Clinical Pathways in Neuro-ophthalmology : An ... - E-Lib FK UWKS

200 Clinical Pathways in Neuro-Ophthalmology, second edition
Although the study of Wilhelm et al suggests that a RAPD may occasionally be present
with lateral geniculate body or parageniculate optic radiation lesions (Wilhelm, 1996),
this observation has not been confirmed by other investigators.
Although lesions of the optic tract or lateral geniculate body often cause incongruous
field defects, two relatively specific patterns of congruous homonymous field defects
with abruptly sloping borders, associated with sectorial optic atrophy, have been
attributed to focal lesions of the lateral geniculate body caused by infarction in the
territory of specific arteries. Occlusion of the anterior choroidal artery may cause a
homonymous defect in the upper and lower quadrants with sparing of a horizontal
sector (quadruple sectoranopia) (Luco, 1992). This defect occurs because the lateral
geniculate body is organized in projection columns oriented vertically that represent
sectors of the field parallel to the horizontal meridians, and the anterior choroidal artery
supplies the hilum and anterolateral part of the nucleus. Bilateral lateral geniculate
lesions may therefore cause bilateral hourglass-shaped visual field defects (Donahue,
1995) or bilateral blindness. In three reported cases of isolated bilateral involvement of
the lateral geniculate bodies, the pathogenesis included anterior choroidal syphilitic
arteritis, methanol toxicity-producing coagulative necrosis of the lateral geniculate body,
and geniculate myelinolysis associated with the rapid correction of hyponatremia,
respectively (Donahue, 1995). Barton described another patient with bilateral sectoranopia
(‘‘hourglass’’ pattern) due to probable osmotic demyelination (Barton, 2001).
Interruption of the posterior lateral choroidal artery that perfuses the central portion of
the lateral geniculate causes a horizontal homonymous sector defect (wedge shaped)
(Borruat, 1995; Luco, 1992; Neau, 1996; Wein, 2000). In posterior lateral choroidal
territory infarction, the homonymous quadrantanopia may be associated with hemisensory
loss and neuropsychological dysfunction (transcortical aphasia, memory disturbances),
and delayed contralateral abnormal movements (Neau, 1996). A homonymous
horizontal sectoranopia is not diagnostic of a lateral geniculate body lesion, however, as
a similar sector defect may occur with lesions affecting the optic radiations (Carter, 1985)
or, rarely, the occipital cortex in the region of the calcarine fissure (Grossman, 1990),
the temporooccipital junction, the parietotemporal region, or in the distribution of
the superficial sylvian artery territory (Growchowicki, 1991). Finally, a patient has
been described with bilateral lateral geniculate lesions with bilateral sector defects
with preservation of the visual fields in an hourglass distribution (Greenfield, 1996).
The patient was a 28-year-old woman who developed incongruous binasal and bitemporal
visual field defects 1 week after having a febrile gastroenteritis, characterized
by severe diarrhea, while traveling in Mexico. MRI demonstrated bilaterally increased
signal intensity within the lateral geniculate bodies. The severe diarrhea was thought to
be associated with an aseptic bilateral lateral geniculitis resulting in the hourglassshaped
visual fields.
Patients with lesions of the lateral geniculate body may have no other signs or
symptoms of neurologic involvement or may have associated findings related to
thalamic or corticospinal tract involvement. Etiologies for lateral geniculate damage
include infarction, arteriovenous malformation, trauma, tumor, inflammatory disorders,
demyelinating disease, and toxic exposure (e.g., methanol) (Borruat, 1995; Donahue,
1995; Greenfield, 1996; Groomm, 1997; Kosmorsky, 1998; Luco, 1992; Neau, 1996). MRI,
with attention to the lateral geniculate region, is indicated in all cases (Borruat, 1995;
Horton, 1990; Neau, 1996).