Junctional Scotoma and Junctional Scotoma of Traquair
Junctional scotoma and the junctional scotoma of Traquair are visual field defects that arise from damage to the junction of the optic nerve and the optic chiasm. Sellar masses including pituitary tumors are the most common cause of these visual field defects. Ophthalmologic findings include ipsilateral central scotoma and contralateral superior temporal quadrantanopia (junctional scotoma, JS) or monocular nasal or temporal hemianopia, junctional scotoma of Traquair (JST).
Optic Chiasm Anatomy
The optic chiasm is formed by the union of the two optic nerves. At the junction of the optic nerve with the chiasm, 53% of the fibers from the nasal hemiretina of each eye will cross over while the fibers from the temporal hemiretina (47%) of each eye remain uncrossed. The optic chiasm has a transverse length of 12 - 18 mm, an anteroposterior width of 8 mm, and a height of 4 mm. It lies over the sella turcica and the pituitary gland. The optic chiasm is in direct contact with cerebrospinal fluid in the subarachnoid space anteriorly and forms the floor of the third ventricle posteriorly.
Lesions that produce the junctional scotoma or the junctional scotoma of Traquair are typically extrinsic compressive mass lesions at the junction of the optic nerve and the chiasm. Other demyelinating, infectious, inflammatory, infiltrative, traumatic, and other etiologies can occur in this location however. Below are some common compressive causes of the junctional scotoma and the junctional scotoma of Traquair:
- Suprasellar tumors (commonly pituitary adenoma)
- Suprasellar meningioma
- Aneurysms of the internal carotid or the anterior communicating artery
Pathology of Junctional Scotoma
The junctional scotoma classically presents as a central scotoma (or other optic nerve type of visual field defect) in one eye as well as a superior temporal visual field defect respecting the vertical meridian in the other eye. The compressive or other lesion involves the ipsilateral optic nerve at the junction but also the contralateral crossing inferior nasal retinal fibers (producing the superotemporal visual field loss in the fellow eye).
Patients with either the junctional scotoma or junctional scotoma of Traquair complain of ipsilesional visual loss. In the contralateral visual field loss in the superior temporal quadrant of the junctional scotoma however the patient typically only complains about the central loss in the ipsilateral eye and not the fellow eye. Often these patients also present with endocrine abnormalities and headaches due to either mechanical compression of nervous structures or hormonal dysregulation.
Patients may present with varying levels of decreased visual acuity (in addition to the visual field defects above). There will be a relative afferent pupillary defect (RAPD) in both junctional visual field defects. Band type optic atrophy may be seen on fundus exam in cases which involve nasal fibers. Involvement of temporal fibers which causes the nasal hemianopic field loss may result in hour glass pattern of optic disc atrophy. In the junctional scotoma the band atrophy is in the contralesional eye (superotemporal visual field loss) and in the junctional scotoma of Traquair will be in the ipsilesional eye if the defect is monocular and a temporal hemianopsia. In the nasal hemianopic variety (rare) of the junctional scotoma of Traquair the optic atrophy will be more likely in the hour glass (temporal fiber atrophy) and not the band configuration (nasal fiber atrophy). Figure 1 shows the junctional scotoma of Traquair and Figure 2 shows the junctional scotoma
Formal visual field imaging is necessary to accurately diagnose patients with junctional visual field loss Automated (e.g., Humphrey visual field testing) perimetry has been shown to be sensitive and specific in patients with visual field defects including junctional loss. Optical Coherence Tomography (OCT) can also aid in identifying band atrophy when the damage involves nasal fibers, or the hour glass pattern of atrophy in cases affecting the temporal fibers. OCT of the macular ganglion cell layer can also document the findings and may predict final visual recovery following surgical correction of the underlying compressive cause.
Laboratory studies may be considered in cases suspected to be from pituitary adenoma. Infectious (e.g., syphilis, tuberculosis), inflammatory (e.g., sarcoid, granulomatous disease, vasculitis), infiltrative (e.g., lymphoproliferative), and demyelinating (e.g., multiple sclerosis, neuromyelitis optica, myelin oligodendrocytic glycoprotein) disorders should also be considered in the differential diagnosis especially if the neuroimaging does not disclose a compressive etiology or shows optic nerve/chiasmal enhancement after contrast administration.
The treatment should be aimed at the underlying etiology but in general compressive lesions require surgical decompression. Corticosteroids may be used for inflammatory etiologies and antimicrobial therapy for infectious etiologies.
Computed tomography (CT) Scan can be used in traumatic cases to identify skull fractures in the frontal and anterior skull base, the orbital roof, the sphenoid bone. Damage to the sella turcica can also be visualized through this method. CT scan is also a more rapid initial neuroimaging for acute cases but in general MRI is superior for imaging the junctional visual field loss. Magnetic resonance imaging (MRI) with contrast may show the chiasmal compressive lesion. High resolution MRI with contrast provides excellent imaging of the soft tissues and can be used to identify other causes such as enhancement, edema or herniation around the optic chiasm. MRI can also identify chiasmal contusion, hemorrhage, or tumor infiltration.. Cerebral Angiography is usually not necessary in junctional visual field loss but if initial neuroimaging suggests a vascular etiology then cerebral angiography may be helpful. The optic chiasm is surrounded by the anterior cerebral artery, the anterior communicating artery, the internal carotid artery, the middle cerebral artery, and the cavernous sinus. An aneurysm in these vascular structures can compress the adjacent nervous structures and a junctional visual field change can develop.
Treatment differs according to the cause of the junctional visual field defect.
Visual prognosis depends on the cause and duration of symptoms. Analysis of the macular ganglion cell layer using OCT can help predict visual recovery in these cases.
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