the striateortex of the occipital lobe and divide into two groups of
bres:a ventral bundle goes around the temporal lobe ofthe lateral ventricle and reaches the lower lip of thecalcarine fissure. This ventral bundle makes a loop within
Imaging of the optic chiasm and retrochiasmal visual pathways 959
Figure 1. Anatomy of the retrochiasmal visual pathways. Series of inversion-recovery T1-weighted coronal acquisitions at 3 Tesla identi-fying the prechiasmal portion of the optic nerves (a, tip of white arrow), the optic chiasm (b and c, white arrows), the optic tracts (d to i,tip of grey arrows) and the lateral geniculate bodies (j and k, tip of black arrows).
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the temporal lobe, moving forward and outside, aroundthe temporal lobe of the lateral ventricle, then runstowards the rear to join the striate cortex. This anteriordeviation of the lower optic radiations is more commonlycalled Meyer’s loop. It is located at the level of the ante-rior end of the temporal lobe of the lateral ventricle,about 1 cm outside of it;
• a dorsal bundle goes around the occipital lobe of the lat-eral ventricle and ends in the upper lip of the calcarinefissure.
Cortical centre of the visual field: striate
cortex
The cortical centre of the visual field (striate cortex orbrodmann area 17) is located at the level of the upper
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nd lower lips of the calcarine fissure, at the medial sidef the occipital lobe. Its anterior limit is the parieto-ccipital fissure, the posterior limit is the occipital pole or,f present, the lunate sulcus. The upper lip of the calcarinessure belongs to the cuneus, the lower lip to the lingualyrus.
lassification of disorders of the visualeld by chiasmal and retrochiasmal
mpairment: anatomofunctional
orrelation
he semiology of disorders of the visual field according tohe site of the lesion is summed up in Table 1.
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Table 1 Summary table of visual disorders according to the site of the lesion.
Site of the impairment Visual disorder Associated signs
Optic chiasm Sellar or suprasellar lesion:heteronymous bitemporalhemianopsia, central bitemporalscotomaSupra-chiasmatal lesion:heteronymous binasal hemianopsia
Optic tract Homonymous lateral hemianopsia Absence or pupil contraction to lightwith visual stimulation of the blindhemifield
Persistence of the pupil contraction tolight with stimulation of the blindhemifield
Optic radiations (parietal contingent) Contralateral homonymous inferiorquadranopia, full homonymous lateralhemianopsia
Persistence of the pupil contraction tolight with stimulation of the blindhemifieldAbolition of contralateral optokineticnystagmus
Visual cortex Deficiency in areas of the visual field:homonymous central hemianopsalscotomaUnilateral lesion: homonymous lateralhemianopsia with respect of macularvisionBilateral lesions: double hemianopsiaLesions located in the area striate (lipsof the calcarine fissure): homonymoussuperior or inferior quadranopiaBilateral and symmetrical lesions ofthe upper or lower lip of the calcarinefissure: inferior or superior altitudinalhemianopsiaBilateral impairment of the visual
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he scotomas
cotomas are gaps in the visual field. The ones most impor-ant to know are central scotomas related to impairmentf the macular bundles. The central scotoma occupies theacular visual field around the fixation point. It induces aajor loss of visual acuity resulting in discomfort in every-ay life (reading). The clinical aspect varies according to theeat of the lesion:
a single or bilateral central scotoma attests to a lesion inthe optic nerve;a bitemporal central scotoma attests to a chiasmal lesion;a junctional scomota of Traquair attests to a compres-sion of the anterior angle of the chiasm and associates acentral temporal hemiscotoma on one side and an uppertemporal peripheral notch on the other side;
a homonymous central hemianoptic scotoma attests to aretrochiasmal lesion. Hemianoptic scotomas are gaps inthe visual field affecting each side of the macular visionor peripheral vision.
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he hemianopsias
his consists of a loss in visual acuity in half of the visualeld. When the limit of the impairment is horizontal, theemianopsia is said to be altitudinal, superior or inferior,epending on whether the loss in visual acuity involves thepper or lower half of the visual field.
The limit of the loss of the visual field may be verti-al. The hemianopsia is said to be homonymous when theoss in visual acuity involves both right visual hemifields oroth left visual hemifields. It is said to be heteronymoushen it involves both nasal hemifields, or both temporalisual hemifields. Macular vision is often not affected dur-ng hemianopsia due to its bilateral projection on the visualortex.
he altitudinal hemianopsiashese hemianopsias are rare, often due to bilateral occipital
esions affecting the optic radiations or the cortex itself, in
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particular during traumas. Inferior altitudinal hemianopsiais the most common of the two.
The heteronymous hemianopsiasBitemporal heteronymous hemianopsia, relatively frequentand characteristic of the chiasmal syndrome, provokes a lossof visual acuity in both temporal hemifields by affecting thefibres leaving both nasal hemiretinas. It attests to a lesionof the optic fibres that criss-cross in the optic chiasm andusually results from an external compression, in particularduring the evolution of a tumor in the sellar region. Initially,it may only affect one quadrant, usually the upper quadrant.
Binasal heteronymous hemianopsia is rare. It provokes aloss of visual acuity in both nasal hemifields by impairmentof the fibres leaving both temporal hemiretinas. It followsdirect impairment of the visual fibres to the optic nerve orchiasm. This type of hemianopsia is especially found withtumors of the third ventricle.
Therefore, heteronymous hemianopsias are due to chias-mal impairment. The chiasma syndrome is based on a triadof symptoms associating campimetric deficiency, a reductionin visual acuity and optic atrophy.
The homonymous lateral hemianopsiasDefinitionThe homonymous lateral hemianopsias are most common,attesting to a retrochiasmal lesion of the visual pathways.It may affect all of the right or left visual hemifields andare contralateral to the lesion, that is, a left retrochiasmallesion will induce right homonymous lateral hemianopsiaaffecting the nasal field of the left eye and the temporalfield of the right eye.
The impairment may only involve the upper or lowerhalf of the visual hemifields, thereby creating homonymouslateral quadrant hemianopsia (or quadranopsia). The impair-ment is sometimes even more localized, occurring in theform of a hemianoptic scotoma.
Location of the lesions responsible for homonymouslateral hemianopsiaThe lesions are found on the retrochiasmal visual pathwaysand study of the papillary light reflex may specify the loca-tion of the lesion.
Lesion of the optic tract. In unilateral lesions of theoptic tract, the homonymous lateral hemianopsia is charac-terised by the lack of pupil contraction in response to visualstimulation in the blind hemifield (Wernicke’s hemianopicpupil reaction), while the pupil contraction is normal whenthe stimulation is on the healthy visual hemifield.
Lesion of the optic radiations. When the lesionaffects the optic radiations, in their parietal or temporalpathway, the resulting hemianopsia is characterised by thepersistence of the pupil contraction in light during the stim-ulation of the blind visual hemifield.
Lesion of the temporal lobe. In the temporal syn-drome, the deficiency in the visual field is due to theimpairment of the fibres that reach the lower lip ofthe calcarine fissure, resulting in a contralateral superior
homonymous quadranopsia. It does not respect the macularvision.
The semiology of impairment to the temporal lobe is com-plex and heterogeneous. Other sensory and gnostic disorders
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ay be involved (cortical deafness by bilateral impairmentf the transverse temporal gyrus, auditive agnosia, auditoryllusions and hallucinations, olfactory disorders and balanceisorders), aphasia, or finally seizures.
When present, these seizures may be simple partialeizures. Complex visual hallucinations and illusions of anesthetic nature are then possible.
Lesion of the parietal lobe. The parietal lobe syn-rome involves a deficiency in the visual field relatedo impairment of the fibres that reach the upper lip ofhe calcarine fissure. It consists of contralateral inferioromonymous quadranopsia, even if the occurrence of com-lete homonymous lateral hemianopsia is not exceptional.
The blink reflex in response to a threat may be abolishedith parietal lesions even without hemianopsia. A conjugateye deviation is possible but, above all, the abolition of con-ralateral optokinetic nystagmus (rapid movement towardshe opposite side of the lesion) should be searched for.
The other elements of the parietal lobe syndrome maye found: objective sensory disorders and tactile agnosia,ody image disorders (hemiasomatognosia, anosognosia,nosodiaphoria in case of lesion of the minor hemisphere;utotopoagnosia, digital agnosia and right-left disorienta-ion, in case of a lesion of the dominant hemisphere), spatialgnosia, praxis disorders, language disorders and trophicisorders (amyotrophy).
Cortical lesions of the occipital lobe. Impairmentf the visual cortex (Brodmann area 17) may induce homony-ous lateral hemianopsia with respect of the macular vision
n case of a unilateral lesion, or a double hemianopsia in casef bilateral lesions. Respect of macular vision is certainlyue to its bilateral projection on the visual cortex.
Homonymous quadrant hemianopsia, whether superior ornferior, is found with localized lesions of the striate area,nly damaging one of the lips of the calcarine fissure. Theoss of vision affects the upper or lower half of the con-ralateral visual hemifield depending on whether the lesionnvolves the lower or upper lip of the calcarine fissure. Bilat-ral and symmetrical lesions of the upper or lower lip ofhe calcarine fissure are manifested by inferior or superiorltitudinal hemianopsia.
Central homonymous hemianopic scotomas have alreadyeen mentioned and correspond to deficiencies in areas ofhe visual field.
Finally, the double hemianopsis is possible and is mani-ested by the loss of peripheral vision in the entire visualeld while the macular vision may be respected.
Bilateral impairment of the visual cortex is responsibleor cortical blindless. It creates a bilateral destruction ofhe Brodmann area 17. Here, the loss of vision is totalnd affects both macular vision and peripheral vision. How-ver, the pupil reflexes are maintained. The blink reflex inesponse to a threat, and optokinetic nystagmus are abol-shed, voluntary and reflex eye movements are maintained.he duration of such cortical blindness is variable (transitoryr definitive) and may be accompanied by anosognosia withecognition disorders and visual hallucinations.
The other elements of the occipital syndrome should be
earched for: dyschromatopsia and achromatopsia, visualllusions or hallucinations in case of peri- and parastriatedesion, seizures with visual manifestations, visual agnosiatrouble recognizing objects, people or graphic symbols),
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patial agnosia, oculomotor and visual motor disorders andnally psychic disorders (transitory or lasting fixation amne-ia).
he causes of chiasmal impairment
hiasmal lesions mainly result from sellar tumors (pituitarydenomas) as well as suprasellar tumors (craniopharyn-ioma, meningioma of the tubercle of sella turcica, chiasmlioma).
umoral causes
nfrachiasmal tumorsituitary adenomahe macroadenomas (diameter greater than 10 mm) andhe invasive adenomas may be responsible for chiasmompression in case of extrapituitary extension towardshe suprasellar regions. Most cases are non-secretory asecreting adenomas are most often discovered at theicroadenoma stage.Solid macroadenoma. The (non-necrotic) solid
acroadenomas most often appear isointense to theerebral cortex in T1, isointense or slightly hyperintensend heterogeneous in T2. Contrast infusion determines anntense and homogenous enhancement. The dura materay be thickened and enhanced. GH adenomas often
ppear hypointense in T2.The relationship between the upper pole of the adenoma
n the one hand and the chiasm and the optic nerves on thether hand is best assessed on coronal sections in T2 and T1ithout injection. The chiasmal compression may be associ-ted with a hypersignal of the optic tracts. This hyperintenseignal of the optic tracts in T2 attests to an edema inducedy the blocked communication of the perivascular spacesf the nervous system with the subarachnoid space, dueo the tumoral compression [1]. The macroadenomas maye enclosed, thereby presenting regular limits, or invasive,here their contours are irregular and they often presentn extension to the cavernous sinus space. The intracav-rnous extension may be assessed using the Knosp method2].
CT imaging, carried out in bone window, reveals annlarged sella turcica, an erosion of the dorsum sellae, thin-ing and depression of the sellar floor. Giant adenomas,ften invasive, develop towards the suprasellar regions, theavernous sinus spaces, the sphenoid sinus and the basisphe-oid.
Necrotic macroadenoma. The necrotic macroadeno-as often present a hypointense central part in T1, highly
yperintense in T2, with peripheral enhancement. Theseacroadenomas with necrosis are hemorrhagic in 30% of the
ases. In CT imaging, they appear hypo-, iso-, or hyperdenseith possibility of liquid-liquid level.
In MRI, the hemorrhagic necrosis appears iso- or hyper-ntense in T1. A liquid-liquid level may be identified on
he sagittal and transverse sections, where the anteriorart appears hyperintense in T2, and the posterior partypointense in T2. The enhancement is usually peripheralnd annular.
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The sudden hemorrhagic necrosis of the macroadenomaay be associated with a clinical picture of pituitary
poplexy. In this case, the T1 hyperintensity is generallybsent and the T2 gradient echo sequence alone revealsntratumoral hyperintense areas. The hemorrhagic necrosiss identified in the acute phase by CT scan in the form ofntratumoral areas of hyperdensities. This pituitary apoplexys often associated with the thickening of the sphenoidinus.
The differential diagnosis of macroadenoma with hemor-hagic necrosis should be carried out with:
Rathke’s cleft cyst: median topography, absence of con-trast enhancement, absence of liquid-liquid level;a cystic craniopharyngioma;a giant thrombotic aneurysm.
ther intrasellar lesions responsible for chiasmalompression
Fleshy lesions enhanced by the injection of con-rast product: hypophysitis. The group of hypophysitisncludes three entities:
lymphocytic adenohypophysitis (touches the anteriorpituitary) corresponds to a lymphocytic, plasmocytic andeosinophilic infiltration of the pituitary and the pituitarystalk, with progressive appearance of a fibrosis. It isespecially found in the post-partum woman. The heightof the gland seems to be higher, of iso- or hypoitensesignal in T1 and hyperintense in T2, with intenseenhancement extending to the thickened pituitarystalk;lympocytic infudibulo-neurohypophysitis reaches the pos-terior pituitary, pituitary stalk and the hypothalamus. Itis clinically manifested by diabetes insipidus;giant cell granulomateous hypophysitis.
Other fleshy and enhanced pituitary lesions may finallyead to a compression of the intracranial portion of theptic chiasm or the optic nerve: pituitary metastases, ger-inomes, choristomas, chordomas, giant arterial aneurysmsith thrombosis.Liquid lesions. Certain liquid pituitary lesions may
ause compression of the chiasmal visual pathways: intrasel-ar subarachnoid cysts, Rathke’s cleft cyst, intrasellarraniopharyngiomas and more rarely abscesses, epidermoidysts or colloid cysts.
uprachiasmal and prechiasmal tumorsifteen to 20% of all brain tumors are located in the regionf the chiasm, including 50% pituitary adenomas, 25% cran-opharyngiomas, 10% meningiomas, and 5% gliomas.
eningiomashey account for 20% of all intracranial tumors. Whenhey are responsible for clinical signs, the meningiomasay cause visual signs, inducing unilateral central sco-
oma or monocular blindness, by compression of one of thenterior angles of the chiasm. Only meningiomas with pos-erior development induce a chiasmal syndrome. They are
ometimes responsible for a Foster-Kennedy syndrome, asso-iating unilateral optic atrophy and contralateral papillarydema, sometimes with anosmia on the side of the optictrophy. It is above all provoked by meningioma of the small
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wing of the sphenoid, olfactory meningiomas and frontaltumors.
CraniopharyngiomasThe craniopharyngiomas are embryonal tumors usuallyfound in the child. These tumors present a first frequencypeak in the child and a second peak in the adult after theage of 50. In most cases, they are located in the suprasellarregion and more rarely within the third ventricle, or evenintrasellar. Adamantine craniopharyngiomas are most com-mon in the child, associating fleshy and cystic components,and are often calcified. In MRI, the cystic portion most oftenappears hyperintense in T2 and FLAIR, of variable signalin T1. The walls of the cyst may be enhanced after injec-
tion. After injection, the fleshy component presents intenseenhancement. Papillary craniopharyngiomas are more com-mon in the adult. They are solid or solid and cystic and mostoften without calcification (Fig. 2).
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Figure 2. Craniopharyngioma in a 51-year-old patient. This nodular lesiT1 (a), heterogeneous hypersignal T2 (b and e), hypersignal FLAIR (c), egadolinium salts (d and f). It comes into contact with the posterior side
arrow). Narrowing of the retrochiasmal visual pathways is noted in the foThe CT-scan does not reveal any calcifications (i).
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ntrachiasmal tumor: optic chiasm gliomahe optic chiasm glioma arises from the proliferation of neu-ological tissue found in nerve fibres. It is found in the childnd is sometimes associated with type I neurofibromatosis.he association of a chiasmal syndrome, bilateral opticaltrophy and signs of intracranial hypertension is indicativef the diagnosis (Fig. 3).
ascular causes
neurysms of the inner carotid artery and the circle ofillis (supraclinoid aneurysms, of the anterior communicat-
ng artery or anterior cerebral artery) may cause chiasmalompression.
ost-traumatic chiasmal syndrome
t usually follows serious cranial traumas with fracture ofhe lower level of the base of the skull.
on is centred on the infundibulum of the third ventricle, in isosignalnhanced in a homogenous and massive way after the injection ofof the optic chiasm that presents a T2 hypersignal (g, tip of blackrm of a T2 hypersignal of the optic tracts (h, tip of white arrows).
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Figure 3. Mesencephalo-diencephalic glioma in a 5-year-old. Mesencephalic gliomatous infiltration in hypersignal T2, hyposignal T1,presenting several enhancements after injection, extending to the diencephalic region, the optic tracts, the optic chiasm and the prechiasmalportion of both optic nerves.
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he causes of retrochiasmal impairment
he optic tract may be damaged by a tumor, a thrombosis ofhe anterior choroidal artery, or an aneurysm of the internalarotid artery.
Lesions of the optic radiations are actually includedn those of the parietal and temporal lobes, strokes andumors being most common. Transitory deficiencies mayollow ischemia in the vertebrobasilar territory or a basilarigraine.
umoral
he symptoms most often seen with brain tumors areeadache, neurological deficiency, seizures, or visual symp-oms such as ocular motor disorders, colour vision disorders,
apillary edema or visual field disorders. The tumors mostften seen are of neuroepithelial origin (pilocytic astrocy-omas, low-grade gliomas, glioblastomas), and of secondaryrigin (intracranial metastases).
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ow-grade gliomasow-grade gliomas affect the subject between the agef 20 and 50. Beyond this age, high-grade gliomasre most often seen. They mainly involve the fronto-emporo-insular regions, and preferentially diffuse alonghe fibres of white matter [3]. This accounts for thempairment of the optic radiations. Low-grade gliomasre thereby responsible for homonymous lateral hemianop-ias where the installation is slow, over several monthsFig. 4).
These lesions appear in hyperintensity on T2 andLAIR sequences, in T1 hypointensity, not enhanced afternjection, the increase in the cerebral blood volumerCBVmax) if present, is moderate and the spectroscopynds a moderate increase in choline, a drop in N-cetyl-aspartate (NAA), without a lipid or lactate peak.
he borders of the lesions are poorly defined and theass effect is moderate. The growth of the tumor is
low, with an average diameter of under 4 mm per year4].
Imaging of the optic chiasm and retrochiasmal visual pathways 965
Figure 4. Homonymous lateral hemianopsia right in a 31-year-old patient, revealing a pilocytic astrocytoma of the left optic tract. Theents
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intraparenchymatous lesion in isosignal T1, hypersignal FLAIR presblack arrow). It induces a hypersignal of the left optic tract on the
High-grade gliomasThe anaplastic gliomas and glioblastomas are the most com-mon high-grade gliomas. Especially found in the elderly, theyall have an unfavorable prognosis.
The kinetics of tumor growth is superior than thatof low-grade gliomas, provoking fast-evolving neurologicaldeficiencies. A papillary edema of the fundus oculi may befound, attesting to intracranial hypertension. These lesionsare heterogeneous, comprising hemorrhagic or necroticrearrangements, enhanced by the intravenous injection in anodular or annular fashion, and are surrounded by an edema.In first passage perfusion, the rCBVmax is increased. In pro-ton spectroscopy, a choline peak of great amplitude, a dropin the NAA, the presence of lipids and/or lactate indicatemalignancy.
Vascular
Any sudden deficiency in the visual field, whether regres-sive or not, should raise the possibility of an ischemic orhemorrhagic vascular origin. Once the vascular origin iseliminated, the main cause of transient visual disorder ismigraine.
Ischemic vascular disease6An ischemic stroke in the posterior cerebral arteries may bethe cause of a sudden deficiency in the visual field (Fig. 5).
Cerebral venous thrombosisHemianopsis is found in 4% of all cerebral venous throm-boses, most often attesting to distress of the visual cortex
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an enhancement after the injection of gadolinium salts (c, tip of sequences (b, tip of white arrow) and T2 (e, f, g, black arrows).
5]. In the sub-acute phase, the thrombus appears in hyper-ignal T1 and T2. Venous infarctions are not systematized ton arterial vascular territory, of cortical-subcortical topog-aphy and are visible in the form of sometimes hemorrhagic2 and FLAIR hyperintensities. The presence of an endolu-inal defect is corroborated by a venous angiography-MRI
equence.
igraine with visual aura scintillating scotoma lasting for 5 minutes to 1 hour mayometimes precede a migraine. During the episode, theRI is most often normal. However, the perfusion imaging
6,7] and the T1 imaging after the injection of con-rast agent may be perturbed. The anomalies found areilations of the pial vessels [8] on the one hand and,n first passage perfusion, an elongation of the meanime of transit and the time until the crest value onhe other hand, while the cerebral blood volume andhe blood flow remain normal. These perfusion disordersay be found in migraine with [9] or without aura [10].igraines are sometimes complicated by ischemic accidents
11].
nflammatory
he other inflammatory causes group different entities. Onlywo of them will be mentioned here.
ultiple sclerosisultiple sclerosis is a common disease, affecting the young
ubject. The disease evolves in stages, the origin of a major
966 N. Menjot de Champfleur et al.
Figure 5. Ischemic stroke in the area of the posterior cerebral artery. Homonymous right lateral hemianopsia, right hypoesthesia andright hemibody weakness in an 82-year-old patient revealing an ischemic stroke in the left posterior cerebral artery. The stroke is visible int n on
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he diffusion imaging in hypersignal b = 1000 s/mm2 (a), in restrictio
isability. The lesions are typically multifocal, the seat ofnflammatory phenomena, demyelination and then a gliosis.he most common seats involve the periventricular regions,he corpus callosum, the optic pathways and in particularhe optic chiasm or optic nerves, the brain stem and theerebellum and finally the spinal cord. The lesions suggest-ng the diagnosis are of ovoid morphology, callosofugal, withhe great axis perpendicular to the ventricles. The location isreferentially periventricular predominant around the tem-oral horns of the lateral ventricles, or sub-tentorial (wherehey may involve the spinal cord). MRI provides informationbout the activity of the disease. The enhancement of theesions of active multiple sclerosis is nodular, annular or inn open ring.
arcoidosisarcoidosis is a multisystemic granulomatosis. The impair-ent of the central nervous system results from an
nfiltration of the meningeal spaces that then diffuse tohe cranial and spinal nerves, to the vessels, to theypothalamus-pituitary axis or to the brain parenchyma.he leptomeningeal impairment is manifested in the formf a contrast enhancement according to the relief of therain. The impairment of the dura mater is revealed by aiffuse or focal thickening of the meninges. Hypothalamic-ituitary and chiasmal impairment is classic, by extension ofhe meningeal granulomas of the supracellar cisterns. Thearenchymatous impairment may take the appearance of aseudo-tumor by coalescence of the granuloma that appearsn hyposignal T2, enhanced after injection. The coexistencef leptomeningeal and parenchymateous enhancement sug-ests the diagnosis (Fig. 6). The edema and mass effectre in general discrete. Hydrocephaly is often associated.nomalies of the white matter, in the form of T2 hypersig-
als, are common. Non-specific, they predominate in theegions and ventricles, and may affect the deep regionsbasal ganglia, brain stem), and are not enhanced afternjection.
osterior cortical atrophy (PCA) is a neurodegenerativeisease in the young subject, before 60 years of age,ssociating visual disorders of progressive evolution withtrophy of the posterior cortical regions. It is histologicallyelated to Alzheimer’s disease, with an atypical distribu-ion sparing the hippocampus and predominating in thearieto-occipital regions. The structural imaging classicallyiscovers focal, parieto-occipital cortical atrophy and theunctional imaging (scintigraphy) demonstrates hypoper-usion and hypometabolism of the same areas (Fig. 7)12—15].
oxic and metabolic
ypoglycemiahe brain lesions induced by hypoglycemia may affect therain cortex, the hippocampus, the splenium of the corpusallosum, the inner capsules, and the white brain matter. Inhe MRI, they appear in the form of hyperintensities in diffu-ion imaging, in restriction on the mapping of the apparentiffusion coefficient (Fig. 8), and are sometimes reversible.
tatus epilepticus prolonged state of epilepsy (status epilepticus) may behe cause of cortical (Fig. 9), or hippocampus impairment.he atypical forms involve the central grey nuclei (thala-us, striatum, cerebellum). The diffusion imaging is most
ften suggestive, revealing a non-systematized hypersignalt an arterial territory, where the evolution occurs towardsestitution ad integrum.
Imaging of the optic chiasm and retrochiasmal visual pathways 967
Figure 6. Neurosarcoidosis in a 47-year-old patient. Multiple nodular, confluent, cortico-pial enhancements of the Sylvian fissures as well
rvaiapioften reduced) [17,18], without mass effect or enhance-ment (Fig. 11). The Heidenhan form, also sporadic [19],involves an elective impairment of the parieto-occipital
as the edges of the calcarine fissure (tip of white arrows).
nausea and vomiting, awareness disorders, arterial hyper-tension and kidney failure. Most often a favouringcircumstance is found (eclampsia, transfusion, drug tox-icity). The signal modifications most often involve theposterior regions, in a bilateral and symmetrical mannerwith a vasogenic edema on the diffusion imaging (Fig. 10).They classically regress in ten to fifteen days without seque-lae. The atypical forms involve the central grey nuclei orposterior fossa, and may be hemorrhagic.
Infectious: prion infections
Prion infections (sub-acute, transmissible spongiformencephalopathies or Creutzfedlt-Jakob’s disease) may be
c
esponsible for posterior cortical impairment resulting inisual symptomatology such as cortical blindness or visualgnosia. Certain types of cortical impairment are predom-nantly found in the sporadic form of the disease, oftenssociated with bilateral striatal impairment. The topogra-hy of these cortical hypersignals is variable, fully visiblen FLAIR [16], and on diffusion imaging (the ADC is most
ortex.
968 N. Menjot de Champfleur et al.
Figure 7. Visual and cognitive disorders in a 62-year-old patient revealing posterior cortical atrophy (Benson’s syndrome). The MRI findsfocal, parieto-occipital atrophy creating a bilateral sulcal enlargement (a to e). The perfusion CT-scan reveals parieto-occipital hypoperfusion(f and g).
Imaging of the optic chiasm and retrochiasmal visual pathways 969
Figure 8. Sixty-eight-year-old, diabetic patient. The day before hospitalization, spontaneously regressive phasic disorder followed bythe installation of a coma the following day. Upon care by the emergency medical aid, capillary glycaemia at 0.14 g/L. Signal anomalies ofthe occipital forceps and the bilateral occipital subcortical white matter related to severe hypoglycemia, in hypersignal on the diffusionimaging b = 1000 s/mm2 (a, tip of arrows), in restriction on the ADC mapping (b), without translation on the FLAIR sequence.
Figure 9. Seventy-six-year-old patient with a past history of left posterior ischemic stroke, hospitalized for partial status epilepticus.The initial MRI found the old ischemic sequence (tip of arrow, d) and identified the signal anomalies of the left occipital ribbon (whitearrows), in hypersignal on the diffusion imaging b = 1000 s/mm2 (a), increase in the apparent diffusion coefficient (b), FLAIR hypersignal (c).The follow-up MRI carried out 10 days after the episode revealed a regression of the previously described lesions, in relation to the statusepilepticus.
970 N. Menjot de Champfleur et al.
Figure 10. Sixty-five-year-old patient treated by chemotherapy for a pulmonary adenocarcinoma. Emergency hospitalization for general-ized seizures and cortical blindness. An emergency MRI revealed posterior, bilateral and asymmetrical cortico-subcortical signal anomaliesin T2 (a) and FLAIR (b), in hyposignal T1 (c) presenting several ruptures of the hemato-encephalic barrier after the injection of gadoliniumsalts (d), in hypersignal on the diffusion imaging (e), attesting to a vasogenic edema on the ADC map (f). The control MRI after 1 monthreveals the ad integrum restoration on the T2 (g) and FLAIR (h) sequences.
Figure 11. Seventy-two-year-old patient presenting visual disorders for the last 3 months, then progressive, rapidly installed ataxia,followed by a behaviour disorder and extrapyramidal impairment. Signal anomaly of the cortical ribbon in hypersignal on the diffusionimaging (b = 1000 s/mm2) (a), in restriction on the ADC mapping (b), in FLAIR hypersignal (c) and T2 (d).
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Imaging of the optic chiasm and retrochiasmal visual pathwa
Conclusion
The exploration of the chiasmal and retrochiasmal visualpathways is based on MRI. A bitemporal hemianopsis shouldcall to mind a lesion of the optic chiasm while a homony-mous lateral hemianopsis should lead to a search for a lesionof the retrochiasmal visual pathways. The causes of chias-mal impairment are mainly tumoral. In view of a seeminglyretrochiasmal impairment, the tumoral or vascular originshould be suspected initially.
TAKE-HOME MESSAGES
• The exploration of the chiasmal and retrochiasmalvisual pathways is based on magnetic resonanceimaging.
• A bitemporal hemianopsis should suggest a lesionof the optic chiasm while a homonymous lateralhemianopsis should lead to a search for a lesion ofthe retrochiasmal visual pathways.
• The causes of chiasmal impairment are mainlytumoral.
Disclosure of interest
The authors declare that they have no conflicts of interestconcerning this article.
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