Foster Kennedy syndrome is a rare condition caused by a frontal lobe tumor and presents with simultaneous optic disc edema in one eye and optic disc atrophy in the fellow eye.

• A. Foster Kennedy syndrome
• B. Horner syndrome
• C. Leber's optic neuropathy
• D. Optic neuritis

Answer: (A)

Foster Kennedy syndrome is defined by an asymmetric optic neuropathy pattern produced by a frontal lobe mass: the eye on the same side as the tumor shows optic disc edema, while the other eye develops optic disc pallor or atrophy. This happens because the tumor directly irritates or compresses the ipsilateral optic nerve, causing edema from impaired axoplasmic flow and local inflammation. At the same time, the tumor can involve or compress structures near the optic chiasm, leading to degeneration of the crossing fibers and resulting in contralateral optic nerve atrophy over time. Anosmia may accompany the tumor, reinforcing the diagnosis.

Other conditions don’t produce this distinctive combination. Horner syndrome affects sympathetic pathways and causes ptosis, miosis, and anhidrosis, not a unilateral disc edema with opposite disc atrophy. Leber’s optic neuropathy presents with subacute central vision loss, typically bilateral and without a mass lesion causing this asymmetrical disc pattern. Optic neuritis causes acute unilateral vision loss with pain and sometimes disc edema, but it does not create the contralateral atrophy pattern seen in Foster Kennedy syndrome.