Neuroanatomy Draw It To Know It

398 Neuroanatomy: Draw It to Know It

Visual Field Defi cits (Cont.)

Case VIII (Advanced )

Patient presents with blurry vision in the right eye. Exam
reveals a central scotoma in the right eye, only.
Our diagnosis is a right-side retinal lesion, specifi -
cally a lesion within the macula. Th e restriction of
the defi cit to one eye makes this a prechiasmatic lesion,
localizing to either the retina or optic nerve. However,
the limited pattern of visual fi eld defect allows us to
further localize this as a retinal lesion (with the caveat
noted at the end). Retinal lesions typically parse into the

following categories: central or cecocentral scotomas

from injury to the papillomacular bundle; arcuate fi eld

defects, which obey the horizontal meridian; and tem-

poral wedge defects from nasal retinal wedge fi ber injury.

We must appreciate, however, that a partial optic nerve

injury can potentially assume the same defi cit pattern as

any retinal layer injury, and we must go beyond visual

fi eld testing to distinguish the localization of a prechias-

matic lesion.^14

Case IX ( Advanced )

Patient presents with bilateral visual loss. Exam reveals
a central scotoma on the right and a left superior
quadrantanopia.
Our diagnosis is a junctional scotoma. To understand
the pathogenesis of junctional scotoma, show a fi ber
project from the left nasal hemiretina through the optic
chiasm, and then bend anteriorly into the contralateral
optic nerve (the nerve on the right) before projecting
posteriorly into the right optic tract. Indicate that this
bend is called Wilbrand’s knee, and show that it carries
inferonasal fi bers. Wilbrand’s knee has actually been
proven to be an artifact of pathologic processing and not
a true anatomic entity; however, it is still commonly dis-
cussed and still teaches us about the separation of the
inferior and superior nasal projections. Although the
bend into the optic nerve does not exist, the inferonasal
fi bers do collect in the anterior optic chiasm and the supe-
ronasal fi bers do collect in the posterior optic chiasm.^15 , 16
Junctional scotoma is a lesion at the junction between
the optic nerve and optic chiasm. Two forms of anterior
junctional defect are commonly recognized: junctional

scotoma (aka anterior junction syndrome) and junc-

tional scotoma of Traquair. Both forms of anterior junc-

tional defect involve the ipsilateral optic nerve. Junctional

scotoma results in an ipsilateral central scotoma (from

subtotal involvement of the ipsilateral optic nerve) and

contralateral superior temporal quadrantanopia from

injury to the crossed inferonasal fi bers from the opposite

eye. Whereas, junctional scotoma of Traquair is an ante-

rior junction injury with isolated ipsilateral optic nerve

defi cit and results in an ipsilateral temporal hemifi eld

defect, only.^15 , 17 , 18

Let’s not let the diff erences of the junctional scotoma

and junctional scotoma of Traquair distract us from a

key similarity between the two. Both syndromes are

perichiasmatic, and yet they both can easily be mistaken

for optic nerve lesions. Distinguishing perichiasmatic

from optic nerve lesions is important because perichias-

matic lesions are almost universally secondary to para-

sellar tumors or aneurysms, whereas optic nerve lesions

occur from both compressive and also noncompressive

causes.^15 , 17 , 18